Sedimentology of the Dakota Formation (Cretaceous), Uinta Mountains, Northeastern Utah

Beds of the Dakota Formation in northeastern Utah represent a fluvial environment in which deposition occured in two basic types of streams: large meandering streams and smaller alluvial plain streams. The large meandering streams were characterized by lateral migration and point-bar deposits. These deposits are relatively thick have high sand/shale ratios ranging from 2.3/1 to 13/1 and have laterally continuous individual channels. Also, the outcrop itself is laterally continuous over several hundred feet forming thick, unbroken exposures of sandstone. Deposition was cyclical with as many as six vertically adjacent channel deposits. The alluvial plain streams were characterized by channel avulsion and abundant overbank material resulting in an en echelon arrangement of ancient channels. These deposits are thinner and have lower sand/shale ratios that are about 1/1. Individual channels, as well as the entire outcrop, are less extensive laterally than in the larger meandering stream deposits. text;ural parameters, especially grain size, are useful in distinguishing sandstone and siltstone originating in both types of streams and overbank areas. Petrographic differences are more limited in usefulness. The significant differences occurred in sandstone and siltstone that were deposited in different flow conditions within the large meandering stream channels. The contrasts are in the percents of matrix and cement and in the relationship of quartz to matrix and cement. All of the Dakota channel deposits are quartz-rich and are quartzarenite, sublitharenite and subarkose. Evaluation of paleocurrent azimuths taken from cross-stratified sedimentary structures showed that the azimuths are fairly well concentrated in the channels for both types of streams. The similarity of paleocurrent information suggests that the alluvial plain streams were also meandering. The net regional direction of sediment movement was to the north with the ultimate site of deposition possibly being west-central Wyoming. In studying the overall dispersal system, it was found that the large meandering streams evolved through two stages of development. First, this stream system was characterized by degrading streams in disequilibrium with the surroundings. Later, (in Dakota time) this stream system reached "grade" and equilibrium with the surroundings. Both stages of stream development are registered in all outcrops of large meandering stream deposits. A new upper contact is proposed at the base of the "coarsegrained unit". This unit is a pebbly sandstone and conglomerate heretofore included within the Dakota. It is believed, however, that this unit is genetically related to the transgressing Mowry sea, represents a transitional environment between continental and marine conditions, and was strongly affected by tidal currents. The unit is therefore considered part of the Mowry Formation. The source area for Dakota sediment was probably the Meso- cordilleran geanticline. The composition of the source terrane was was strongly dominated by sedimentary rocks. The environment of deposition probably was a low-lying alluvial, coastal plain. The first stage of development of the large meandering streams was farthest from the sea. The second stage and the alluvial plain streams were evidently much closer to the sea.

SEDIMENTOLOGY SEDIMENTOLOGY OF OF THE THE DAKOTA DAKOTA FORnATION FORMATION (CRETACEOUS), MOUNTAINS, NORTHEASTERN UTAH (CRETACEOUS), UINTA UINTA MOUNTAINS, NORTHEASTERN UTAH by Rodney Lynn Vaughn A thesis A t h e s i s submitted s u b m i t t e d to t o the t h e faculty f a c u l t y of o f the the University U n i v e r s i t y of o f Utah in i n partial p a r t i a l fulfil1m2nt f u l f i l l m e n t of of tthe h e requirEments requirements for f o r the t h e degree d e g r e e of Master M a s t e r of of Science Science Department D e p a r t m e n t of of Geological G e o l o g i c a l and Geophysical G e o p h y s i c a l Sciences Sciences University U n i v e r s i t y of of Utah Utah December 1973 UNIVERSITY UNIVERSITY OF UTAH GRADUATE GRADUATE SCHOOL SCHOOL SUPERVISORY COMMITTEE APPROVAL S U P E R V I S O R Y C O M M I T T E E A P P R O V A L of a thesis sub.nittcd submitted by Rodney Lynn Lynn Vaughn I have read this thesis and have found it to be of satisfactory satisfactory quality for a master's degree, . & (:~~/~-~=----=---- CJlvvh \ M. DanePlcard M, Dane Pi c a r d Date Date Chaimlar., Supervisory Committee Chairman, I. I have read tlus this thesis and have found it to be of satisfactory satisfactory quality fOl' for a master's degree, degree. 4d.).), < j w ^ , (Pi c m Date Date ^ flmTTee c v % ^ ? r ^ - A n ^ A ^ Stokes Member, Supervisory Committee I have read this thesis and have found it to be of satisfactory satisfactory quality for a master's degree. . Sr. / SLD, f °IT^ ~D,(971 Date'/ D a t e . A^gfiin&kgA C UOf (s&^ J o n a t h a n ~ M . Goodwin Member, Supervisory Committee t fvV .:..--- UNIVERSITY UNIVERSITY OF UTAH GRADUATE GRADUATE SCHOOL SCHOOL FINAL READING F I N A L R E A D I N G APPROVAL A P P R O V A L To the Graduate Council of the University of Utah: Vaughn I have read the thesis of - - - - -Rodney gggggg Lynn ^ ? ------------------in its final form and have found that (1) changes suggesteci suggested by the SlJpervisory Supervisory Committee have been completed in the manuscript; (2) reference citations and bibliography are consistent and in an acceptable all illustrative materials acceptabie form; (3) ail including figures, tables, and charts are in place; and (4) the final manuscript is satisfactory and ready for submission to the Graduate School. School, satisfactory L n n V a u /n, i). Date f1.D~ W. Dane Pi c a r d h n I~ ---- Member, Supervisory Committee Comn:ittee Approved for the Majo(\~eparlment Major Department Approved f();;he (/' j., \ ~. ~ // Chairman/Dean Chairman /Dean Approved for the Graduate Council ~~~,~7jd~)1IA~ S t e r l i n g M. ~-kMurri McMurririn / Graduate Dean ACKNOWLEDGMENTS ACKNOWLEDGMENTS The author Dane Picard a u t h o r extends e x t e n d s hhis i s sincere s i n c e r e tthanks h a n k s to t o Dr. D r . M. Dane Picard for f o r suggesting s u g g e s t i n g the t h e problem p r o b l e m and and for f o r his h i s ccontinued o n t i n u e d assistance a s s i s t a n c e throughout throughout all a l l pphases h a s e s of of the t h e study. study. Gratitude Dr. William G r a t i t u d e is i s also a l s o expressed e x p r e s s e d to t o Dr. William Lee and D Dr. H. Goodwin Lee Stokes S t o k e s and r . Jonathan J o n a t h a n H. Goodwin who who ccritically r i t i c a l l y rreviewed e v i e w e d the the and content, manuscript, m a n u s c r i p t , which w h i c h iimproved m p r o v e d its i t s form form and c o n t e n t , and and for f o r numerous numerous c o n v e r s a t i o n s concerning c o n c e r n i n g the t h e pproblem r o b l e m tthroughout h r o u g h o u t the t h e pperiod e r i o d of o f study. study. conversations Thanks Rog who assisted T h a n k s is i s also a l s o due to t o Ernest E r n e s t P. P . Otto O t t o and Stephen S t e p h e n Rog assisted w i t h some of t h e field f i e l d work. work. with of the C h a r l e s L. Rutherford R u t h e r f o r d ppermitted e r m i t t e d samples samples Charles tto o be a k e n from from w i t h i n tthe h e Dinosaur Dinosaur N a t i o n a l Monument. be ttaken within National Monument. d r a f t e d by D. O l s o n ; the t h e manuscript m a n u s c r i p t was t y p e d by drafted D. L. Olson; was typed by F i g u r e s were were Figures M a r i o n Vaughn. ~1arion Acknowledgment is made ttoo tthe Acknowledgment i s made h e donors d o n o r s of of tthe h e Geological Geological Research Research Fund, Department F u n d , administered a d m i n i s t e r e d by the the D e p a r t m e n t of of Geological G e o l o g i c a l and Geophysical Geophysical Sciences, U n i v e r s i t y of of Utah, U t a h , for f o r ppartial a r t i a l support s u p p o r t of of tthis h i s research. research. Sciences, University U N I V E R S I T Y OF O F UTAH U T A H UBHARIES LIBRARIES UNIVERSITY CONTENTS CONTENTS ILLUSTRATIONS ILLUSTRATIONS vii vii ABSTRACT ABSTRACT I NTRODUCTI ON INTRODUCTION ix ix , 11 GENERAL STRATIGRAPHY STRATIGRAPHY GENERAL r'~ethods .... Methods 33 44 STRATIGRAPHY OF OF THE THE DAKOTA DAKOTA FORMATION FORMATION STRATIGRAPHY Types of ooutcrops ..... . T y p e s of utcrops Channel ffacies Channel a c i e s ooutcrops u t c r o p s •. * Overbank ffacies Overbank a c i e s ooutcrops utcrops Formational F o r m a t i o n a l ccontacts ontacts . 7 77 77 14 15 FLUVIAL CHANNELS CHANNELS . . . . . . FLUVIAL Rock ttypes Rock ypes . . . . . . Channel tthicknesses Channel hicknesses Sedimentary S e d i m e n t a r y sstructures tructures . Cross-stratification .. C ross-stratification Horizontal H o r i z o n t a l stratification stratification Bedding ....... . B e d d i n g plane p l a n e features features marks Ripple Ripple m a r k s and and ripple r i p p l e cross-lamination cross-lamination Other O t h e r ttypes ypes . . . . . . Vertical structure V e r t i c a l s t r u c t u r e profile. profile Fluvial F l u v i a l cycles cycles ...... . Cycle C y c l e tthicknesses hicknesses .. . IIntercycle n t e r c y c l e coset c o s e t tthicknesses hicknesses Weathering Weathering Color Color . 16 16 17 20 20 20 TEXTURE TEXTURE . Grain G r a i n size size Sorting .... Sorting Grain G r a i n morphology morphology . Roundness Roundness . . Grain G r a i n surfaces surfaces Textural T e x t u r a l maturity maturity ", . . . . . . PETROGRAPHY . . . . . . . . . . . . . Pebbly P e b b l y sandstone s a n d s t o n e and and conglomerate conglomerate Sandstone S a n d s t o n e and and siltstone siltstone Quartz Quartz . . . . . . . . . . . . . . Rock Rock fragments fragments . . . . . . . . . . Petrographic P e t r o g r a p h i c comparisons c o m p a r i s o n s of of sandstone s a n d s t o n e and and siltstone. siltstone Diagenesis Diagenesis ...... . . . 21 21 22 22 23 26 26 28 28 28 30 31 31 31 36 36 38 38 38 38 42 42 42 42 44 44 44 44 46 46 47 47 49 49 51 51 56 56 PALEOCURRENTS PALEOCURRENTS . . . r~ethods . . . Methods ... Results R esults IInterpretation nterpretation .'- "COARSE-GR,llJ NED UNIT" "COARSE-GRAINED UNIT" Description 62 62 62 62 67 67 67 Description PROVENANCE 60 60 60 67 . . . 70 PROVENANCE 70 DISPERSAL SYSTEM 72 DISPERSAL SYSTEM 72 DEPOSITIONAL ENVIRONMENTS 76 DEPOSITIONAL ENVIRONMENTS 76 CONCLUSIONS 78 CONCLUSIONS 78 REFERENCES CITED 80 REFERENCES CITED 80 VITA . . . . . . . 85 VITA 85 vi vi ILLUSTRATIONS Figure Figure Page 1. 1. Index I n d e x and outcrop o u t c r o p map 2 2. 2. Regional R e g i o n a l map showing s h o w i n g location l o c a t i o n of of cross-sections cross-sections 8 3. 3. E a s t - w e s t cross-section c r o s s - s e c t i o n on north n o r t h flank f l a n k of of Uinta Uinta East-west Mountains Mountains 9 4. 4. E a s t - w e s t cross-section c r o s s - s e c t i o n on south s o u t h flank f l a n k of of Uinta Uinta East-west Mountains Mountains 10 5. 5. North-south N o r t h - s o u t h cross-section c r o s s - s e c t i o n across a c r o s s Uinta U i n t a Mountains Mountains 11 6. 6. Outcrop O u t c r o p of of large l a r g e meandering m e a n d e r i n g stream s t r e a m deposits deposits 13 7. 7. Outcrop O u t c r o p of of alluvial a l l u v i a l plain p l a i n stream s t r e a m deposits deposits 13 8. 8. Histogram H i s t o g r a m showing s h o w i n g frequency f r e q u e n c y of of channel c h a n n e l thicknesses thicknesses 19 9. 9. V e r t i c a l sequence s e q u e n c e of of sedimentary s e d i m e n t a r y structures s t r u c t u r e s in in Vertical t h e channel c h a n n e l deposits deposits the 24 10. 10. I n t r a c y c l e thickness t h i c k n e s s of of cosets cosets Intracycle 25 11. 11. Thicknesses T h i c k n e s s e s of of cycles c y c l e s in i n outcrops o u t c r o p s of of large large meandering m e a n d e r i n g stream s t r e a m deposits deposits 27 12. 12. of ccosets IIntercycle n t e r c y c l e tthicknesses h i c k n e s s e s of o s e t s iin n vertically vertically aadjacent d j a c e n t channels channels 29 13. 13. of ggrain Frequency F r e q u e n c y pprofile r o f i l e chart c h a r t of r a i n sizes sizes 36 14. 14. V e r t i c a l ggrain r a i n ssize i z e pprofile r o f i l e cchart h a r t of fluvial Vertical of fluvial ccycles y c l e s of e a n d e r i n g sstream t r e a m deposits deposits of m meandering 37 15. 15. F r e q u e n c y pprofile r o f i l e cchart h a r t of o r t i n g values values of ssorting Frequency 40 16. 16. Dominant ggroupings of ggrain Dominant r o u p i n g s of r a i n roundness roundness 41 17. 17. of tthe Ternary T e r n a r y pplot l o t sshowing h o w i n g ccomposition o m p o s i t i o n of h e Dakota ssediments ediments 48 118. 8. of sandstone Ternary T e r n a r y pplot l o t sshov.Jing h o w i n g ccomposition o m p o s i t i o n of sandstone and i l t s t o n e ffor o r ddifferent i f f e r e n t modes deposition and ssiltstone modes of of deposition 52 Page Page Figure Figure 19. 19. G r a i n s - m a t r i x - c e m e n t ternary t e r n a r y pl p l oot t of of sa s a nndstone d s t o n e and siltstone Grains-matrix-cement and siltstone 52 20. 20. G r a i n s - m a t r i x --cement c e m e n t ternary t e r n a r y plot p l o t showing showing Grains-matrix d i f f e r e n c e in i n large l a r g e meandering m e a n d e r i n g stream s t r e a m depos d e p o sits its difference o f sections s e c t i o n s SM-B and OA of QA 54 21. 21. S c a t t e r pl p l oott of authigenic a u t h i g e n i c cement c e m e n t vversus e r s u s matri m a t r i xx Scatter 55 22. 22. S c a t t e r plot p l o t of of quartz q u a r t z versus versus m atrix Scatter matrix 57 23. 23. S c a t t e r plot p l o t of quartz q u a r t z versus v e r s u s ceme c e m e nt nt Scatter 58 24. 24. C y cll ic i c var'iat v a r i a t iioon n of of Cyc 64 25. 25. R e gii oonal n a l map map sho\'/ing s h o w i n g net n e t pal p a l eeocurrent o c u r r e n t ddirection irection Reg a t each e a c h locality locality at 65 26. 26. r e g i o n a l paleocurrent p a l e o c u r r e n t ddispersion i s p e r s i o n ppattern a t t e r n iin n Net regional t h e study s t u d y area area the 66 27. 27. " C o a r s e - ggrained r a i n e d unit" unit" "Coarse- 68 28. 28. i n the t h e dispersal d i s p e r s a l system s y s t e m and h e rresu e s u llting ting Changes in and tthe o u t c r o p pattern pattern outcrop 73 X Jr Page Page T a b l ee Tab 11.. Unimodal i l ttstone s t o n e and sandstone s a n d s t o n e ooccurrences c c u r r e n c e s with w i t h in in Uni moda l ssil g r a i n ssize i z e boundaries boundaries grain 32 32 2. 2. Unimodal i l t s t o n e and ssandstone a n d s t o n e occurrences occurrences Unimoda l ssiltstone a t gra g r a iinn ssize i z e boundaries boundaries at 32 32 33.. T o t a l unimodal i l tts s t tone o n e and a n d s t o n e grain grain Total uni moda l ssil and ssandst9ne ssize i z e frequency frequency 33 33 44.. F r e q u e n c y of o r t i n g va v alues lues Frequency of ssorting 39 39 55.. C h a r a c t e r i s i t c s of o c k fragments fragments Characterisitcs of rrock 50 50 66, . P a l e o c u r r e n t aazi zim t h cconcentration o n c e n t r a t i o n (L) of Paleocurrent muuth (L) of Dakota t r e a m deposits deposits Dakota sstream 63 63 vvii i i ii ABSTRACT ABSTRACT Beds of Dakota FFormation Beds of tthe h e Dakota o r m a t i o n iin n northeastern n o r t h e a s t e r n Utah rrepresent epresent a two bbasic ffluvial l u v i a l environment e n v i r o n m e n t in i n which which deposition d e p o s i t i o n occured o c c u r e d iin n two a s i c types types of o f streams: streams: streams. streams. meandering llarge arge m e a n d e r i n g streams s t r e a m s and smaller s m a l l e r aalluvial lluvial plain plain The large m e a n d e r i n g streams streams w e r e characterized c h a r a c t e r i z e d by lateral lateral The large meandering were m i g r a t i o n and point-bar p o i n t - b a r deposits. deposits. migration T h e s e deposits d e p o s i t s aare r e relatively r e l a t i v e l y thick; thick These hhave a v e high h i g h sand/shale s a n d / s h a l e ratios r a t i o s ranging r a n g i n g from from 2.3/1 2 . 3 / 1 to t o 13/1 1 3 / 1 and and have have l a t e r a l l y continuous c o n t i n u o u s individual i n d i v i d u a l channels. channels. laterally A l s o , tthe h e outcrop o u t c r o p itself itself Also, i s laterally l a t e r a l l y continuous c o n t i n u o u s over o v e r several s e v e r a l hundred h u n d r e d feet f e e t forming f o r m i n g thick, thick, is u n b r o k e n exposures e x p o s u r e s of of sandstone. sandstone. unbroken D e p o s i t i o n was cyclical c y c l i c a l with w i t h as as Deposition a s six s i x vertically v e r t i c a l l y aadjacent d j a c e n t channel c h a n n e l deposits. deposits. many as The alluvial by channel The a l l u v i a l pplain l a i n streams s t r e a m s were w e r e chara.cterized c h a r a c t e r i z e d by channel avulsion avulsion and abundant material a b u n d a n t overbank overbank m a t e r i a l rresulting e s u l t i n g iin n an en echelon e c h e l o n arrangement arrangement of of aancient n c i e n t channels. channels. These T h e s e deposits d e p o s i t s are a r e thinner t h i n n e r and have h a v e lower lower s a n d / s h a l e rratios a t i o s that t h a t are a r e aabout b o u t 1/1. 1/1. sand/shale IIndividual n d i v i d u a l channels, c h a n n e l s , aass well well a s the t h e entire e n t i r e outcrop, o u t c r o p , are a r e less l e s s extensive e x t e n s i v e laterally l a t e r a l l y than t h a n in i n tthe h e larger larger as m e a n d e r i n g stream s t r e a m deposits. deposits. meandering Textural T e x t u r a l pparameters, a r a m e t e r s , especially e s p e c i a l l y ggrain r a i n size, s i z e , are a r e uuseful s e f u l in in distinquishing d i s t i n g u i s h i n g sandstone s a n d s t o n e and siltstone s i l t s t o n e originating o r i g i n a t i n g iin n bboth o t h ttypes y p e s of s t r e a m s and ooverbank v e r b a n k areas. areas. streams limited l i m i t e d in i n usefulness. usefulness. P e t r o g r a p h i c differences d i f f e r e n c e s are a r e more Petrographic The ssignificant The i g n i f i c a n t differences d i f f e r e n c e s occurred o c c u r r e d in in s a n d s t o n e and siltstone s i l t s t o n e that t h a t were w e r e deposited d e p o s i t e d in i n different d i f f e r e n t flow f l o w concon­ sandstone d i t i o n s within w i t h i n the t h e llarge a r g e meandering m e a n d e r i n g stream s t r e a m channels. channels. ditions The contrasts contrasts a r e in i n the t h e percents p e r c e n t s of of m a t r i x and cement c e m e n t and i nn the t h e relationship r e l a t i o n s h i p of of are matrix q u a r t z to to m a t r i x and cement. cement. quartz matrix All l l of of the t h e Dakota channel c h a n n e l deposits d e p o s i t s are are A q u a r t z - r i cch h and and are a r e quartzarenite, q u a r t z a r e n i t e , sublitharenite s u b l i t h a r e n i t e and subarkose. subarkose. quartz-ri E v a l u a t i o n of of paleocurrent p a l e o c u r r e n t azimuths a z i m u t h s taken t a k e n from from cross-stratified cross-stratified Evaluation s e d i m e n t a r y structures s t r u c t u r e s showed t h a t tthe h e aazimuths z i m u t h s are a r e fairly f a i r l y we w ell ll sedimentary sho\"led that c o n c e n t r a t e d in i n tthe h e cchannels h a n n e l s for f o r both b o t h ttypes y p e s of of streams s t r e a m s .. The similarsimilar­ concentrated ii tty y of of ppaleocurrent a l e o c u r r e n t information i n f o r m a t i o n ssuggests u g g e s t s tthat h a t tthe h e alluvial alluvial s t r e a m s were w e r e aalso lso m e a n d e r ing. ing. streams meander plain plain The nnet e t rregiona e g i o n a ll ddirection i r e c t i o n of of sediment sediment movement t h e nnorth orth w i t h tthe h e uull ttiimate m a t e ssite i t e of d e p o siitt i oon n movement was \,Ias ttoo the \,Iith of depos pposs o s s ii bbll yy bbeing eing w e s t - c e n t r a ll Wyom Wyoming. west-centra i ng . IIn n sstudying t u d y i n g tthe h e ooverall v e r a l l ddispersal i s p e r s a l ssystem y s t e m ,, it i t was o u n d tthat h a t the the >las ffound meandering two sstages of development. ll aarge rge m e a n d e r i n g streams s t r e a m s eevolved v o l v e d tthrough h r o u g h two t a g e s of development. F i r s t , tthis h i s sstream t r e a m ssystem y s t e m was h a r a c t e r i z e d by e g r a d iing n g sstreams t r e a m s in in First, was ccharacterized by ddegrad ddisequilibr i s e q u i l i b r i uium m w i t h tthe h e ssurroundings. urroundings. with L a t e r , ((in i n Dakota e) Later, Dakota ttiimme) this this sstream t r e a m ssystem y s t e m rreached e a c h e d ""grade" g r a d e " and quilibrium w i t h tthe h e surroundings. surroundings. and eequilibrium with Both t a g e s of t r e a m ddevelopme e v e l o p m e nnt t aare r e rregistered e g i s t e r e d iin n aall l l ooutcrops u t c r o p s of of Both sstages of sstream ll aarge rge m e a n d e r i n g sstream t r e a m deposits. deposits. meandering A p p e r ccontact o n t a c t iiss pproposed r o p o s e d aat t tthe h e bbase a s e of h e "coarse"coarse­ A new new uupper of tthe ggrained r a i n e d uunit". nit". T h i s uunit n i t iis s aa ppebbly e b b l y ssa a nndsto d s t o nne e and conglomerate and conglomerate This hheretofore e r e t o f o r e iinc n c lluuded ded w i t h i n tthe he D akota. within Dakota. IIt t iis s bbel e l iieeved, v e d , however, however, tthat h a t tthis h i s uunit n i t iis s ggeneticall e n e t i c a l l yy rrelated e l a t e d tto o tthe h e ttransgressing ransgressing 1 Mowry 1o>lry ssea, e a , rrepre e p r e ssents e n t s aa ttran r a n ssitional i t i o n a l eenvironment n v i r o n m e n t bbetween e t w e e n ccontinental o n t i n e n t a l and m a r i n e cconditions, o n d i t i o n s , and t r o n g l y aaffected f f e c t e d by i d a l ccurrents. urrents. marine and was was sstrongly by ttidal The uuni n i ttis i s ttherefore h e r e f o r e ccons o n s iiddered e r e d ppart a r t of h e Mowry F o r m at; t i on. on. of tthe r·1o\,IrY Forma The o u r c e aarea r e a ffor o r Dakota e d i m e nnt t was r o b a b l y tthe h e 1·1esoMesoThe ssource Dakota ssedime was pprobably ccordilleran o r d i l l e r a n ggeanti e a n t i ccl;ne. line. The o m p o s i t i o n of h e ssource o u r c e tterrane e r r a n e was The ccomposition of tthe was x s t r o n g l yy dominated d o m i n a t e d by sed s e d iimen m e ntary t a r y rocks. rocks. was strongl e n v i rronment o n m e n t of of depos d e p o s i ttion i o n pprobably robably w was g aa11 l l uvi u v iaa1l , The envi "as aa 1l ooww ~- 1l yyii nng c o a s t a ll pl p l ai a i nn.. coasta r s t stage s t a g e of o f developme d e v e l o p m e nt n t of of the t h e large l a r g e meandering meandering The f iirst s t r e a m s was farthest f a r t h e s t from from tthe h e ssea. ea. streams The second s e c o n d stage s t a g e and tthe h e a11 a l l uuvia vial pplain l a i n streams s t r e a m s were w e r e evidently evidently m much c l o s e r tto o tthe h e sea. sea. uch closer xxii IINTRODUCTION NTRODUCTI ON F o r m ation t i o n in i n northeastern n o r t h e a s t e r n Utah is is a a nonmari n o n m a r ine n e ., The Dakota Forma c o n tt inental i n e n t a l deposit d e p o s i t of of Cretaceous C r e t a c e o u s age a g e .. con p r e c i sse e esti estim a t e s of of More preci mates i t s age a g e are a r e very v e r y di d i fficu f f i c u ll tt to t o determine d e t e r m i n e because b e c a u s e of of a a complete c o m p l e t e lack l a c k of of its s s il i l ss wi w i th t h iinn the t h e forma f o r m a t iioon n ;i nn the t h e study s t u d y area. area. f ooss h a s , however h o w e v e r, I t has, been bracketed b r a c k e t e d by the t h e dated d a t e d t10"ry Mowry and Ceda Cedarr t10unta M o u n t a i nn Forma F o r m attii ons. ons. The Dakota F o r m a t i o n is i s considered c o n s i d e r e d by many authors a u t h o r s (Hau ( H a u n ,, 1959, 1 9 5 9 , 1963; 1963; akota Formation D Haverfie a v e r f i e l dd, , 1970; 1 9 7 0 ; Kinney, K i n n e y , 1955; 1 9 5 5 ; Reeside, R e e s i d e , 1923; 1 9 2 3 ; Suttner, S u t t n e r , 1969; 1969; H W a l t o n , 1944 1 9 4 4 ;; \lei Weimer, 1 9 6 2 , 1970) 1970) as a s both b o t h Lo"er Lower and Lo"e,' Lower-Upper Walton, me r, 1962 - Upper C r e t a c e o u s age. age. Cretaceous I t iis s the t h e object o b j e c t of of this t h i s thes t h e s ii ss tto o determine d e t e r m i n e tth h ee environment e n v i r o n m e n t of of It d e p o s i t i o n oof f the t h e Dakota o r m a t i o n and to t o evaluate e v a l u a t e tthat h a t env e n vironment ironment deposition Dakota FFormation iin n aa ddetailed etailed m a n n e r .. manner Knowledge of tthe he D akota F o r m a t i o n in i n north n o r t h -­ Kno\,/l edge of Dakota Formation e a s t e r n Utah Utah .w i l l be be hhe e ll ppful f u l iin n i nnterpreting t e r p r e t i n g the t h e geo g e o l oog g iicc hi h i sstory t o r y of of eastern . till tth h ee rre9 e g iioon n ddurin u r i n g9 tthe h e Cretaceous C r e t a c e o u s .. I t may a l sso o pprove r o v e hhee l ppfu f u ll ii nn It uunderstanding n d e r s t a n d i n g some C r e t a c e o u s ccorrel o r r e l aation t i o n and ffac a c iiees s some Cretaceous stratigraphic stratigraphic pproblems r o b l e m s because b e c a u s e tthe h e sstudy t u d y area a r e a i nncludes c l u d e s ,some some of t h e \'Iesternmost westernmost of the eexposures x p o s u r e s of h e Dakota a n d , ttherefore, h e r e f o r e , may be cclosest l o s e s t tto o the t h e source source of tthe Dakota and, aarea r e a .. The a s been t u d i e d pprevious r e v i o u s lly y iin n Colorado, C o l o r a d o , the the The Dakota Dakota hhas been sstudied C o l oorado rado P t e a u of o l o r a d o on h e ssou o u th, t h , and f o r m ations tions Col Pll aateau of Utah Utah and and CColorado on tthe and forma pprobably r o b a b l y eequivalent q u i v a l e n t tto o tthe h e Dakota n Wyoming h e nnorth, orth. Dakota iin Hyomin9 on on tthe iis s an n d e x and u t c r o p map of h e sstudy t u d y area. area. an iindex and ooutcrop of tthe F i g u r e 11 Figure 22 WYOMING W Y O M I N G ------:E J> f i l l MOUNTAINS (/) ~ (1 ~ VERNAL • ~ o c ROOSEVELT • ROOSEVELT' Z -I - UINTA UINTA BASIN BASIN J> Z I RANGELY RANGELY * I (/) i UTAH U T A H (") O o O r o• PPRICE· RICE © SAN RAFAEL SWELL : .;:: ::; ;;~;;:: rr--------. ;,:,:; N 0o 10 10 220 0 --~ SCALE IN IN MILES MILE S SCALE INDEX MAP FORMATION NDEX AAND N D OOUTCROP U T C R O P M A P OOF F DDAKOTA AKOTA FORMATION UTAH UUNITA N I T A MMOUNTAIN OUNTAIN AAREA, REA, U TAH FFig. i g . 11 I GENERAL STRATIGRAPHY L a t e JJurassic-Early u r a s s i c - E a r l y Cretaceous C r e t a c e o u s stratigraphy s t r a t i g r a p h y ppresents r e s e n t s some of of Late tthe h e most m o s t comp complex t r a t i g r a p h i c pproblems r o b l e m s iin n the the w estern l ex sstratigraphic western i nterior. terior. in T h i s ssubject u b j e c t has h a s been been discussed d i s c u s s e d by many authors authors w i t h almost a l m o s t as as This with many d i f f e r e n t iinterpretations n t e r p r e t a t i o n s ((Burk, B u r k , 1957; 1 9 5 7 ; Cobban e e s i de, d e , 1952; 1952; many different Cobban and RRees E y e r , 1969; 1969; F u r e r , 11970; 9 7 0 ; Hale H a l e and and Van r a f f , 1964; 1 9 6 4 ; Haun, 1959; Eyer, Furer, Van De De G Graff, Haun, 1959; Haun B a r l o w , 11962; 9 6 2 ; MacKenzie o o l e , 11962; 962; R e e s i d e , 11944, 9 4 4 , 1955; 1955; Haun and and Barlow, MacKenzie and and PPoole, Reeside. S c o t t , 1970; 1970; S t o k e s , 1944, 1 9 4 4 , 1952, 1 9 5 2 , 11955; 9 5 5 ; Young, 1960, 1 9 6 0 , 11970). 970). Scott, Stokes, iit t iis s beyond h e sscope c o p e oof f tthis h i s sstudy t u d y tto o make egional beyond tthe make aa rregional Because Because interpretation interpretation of C r e t a c e o u s bboundaries o u n d a r i e s and a c i e s cchanges, h a n g e s , llocal o c a l stratigraphy stratigraphy of Cretaceous and ffacies w i t h i n tthe h e sstudy t u d y aarea r e a was used. within was used. The o r m a t i o n iis s bounded b o v e and e l o w by h e Mowry The Dakota Dakota FFormation bounded aabove and bbelQ1' by tthe ~lo"ry and Cedar o u n t a i n FFormations o r m a t i o n s rrespectively. espectively. Cedar M Mountain tto o bbll aack, c k , ssiliceous iliceous m a r i n e "Hshale". shale". marine The s aa ddark a r k gray gray The Mowry ~'OI."ry i;s IIt t iis s eeasily a s i l y rrecognized o c o g n i z e d iin n the the f i eel l dd by t s ccolor, o l o r , ffissility, i s s i l i t y , ddiagnostic i a g n o s t i c ffish i s h sscales c a l e s and t s sl s l oopepe"fi by iits and by by iits fforming o r m i n g ttopography o p o g r a p h y .. V e g e t a t iioon n ggr0l1 r o w iing n g on h e Mowry s rrather a t h e r sparse. sparse. Vegetat on tthe t·1owry i;s The edar M o u n t a i n FFormation, o r m a t i o n , of o n t i n e n t a l oorigin, r i g i n , iis s aalso l s o easily easily The C Cedar ~1ountain of ccontinental rrocognized o c o g n i z e d by t s sslloope-form p e - f o r m iing n g ccharacteristics h a r a c t e r i s t i c s and t s variegated variegated by iits and iits ccolors o l o r s of e d , ppurple u r p l e and ray. of rred, and ggray. SSediments e d i m e n t s of he C e d a r ~1ountain Mountain of tthe Cedar FFormation ormation w e r e nnot o t eexamined x a m i n e d iin n ddetail e t a i l , , bbut u t ccursory u r s o r y observations observations \'/ere iindicate n d i c a t e tthat h a t iit t iis s pprimarily r i m a r i l y composed l a y s t o n e and siltstone composed of of cclaystone and siltstone and a r e ssandstone a n d s t o n e lenses. lenses. and rrare The o r m a t i o n iin n nnortheastern o r t h e a s t e r n Utah e p o s i t e d i nn The Dakota Dakota FFonnation Utah was \'/as ddeposited ffluvial l u v i a l eenv n v iironments. ronments. Two a c i e s ·can c a n be e c o g n iizzed e d iin n tthe h e fie f i e l dd;; Two main main ffacies be rrecogn 4 aa chan c h a n nnel e l facies f a c i e s consisti c o n s i s t i nng g of o f sandstone s a n d s t o n e ,, pebbly p e b b l y sandstone s a n d s t o n e and and con c o n-­ gl g l oomerate m e r a t e and an an overba o v e r b a nnk k facies f a c i e s cons c o n s i sting s t i n g of of sandstone s a n d s t o n e ,. sil s i l tsto t s t o nnee and and mudstone m u d s t o n e (Fo ( F o l kk,, 1968, 1 9 6 8 , p.27p . 2 7 - 331) 1 ) .. Thi T h i ss tthesis h e s i s is i s concerned c o n c e r n e d pr p rimar i m a rily ily with w i t h the t h e channel c h a n n e l facies. facies. Exposures of the E x p o s u r e s of t h e cha c h a nnnel n e l ffacies a c i e s ar a r ee numerous numerous and easily e a s i l y accessibl a c c e s s i b l ee \'Iithin w i t h i n tthe h e study s t u d y aarea r e a and resistant and and form form resistant hhogbacks o g b a c k s or o r cl c l ii fffs. fs. T h i cckness k n e s s of of tt hhe e channe c h a n n e ll facies f a c i e s i ss variabl v a r i a b l e, e, Th b u t tt hhe e main main f lluuv v iiaal l channe c h a n n e ll deposi d e p o s i ttss are a r e iin n eexcess x c e s s of of 100 feet f e e t on on but tthe h e south s o u t h f llaanks n k s of tt hhe e U ta M o u nttains a i n s and tthicken h i c k e n tto o oover v e r 200 f e e tt Uii nnta Moun 200 fee on tthe Uin Mountai on h e nnort o r t hh ff llaanks n k s of of tthe he U i n t aa M o u n t a i nns s .. The tt hhii cckness of the The k n e s s of the form t i oon n w h e r e tthe h e channe c h a n n e ll ffac a c iiees s i ss aabsent b s e n t was nnot o t determ d e t e r mii ned ned. for maa ti \'/here Workabl of tthe W o r k a b l ee eexposures x p o s u r e s of h e ooverbank v e r b a n k ffacies a c i e s aare r e ll iimi m i tted e d .. Only x p o s u r e of v e r b a n k ssed e d iime m e nts n t s was measured. of ooverbank was measured. one eexposure Methods Methods O u t c r o p s of h e Dakota ormation w ere m e a s u rred e d aa tt Outcrops of tthe Dakota FFormation \'/ere measu e l eeven ven el ll oocati c a t i oons n s on h e nnorth o r t h and o u t h ffllaanks n k s of he U inta M o u n t aii nns. s. on tthe and ssouth of tthe Uinta Mounta ssection e c t i o n was easured w i t h aa ttape a p e and r u n t o n ccompass. ompass. \'las m measured . .lith and bbrunton Each D e t ail i l eed d Deta d e s c r i p t i o n s of h e lli i t thol h o l oogy g y and e d i m e n t a r y sstructu t r u c t u rres es w e r e made "descriptions of tthe and ssedimentary were iin n tthe h e ff iieel l dd. . SSpec p e c iiaal l aatte t t e nntion t i o n was e nn tto o tthhe e was ggii vve d e ntit iff ii cation, cation, iiden tt hhickness i c k n e s s and t h e r ccharacteri h a r a c t e r i ssti t i ccs s of h e ccycl y c l iic c iitty y of h e channels. channels. and oother of tthe of tthe S a m pl ees s of h e ooutcrop utcrop w e r e ttaken a k e n aatt aappropriate p p r o p r i a t e iinnterva t e r v a llss tto o check check Samp of tthe were ffor o r lliithol t h o l oog g iicc vvariati a r i a t i oon n iinn tthe h e vverti e r t i ccal a l ssequence e q u e n c e .. SSamp a m pl ees s were were ccarefu a r e f u lll l yy nnoted o t e d aas s tto o which l u v i a l l ccyc y c llee tthey h e y represented r e p r e s e n t e d .. " hi ch ffluvia A o t a l of a l e o c u r r e n t aazimuths zimuths w e r e ttaken a k e n oover v e r tthe h e ent e n t ii re re of 353 353 ppaleocurrent were A ttotal sstudy t u d y aarea. rea. lleevel v e l ss.. They e r e eeva v a lluuated a t e d aat t tthhree r e e ddifferent i f f e r e n t interpretative interpretative They wIt/ere PPaa l eeocurrent o c u r r e n t aazimuths zimuths w e r e ggrouped r o u p e d iinto n t o ccycl y c l ees s aat t each each were m e a s u r e d ssection e c t i o n tto o ddetermine e t e r m i n e tthe h e vvar a r ii aabil b i l iity t y of w di d i rect r e c t iioons ns of fflloow measured 5 t h rroough u g h time. time. th S e c o ndl n d l y. y , the t h e azimuths a z i m u t h s were w e r e ttota o t a lleed d tto o determine d e t e r m i n e the the Seco a v e r aage g e pa p a l eeoflol'l o f l o w d i rrections e c t i o n s tthrough h r o u g h Dakota Dakota time t i m e for f o r each e a c h outcrop. outcrop. aver T h i rd r d l y, y , a grand g r a n d tota t o t a ll of of all a l l az a z iim u t h s in i n the t h e study s t u d y area a r e a vias was evaluated evaluated Thi muths d e t e r m i n e the t h e average a v e r a g e pa p a ll eeoslope o s l o p e direction d i r e c t i o n of t h e study s t u d y area area t oo determine of the tth h rroughout o u g h o u t Dakota D a k o t a deposition deposition. T h i nn secti s e c t i oons n s of of 50 ssamples a m p l e s ""ere w e r e studied s t u d i e d in i n ddeta e t a il i l .. Thi of tthese hese w e r e aanalyzed n a l y z e d by modal n a l ys y s i ss.. of ""ere moda l aana ccoun o u n tted e d pper e r tth h iin-secti n - s e c t i oon. n. Thirty-five Thirty-five Two hhundred u n d r e d ppoints o i n t s were were Each modal a n a l ysis y s i s was n d e r high high modal ana \,Ias made u under m g n ifica f i c a ttiio o nn (x 320) h aa m a n u all l l yy ooperated perated m e chanica h a n i c a ll maagni 320) w wii tth manua mec stage. stage. One u n d r e d - f i f t y rrock o c k ssam a mples ples w e r e eexamined x a m i n e d uunder n d e r aa bi b i nocu n o c ullar ar One hhundred-fifty were m c r o s c o p e .. mii croscope The o b j e c t of h i s eexami x a m i nation n a t i o n was tto o ddetermine e t e r m i n e the the The object of tthis modal r a i n ssize i z e ,, frosting, f r o s t i n g , ssorting, o r t i n g , ccolor o l o r and o u n d n e s s of sandmodal ggrain and rroundness of sandssii zzed e d ddetrital etrital grains. grains. S i x t e e n ssamples amples w e r e sse e lleected c t e d ffor or X - r a y aanalysis n a l y s i s .. Sixteen >lere X-ray Some oof f the the ssampl a m p l ees s w e r e pprepared r e p a r e d tto o ddetermine e t e r m i n e tthe h e bbulk ulk m i n e r a lloogy g y of h e channel channel were minera of tthe ssandstones a n d s t o n e s and h e ooverbank v e r b a n k ddeposits. eposits. and tthe O t h e r ssamp a m p les les w e r e prepared prepared Other were p e c i fi f i cca a llly l y tto o aana n a l1yyze z e ffor o r ccl l aay y m e r a l1 ccontent o n t e n t of h a n n e l sands s a n d s tones tones mii nnera of cchannel ,sspec and v e r b a n k ddeposits e p o s i t s .. and ooverbank A l l ssamp a m p l ees s w e r e rrun u n aat t 40KV and with All were and 20MA 20i-1A >lith Cu K - a llppha ha X X- -rad r a diiation. ation. K-a B e c a u s e tthe h e Dakota o r m a t i o n hhas a s nnot o t been a t e d by paleontological Because Dakota FFormation been ddated by paleontological ee~idenceJ v i d e n c e , aa sspecial p e c i a l eeffort f f o r t was n tthe h e ffie i e l ldd and a b o r a t o r y to to was made made iin and llaboratory ffind i n d ffossils o s s i l s .. ffiield. eld. No ffoss o s s iil l rremains e m a i n s of n y kkii nnd d w e r e oobserved b s e r v e d iin n the the of aany were T - s e c t i oon n work r o d u c e d no o s s i l s iindigenous n d i g e n o u s tto o the the Thh i nn-secti work pproduced no ffossils Dakota o r m a t i oon. n. Dakota FFormati Two ssamp a m p l ees s of v e r b a n k ddeposits e p o s i t s and n e oof f aa of ooverbank and oone ppossibl o s s i b l ee ppa a lluuda d a ll eenvironme n v i r o n m e nnt t tthat h a t seemed k e l y tto o pproduce r o d u c e microfossi m i c r o f o s s il s s seemed lliikely w e sselected e l e c t e d ffor o r ffurther u r t h e r oobservat b s e r v a t iioon. n. wee rre Each a m p l ee was d i sintegrated sintegrated Each ssampl was di 6 t r eea a ttin i n gg "ith w i t h kerosene k e r o s e n e and ,later. water. by tr T h e i r examination e x a m i n a t i o n under under a Thei b i n o c u l a r microscope m i c r o s c o p e showed no m mi crofossi i c r o f o s s ills. s. binocular STRATIGRAPHY OF THE DAKOTA FORMATION Various V a r i o u s internal i n t e r n a l stratigraphic s t r a t i g r a p h i c features f e a t u r e s are a r e diagnostic d i a g n o s t i c of o f the the Dakota FFormation. Dakota ormation. These be helpful T h e s e may be h e l p f u l in i n recognition r e c o g n i t i o n of of the the f o r m a t i o n and in i n understanding u n d e r s t a n d i n g tthe h e environment e n v i r o n m e n t of of deposition d e p o s i t i o n and formation paleotopography. paleotopography. Two east-\'/est Two e a s t - w e s t cross-sections c r o s s - s e c t i o n s (figure (figure 3 3 and 44 ) on e a c h side s i d e of the U i n t a Mountains M o u n t a i n s and a a north-south n o r t h - s o u t h cross-section cross-section each of the Uinta ( f i g u r e 5) across a c r o s s the the m o u n t a i n s summarize s u m m a r i z e tthe h e stratigraphic s t r a t i g r a p h i c features features (figure mountains w i t h i n the t h e Dakota. Dakota. within Figure 2 2 is is a a regional r e g i o n a l map showing s h o w i n g the t h e location location Figure o f tthe h e cross-sections c r o s s - s e c t i o n s in i n the t h e study s t u d y area. area. of Types T y p e s of of Outcrops Outcrops Sedimentary of the Uinta lountains S e d i m e n t a r y deposits d e p o s i t s on tthe h e flanks f l a n k s of the U i n t a r'M ountains are be traced a r e tilted t i l t e d almost a l m o s t vvertical e r t i c a l and and can c a n be t r a c e d in in a a general g e n e r a l east-west east-west ddirection i r e c t i o n for f o r many miles. miles. ·pattern. pattern. outcrops. outcrops. The Dakota Dakota conforms c o n f o r m s tto o that t h a t regional r e g i o n a l outcrop outcrop Locally, Dakota has L o c a l l y , holt/ever, h o w e v e r , the t h e Dakota h a s three t h r e e eexclusive x c l u s i v e types t y p e s of of Two aare and one of r e of of the t h e channel c h a n n e l facies f a c i e s and of the t h e overbank overbank faci f a c i ees. s. Channel two types Channel Facies F a c i e s Outcrops.--The O u t c r o p s . - - T h e two t y p e s of o f channel c h a n n e l facies facies o u t c r o p s differ d i f f e r in i n thickness, t h i c k n e s s , sand/shale s a n d / s h a l e ratio, r a t i o , and lateral l a t e r a l concon­ outcrops t i n u i t y of of individual i n d i v i d u a l channels c h a n n e l s and tthe h e outcrop o u t c r o p itself. itself. tinuity These These differences by vvariation d i f f e r e n c e s are a r e caused c a u s e d by a r i a t i o n of of stream s t r e a m characteristics. characteristics. Some of of tthe h e channel c h a n n e l facies f a c i e s outcrops o u t c r o p s rrepresent e p r e s e n t deposition d e p o s i t i o n in i n large large m e a n d e r i n g streams. streams. meandering T h e s e sandstones s a n d s t o n e s form the t h e tthickest h i c k e s t exposures e x p o s u r e s of of These 8 WYO MING 1-- - - - - - - -i - .",;-----::::;~;;= - - -,-- 3 ............ .................. .... :::. :::;;:::: :::::::;::::: .................. ........ ......... ..... . 7 8 • ROOSEVELT I" UI NTA I BASIN I RANGELY, COLO.· scale in miles 1 - M 7 - SM-B 2 - F 3 - C 8 - SM-C 4 - S 5 - SM-A 9 - QA 10 - GM 11 - DC 6 - SM-D FFig. i g . 22 — o c a t i o n of r o s s - s e c t i o n s iin n sstudy t u d y area area -- Llocation of ccross-sections LEGEND Lilhology Sedimenlary Struclures Claystone Trough Mudstone Planar ~} Cross-stratIf,cation -;;_~ Siltstone HOrizontal Very Fine Sandstone Ripples Fine Sandstone Medium Sandstone Coarse Sandstone Pebbly Sondslone a Conglomerate SortlnQ Cycles Very well V Well W Moderote M Poorly to P Interbedded Sor.dstone S mudstone Mixed Sand Sizes Carbonaceous Shale very poorly Covered T 3 t 2 t X Cross- stratitication H Horizontal stratification S Structureless R Ripples Flosure bedding G,oded bedding Unconformity 20 ~ Verticol 10 Scale o In Feet MOUNTAIN Fig. East-west on nnorth of U Uinta F i g . 33 --- E a s t - w e s t cross-section c r o s s - s e c t i o n on o r t h fflank l a n k of i n t a Mountains Mountains B 7 - - - - - . ! - I I - - - - - - I I MILES w H w x 6 ----_.~10i---- MOWRY SHALE STAGE I W~~'~X F i g . 4 -— East-west E a s t - w e s t cross-section c r o s s - s e c t i o n on south s o u t h flank f l a n k of of U i n t a Mountains Mountains F"ig. Uinta o C 2 ~---37 MILES 7 4.5 MILES 9 ----~----9 MILES c' 10 ----~ MOWRY SHALE z o I« 2 a:: o l..i.. ~ o ~ « o w~'tI.~" V w '. ~x H " x Fig. 5 -- North-south cross-section across Uinta Mountains - 12 the Dakota in the study area. t h e Dakota i n t h e s t u d y a r e a . The section at Finch Draw, for example, The s e c t i o n a t F i n c h Draw, f o r e x a m p l e , is approximately 250 feet thick, section section i s a p p r o x i m a t e l y 250 f e e t t h i c k , sr~-B is 112 feet thick, and t h i c k , and SM-B i s 112 f e e t at Draw the a t Steinaker S t e i n a k e r Draw t h e Dakota Dakota is i s also a l s o 112 112 feet f e e t thick. thick. Other O t h e r sections sections were also deposited in the same type of fluvial system, but are not w e r e a l s o d e p o s i t e d i n t h e same t y p e of f l u v i a l s y s t e m , b u t a r e n o t as thick. as t h i c k . Recognition of meandering stream deposits will be discussed R e c o g n i t i o n of m e a n d e r i n g s t r e a m d e p o s i t s w i l l be d i s c u s s e d under the heading of fluvial channels. channels. These sandstones also have T h e s e s a n d s t o n e s a l s o have under t h e heading of f l u v i a l aa high sand/shale ratio compared to the other channel deposits, h i g h s a n d / s h a l e r a t i o compared t o t h e o t h e r c h a n n e l d e p o s i t s , ranging from 2.3/1 ttoo 13/1 (figure 6). 13/1 ( f i g u r e 6 ) . Many fluvial channels can Many f l u v i a l c h a n n e l s c a n r a n g i n g from 2 . 3 / 1 be traced several hhundred feet with little change in channel thickness. undred f e e t with l i t t l e change in channel t h i c k n e s s . be t r a c e d s e v e r a l No channels were observed that completely pinch out within the outcrop. outcrop. No c h a n n e l s w e r e o b s e r v e d t h a t c o m p l e t e l y p i n c h o u t w i t h i n t h e The outcrop The o u t c r o p itself i t s e l f is i s also a l s o laterally l a t e r a l l y continuous, c o n t i n u o u s , forming forming unbroken exposures several hundred feet long. unbroken e x p o s u r e s s e v e r a l hundred f e e t l o n g . thick, thick, The sections at Finch The s e c t i o n s a t F i n c h Draw, Draw and well Draw, Steinaker S t e i n a k e r Draw and SM-B SM-B are a r e all all w e l l over o v e r 1000 1000 feet f e e t long. long. The by sma The other o t h e r type t y p e of of channel c h a n n e l ffac a c iiees s outcrop o u t c r o p It/as was formed formed by s m a11l ler er streams s t r e a m s (figure ( f i g u r e 7). 7). The The exact e x a c t nnature a t u r e of of tthe h e stream s t r e a m characteristics, characteristics, however, h o w e v e r , is i s still s t i l l somewhat somewhat iin n qquestion. uestion. These T h e s e streams s t r e a m s probably probably on an an alluvial rrepresent e p r e s e n t deposition d e p o s i t i o n on a l l u v i a l coastal c o a s t a l pplain l a i n (Allen, ( A l l e n , 1965) 1965) with with tthe h e sea s e a tto o the t h e nnorth. orth. The morphology The outcrop outcrop m o r p h o l o g y of of these t h e s e ssmaller m a l l e r stream stream from tthat channels c h a n n e l s is i s decidedly d e c i d e d l y different d i f f e r e n t from h a t of of the t h e llarger a r g e r channels. channels. suggests s u g g e s t s substantial s u b s t a n t i a l changes c h a n g e s iin n tthe h e stream s t r e a m system. system. This This The The thickness t h i c k n e s s of of these t h e s e deposits d e p o s i t s are a r e less l e s s than t h a n tthose h o s e of of the t h e other o t h e r stream s t r e a m ssystem. ystem. The The section Dra\'1 is s e c t i o n aat t Cholecherry C h o l e c h e r r y Draw i s 82 82 ffeet e e t thick t h i c k and and the t h e Dinosaur, Dinosaur, Colorado C o l o r a d o section s e c t i o n is i s 53.5 5 3 . 5 feet f e e t thick. thick. The The sand/shale s a n d / s h a l e ratio r a t i o for f o r these these two sections and 1/1.5 two s e c t i o n s are a r e 1.1/1 1 . 1 / 1 and 1 / 1 . 5 respectively, r e s p e c t i v e l y , which w h i c h is i s less l e s s than than mentioned meandering tthe h e ppreviously reviously m entioned m e a n d e r i n g channel c h a n n e l system. system. Individual Individual channels c h a n n e l s are a r e much much lless e s s extensive e x t e n s i v e llaterally a t e r a l l y tthan h a n tthose h o s e of of the t h e former former 13 F i g .. 66 ---Outcrop - O u t c r o p of rge m e a n d e r i n g sstream t r e a m ddeposit e p o s i t ((section s e c t i o n SM-B SM-B)) Fig of llaarge meandering sshowing h o w i n g ccyclic y c l i c ddepos e p o s i ttiion o n of v i a l cchannels. hannels. O u t c r o p tthickness h i c k n e s s about about of fflluuvial Outcrop feet. 112 feet. FFig. i g . 77 ---Outcr - O u t c r oop p of l l u v i a l ppll aain i n sstream t r e a m ddeposit e p o s i t ((section s e c t i o n M) s h o w i nng g of aalluvial M) shOl'li low a n d / s h a l e rrat a t i ioo, > ppinching i n c h i n g oout u t of h a n n e l ss and c r e v a s s e - s ppll aay y 1m'/ 'ssand/shale of cchannel and crevasse-s ddeposits e p o s i t s .. 14 stream system. Channels mayor may not have the same lateral dimen- stream system. C h a n n e l s may o r may n o t have t h e same l a t e r a l dimen­ sions as the outcrop. Because of the low sand/shale ratio, those sions as the outcrop. B e c a u s e of t h e low s a n d / s h a l e r a t i o , those channels that do pinch out within an outcrop are completely surrounded c h a n n e l s t h a t do p i n c h o u t w i t h i n an o u t c r o p a r e c o m p l e t e l y by fine-grained overbank material. by f i n e - g r a i n e d overbank m a t e r i a l . surrounded Very few small channel deposits, Very few s m a l l if any) are in direct contact with one another. i f a n y j a r e i n d i r e c t c o n t a c t w i t h one a n o t h e r . separated vertically by overbank material. s e p a r a t e d v e r t i c a l l y by o v e r b a n k m a t e r i a l . channel deposits, Virtually all are Virtually all are The outcrops are also The o u t c r o p s a r e also less extensive than those originating from a large meandering stream l e s s e x t e n s i v e t h a n t h o s e o r i g i n a t i n g from a l a r g e m e a n d e r i n g stream At Dinosaur, Colorado, the lateral exposure of such outcrops system. system. At D i n o s a u r , C o l o r a d o , t h e l a t e r a l e x p o s u r e of such outcrops was not directly measured; however, they were roughly 200-300 feet was n o t d i r e c t l y m e a s u r e d ; h o w e v e r , t h e y were r o u g h l y 200-300 feet long and separated from the next Dakota outcrop by 300-400 feet of l o n g and s e p a r a t e d from t h e n e x t Dakota o u t c r o p by 3 0 0 - 4 0 0 f e e t of very poorly exposed overbank material. very p o o r l y exposed overbank material. Overbank F a c i e s Outcrops.--Informative O u t c r o p s . - - I n f o r m a t i v e outcrops o u t c r o p s of of tthe h e overbank overbank Overbank Facies facies f a c i e s are a r e rrare a r e in i n the t h e study s t u d y area. area. Because B e c a u s e of of tthe h e paucity p a u c i t y of o f sandstone sandstone and and tthe h e llack a c k of of channel c h a n n e l deposits, d e p o s i t s , the t h e overbank o v e r b a n k facies f a c i e s is i s almost a l m o s t always always aa slope-former. slope-former. bboth. oth. It I t is i s usually u s u a l l y covered c o v e r e d with w i t h vegetation, v e g e t a t i o n , talus t a l u s or or The Dakota The overbank o v e r b a n k facies f a c i e s of of tthe he D a k o t a iis s therefore t h e r e f o r e characterized characterized i t s slope-forming s l o p e - f o r m i n g hhabit, a b i t , and rare r a r e sandstone s a n d s t o n e and lack l a c k of of channel channel by its deposits. deposits. T h i s , in i n effect, e f f e c t , pprovides r o v i d e s few a t u r a l exposures. exposures. few nnatural This, A A s i n g l e rroadcut o a d c u t on Highway 40, 4 0 , of o f which w h i c h aatt least l e a s t ppart a r t rrepresents e p r e s e n t s the the single o v e r b a n k facies, f a c i e s , did d i d allow a l l o w meaningful m e a n i n g f u l observations o b s e r v a t i o n s tto o be m ade. made. overbank It It s h o u l d be noted n o t e d tthat h a t tthis h i s ffacies a c i e s is i s also a l s o ppresent r e s e n t iin n outcrops o u t c r o p s of of the the should c h a n n e l facies, f a c i e s , bbut, u t , as a s shown by h e sand/shale s a n d / s h a l e rratio, a t i o , it i t is is a a minor minor by tthe channel c o n s t i t u t e n t in i n tthe h e large large m e a n d e r i n g stream s t r e a m deposits d e p o s i t s and forms forms constitutent meandering a p p r o x i m a t e l y 50 percent p e r c e n t of of the t h e channel c h a n n e l deposits d e p o s i t s originating o r i g i n a t i n g on the the approximately a l l u v i a l coastal c o a s t a l plain. plain. alluvial 15 Formational F o r m a t i o n a l Contacts Contacts The Dakota-Cedar D a k o t a - C e d a r Mountain M o u n t a i n contact c o n t a c t ;s i s uunconformable. nconformable. Relatively Relatively l a r g e Dakota Dakota streams s t r e a m s have h a v e iincised n c i s e d into i n t o tthe h e uunderlying n d e r l y i n g Cedar Cedar Mountain Mountain large F o r m a t i o n as a s shown by e r o s i o n a l channels c h a n n e l s filled filled w i t h sandstone s a n d s t o n e and Formation by erosional with m i n o r conglomerate. conglomerate. minor R e l i e f of of tthis h i s erosional e r o s i o n a l surface s u r f a c e is i s as a s much as as Relief f e e t ((Hansen, H a n s e n , 1965). 1965). 50 feet a g n i t u d e of of the t h e time t i m e hiatus h i a t u s or o r the the The m magnitude amount oof f sediment s e d i m e n t removed a t this t h i s surface s u r f a c e was nnot o t determined. determined. amount removed at W h e r e v e r this t h i s contact c o n t a c t is i s locally l o c a l l y exposed, e x p o s e d , it i t iis s easily e a s i l y recognized recognized Wherever a s an erosional e r o s i o n a l uunconformity. nconformity. as R e g i o n a l l y , it i t is i s considered considered a a disdisRegionally, conformi Boni c o n f o r m i tty y (Hansen (Hansen and B o n i11 l l aa,, 1956, 1 9 5 6 , Hansen, H a n s e n , 1965). 1965). p p e r contact contact w i t h tthe h e Mowry Formati F o r m a t i oon n is i s pprobably r o b a b l y unconuncon­ The uupper \'Jith formable. formable. The marine The contact c o n t a c t separates separates a a ttransgressive ransgressive m a r i n e ddeposit e p o s i t from from a continental c o n t i n e n t a l fluvial f l u v i a l deposit. deposit. Since S i n c e the t h e Dakota is i s continental, continental, i t probably p r o b a b l y represents r e p r e s e n t s a time t i m e of of sub-aerial s u b - a e r i a l erosion e r o s i o n and localized localized it s t r e a m deposition. deposition. stream T h e r e f o r e , it i t iis s likely l i k e l y tthat h a t the t h e uupper p p e r contact contact Therefore, rrepresents e p r e s e n t s an interruption i n t e r r u p t i o n of of deposition d e p o s i t i o n for f o r some unknown l e n g t h of unknown length time. time. I t is i s still s t i l l not n o t known how the t h e sea s e a ttransgressed r a n s g r e s s e d over o v e r the the It s h o r e sands. sands. shore P h y s i c a l l y , the t h e contact c o n t a c t is i s sharp s h a r p above a b o v e the t h e channel channel Physically, f a c i e s and almost a l m o s t uunrecognizable n r e c o g n i z a b l e above a b o v e tthe h e overbank o v e r b a n k facies. facies. facies FLUV IAL CHANNELS FLUVIAL CHANNELS D e t a i l eed d observations o b s e r v a t i o n s of of tthe h e Dakota f l u v i a l cha c h a nnnels n e l s were w e r e mad made Detail Dakota fluvial e tto o ddete e t e rrmine m i n e tthe h e nature n a t u r e of of the t h e anc a n c ient i e n t streams s t r e a m s and uunderstand n d e r s t a n d the the pproces r o c e s sses e s tth h aatt w e r e operative o p e r a t i v e during d u r i n g ddeposition e p o s i t i o n .. \'Iere T h i ss was ac a chie h i e vved ed Thi by eexamining x a m i n i n g rroock c k ttypes, y p e s , channe c h a n n e ll tthicknesses, h i c k n e s s e s , i nntern t e r n aal l vverti e r t i ccal a l pprofil r o f i l ees s and n f e r r e d fflow l o w regimes r e g i m e s .. and iinferred structures, structures, The e x t u r e was a l so so The ttexture was al sstudied, t u d i e d , bbut u t iis s ddii ssc c uussed s s e d uunder n d e r iits t s own hhead e a d iing n g .. C h a r a c t e r ist s t ic i cs Characteri oof f ssingle i n g l e cchanne h a n n e ll ss w i l l be e x a m i n e d ffirst, i r s t , tthe h e nn ffollO\,ed o l l o w e d by "ill be examined by aa ddii sscuss c u s s iioon n of of tthe h e superpositi s u p e r p o s i t i oon n of h a n n e l s and s u l t i n gg cycli cyclic of cchannels and tthhee rr eesultin ffeatur e a t u r ees s of h e cchannel hannel of tthe f a c i e s .. facies Rock Rock Types Each v i a l l cchannel h a n n e l can i v i d e d iinto n t o two i t h o l o g i c units. units. Each fflluuvia can be be ddivided two llithologic The ffirst The i r s t uunit n i t iis s aa ccoarse, o a r s e , ppoorly-sorted o o r l y - s o r t e d bbasal a s a l ssandstone a n d s t o n e oor r concon­ gglomerate l o m e r a t e tthat h a t ddirectly i r e c t l y ooverlies v e r l i e s tthe h e eerosional r o s i o n a l ssurface u r f a c e aat t tthe h e bottom bottom oof f tthe h e cchannels h a n n e l s .. E t r e m e s iin n ggra r a iins n s iizze e rrange a n g e from m e diium-gra u m - g r a i nned ed Exx tremes f rom med ssandstone a n d s t o n e tto o ppebble e b b l e ccongl o n g l oomerate m e r a t e .. IIntenned n t e r m e d i aate t e ggrai r a i nn ssize i z e pebb p e b b ly ly ssandstone a n d s t o n e (5-30% r a v e ll - ssize ize m e r iial) a l ) iis. s , by a r , tthe he m o s t common maatt er by ffar, most (5-30% ggrave llithol i t h o l oogy g y found h e ccoarse-grained o a r s e - g r a i n e d bbasa a s a ll ddeposits e p o s i t s .. fou nd iinn tthe Whenever ggravel r a v e l --s s iize ze m a t e r i a l iiss ppresent r e s e n t , , eeither i t h e r iin n ppebbly e b b l y ssandstone a n d s t o n e or or material ccongl o n g l oomerate m e r a t e ,. ggranule-s r a n u l e - s iized zed m a t e r i aal l iis s more h a n pebbles pebbles materi more common conunon tthan iin n tthe h e bbasa a s a ll uunits n i t s .. T r u e ppebble e b b l e ccongl o n g l oomerate m e r a t e iis s rrare. a r e , bbut u t presen p r e s e n t. t. True Most o n g l o m e rate r a t e iis s aact c t uua a lll l yy ggranul r a n u l ee-conglome - c o n g l o m e rate. rate. Most cconglome The g r a v e l - ssized ized The gravel- m a t e r i aal l iiss composed hert, m e t a morphi o r p h i cc rroock c k ffragments r a g m e n t s and materi composed of of cchert. metam and 17 sedimentary s e d i m e n t a r y rock r o c k fragments. fragments. The basal commonly contain The b a s a l deposits d e p o s i t s commonly contain b o u l d e r - s i z e fragments f r a g m e n t s of of bank bank material. material. boulder-size T h e s e fragments f r a g m e n t s are a r e primarly primarly These m u d s t o n e and lesser l e s s e r amounts a m o u n t s of of siltstone. siltstone. mudstone E x c e p t for f o r the t h e mediummediumExcept g r a i n e d sandstone, s a n d s t o n e , tthe h e bbasal a s a l bbeds e d s are a r e considered c o n s i d e r e d to t o represent r e p r e s e n t channel channel grained Wood f r a g m e n t s and concretions, c o n c r e t i o n s , commonly reported r e p o r t e d in in Wood fragments llag a g deposits. deposits. o t h e r channel c h a n n e l lag l a g deposits, d e p o s i t s , are a r e nnot o t present p r e s e n t in i n the t h e basal b a s a l units u n i t s of other V i s i b l e sedimentary s e d i m e n t a r y structures s t r u c t u r e s are a r e also a l s o absent absent w i t h only only with Visible the D akota. the Dakota. p o s s i b l e exception. exception. one possible agent. agent. C l a y iis s abundant a b u n d a n t and is i s tthe h e pprimary r i m a r y cementing cementing Clay N The second The s e c o n d lithologic l i t h o l o g i c unit u n i t is i s tthe h e finer f i n e r grained g r a i n e d sandstone sandstone d e p o s i t e d above a b o v e the t h e channel c h a n n e l llag a g deposits. deposits. deposited A s i d e from grain g r a i n size, size, Aside t h i s llithologic i t h o l o g i c unit u n i t is i s characterized c h a r a c t e r i z e d by a b u n d a n t sedimentary sedimentary this by abundant s t r u c t u r e s , sorting, s o r t i n g , color c o l o r and tthe h e friable f r i a b l e nature n a t u r e of of tthe h e ssandstone a n d s t o n e in in structures, tthe h e ooutcrop. utcrop. T h i s uunit n i t forms f o r m s as a s much as a s 95 ppercent e r c e n t of of tthe h e thickness thickness This of the t h e llarger a r g e r channel c h a n n e l deposits d e p o s i t s and lesser l e s s e r ppercentages e r c e n t a g e s of of tthe h e smaller smaller of channels. channels. G r a i n size s i z e ranges r a n g e s from from silt s i l t to t o coarse-grained c o a r s e - g r a i n e d sand, s a n d , but but Grain s i l t s t o n e (Folk, ( F o l k , 1968, 1 9 6 3 , pp.. 27-31) 2 7 - 3 1 ) and ccoarse-grained o a r s e - g r a i n e d sandstone s a n d s t o n e are are siltstone rare. rare. S a n d s t o n e of o f iintermediate n t e r m e d i a t e grain g r a i n size s i z e is i s the the m o s t common and Sandstone most f i n e - g r a i n e d sandstone s a n d s t o n e is i s dominant. dominant. fine-grained tto o absent. absent. G r a v e l - s i z e d material m a t e r i a l is i s rare rare Gravel-sized Where present, p r e s e n t , ggravel r a v e l forms f o r m s isolated i s o l a t e d granules g r a n u l e s randomly randomly d i s t r i b u t e d iin n tthe h e sandstone s a n d s t o n e or o r ppebbly e b b l y stringers s t r i n g e r s in i n tthe h e sandstone. sandstone. distributed Thicknesses Channel Thicknesses t h i c k n e s s e s of of separate s e p a r a t e channels channels w ere m e a s u r e d to t o obtain obtain The thicknesses were measured i d e a of of tthe h e size s i z e of of tthe h e Dakota s t r e a m s and to t o see s e e if i f channel channel some idea Dakota streams cor~elations be made made w within c o r r e l a t i o n s could c o u l d be i t h i n the t h e study s t u d y area. area. o n l y ffully u l l y exposed e x p o s e d channels c h a n n e l s were w e r e uused. sed. only Measurements M e a s u r e m e n t s of The tthicknesses h i c k n e s s e s of of overbank overbank 18 1 deposits were excluded when present in channel facies. d e p o s i t s w e r e e x c l u d e d when p r e s e n t i n c h a n n e l facies. The histogram (figure 8) shows the percent of channel deposits The h i s t o g r a m ( f i g u r e 8) shows t h e p e r c e n t of c h a n n e l plotted against thickness. plotted against thickness. Almost 80 percent of all individual A l m o s t 80 p e r c e n t o f a l l channel deposits are less than 20 feet thick. channel deposits d e p o s i t s a r e l e s s t h a n 20 f e e t thick. individual The remaining 20 The r e m a i n i n g percent range from 20 feet tthick to over 40 feet thick. h i c k t o o v e r 40 f e e t t h i c k . p e r c e n t r a n g e from 20 f e e t 20 This suggests This suggests that during Dakota time there was wide variation in the size, and t h a t d u r i n g Dakota t i m e t h e r e was w i d e v a r i a t i o n in the s i z e , and probably morphology as well, of the streams. p r o b a b l y m o r p h o l o g y a s w e l l , of t h e s t r e a m s . Channel thicknesses from the two different types of channel Channel t h i c k n e s s e s from t h e two d i f f e r e n t t y p e s of c h a n n e l facies outcroRs were compared. f a c i e s o u t c r o p s were compared. A total of 22 fully exposed channels of 22 f u l l y e x p o s e d c h a n n e l s A total associated with the main meandering stream systems were measured. a s s o c i a t e d w i t h t h e main m e a n d e r i n g s t r e a m s y s t e m s w e r e m e a s u r e d . Their thicknesses plot in all 5 catagories of the histogram. Their t h i c k n e s s e s p l o t in a l l 5 c a t a g o r i e s of t h e Seventy-three percent are 20 feet thick or less. S e v e n t y - t h r e e p e r c e n t a r e 20 f e e t t h i c k o r l e s s . percent are 20 feet thick or more. p e r c e n t a r e 20 f e e t t h i c k or more. histogram. The remaining 27 The r e m a i n i n g 27 Nine percent of the 22 channels are Nine p e r c e n t of t h e 22 c h a n n e l s 40 feet or more in thickness. 40 f e e t o r more i n t h i c k n e s s . Seven fully exposed channels were measured from channel facies Seven f u l l y e x p o s e d c h a n n e l s w e r e m e a s u r e d from c h a n n e l f a c i e s outcrops that possibly originated on alluvial coastal plains. o u t c r o p s t h a t p o s s i b l y o r i g i n a t e d on a l l u v i a l c o a s t a l p l a i n s . channel deposits are much more restricted in thickness. c h a n n e l d e p o s i t s a r e much more r e s t r i c t e d i n t h i c k n e s s . seven channels (71.5%) are less than 10 feet thick. s e v e n c h a n n e l s (71.5%) a r e l e s s t h a n 10 f e e t t h i c k . two are betvJeen 10 and 20 feet thiC!<.. thick. two a r e b e t w e e n 10 and 20 f e e t Their Their Five of the F i v e of t h e The remaining The r e m a i n i n g Only two channels (29.5%) Only two c h a n n e l s ( 2 9 . 5 % ) plot in the second bar (10-19.9 feet). feet). p l o t in t h e second bar (10-19.9 Correlation of channels by comparing measured sections was C o r r e l a t i o n of c h a n n e l s by c o m p a r i n g m e a s u r e d s e c t i o n s was attempted but proved to be unsuccessful. a t t e m p t e d b u t p r o v e d t o be u n s u c c e s s f u l . The channels that appear The c h a n n e l s t h a t a p p e a r most likely to be correlated are the largest channels that are in m o s t l i k e l y t o be c o r r e l a t e d a r e t h e l a r g e s t c h a n n e l s t h a t a r e i n close proximity to one another. c l o s e p r o x i m i t y t o one a n o t h e r . Draw and at section Draw and a t s e c t i o n St~-B The basal channels at Steinaker Steinaker The b a s a l c h a n n e l s a t are such a possibility. SM-B a r e s u c h a p o s s i b i l i t y . This noticable This n o t i c a b l e lack of cOt'relation is indicative of the temporal nature of streams. l a c k of c o r r e l a t i o n i s i n d i c a t i v e of t h e t e m p o r a l n a t u r e of s t r e a m s . are 19 50,- 45% ~ c o 401- 34.5% 34.5% ~ VI "'0 C ~ 30 - N=29 r- aJ C C cc; "5 ; 20 - ~ c Q) u 10% ~ ~ 10 - 7% 7% 3.5% 3.5% o 10 20 30 40+ Channel sandstone s a n d s t o n e thickness t h i c k n e s s (feet) (feet) H i s t o g r a m showing s h o w i n g frequency f r e q u e n c y of of channel c h a n n e l thicknesses thicknesses Fig. 8 --- Histogram 20 Sedimentary S e d i m e n t a r y Structures Structures Sedimentary S e d i m e n t a r y structures s t r u c t u r e s are a r e abundant a b u n d a n t in i n tthe h e Dakota Dakota Formation. Formation. D e t a i l e d studies s t u d i e s of of the t h e vvarious a r i o u s structures s t r u c t u r e s made o s s i b l e the t h e interinter­ made ppossible Detailed ppretation r e t a t i o n of o f the t h e general g e n e r a l environment e n v i r o n m e n t of of deposition, d e p o s i t i o n , the t h e nnature a t u r e of tthe h e Dakota s t r e a m s , tthe h e dispersal d i s p e r s a l system s y s t e m ppresent r e s e n t during d u r i n g deposition, deposition, Dakota streams, and the t h e direction d i r e c t i o n of of possible p o s s i b l e ssource o u r c e areas. areas. Cross-stratification.--The m o s t common ttypes y p e s of of primary primary Cross-stratification.--The most s e d i m e n t a r y structures s t r u c t u r e s observed o b s e r v e d in i n tthe h e field f i e l d are a r e ttrough r o u g h and planar planar sedimentary cross-stratification. cross-stratification. T r o u g h structures s t r u c t u r e s are a r e pproduced r o d u c e d by scouring scouring Trough a c t i o n and subsequent s u b s e q u e n t in-filling. in-filling. action S e t s of of trough t r o u g h cross-strata c r o s s - s t r a t a range range Sets i n thickness t h i c k n e s s from from less l e s s tthan h a n two centimeters c e n t i m e t e r s to t o slightly s l i g h t l y more than t h a n one one in meter. m eter. Based Weir (1953) Based on the t h e McKee and Weir ( 1 9 5 3 ) classification, c l a s s i f i c a t i o n , aall l l troughs trough are a r e smalls m a l l - and medium-scale. medium-scale. Planer P l a n e r cross-stratification c r o s s - s t r a t i f i c a t i o n is i s probably probably tthe h e product p r o d u c t of of migrating m i g r a t i n g sand s a n d waves 1960). waves (McDowell, 1960). pplanar l a n a r cross-stratification c r o s s - s t r a t i f i c a t i o n is i s smalls m a l l - and m edium-scale. medium-scale. w i t h troughs, trough As with Only one e x a m p l e of of simple s i m p l e cross-stratification c r o s s - s t r a t i f i c a t i o n was observed. observed. example Inclined I n c l i n e d forset f o r s e t beds b e d s are a r e abundant. abundant. ttangential a n g e n t i a l and aavalanche. valanche. Two ttypes y p e s are a r e recognized, recognized, A v a l a n c h e forsets f o r s e t s suggest suggest a a greater g r e a t e r rate rate Avalanche o f deposition d e p o s i t i o n than t h a n tangential t a n g e n t i a l forsets. forsets. of F o r s e t beds beds Forset from inches rrange a n g e iin n height h e i g h t from i n c h e s to t o several s e v e r a l feet. feet. One example, e x a m p l e , a few few hundred measured h u n d r e d ffeet e e t nnorth o r t h of of m e a s u r e d section s e c t i o n SM-B, has h a s a sset e t of of inclined inclined forset f o r s e t beds b e d s with w i t h essentially e s s e n t i a l l y hhorizontal o r i z o n t a l boundary b o u n d a r y surfaces s u r f a c e s that t h a t are are 10 feet f e e t apart. apart. Horizontal H o r i z o n t a l Stratification.--The S t r a t i f i c a t i o n . - - T h e number number of of occurrences o c c u r r e n c e s of horizontal h o r i z o n t a l stratification s t r a t i f i c a t i o n in i n tthe h e Dakota Dakota iis s subordinate s u b o r d i n a t e only o n l y to t o the the 21 cross-stratified c r o s s - s t r a t i f i e d structures. structures. The occurrence o c c u r r e n c e of of this t h i s type t y p e of stratification, s t r a t i f i c a t i o n , in i n terms t e r m s of of its i t s stratigraphic s t r a t i g r a p h i c pposition o s i t i o n within w i t h i n channel channel deposits, d e p o s i t s , suggests s u g g e s t s tthat h a t it i t is i s sensitive s e n s i t i v e tto o flow f l o w conditions. conditions. For eexample, x a m p l e , where w h e r e tthe h e vvertical e r t i c a l sequence s e q u e n c e of of structures s t r u c t u r e s can c a n be observed observed and the t h e llateral a t e r a l exposure e x p o s u r e is i s not n o t extensive, e x t e n s i v e , horizontal h o r i z o n t a l stratification stratification i s uusually s u a l l y ppresent r e s e n t in i n the t h e uupper p p e r portion p o r t i o n of of channel c h a n n e l ssequences. equences. is When exposures e x p o s u r e s are a r e observed o b s e r v e d laterally, l a t e r a l l y , away from from tthe h e main channel, channel, horizontal h o r i z o n t a l stratification s t r a t i f i c a t i o n is i s often o f t e n tthe h e dominant d o m i n a n t structure s t r u c t u r e as the the c h a n n e l ddeposits e p o s i t s tthin. hin. channel to t o ppreferentially referentially f l u v i a l channels. channels. fluvial Horizontal H o r i z o n t a l stratification s t r a t i f i c a t i o n iin n tthe h e Dakota tends tends ddevelo~ e v e l o p in i n hhigher i g h e r stratigraphic s t r a t i g r a p h i c portion p o r t i o n of of the the T h i s relationship r e l a t i o n s h i p iindicates n d i c a t e s tthat h a t in i n the t h e ancient ancient This D a k o t a channels, c h a n n e l s , horizontal h o r i z o n t a l stratification s t r a t i f i c a t i o n formed formed in i n a relatively relatively Dakota nnarrow a r r o w rrange a n g e of of hydrodynamic h y d r o d y n a m i c pparameters. arameters. V a r i a t i o n in i n the t h e position p o s i t i o n of Variation h o r i z o n t a l stratification s t r a t i f i c a t i o n does d o e s exist, e x i s t , bbut u t abundant a b u n d a n t field f i e l d observations observations horizontal i n d i c a t e that t h a t tthe h e pposition o s i t i o n of of this t h i s type t y p e of of stratification s t r a t i f i c a t i o n is is indicate r e a s o n a b l y consistent. consistent. reasonably Thicknesses T h i c k n e s s e s of of bbedding e d d i n g planes p l a n e s range r a n g e from from a minimum of of .0625 .0625 inches i n c h e s tto o a maximum of of 1.5 1.5 inches. inches. (McKee W e i r , 1953). 1953). (~1cKee and Weir, foot f o o t to t o 21.5 2 1 . 5 feet. feet. The majority majority acu~e re laminations laminations T h i c k n e s s e s of of sets s e t s vvary a r y from from less l e s s than than 1 1 Thicknesses The llength The e n g t h of of horizontal h o r i z o n t a l stratification s t r a t i f i c a t i o n also also vvaries a r i e s from from less l e s s tthan h a n 1 foot f o o t tto o more tthan h a n 20 feet. feet. Based on the the McKee and Weir Weir (1953) medium- and large-scale ( 1 9 5 3 ) classification, c l a s s i f i c a t i o n , small-, s m a l l - , mediumlarge-scale examples e x a m p l e s are a r e ppresent. resent. be nnoted IItt should s h o u l d be o t e d that t h a t small-scale s m a l l - s c a l e examples examples a r e rrare, a r e , and medium- and large-scale l a r g e - s c a l e examples e x a m p l e s are a r e common. are Bedding B e d d i n g Plane P l a n e Features.--Bedding F e a t u r e s . - - B e d d i n g pplane l a n e features f e a t u r e s include i n c l u d e primary primary current c u r r e n t lineation l i n e a t i o n marks, m a r k s , sole s o l e marks, m a r k s , and rib-andr i b - a n d - furrow f u r r o w structure. structure. 22 22 Current marks most C u r r e n t lineation lineation m a r k s are a r e the the m o s t abundant a b u n d a n t and and are a r e associated a s s o c i a t e d with with horizontal h o r i z o n t a l stratification. stratification. Sole S o l e marks m a r k s and and rrib-and-furrow f b - a n d - f u r r o w structures structures were w e r e observed o b s e r v e d iin n only o n l y one one locality. locality. The ssole marks were The ole m arks w e r e found found under under aa ledge l e d g e in in a a pebble p e b b l e conglomerate c o n g l o m e r a t e where w h e r e underlying u n d e r l y i n g shale s h a l e beds b e d s had had bbeen e e n eroded e r o d e d away. away. The was found The rrib-and-furrow i b - a n d - f u r r o w sstructure t r u c t u r e was found on on a a piece piece of o f Dakota D a k o t a float. float. Ripple and RRipple Cross-Lamination.--Asymmetric R i p p l e Marks and ipple C r o s s - L a m i n a t i o n . - - A s y m m e t r i c ripple ripple marks m a r k s are a r e rare r a r e in i n the t h e Dakota, D a k o t a , bbut u t are a r e present p r e s e n t in i n the t h e upper u p p e r portions portions o f some channels. channels. of A s m a l l - s c a l e , asymmetric, asymmetric, A few few small-scale, current-formed current-formed marks were rripple ipple m arks w e r e found found in i n fine-grained f i n e - g r a i n e d fluvial f l u v i a l sandstone. sandstone. Likewise, Likewise, two e x c e p t i o n a l l y good exposures e x p o s u r e s of of w e l l ddeveloped e v e l o p e d linquoid l i n q u o i d ripples ripples two exceptionally well were found at w e r e found a t the t h e top t o p of of channels c h a n n e l s at a t section s e c t i o n SM-B. In addition a d d i t i o n to to mal'ks rripple ipple m a r k s as as a a bbedding e d d i n g pplane l a n e feature, f e a t u r e , rripple i p p l e cross-lamination, cross-lamination, or o r flaser f l a s e r bbedding, e d d i n g , is i s also a l s o ppresent r e s e n t in i n the t h e upper u p p e r pportions o r t i o n s of of some fluvial f l u v i a l channels. channels. Occurrences O c c u r r e n c e s of of flaser flaser more common bb~dding e d d i n g are a r e more t h a n ripple r i p p l e marks. marks. than Other Types.--Several Other T y p e s . - - S e v e r a l oother t h e r types t y p e s of of sedimentary s e d i m e n t a r y structures structures were w e r e also a l s o rrecognized. ecognized. They include i n c l u d e bbiogenetic i o g e n e t i c features f e a t u r e s (worm tracks), tracks), s k r i n k a g e cracks, c r a c k s , disturbed d i s t u r b e d bedding, b e d d i n g , overturned o v e r t u r n e d beds b e d s and massive massive skrinkage bbeds. eds. A l l bbut u t the t h e massive m a s s i v e and overturned o v e r t u r n e d bbeds e d s aare r e rrare. are. All The m a s s i v e bbeds e d s constitute c o n s t i t u t e sizable s i z a b l e portions p o r t i o n s of of a a few channels. channels. massive They w e r e ttermed e r m e d massive m a s s i v e if i f sstructures tructures w e r e iinvisible n v i s i b l e or o r too t o o faint f a i n t tto o be were were rrecognized. ecognized. Probably m o s t of of tthese h e s e beds b e d s contain c o n t a i n some ttype y p e of Probably most s t r u c t u r e , probably p r o b a b l y planar p l a n a r cross-stratification c r o s s - s t r a t i f i c a t i o n or o r horizontal horizontal structure, stratification. stratification. 23 Vertical V e r t i c a l Structure S t r u c t u r e Profile Profile D a k o t a channel c h a n n e l depos d e p o s its i t s sho'l' show a recurring r e c u r r i n g sequence s e q u e n c e of o f sedimentary sedimentary Dakota s t r u c t u r e s (figure ( f i g u r e 9). 9). structures A s c e n d i n g upward from the t h e base b a s e of of the the Ascending c h a n n e l s , this t h i s sequence s e q u e n c e begins b e g i n s with w i t h channel c h a n n e l lag l a g deposits, d e p o s i t s , which which channels, u s u a l l y have h a v e no structure. structure. usually t h e channel c h a n n e l lag l a g deposits, d e p o s i t s , in in Above the a s c e n d i n g order, o r d e r , are a r e trough t r o u g h cross-stratification, c r o s s - s t r a t i f i c a t i o n , planar p l a n a r crosscrossascending s t r a t i f i c a t i o n , horizontal h o r i z o n t a l lamination l a m i n a t i o n and ripple r i p p l e cross-lamination cross-lamination stratification, ( n o t ah'lays a l w a y s present). present). (not T h i s sequence s e q u e n c e compares c o m p a r e s vlell w e l l with w i t h studies s t u d i e s of of This p o i n t bar b a r sequences s e q u e n c e s by Bernard B e r n a r d and Major Major (1963) ( 1 9 6 3 ) and Visher V i s h e r (1965). (1965). point T h i s interpretation i n t e r p r e t a t i o n is i s strengthened s t r e n g t h e n e d with w i t h studies s t u d i e s by Allen, Allen, This 1964, 1964~ 1 9 6 5 , 1970; 1 9 7 0 ; Allen A l l e n and Friend, F r i e n d , 1968; 1 9 6 8 ; Frazier F r a z i e r and Osanik, O s a n i k , 1961; 1961; 1965, F r i eend, n d , 1965; 1 9 6 5 ; Harms, 1963. 1963. Fri Channels C h a n n e l s of of possible p o s s i b l e alluvial a l l u v i a l coastal c o a s t a l pplain l a i n deposition d e p o s i t i o n do not not fit of large meandering f i t tthis h i s scheme as a s well w e l l as a s deposits d e p o s i t s of large m e a n d e r i n g streams. streams. d i f f e r e n c e is i s that t h a t trough t r o u g h cross-stratification c r o s s - s t r a t i f i c a t i o n iis s less less The main main difference a b u n d a n t in i n tthe h e former f o r m e r case. case. abundant f i g u r e 9, 9 , is i s 5-3-2-1. 5-3-2-1. figure A more s e q u e n c e , aass numbered in A more common sequence, numbered in W h a t e v e r tthe h e sequence s e q u e n c e is, i s , however, h o w e v e r , ascending ascending Whatever s t r u c t u r e s always a l w a y s indicate indicate a a decrease d e c r e a s e iin n flow f l o w intensity. intensity. structures As already already iindicated, n d i c a t e d , no two cchannels h a n n e l s aare r e eexactly x a c t l y aalike, like, w h i c h rreflects e f l e c t s the the which v a r i a b i l i t y of h e bbasic a s i c sstl'eam t r e a m pparameters a r a m e t e r s of h a n n e l ddepth, e p t h , \'/idth, width, variability of tthe of cchannel and fflow l o w velocity. velocity. and The tthicknesses of ssets of ssedimentary (McKee and The h i c k n e s s e s of e t s of e d i m e n t a r y sstructures t r u c t u r e s (McKee Weir, were W e i r , 1953) 1953) w e r e observed o b s e r v e d qqualitatively u a l i t a t i v e l y tthroughout h r o u g h o u t tthe h e sstudy t u d y area. area. of ttrough and pplanar Ascending A s c e n d i n g ssets e t s of r o u g h and l a n a r ccross-stratification r o s s - s t r a t i f i c a t i o n ddecrease e c r e a s e in in within tthickness hickness w i t h i n aa ssingle i n g l e cchannel. hannel. lless e s s cconsistent. onsistent. Horizontal H o r i z o n t a l sstratification t r a t i f i c a t i o n is is At one one pparticularily well At articularly w e l l eexposed x p o s e d cchannel hannel at at GENERALIZED POINT POINT BAR BAR SEQUENCES SEQUENCES GENERALIZED BERNARD & &MAJOR MAJOR (1963) BERNARD (1963) VISHER (1965) VISHER (1965) l. 1. Small rripple Small i p p l e crosscrosssstratification t r a t i f i c a t i o n ((or o r smallsmallsscale) cale) 22.. 22.. Horizontal H orizontal 33.. 3. 3. Giant G i a n t rripple i p p l e crosscrossstratification s t r a t i f i c a t i o n (or (or medium-scale) medium-scale) Festoon F e s t o o n oor r planer planer sstrati trati 3. 3. Festoon F e s t o o n or o r planar planar stratification; s t r a t i f i c a t i o n ; well well sorted sorted l. 1. I I Ripple R i p p l e crosscrosssstratification t r a t i f i c a t i o n zone zone 4. 4. lamination lamination Poor bedding Poor bedding 44.. Horizontal H o r i z o n t a l llaminated a m i n a t e d zone zone &silt ffine i n e ssand and & silt Basal B a s a l zzone; o n e ; poorly poorly stratified stratified I Fig. Fig. 9 9 DAKOTA DAKOTA FORMATION FORMATION -- N. N. E. E. UTAH UTAH l. 1. R i p p l e crosscrossRipple stratification stratification 22.. Horizontal H orizontal 33.. Planar P lanar 4. 4. Trough cross-stratification cross-stratification 5. 5. B a s a l zone; z o n e ; ppoorly o o r l y sorted; sorted; Basal rred e d color color lamination lamination cross-stratification cross-stratification 25 25 INTRACYCLE DAKOTA I N T R A C Y C L E THICKNESS T H I C K N E S S OF O F COSETS: COSETS: D A K O T A FORMATION FORMATION LOCATION L O C A T I O N SM-C SM-C CYCLE NO.2 --25 25 i)~--'/,,=-~~ t=~-=-:::;- ~ 20 ~/-~'--~ COSET STRUCTURES I HORIZONTAL HORIZONTAL I ./. TROUGH TROUGH TROUGH TROUGH I .~ INCLINED INCLINED • / TROUGH TROUGH • "- --- • HORIZONTAL HORIZONTAL STRUCTURELESS STRUCTURELESS \ ./ \ 15 1 5-- HORIZONTAL HORIZONTAL \ STRUCTURELESS STRUCTURELESS 10 -- I HORIZONTAL HORIZONTAL / STRUCTURELESS STRUCTURELESS / • .~ STRUCTURELESS 5- / STRUCTURELESS ~~ o0 • ~~ ~ -----== --- TROUGH • TROUGH I 0 I I1 22 I 3 THICKNESS THICKNESS ft. ft. Fig. F i g . 10 10 44 26 SM-C, the t h e thicknesses t h i c k n e s s e s of of cosets c o s e t s were w e r e examined e x a m i n e d and checked c h e c k e d ffor or a vertical v e r t i c a l ttrend. rend. As seen upward as s e e n from from figure f i g u r e 10, 1 0 , tthe h e cosets c o s e t s tthin h i n upward as do tthe h e sets. sets. Fluvial F l u v i a l Cycles Cycles One of of tthe h e diagnostic d i a g n o s t i c features f e a t u r e s of of the t h e channel c h a n n e l facies f a c i e s iis s the the rrepetition e p e t i t i o n of o f beds b e d s iindicating n d i c a t i n g episodes e p i s o d e s of of fluvial fluvial deposition. deposition. T h i s imparts imparts a a cyclic c y c l i c nnature a t u r e to t o channel c h a n n e l facies f a c i e s outcrops. outcrops. This IItt is is c o n v e n i e n t , therefore, t h e r e f o r e , tto o describe d e s c r i b e such s u c h ddeposition e p o s i t i o n in i n tterms e r m s of of convenient, cycles. cycles. c y c l e rrepresents epresents a a dingle d i n g l e episode e p i s o d e of of ffluvial l u v i a l deposition, deposition, Each cycle i s bounded s u r f a c e of of erosion e r o s i o n bbetltJeen e t w e e n which which and is bounded above and below below by aa surface sediments w e r e continuously c o n t i n u o u s l y deposited. deposited. sediments were o n l y channel c h a n n e l deposits. deposits. only A cycly c y c l y can c a n be composed composed of of A c y c l e s are a r e ddiagnostic i a g n o s t i c of o f channel c h a n n e l facies facies Such cycles o u t c r o p s that t h a t have h a v e hhigh i g h sand/shale s a n d / s h a l e rratios. atios. outcrops C y c l e s can c a n also a l s o have have Cycles bboth o t h channel c h a n n e l and overbank o v e r b a n k deposits, deposits, a a characteristic c h a r a c t e r i s t i c of o f outcrops o u t c r o p s with with low sand/shale s a n d / s h a l e rratios a t i o s (Allen, ( A l l e n , 1964; 1964; A l l e n and F r i e n d , 1968). 1968). Allen Friend, Cycle were measured C y c l e Thicknesses.--Cycle T h i c k n e s s e s . - - C y c l e tthicknesses h i c k n e s s e s were m e a s u r e d and plotted plotted on graphs g r a p h s (figure ( f i g u r e 11). 11). Thicknesses T h i c k n e s s e s include i n c l u d e bboth o t h channel c h a n n e l facies f a c i e s and o v e r b a n k facies f a c i e s where w h e r e ppresent. resent. overbank c y c l e s iin n w h i c h upper u p p e r and lower lower Only cycles which bboundaries o u n d a r i e s were w e r e observed o b s e r v e d were w e r e utilized u t i l i z e d in i n tthe h e pplots. lots. Figure F i g u r e 11 shows tthe h e results r e s u l t s of of cycle c y c l e measurements m e a s u r e m e n t s for f o r tthree h r e e channel c h a n n e l facies facies w i t h hhigh i g h sand/shale s a n d / s h a l e rratios. atios. with tthe h e base b a s e of of the t h e outcrop. outcrop. outcrops outcrops e a c h case c a s e tthe h e tthickest h i c k e s t cycle c y c l e iis s at at In each P r o c e e d i n g uupwards, p w a r d s , the t h e cycles c y c l e s decrease d e c r e a s e in in Proceeding tthickness, h i c k n e s s , reach r e a c h a minimum, and tthen h e n iincrease n c r e a s e in i n tthickness. hickness. Cycle Cycle tthicknesses h i c k n e s s e s in i n channel c h a n n e l facies f a c i e s outcrops o u t c r o p s of of low sand/shale s a n d / s h a l e rratio a t i o do do nnot o t show aa consistent c o n s i s t e n t pattern. pattern. However, investigation i n v e s t i g a t i o n of of more more However, 27 Tt~IC~(~JESSES CYCLES C Y C L E S • CHANNEL OF FORMATION F O R M A T I O DAKOTA T A Location: Location: S p l i t Mtn Split Location: Location: Steinaker S t e i n a k e r Draw Section B Section B C y c1l ee 5 Cyc Top / C y c1l ee 4 Cyc / • \ C y c1l ee 3 Cyc C y c1l ee 22 Cyc Cyclee 11 Cycl Bottom I . T C y c1l ee 4 Cyc C y c1l ee 3 Cyc . / • Top e~ Cyc C y c1l ee 2 .~ C y c l ee 11 Cycl ~ «I J 35 5 15 25 35 THICKNESS (ft.) (ft.) T otal T h i c k n e s s = 102 ft. ft Total Thickness Location: L ocation: • Bottom Bottom 10 i_—i—i—i— 30 50 .• THI CKNESS (ft.) THICKNESS (ft.) Total Thickness T otal T h i c k n e s s = 102 ft. ft, Dinosaur Natl. Quarry D inosaur N a t l . Mon. Q u a r r y Area C y c l e 66 Cycle —i—i—rT CIi Top © I • // C y c1 l ee 55 Cyc C y c l e 44 Cycle C y c1 l ee 3 Cyc C ycle 2 Cycle? C y c l e 11 Cycle I- ."" "e / • Bottom \ Bottom 1 1 L 0o 10 20 THI CKNESS (ft.) THICKNESS (ft.) T otal T h i c k n e s s = 667.5 7 . 5 ft. ft. Total Thickness 11 FFig. i g . 11 28 28 e x p o s u r e s is i s needed n e e d e d to t o confirm c o n f i r m this t h i s observation. observation. exposures I n t e r c y c l e Coset C o s e t Thicknesses.--Coset T h i c k n e s s e s . - - C o s e t thicknesses t h i c k n e s s e s within w i t h i n vertically vertically Intercycle a d j a c e n t cycl c y c l ees s ",ere w e r e measured m e a s u r e d to t o examine e x a m i n e thickness t h i c k n e s s trends t r e n d s across across adjacent cycle c y c l e boundaries b o u n d a r i e s and to t o determine d e t e r m i n e the t h e relationship r e l a t i o n s h i p between b e t w e e n coset coset thicknesses t h i c k n e s s e s and corresponding c o r r e s p o n d i n g cycle c y c l e thicknesses. thicknesses. Sections S e c t i o n s at a t Steinaker Steinaker Draw (S) ( S ) and one on the t h e northside n o r t h s i d e of of Split S p l i t Mountain M o u n t a i n (SM-D) show c o s e t thicknesses t h i c k n e s s e s that t h a t decrease d e c r e a s e upwards u p w a r d s both b o t h within w i t h i n their t h e i r respective respective coset c y c l e s and across a c r o s s the t h e cycle c y c l e boundaries b o u n d a r i e s as a s well w e l l (figure ( f i g u r e 12). 12). cycles At s e c t i o n QA, however, h o w e v e r , no such s u c h ppattern a t t e r n exists. exists. section In I n aaddition d d i t i o n to t o the t h e determination d e t e r m i n a t i o n of of iindividual n d i v i d u a l coset c o s e t thicknesses, thicknesses, mean coset within tthe h e mean c o s e t thickness thickness w i t h i n each e a c h ccycle y c l e was also a l s o determined d e t e r m i n e d and compared compared to t o its i t s ccycle y c l e tthickness. hickness. This mean coset T h i s comparison c o m p a r i s o n of of mean coset thicknesses t h i c k n e s s e s and cycle c y c l e tthicknesses h i c k n e s s e s was found found tto o be essentially essentially a which suggests ddirect i r e c t rrelationship, e l a t i o n s h i p , which s u g g e s t s tthat h a t aas s tthe h e sstream t r e a m channels channels ddecrease e c r e a s e iin n ssize i z e tthe h e sstructures tructures w i t h i n tthe h e cchannel h a n n e l ddeposits e p o s i t s also also within ddecrease e c r e a s e pproportionally r o p o r t i o n a l l y iin n ssize. ize. A l t h o u g h nnot o t sso o oobvious, b v i o u s , tthis h i s same Although QA. rrelationship e l a t i o n s h i p eexists x i s t s for f o r ssection e c t i o n QA. Cycle C y c l e 33 iis s tthe h e tthinnest h i n n e s t cycle cycle and l s o hhas a s tthe h e lleast e a s t mean o s e t tthickness. hickness. and aalso mean ccoset T h i c k e r ccycles, y c l e s , such such Thicker and 66,, have have llarger mean ccoset aas s 1, 1 , 22,, 55 and a r g e r mean o s e t thicknesses. thicknesses. weathering W e a t h e r i n g . - - A ddistinctive istinctive w e a t h e r i n g ppattern a t t e r n iis s uuseful seful Weathering.--A rrecognizing e c o g n i z i n g uupper p p e r and o w e r bboundaries o u n d a r i e s of ycles. and llower of ccycles. for for T h i s iis s especespec­ This iially a l l y hhelpful e l p f u l iin n sstudying t u d y i n g ooutcrops u t c r o p s tthat h a t hhave a v e llittle i t t l e oor r no overbank no overbank ffacies. acies. The h a n n e l llag a g ddeposits e p o s i t s aat t tthe h e bbase a s e of a c h ccycle y c l e are are The cchannel of eeach nnot o t aas s rresistant e s i s t a n t tto o w e a t h e r i n g aas s tthe h e ffiner i n e r ggrained r a i n e d ssandstone a n d s t o n e and weathering commonly o n s p i c u o u s lledges e d g e s oor r iindentations n d e n t a t i o n s iin n outcrops, outcrops, commonly form form cconspicuous 29 INTERCYCLE I N T E R C Y C L E THICKNESSES T H I C K N E S S E S OF O F COSETS:DAKOTA C O S E T S : D A K O T A FORMATION FORMATION LOCATION: LOCATION: S S LOCATION: LOCATION^ SM-D SM-D COSET I CKNESS (ft) COSET TH THICKNESStft) o 5 : COSET THI CKNESS (ft) THICKNESS(ft) o 10 15 15 20 25 T LOCATION: L O C A T I O N QA QA 2 4 6 8 COSET THICKNESS (ft) (ft) -r 12 10 1 T Cyc 1e 6 + + N OJ N Cyc 1e 5 OJ U >, U Cycle 4 t +- Cycle 3 + + Cycl e 2 OJ u >, u Cycle 1 Mean Mean coset thickness Mean coset thickness Mean coset thickness Mean Mean coset coset thickness thickness ft. cycle 6 == 6.0 ft. cycle cycle 22 == 33.7 .7 ft. ft. cycle = 1.9 cycle 2 = 1.9 ft. ft. cycle 1 == 88.1 .1 ft. ft. cycle 1 = 5.3 ft. ft. ft. cycle 5 = 5.5 ft. ft. cycle 4 == 4.0 ft. ft. cycle 3 = 2.5 ft. ft. cycle 2 = 6.5 ft. ft. cycle 1 ==6.1 6.1 ft. Fi F i gg.. 12 \ 30 thereby, marking the vertical limits of each cycle. t h e r e b y , marking the v e r t i c a l l i m i t s of e a c h c y c l e . Rarely, channel Rarely, channel lag deposits are absent and other methods of describing boundary l a g d e p o s i t s a r e a b s e n t and o t h e r m e t h o d s of d e s c r i b i n g locations were used. l o c a t i o n s were used. boundary One of these mehtods involved color changes. One of t h e s e m e h t o d s i n v o l v e d c o l o r changes. Color.--Color C o l o r . - - C o l o r changes c h a n g e s in i n the t h e channel c h a n n e l sandstone s a n d s t o n e ffrequently r e q u e n t l y are are cyclic. cyclic. The eeasily The a s i l y weathered w e a t h e r e d channel c h a n n e l llag a g deposits d e p o s i t s generally g e n e r a l l y are are rreddish-brown. eddish-brown. The ssandstone The a n d s t o n e above a b o v e the t h e channel c h a n n e l llag a g deposits deposits white, w h i t e , bbuff u f f and llight i g h t brown. brown. White when ppresent, W h i t e sandstone, s a n d s t o n e , when resent, is is is is always a l w a y s found f o u n d at a t the t h e top t o p of of channels c h a n n e l s and and is, i s , ttherefore, h e r e f o r e , hhelpful e l p f u l in in delimiting d e l i m i t i n g tthe h e upper u p p e r boundaries b o u n d a r i e s of of cycles. cycles. The w white h i t e coloration c o l o r a t i o n is is matrix rrelated e l a t e d to t o llarge a r g e amounts a m o u n t s of of clay clay m a t r i x (25%). (25%). weathers w e a t h e r s to t o smooth, s m o o t h , rounded rounded surfaces. surfaces. Also, white A lso, w h i t e sandstone sandstone TEXTURE TEXTURE The ttextural e x t u r a l pparameters a r a m e t e r s grain g r a i n size, s i z e , ssorting, o r t i n g , grain g r a i n morphology morphology and maturity m a t u r i t y were w e r e studied s t u d i e d to t o determine d e t e r m i n e what w h a t textural t e x t u r a l features f e a t u r e s are are characterisitic Dakota, c h a r a c t e r i s i t i c of of the the D a k o t a , to t o examine e x a m i n e vvertical e r t i c a l changes c h a n g e s in i n grain grain size, s i z e , and and to t o see s e e if i f any any are a r e uuseful s e f u l in i n iinterpreting n t e r p r e t i n g the t h e depositional depositional envi e n v i rronment. onment. Grain G r a i n Size Size A total A t o t a l of of 150 hand samples s a m p l e s was evaluated e v a l u a t e d for f o r grain g r a i n size s i z e with with the of aa binocular microscope. t h e aid a i d of binocular m icroscope. Grains G r a i n s from from each e a c h sample s a m p l e were were compared with known ggrain compared w i t h sand s a n d samples s a m p l e s of of known r a i n size s i z e and classified c l a s s i f i e d accordaccord­ i n g tto o Wentworth (1922). ing Wentworth (1922). Unimodal s a n d s t o n e and siltstone s i l t s t o n e accounts accounts Unimodal sandstone f o r 83.3 8 3 . 3 percent p e r c e n t of of all a l l samples. samples. for N i n t y - s i x percent p e r c e n t of of the t h e unimodal unimodal Ninty-six s a m p l e s ranges r a n g e s from from very v e r y fine f i n e tto o m edium-grained. samples medium-grained. Bimodal Bimodal sandstone, sandstone, s i l t s t o n e , ppebbly e b b l y sandstone s a n d s t o n e and conglomerate c o n g l o m e r a t e represent r e p r e s e n t tthe h e remaining remaining siltstone, 1 6 . 7 ppercent e r c e n t of of all a l l samples. samples. 16.7 Because B e c a u s e of o f tthe h e abundance a b u n d a n c e of of uunimodal n i m o d a l sandstone s a n d s t o n e and siltstone s i l t s t o n e in in the Dakota, the D a k o t a , a cconcentrated o n c e n t r a t e d effort e f f o r t was made tto o determine d e t e r m i n e and evaluate evaluate unimodal samples. grain g r a i n ssize i z e vvariation a r i a t i o n of of unimodal samples. Such ssamples a m p l e s are a r e useful useful iin n tthis h i s ttyp"e y p e of of study s t u d y bbecause e c a u s e tthey h e y can c a n be rrapidly a p i d l y classified c l a s s i f i e d by grain g r a i n size. size. Where were with Where possible, p o s s i b l e , samples samples w e r e classified classified w i t h grain grain size s i z e categories c a t e g o r i e s (table ( t a b l e 1). 1). Some samples, s a m p l e s , however, h o w e v e r , could c o u l d nnot o t be definitely of them d e f i n i t e l y pplaced l a c e d with w i t h grain g r a i n size s i z e bboundaries o u n d a r i e s even e v e n tthough h o u g h all a l l of a r e well w e l l to t o very v e r y well w e l l sorted. sorted. are T h e s e samples samples w e r e nnoted o t e d and placed p l a c e d at at These were 32 1: TABLE 1: Unimodal siltstone s i l t s t o n e and sandstone sandstone within ooccurances ccurances w i t h i n ggrain r a i n size s i z e boundaries* boundaries* ~ledi urn Medium Very Fine Silt F i n e Fine Fine L o c a t i o n Silt Location SM-A SM-B SM-C Meandering Meandering Stream Stream Deposits Deposits SM-D sr~-D QA QA S S M F Alluvial Alluvial Plain P l a i n Stream S t r e a m DC DC C Deposits C Deposits Overbank Overbank Deposits Deposits GM GM 1 1 2 - - 1 5 6 2 3 3 2 6 9 1 1 1 77 9 77 7 7 2 1 1 Coarse Coarse 5 7 1 No. of No. of Samples Samples 8 - 15 13 11 10 12 9 9 10 1 1 22 2 - 1 6 44 2 44 1 - 7 *A11 samples s a m p l e s vie w e11 l l tto o vvery-well e r y - w e l l sorted sorted *All TABLE 2: 2: Unimodal ssiltstone i l t s t o n e and sandstone sandstone occurances o c c u r a n c e s at a t grain g r a i n size s i z e boundaries* boundaries* Location Very FFine Medium Coarse L o c a t i o n Silt Silt Very i n e Fine F i n e Medium Coarse No. of No. Samples Samples SM-A St~-A Meandering Meandering Stream Stream Deposits Deposits SM-B Sr·1-B SM-C Sf·1-C SM-D QA QA S S M M m ...*» m ™ « - F Alluvial A lluvial P l a i n Stream Stream Plain Deposits Deposits Overbank Overbank Deposits Deposits 3 3 3· 22 22 1 1 2 2 2 • DC DC C 1 3 1 1 1 5 GM GM - 3 22 55 *All *A11 samples s a m p l e s well w e l l to t o vvery-well e r y - w e l l sorted sorted 1 TABLE 33:: TABLE • Meandering M e a n d e r i n g Stream Stream Deposits D eposits All A l l uuvia v i a l1 Pl P lai a i nn Stream S t r e a m Depos D e p o siits ts Total and ssandstone T o t a l uunimodal n i m o d a l ssiltstone i l t s t o n e and a n d s t o n e ggrain r a i n ssize i z e frequency frequency Location L ocation Sil S i l tt SM-A SM-A SM-8 SM-B SM-C SM-C SM-D SM-D QA QA S S M M F F Total Total Percent Percent mm 1 1 22 2.0 2.0 "0 0 00 DC DC C C Total Total Percent P ercent 1 _ GM GM Overbank Deposits Total T otal Overbank D e p o s i t s Percent Percent - 1 I 1 -11 6.25 6.25 6 . 2 5 6.25 _ _ -00 0 -0 0 0 Very Fine Very Fine Fine F ine 1 1 1 6 -' 2 2 1 1 1 -66 66.2 .2 2 1 -33 18.75 18.75 22 -22 16.6 16.6 r,1edium Medium C oarse Coarse 1 55 66 22 33 33 22 1 23 23 23.7 23.7 0 00 1 1 1 33 -2-13 44 2 1 5 . 0 12.5 18.75 1 8 . 7 5 225.0 1 2 . 5 6.25 6.25 _ -00 0 1 I1 1.0 1.0 9 77 99 77 77 55 77 r;r 57 558.8 8.8 33 22 22 1 -88 8.2 8.2 22 22 3 33 25.0 25.0 22 -22 16.6 33.3 3 3 . 3 16.6 4 4 44 1 -11 8.3 8.3 m mm 0 00 _ 1 -11 6.25 6.25 _ _ 00 0 00 0 No. of No. of S amples Samples 8 15 13 14 10 10 14 14 11 12 12 97 97 7 9 T6 16 12 12 12 CO w CO w 34 the t h e appropriate a p p r o p r i a t e grain g r a i n size s i z e boundary b o u n d a r y (table ( t a b l e 2). 2). and 22 are are 1 and summarized su~marized The results r e s u l t s of of tables tables i n table t a b l e 3. 3. in Samp S a m p1l es e s VJere w e r e grouped g r o u p e d and compared for f o r the t h e three t h r e e types t y p e s of of fl f luvi u v i a1 l deposits: deposits: large l a r g e meandering m e a n d e r i n g stream s t r e a m deposits, d e p o s i t s , alluvial a l l u v i a l plain p l a i n stream stream deposits, d e p o s i t s , and overbank o v e r b a n k deposits. deposits. The results r e s u l t s are a r e listed l i s t e d below. below. P e r c e n t Samples S a m p l e s Ranging from Fine F i n e to t o Medium Grain Grain Percent l a r g e meandering m e a n d e r i n g stream s t r e a m deposits d e p o s i t s - - - 90.7% large a l l u v i a l plain p l a i n stream s t r e a m deposits d e p o s i t s - - - - 43.75% 43.75% alluvial o v e r b a n k deposits deposits 58.2% overbank - - -- -- -- -- - - - - P e r c e n t Samples S a m p l e s Ranging from Very Fine F i n e to t o Fine F i n e Grain Grain Percent l a r g e meandering m e a n d e r i n g stream s t r e a m deposits deposits - - large a l l u v i a l plain p l a i n stream s t r e a m deposits deposits - - - alluvial o v e r b a n k deposits deposits overbank - -- -- -- -- -- - - - - - - 66.,0% 66,0% 62.5% 74.9% P e r c e n t Samples S a m p l e s Excluding Percent E x c l u d i n g Fine F i n e - Grained G r a i n e d Samples Samples l a r g e meandering m e a n d e r i n g stream s t r e a m deposits deposits large aalluvial l l u v i a l plain p l a i n stream s t r e a m deposits deposits o v e r b a n k deposits deposits overbank R a t i o of of Very Fine F i n e to to Ratio greater g r e a t e r than than fine-grain fine-grain less l e s s than than fine-grain fine-grain 31.9% 25.0% 24.9% 50.0% 41.6% 41.6% Medium - Grained Grained t~edium large m e a n d e r i n g sstream t r e a m ddeposits eposits - - large meandering aalluvial l l u v i a l pplain l a i n sstream t r e a m ddeposits eposits - - - ooverbank v e r b a n k deposits deposits - -- -- -- -- - - - - - - - 9. 2~~ 9.2% Samples Samples 1/3.8 1/3.8 3/1 3/1 2/1 2/1 P ercent F i n e - Grained G r a i n e d Samples S a m p l e s Only Percent Fine large m e a n d e r i n g stream s t r e a m ddeposits eposits - - large meandering aalluvial l l u v i a l pplain l a i n sstream t r e a m ddeposits e p o s i t s -- - - ooverbank v e r b a n k ddepositse p o s i t s - -- -- -- -- - - - - - - - - - 58.8% 25.0% 333.3% 3.3% 35 On tthe On h e bbasis a s i s of of ggrain r a i n size, s i z e , certain c e r t a i n comparisons c o m p a r i s o n s apparently a p p a r e n t l y are are uuseful s e f u l in i n rrecognizing e c o g n i z i n g llarge arge m e a n d e r i n g stream s t r e a m deposits d e p o s i t s as a s compared compared with wi meandering alluvial a l l u v i a l pplain l a i n stream s t r e a m deposits d e p o s i t s and overbank o v e r b a n k deposits. deposits. The The two y p e s , hhowever, o w e v e r , are a r e similar s i m i l a r in i n each e a c h comparison c o m p a r i s o n and, and, two ttypes, latter latter therefore, therefore, i t is i s nnot o t possible p o s s i b l e to t o distinguish d i s t i n g u i s h them from each e a c h other o t h e r by g r a i n size size it them from by grain comparisons. comparisons. The m o s t significant s i g n i f i c a n t grain g r a i n size s i z e comparisons c o m p a r i s o n s for for most differ­ differ- e n t i a t i n g large large m e a n d e r i n g stream s t r e a m deposits d e p o s i t s from from the t h e other o t h e r two fluvial fluvial entiating meandering d e p o s i t s are: are: deposits a. unimodal samples medium a . ppercent e r c e n t unimodal s a m p l e s rranging a n g i n g from from fine f i n e - tto o medium grained; grained; unimodal samples bb.. ppercent e r c e n t unimodal s a m p l e s less l e s s tthan h a n fine f i n e ggrain r a i n size; size; c. of vvery medium -- grained unimodal samples; c . rratio a t i o of e r y fine f i n e tto o medium g r a i n e d unimodal samples; d. unimodal fine d . ppercent e r c e n t unimodal f i n e -- ggrained r a i n e d samples s a m p l e s only. only. Less L e s s significant s i g n i f i c a n t grain g r a i n size s i z e ccomparisons o m p a r i s o n s are: are: a. a . ppercent e r c e n t unimodal samples s a m p l e s rranging a n g i n g from from very v e r y fine f i n e to to fine f i n e grained; grained; unimodal samples b . ppercent e r c e n t unimodal s a m p l e s greater g r e a t e r than t h a n fine f i n e grained. grained. b. Figure F i g u r e 13 iis s a a frequency f r e q u e n c y pprofile r o f i l e chart c h a r t of o f grain g r a i n sizes s i z e s for f o r each each of o f the t h e tthree h r e e ttypes. ypes. The large meandering The large m e a n d e r i n g stream s t r e a m deposits d e p o s i t s are are characterized by aa limited c h a r a c t e r i z e d by l i m i t e d rrange a n g e of of preferred p r e f e r r e d grain g r a i n sizes s i z e s centering centering a r o u n d fine-grained fine-grained m aterial. around material. The a l l u v i a l pplain l a i n stream s t r e a m deposits deposits The alluvial and overbank by fine-grained o v e r b a n k deposits d e p o s i t s aare r e also a l s o dominated d o m i n a t e d by f i n e - g r a i n e d material, material, b u t lless e s s drastically d r a s t i c a l l y so. so. but of tthe A vvertical A e r t i c a l grain g r a i n size s i z e pprofile r o f i l e chart c h a r t was made of h e large large meandering m e a n d e r i n g stream s t r e a m deposits d e p o s i t s and compared compared with w i t h an iidealized d e a l i z e d grain g r a i n size size p r o f i l e chart c h a r t (Selley, ( S e l l e y , 1972) for for m e a n d e r i n g streams. streams. profile meandering chart The chart iindicates n d i c a t e s the t h e rrepetition e p e t i t i o n of of channel c h a n n e l conditions c o n d i t i o n s at a t tthese h e s e locations. locations. 36 The fining-upward of grain sizes within each cycle is indicative of The f i n i n g - u p w a r d of g r a i n s i z e s w i t h i n e a c h c y c l e i s i n d i c a t i v e of point bar deposits in which laterial accretion was the mode of p o i n t b a r d e p o s i t s i n w h i c h l a t e r i a l a c c r e t i o n was t h e mode of deposition. deposition. The The fining-upward f i n i n g - u p w a r d sequences s e q u e n c e s also a l s o iindicate n d i c a t e decreasing decreasing flow upward w within f l o w intensities i n t e n s i t i e s upward i t h i n each e a c h cycle c y c l e (figure ( f i g u r e 14). 14). As previously noted, bimodal samples account for a small portion samples a c c o u n t f o r a small p o r t i o n As p r e v i o u s l y n o t e d , bimodal of o f the t h e samples. samples. Most Most are a r e pebbly p e b b l y sandstone s a n d s t o n e and and conglomerate c o n g l o m e r a t e and and rrepresent e p r e s e n t channel c h a n n e l lag l a g deposits. deposits. 70 meandering m e a n d e r i n g streams streams 11'1' 60 (]) r- 0- E ro 50 If- 40 .fJ C 30 11'1 o alluvial plain streams /0 (]) U 20 0.. 10 ~ (]) ./----e~~ /. ------." ,,," O~~~~---r--~+---~----'-----r-~-~-~-~-·---, silt very fine fine medium coarse . Grai n size Fig. 13 -- Frequency profile chart of grain sizes Sorting Sorting A A ttotal o t a l of of 138 sandstone s a n d s t o n e and siltstone s i l t s t o n e samples s a m p l e s was examined examined uunder n d e r a bbinocular i n o c u l a r microscope m i c r o s c o p e to t o determine d e t e r m i n e sorting. sorting. classified by visual with c l a s s i f i e d by v i s u a l comparison comparison w i t h a sorting s o r t i n g chart chart pp.. 214). 214). Each sample Each s a m p l e was ((Compton~ C o m p t o n , 1962, 1962, The degree most d e g r e e of of sorting s o r t i n g for for m o s t samples s a m p l e s can c a n be readily readily classified. classified. Some samples, s a m p l e s , hhowever, o w e v e r , aapparently p p a r e n t l y have h a v e intermediate intermediate VERTICLE V E R T I C L E Idealized I d e a l i z e d Meandering Meandering Channe Channel1 Profil P r o f i le (after ( a f t e r Selley, S e l l e y , 1970) 1970) Gravel G r a v e l Sand Sand Si 1 11t Clay Clay GRAIN G R A I N PROFILE SIZE S I Z E P R O F I L E CYCLES DAKOTA OF O F FOR~1ATION Steinaker S t e i n a k e r Draw Sp S p1l it i t Mtn. Area Dinosaur Natl. D inosaur N a t l . Monument Quarry Q u a r r y Area Section S~1-8 S e c t i o n SM-B • .... i i - 100 100 100 J 7 - 80 80 60 60 ft. ft, - 40 - 40 20 20 (No Scale) Scale) FLUVIAL F L U V I A L Fi F i gg.. 14 14 60 38 degrees of sorting and are so classed. The results are presented d e g r e e s of s o r t i n g and a r e s o c l a s s e d . The r e s u l t s a r e presented in table 4. in t a b l e 4. Degrees of sorting ranging from well to very \'/ell are dominant D e g r e e s of s o r t i n g r a n g i n g from w e l l and account for 81.8% of all samples. and a c c o u n t f o r 81.8% of a l l t o v e r y v/ell a r e dominant The single most common sorting samples. The s i n g l e m o s t common sorting category is \'/ell sorted and 39.8% of all samples fall in this class. c a t e g o r y i s well s o r t e d and 39.8% o f a l l samples f a l l in t h i s class. Samples ranging from very well to \'/ell sorted plus very poorly sorted S a m p l e s r a n g i n g from v e r y w e l l t o well samples total 89.7% of all the samples. samples t o t a l 89.7% of a l l the samples. sorted plus very poorly sorted Instances of sorting between I n s t a n c e s of s o r t i n g between well and very poorly sorted material are much less common (9.4%). well and v e r y p o o r l y s o r t e d m a t e r i a l a r e much l e s s common ( 9 . 4 % ) . Contrary to grain size, sorting does not appear to be a reliable C o n t r a r y t o g r a i n s i z e , s o r t i n g d o e s n o t a p p e a r t o be a reliable indicator by which to differentiate the three fluvial types of i n d i c a t o r by w h i c h t o d i f f e r e n t i a t e deposits. deposits. the three fluvial types of Slight differences are present, such as the relatively Slight differences are present, such as t h e relatively limited ranges of degrees of sorting for alluvial plain stream samples l i m i t e d r a n g e s of d e g r e e s of s o r t i n g f o r a l l u v i a l plain stream samples and the dominance of very \vell sorted samples in overbank sandstone. and t h e d o m i n a n c e of v e r y w e l l s o r t e d samples in overbank sandstone. These differences, however, are not considered significant because These d i f f e r e n c e s , however, a r e not c o n s i d e r e d significant the accuracy of visual estimates of sorting is limited. t h e a c c u r a c y of v i s u a l e s t i m a t e s of s o r t i n g is limited. magnitude and number of differences is small. m a g n i t u d e and number o f d i f f e r e n c e s is small. because Also, the Also, the Figure 15 illustrates F i g u r e 15 illustrates the close similarities of the different fluvial deposits. the close s i m i l a r i t i e s of t h e d i f f e r e n t fluvial deposits. Grain G r a i n Morphology Morphology Roundness.--Roundness and coarse R o u n d n e s s . - - R o u n d n e s s for f o r sand s a n d and c o a r s e silt-sized s i l t - s i z e d grains g r a i n s was determined Powers' d e t e r m i n e d for f o r each e a c h sample s a m p l e by comparing c o m p a r i n g grains g r a i n s tto o P o w e r s ' 1953 roundround­ with microscope. ness n e s s scale scale w i t h a binocular binocular m icroscope. All A l l samples s a m p l e s from from eeach a c h location location were w e r e compared compared and checked c h e c k e d for for a a dominant d o m i n a n t natural n a t u r a l ggrouping. rouping. are a r e shown in i n figure f i g u r e 16. 16. The results results The percent p e r c e n t vvalues a l u e s iin n the t h e figure f i g u r e indicate indicate tthe h e ppercent e r c e n t of of tthe h e samples s a m p l e s at a t that t h a t location l o c a t i o n that t h a t establish e s t a b l i s h the the d o m i n a n t rrange a n g e of of rrounding o u n d i n g as a s shown. shown. dominant TABLE 44:: Location L ocation Very-Well V ery-Well Sorting Sorting ~~oderate M oderate Hell Well SM-A SM-A SM-B SM-B SM-C SM-C SM-D SM-D QA QA S S M M F F Total" Total Percent Percent 20.9 20.9 Alluvial A l l u v i a l Plain Plain St S t rream e a m Depos D e p o sits its DC DC C C Total Total Percent Percent _ 2 3 11 11 3 5 -5-2-08 0 5 2 29.4 47.0 0 2 9 . 4 11.7 1 1 . 7 47.0 Overbank O v e r b a n k Deposits Deposits GM GM Total Total Percent Percent 5 4 11 - 22 ---54 1 5 31.25 2 5 . 0 6.25 6.25 3 1 . 2 5 12.5 1 2 . 5 25.0 Meandering M e a n d e r i n g Stream Stream Deposi D e p o s i ts ts 1 1 3 1 1 33 3 5 5 22 22 •66 44 44 6 5 3 9 2 4 2 8 1 1 4 3 3 0 -319 43 43 3 18.0 4 0 . 9 2.8 2.8 1 8 . 0 40.9 -,- 11 22 1 1 1 0 66 5.7 5.7 _ 00 0 2 -22 12.5 12.5 PPoorly oorly 11 0 -11 0.95 0.95 1 0 1 0.95 0.95 _ 00 0 00 0 _ 00 _ 0 -,- Very oorly Very PPoorly - No. of No. of SSamples amples 0 -22 1.9 1.9 1 11 33 2 2 1 0 88 7.6 7.6 99 16 13 14 14 13 16 1 133 11 11 105 T55 _ -00 0 1 1 -22 11.7 11.7 7 10 -,- 1 -,1 1 1 1 1 1 6.25 6.25 17 17 16 *T6~ 16 6.25 6.25 CO 40 Certain bebJeen the C e r t a i n differences d i f f e r e n c e s apparently a p p a r e n t l y are a r e ppresent r e s e n t between t h e three three f l u v i a l ttypes. ypes. fluvial L a r g e meandering m e a n d e r i n g stream s t r e a m deposits d e p o s i t s are a r e dominated d o m i n a t e d by by Large g r a i n rroundnesses o u n d n e s s e s ranging r a n g i n g from from subangular s u b a n g u l a r to t o subrounded s u b r o u n d e d and 83.05% 83.05% grain of tthese h e s e samples s a m p l e s are are w i t h i n tthe h e rrange a n g e of of subangular s u b a n g u l a r to t o rounded. rounded. of within A l l u v i a l pplain l a i n stream s t r e a m ddeposits e p o s i t s ttend e n d to t o be less l e s s rounded. rounded. Alluvial L o c a t i o n s DC Locations DC C together t o g e t h e r have h a v e 90% of of ttheir h e i r samples samples w i t h i n tthe h e roundness r o u n d n e s s range range and C within The m o s t distinctive d i s t i n c t i v e suite s u i t e of of samples, samples, most of angular a n g u l a r tto o subrounded. subrounded. of in in t e r m s of o f rroundness o u n d n e s s vvalues, a l u e s , is i s tthe h e overbank o v e r b a n k samples s a m p l e s from section s e c t i o n GM. terms 00 50 E 40 VI Q) ..... cL 0.. r E It1 VI to <+If0o of.,) 4-> s:: c Q) <D u O s... Q) JQ.. <D 30 20 a l l u v i a l plain p l a i n streams streams alluvial \* ~ overbank meandering m e a n d e r i n g streams streams 10 0 very w ell well i r well well moderate m oderate poorly poorly vvery e r y poorly poorly Sorting Sorting Fig. F i g . 15 -- Frequency F r e q u e n c y pprofile r o f i l e chart c h a r t of of sorting s o r t i n g values values Almost wide A l m o s t every e v e r y sample s a m p l e hhas as a a w i d e rrange a n g e of of roundness r o u n d n e s s values v a l u e s relative r e l a t i v e to to samples s a m p l e s at a t other o t h e r locations. locations. As aa result, As r e s u l t , the t h e tendency t e n d e n c y for f o r grains grains to t o group g r o u p themselves t h e m s e l v e s in i n terms t e r m s of of rounding r o u n d i n g is i s weaker weaker than t h a n at a t other other llocations. ocations. Of a l l samples s a m p l e s at a t GM, a n g e from vvery e r y aangulal' n g u l a r to to Of all GM, 82.4% rrange subrounded, much llarger subrounded, a a much a r g e r range r a n g e tthan h a n for f o r similar s i m i l a r ppercentages e r c e n t a g e s iin n the the o t h e r two ttypes y p e s of of fluvial f l u v i a l deposits. deposits. other / GRAIN ROUNDNESS Well-Rounded u b r o u n d e d ____~Ro~u~n~d~e~d Rounded ____~W~e~l~l_-~Ro~b~'n~de~d u b a n g u l a r _____S Very-Angul a r __~A~ul~a~r Angul a r _____S ~Lo~c~a~t~i~on~' L o c a t i o n __r-~~~le~ry~-~A~n~g~u~la~r~ S~u~b~a~ng~u~l~a~r S~u~b~ro~un~d~e~d SM-A SM-B Si~-C SM-C S~l-D SM-D QA QA S s DC DC C C GM GM f - - 66.6% I - 887.5% 7 . 5 % -------i f100.0%------i 100.0% f-100.0% 100.0% - - - - - - - i f--69.2%---1 69.2%1 f-75% - - - - - I f-- 1------100.0% 100.0% -------I f - - 80.0% - - - I 82.4% - - - - - - - - - - - 1 F i g . 16 -- - Dominant Dominant groupings g r o u p i n g s of o f grain g r a i n roundness roundness . Fig. 42 G r a i n Surfaces.--Surface S u r f a c e s . - - S u r f a c e ttextures e x t u r e s of of quartz q u a r t z ggrains rains w e r e examined examined Grain were microscope. uunde;' n d e r a binocular binocular m icroscope. Gra'ins from each G r a i n s from e a c h sample s a m p l e were w e r e observed observed uunder n d e r hhigh i g h intensity i n t e n s i t y light l i g h t on a bblack l a c k background. background. V i r t u a l l y every every Virtually s a m p l e contains c o n t a i n s abundant a b u n d a n t frosted f r o s t e d quartz q u a r t z grains; g r a i n s ; iindeed, ndeed, m o s t samples samples sample most a r e dominated d o m i n a t e d by such s u c h grains. grains. are A l t h o u g h no quantitative q u a n t i t a t i v e studies s t u d i e s were were Although m a d e , tthe h e larger l a r g e r and bbetter e t t e r rounded r o u n d e d sand-sized s a n d - s i z e d ggrains r a i n s are a r e more often often made, ffrosted r o s t e d tthan h a n are a r e the t h e more aangular n g u l a r grains g r a i n s at a t the t h e lower l o w e r limit l i m i t of sandof sandsized m aterial. material. sized S p o t checks checks w e r e made tto o see s e e "if i f tthe h e ffrosting r o s t i n g VIas was Spot were t h e rresult e s u l t of of coating c o a t i n g by calcium c a l c i u m carbonate. carbonate. the T h i s iinvolved n v o l v e d dropping dropping This HC1 on the t h e grains, g r a i n s , dissolving d i s s o l v i n g the t h e ccarbonate, a r b o n a t e , and then t h e n allowing allowing warm HCl t o dry. dry. them to e s u l t s vlere w e r e nnegative e g a t i v e in i n each e a c h case. case. The rresults Other O t h e r quartz q u a r t z gr'ains g r a i n s are a r e Iisparkly" " s p a r k l y " in i n appearance. appearance. The~;e T h e s e gtains grains h a v e flat, f l a t , smooth smooth surfaces s u r f a c e s as as a a result r e s u l t of of silica s i l i c a overgrowths. overgrowths. have Their Their o c c u r a n c e is i s limited, l i m i t e d , hhowever, o w e v e r , and iis s iimportant m p o r t a n t aat t only o n l y two locations, two locations, occurance s e c t i o n s GM GM and DC. sections Textural Textural ~1atL!rity Maturity Fifty F i f t y thin·-sections t h i n - s e c t i o n s It,ere w e r e studied s t u d i e d to t o determine d e t e r m i n e the t h e textural textural matudty m a t u r i t y of of the t h e Da.kota Dakota sediments. sediments. Determinations \\'er-e made accofding Determinations w e r e made according method prepared tto o a a method p r e p a r e d by Folk F o l k (1968, ( 1 9 6 8 , pp.. 102-103). 102-103). Effects E f f e c t s of of diagenesis, diagenesis ssuch u c h aass the t h e fformation o r m a t i o n of of authigenic a u t h i g e n i c clay c l a y minerals m i n e r a l s and quartz q u a r t z overover­ were growths, growths, w e r e carefully c a r e f u l l y discounted. discounted. Sandstone S a n d s t o n e and and siltstone s i l t s t o n e is is d o m i n a n t ! y mature m a t u r e as a s determined d e t e r m i n e d by l e s s tthan han 5 5 ppE:rcent e r c e n t detrital detrital dominantly by less clay, c l a y , subangular s u b a n g u l a r tto o very v e r y angular a n g u l a r grains, g r a i n s , and being b e i n g \\Iell w e l l sorted s o r t e d or or bbetter. etter. L e s s e r amounts a m o u n t s of of sandstone s a n d s t o n e and s ii l1ttstone s t o n e are a r e submatuY'e submature Lesser supermature. and supermature. 43 Occasional were by examining O c c a s i o n a l ttextural e x t u r a l inversions inversions w e r e found found by e x a m i n i n g thinthins e c t i o n s of of channel c h a n n e l lag l a g deposits. deposits. sections T h e s e inverted i n v e r t e d samples s a m p l e s contain contain These r o u n d e d , ppoorly-sorted o o r l y - s o r t e d grains g r a i n s iin n a clay clay m atrix. rounded, matrix. c l a y material material The clay of the t h e channel c h a n n e l llag a g deposits d e p o s i t s presumably p r e s u m a b l y came from lateral l a t e r a l erosion e r o s i o n of of s t r e a m hanks. banks. stream o t h e r case c a s e of of ttextural e x t u r a l iinversion n v e r s i o n iis s represented represented One other by an overbank o v e r b a n k ssandstone a n d s t o n e at a t section s e c t i o n GM. Gr~. t h i s case, case, w e l l sorted sorted In this vlell b u t nnot o t well w e l l rrounded o u n d e d grains g r a i n s were w e r e deposited d e p o s i t e d as a s aa clay clay m atrix. but matrix. s a m p l e also a l s o hhas a s almost a l m o s t no porosity. porosity. sample This This T h i s type t y p e of of inversion i n v e r s i o n in i n the the This o v e r b a n k setting s e t t i n g indicates i n d i c a t e s tthe h e high h i g h energy e n e r g y conditions c o n d i t i o n s aassociated s s o c i a t e d with with overbank flooding. flooding. I r o n i c a l l y , other o t h e r overbank o v e r b a n k material m a t e r i a l ddoes o e s nnot o t shoh' show textural textural Ironically, i n v e r s i o n , which w h i c h suggests s u g g e s t s that t h a t overbank overbank m aterial inversion~ materlal c a n be well w e l l sorted sorted can n o t result r e s u l t solely s o l e l y from e r t i c a l accretion a c c r e t i o n simply simply and not from vvertical o u t of of particles. particles. out t h e settling settling by the PETROGRAPHY Thirty-five T h i r t y - f i v e moda.l modal analyses a n a l y s e s provide p r o v i d e information i n f o r m a t i o n for f o r the t h e descripdescrip­ t i o n and evaluation e v a l u a t i o n of of the t h e petrographic p e t r o g r a p h i c aspects a s p e c t s of of the t h e Dakota. Dakota. tion V i r t u a l l y all a l l samples s a m p l e s required r e q u i r e d impregnation i m p r e g n a t i o n with w i t h epoxy e p o x y because b e c a u s e they they Virtually a r e friable. friable. are A l l samples s a m p l e s were w e r e stained s t a i n e d for f o r potassium p o t a s s i u m feldspar. feldspar. All X - r a y diffraction d i f f r a c t i o n analysis a n a l y s i s of o f 16 samples s a m p l e s made possible p o s s i b l e the t h e mineramineraX-ray l o g i c a l determination d e t e r m i n a t i o n of o f the t h e matrix. matrix. logical r o c k s studied s t u d i e d in i n thin thin All rocks s e c t i o n s were w e r e classified c l a s s i f i e d according a c c o r d i n g to t o the t h e system s y s t e m prepared p r e p a r e d by Folk Folk sections (1968). (1968). The t h r e e end members of of this t h i s classification c l a s s i f i c a t i o n are a r e quartz, quartz, The three f e l d s p a r , and rock r o c k fragments. fragments. feldspar, q u a r t z pole p o l e includes i n c l u d e s all a l l quartz quartz The quartz ttypes y p e s except e x c e p t quartzite q u a r t z i t e and chert. chert. The feldspar f e l d s p a r pole pole s i n g l e ffeldspars e l d s p a r s plus p l u s granite g r a n i t e and gneiss g n e i s s fragments. fragments. single f r a g m e n t s fall f a l l at a t the t h e rrock o c k fragment f r a g m e n t ppole. ole. fragments includes includes A l l other o t h e r rock rock All M a t r i x , ttherefore, h e r e f o r e , consists consists Matrix, of authigenetic a u t h i g e n e t i c clay, c l a y , ddetrital e t r i t a l clay clay m a t e r i a l s in in w h i c h definite definite of materials which g r a i n boundaries b o u n d a r i e s are a r e not n o t vvisible, i s i b l e , and tterrigenous errigenous m a t e r i a l less less grain material tthan h a n 1/16 1/16 mm. C h e m i c a l l y pprecipitated r e c i p i t a t e d ppore-filling o r e - f i l l i n g silica silica Chemically (rare), (rare), and i l i c a oovergrowths v e r g r o w t h s and alcite w e r e counted c o u n t e d aas s cement. cement. and ssilica and ccalcite were P ebbly S a n d s t o n e and Conglomerate and Conglomerate Pebbly Sandstone and cconglomerate Mineralogically, M i n e r a l o g i c a l i y , tthe h e ppebbly e b b l y ssandstone a n d s t o n e and o n g l o m e r a t e that that by rrock cconstitutes o n s t i t u t e s tthe h e cchannel h a n n e l llag a g ddeposits e p o s i t s iis s ddominated o m i n a t e d by o c k fragments, fragments, matrix and qquartz m a t r i x and u a r t z ggrains. rains. Both ffeldspar and cchemical Both e l d s p a r and h e m i c a l ccement e m e n t are are a~d rrange from zzero one ppercent. minor m i n o r cconstitutents o n s t i t u t e n t s and a n g e from e r o tto o one ercent. These T h e s e rocks rocks aare r e ppoorly o o r l y tto o vvery e r y ppoorly o o r l y ssorted o r t e d and e n e r a l l y aare r e reddish-brm·m. reddish-brown, and ggenerally 45 This coloration This c o l o r a t i o n rock fragments. rock fragments. 15 present in the matrix and in soft sedimentary i s p r e s e n t i n t h e m a t r i x and i n s o f t sedimentary It is apparently hematite stain emanating from I t i s a p p a r e n t l y hematite s t a i n emanating sedimentary rock fragments and staining the matrix. sedimentary rock fragments and s t a i n i n g from This suite of the m a t r i x . This s u i t e of rocks is less mature than the sandstone and siltstone because of the rocks is l e s s m a t u r e t h a n t h e s a n d s t o n e and s i l t s t o n e b e c a u s e of the presence of detrital clay and labile soft sedimentary rock fragments. p r e s e n c e of d e t r i t a l c l a y and l a b i l e s o f t sedimentary rock fragments. Rock fragments range in grain size from sand to pebbles. Rock f r a g m e n t s r a n g e i n g r a i n s i z e All from s a n d t o p e b b l e s . All granule- and pebble-sized material are rock fragments consisting of g r a n u l e - and p e b b l e - s i z e d m a t e r i a l are rock fragments c o n s i s t i n g of metamOl~phic rock fragments (~1RF'S)) and sedimentary rock c h e r t , m e t a m o r p h i c r o c k f r a g m e n t s ( M R F ' s ) , and s e d i m e n t a r y r o c k chert, fragments (SRF's) other than chert. fragments (SRF's) o t h e r than c h e r t . to rounded. to rounded. Chert and MRF's are subrounded C h e r t and MRF's a r e subrounded SRF's are irregular in form because of compaction. SRF's a r e i r r e g u l a r i n form b e c a u s e of compaction. Compositionally, chert and MRF's average 17.8 and 17.9 percent resC o m p o s i t i o n a l l y , c h e r t and MRF's a v e r a g e 1 7 . 8 and 1 7 . 9 p e r c e n t pectively of t.he pebbly sandstone and conglonJel~ates. p e c t i v e l y of t h e p e b b l y s a n d s t o n e and c o n g l o m e r a t e s . 4.2 percent. 4.2 percent. SRF's average SRF's Totally, rock fragments ave)'age aboL!t 4-0.C Totally, rock fragments res­ average pe~~cent average about 40.0 percent of the composition of these rocks. of t h e c o m p o s i t i o n o f t h e s e rocks. The nEltrix is authigenic and det-rital clay. The m a t r i x i s a u t h i g e n i c and d e t r i t a l clay. X-ray dHfraction X-ray diffraction indicates that kaolinite is the most common c"lay mineral. indicates t h a t k a o l i n i t e i s t h e m o s t common c l a y m i n e r a l . Distinction Distinction betvleen matrix and SRF's is often difficult because of tIle reddish- b e t w e e n m a t r i x and S R F ' s i s o f t e n d i f f i c u l t brown stain, which sometimes is opaque. brown s t a i n , w h i c h s o m e t i m e s i s o p a q u e . b e c a u s e of t h e reddish- The matrix mater1al is The m a t r i x m a t e r i a l is present l'Jithin pore spaces in some samples and forms "floating p r e s e n t w i t h i n p o r e s p a c e s i n some s a m p l e s and f o r m s grains" in others. g r a i n s " in o t h e r s . "floating Sand-size material is mainly quartz Sand-size material for exce~t is mainly quartz except for lesser amOL:nts of rock fragments and rate gY'ains of potassium l e s s e r a m o u n t s of r o c k f r a g m e n t s feldspar (orthoclase). feldspar (orthoclase). and r a r e g r a i n s of potassium Chemically precipitated silica, in the form Chemically p r e c i p i t a t e d silica, in t h e form of quartz overgrowths and pore-filling cement. ranges from zero o f q u a r t z o v e r g r o w t h s and p o r e - f i l l i n g to 2.5 percent. to 2.5 percent. Porosity ranges from zero to 13 percent. P o r o s i t y r a n g e s from z e r o t o 13 p e r c e n t . average porus"it:.y is 4.7 percent. average porosity is 4,7 percent. the matrix. the matrix. c e m e n t , r a n g e s from zero The The The pt'inciple bonding agent is The p r i n c i p l e b o n d i n g a g e n t Chemically precipitated cement (silica) is only a is only a Chemically p r e c i p i t a t e d cement ( s i l i c a ) is 46 minor m i n o r bonding b o n d i n g agent. agent. samples samples Figure F i g u r e 17 is is (l a ternary t e r n a r y d-iagram d i a g r a m of nine nine of pebbly p e b b l y sandstone s a n d s t o n e and conglomerate, c o n g l o m e r a t e ; , which are a r e all all o~ lithlith- arenite. arenite. S a n d s t o n e and Siltstone Siltstone Sandstone Mineralogically, M i n e r a l o g i c a l l y , the t h e sandstone s a n d s t o n e and siltstone s i l t s t o n e are a r e strongly strongly dominated dominated q u a r t z grains. grains. by quartz O t h e r important i m p o r t a n t constitutents c o n s t i t u t e n t s are a r e rock rock Other fragments, f r a g m e n t s , inatrix m a t r i x and cement. cement. t o nine n i n e percent. percent. to of feldspar. feldspar. of Feldspar F e l d s p a r is i s rare r a r e and ranges r a n g e s from zero zero s a m p l e s s however, h o w e v e r , contain c o n t a i n only o n l y trace t r a c e amounts amounts Most samples s r e a l a t i v e abundance a b u n d a n c e of of feldspar f e l d s p a r types t y p e s -is is The realative Na-plagioclase> microcline. Na-plagioclase>microcline. orthoclase o·~,thoclase> Mica flakes f l a k e s are a r e rare r a r e and are a r e present present Hica i n trace t r a c e amounts a m o u n t s in i n only only a a few samples. samples. in q u a r t z gra g r a iins n s are a r e mai m a i nnly l y monocrystall m o n o c r y s t a l l ii nfie, e , non-Lindul n o n - u n d u l OSC, o s e , and and The quartz a r e generally generally w e l l sorted sorted w i t h intermediate i n t e r m e d i a t e degrees d e g r e e s of of rrounding. ounding. are well with m a t r i x is i s almost a l m o s t exclusively e x c l u s i v e l y authigenic a u t h i g e n i c clay. clay. matrix X - r a y diffraction diffraction X-ray i n d i c a t e s that t h a t kkaolinite a o l i n i t e is i s tthe h e dominant d o m i n a n t clay c l a y mineral. mineral. indicates Lesser Lesser a m o u n t s of of i l11l iHe t e and m o n t m o r i11 l l onite o n i t e are a r e also a l s o present. present. amounts montmori eevidence v i d e n c e of of cchlorite h l o r i t e was a l s o noted. noted. was also The O p t i cal cal Opt"i However, chlorite c h l o r i t e is i s present p r e s e n t in in However, ttoo o o ssmall m a l l aamounts m o u n t s ffor o r ddetection e t e c t i o n by X - r a y ttechniques. echniques. X-ray The cclay l a y matr-iX matrix iis s cconsidered o n s i d e r e d tto o be o s t - d e p o s i t i o n a l bbecause e c a u s e iit t iis s nnot o t ppresent r e s e n t at at be ppost-depositional ggr.ain r a i n ccontacts o n t a c t s bbut u t ddoes o e s fill f i l l iinterstices n t e r s t i c e s bbetween e t w e e n ggra.-insrains. Rock f r a g m e n t s aare r e cchert h e r t and RF's, w h i c h aaverage v e r a g e 22.04 . 0 4 and 1.55 percent percent fragments and M MRF's, which and 1.55 oof f tthese h e s e ssamples, a m p l e s , rrespectively. espectively. S e d i m e n t a r y rrock o c k ffragments r a g m e n t s are are Sedimentary aabsent b s e n t from o s t ssandstone a n d s t o n e and i l t s t o n e ssamples. amples. from m most and ssiltstone S i l i c a iis s the the Silica main h e m i c a l ccement, e m e n t , uusually s u a l l y aas s qquartz u a r t z oovergrowths. vergrowths. main cchemical However, it Hm<lever, it iis s ppresent r e s e n t iin n oonly nly m i n o r aamounts, m o u n t s , and o tthe he m a t r i x iit t is is minor and compared compared tto matrix 47 For F o r tthis h i s reason r e a s o n tthe h e Dakota Dakota sandstone sandstone nnot o t aa significant s i g n i f i c a n t bbonding o n d i n g agent. agent. i s uusually s u a l l y fJ'iable. friable. is P o r o s i t y for f o r this t h i s ssuite.of u i t e - o f samples s a m p l e s t'anges r a n g e s from from Porosity 0.5 22 ppercent. 0 . 5 ppercent e r c e n t to t o 22 ercent. The aveJ"age The a v e r a g e pporosity o r o s i t y is i s 10.6 1 0 . 6 percent. percent. F i g u r e 17 is i s aa ternary t e r n a r y di.3.gram d i a g r a m for f o r tthese h e s e rocks. rocks. Figure quartzarenites. quartzarenites. subarkoses. subarkoses. Fifty Fifty ppe~cent e r c e n t are are The remaining r e m a i n i n g samples s a m p l e s are a r e ssub1itharenites u b ! i t h a r e n i t e s and E i g h t y percent p e r c e n t of h e s e samples s a m p l e s contain c o n t a i n more than than Eighty of tthese n i nnety e t y ppercent e r c e n t quartz. quartz. ni Quartz Quartz Each tthi h i nn ssect; e c t i oon n \'las was examined e x a m i n e d for f o r different d i f f e r e n t quartz q u a r t z types. types. Q u a r t z grains g r a i n s are a r e classified c l a s s i f i e d as a s nnon-undu10se, o n - u n d u l o s e , uundu10se n d u l o s e anj and po1ypolyQuartz crystalline c r y s t a l l i n e (Blatt, ( B l a t t , 1967; 1 9 6 7 ; Conolly, C o n o l l y , 1965). 1965). of o f the t h e quartz q u a r t z ttypes y p e s iis s nnonundulose onundulose The rre1ativ(:~ The e l a t i v e abundance abundance uundulose ndulose polycrystall p o l y c r y s t a l l inc. ine. A c c o r d i n g tto o F o l k ' s ssystem y s t e m (1968), (1968), m o s t of of the t h e quartz q u a r t z grains g r a i n s are are According Folk's most cominon common with of vvein oOl~r pplutonic l u t o n i c quartz quartz w i t h lesser l e s s e r amounts a m o u n t s of e i n qU3.t'tz q u a r t z and stretched m e t a m o r p h i c qual'tz q u a r t z (polycl'ystalline), (polycrystal1ine). stl"etched metamorphic q u a r t z grains grains quartz G e n e r a l l y the the Genercllly ccont~in o n t a i n few iinclusions n c l u s i o n s except e x c e p t for f o r some vvacuoles acuoles that that s c a t t e r e d or o r arranged a r r a n g e d in i n lines l i n e s aacross c r o s s the t h e grain. grain. may be scattered Two y p e s of of quartz q u a r t z overgrowths overgrowths w e r e recognized: recognized: Two ttypes were postpost- depositional d e p o s i t i o n a l quartz q u a r t z overgrowths o v e r g r o w t h s and reworked r e w o r k e d quartz q u a r t z overgrowths. overgrowths. The f o r m e r type t y p e is i s rrecognized e c o g n i z e d by s t r a i g h t crystal c r y s t a l faces. faces. The former by straight They usually u s u a l l y do nnot o t completely c o m p l e t e l y fill f i l l tthe h e iintersticies n t e r s t i c i e s bbetween e t w e e n grains. grains. W h e r e v e r tthey h e y do, do, Wherever grains. grains. hhowever~ o w e v e r , they t h e y form i n t e r l o c k i n g network n e t w o r k of form an interlocking o v e r g r o w t h s were w e r e recognized r e c o g n i z e d by o b s e r v i n g nnuclei u c l e i of of Reworked overgrm"ths by observing r o u n d e d quartz q u a r t z ggrains r a i n s in i n which w h i c h the t h e oovergrov/ths v e r g r o w t h s have h a v e a vvery e r y irregular irregular rounded o u t l iine n e and hhave a v e bbeen e e n !'clrlpped " c h i p p e d " away iin n pplaces l a c e s down tto o tthe h e sUI'face surface out1 ll of the t h e oorigindl r i g i n a l grain grain of ((Folk~ F o l k . 1968: 1 9 6 8 ; Pettijohn, P e t t i J o h n , 1957). 1 9 5 7 ) . Sometimes S o m e t i m e s the the A8 Quartz Quartz FJg. Ternary F i g . 17 -— T e r n a r y plot plot s h o w i n g composition c o m p o s i t i o n of showing tthe h e Dakota Dakota sediments sediments Quartzarenite • Subl S u b !itho.renite itharenite Kl/ 1 .- sandstone s a n d s t o n e and and siltstone siltstone ppebbly e b b l y sandstone sandstone and conglomerate and conglomerate I Litha re nite Feldspathic F eldspathic Lithic L i t h i c Arkose Arkose Li L i tha t h a ren r e n ite ite -E----- Feldspar Feldspar Rock Fragments Fragments 49 "chipped " c h i p p e d "li surfaces s u r f a c e s penetrate p e n e t r a t e through t h r o u g h the t h e overgrowth o v e r g r o w t h and into i n t o the the original o r i g i n a l grain. grain. Fragments Rock Fragments Special S p e c i a l aattention t t e n t i o n was given g i v e n tto o rock r o c k ffragments r a g m e n t s because b e c a u s e of of their their abundance a b u n d a n c e iin n the t h e channel c h a n n e l lag l a g deposits, d e p o s i t s , their t h e i r uubiquity b i q u i t y iin n the t h e formation formation iin n general, g e n e r a l , and ttheir h e i r significance s i g n i f i c a n c e iin n determining d e t e r m i n i n g tthe h e llithology i t h o l o g y of tthe h e ssow'ce o u r c e area. area. a s i c types t y p e s of of rock r o c k ffragments r a g m e n t s are a r e present: present: Two bbasic s e d i m e n t a r y rock r o c k fragments f r a g m e n t s (SRF's) ( S R F ' s ) and and m e t a m o r p h i c rock r o c k fragments fragments metamorphic sedimentary (MRF's). (MRF's). g n e o u s rock r o c k fragments fragments w e r e nnoted. oted. No iigneous were a r e represented r e p r e s e n t e d by the t h e fo f o l11 l oowi w i nng g rock r o c k ttypes: ypes: are s i l t s t o n e , mudstone m u d s t o n e and claystone. claystone. siltstone, chert, m u d s t o n e and claystone. claystone. chert, mudstone S p e c i f i c a l l y , SRF's SRF's Specifically, c h e r t , sands s a n d stone, tone, chert, The m o s t abundant a b u n d a n t SRF's S R F ' s are are most o t h e r ttypes y p e s are a r e rrare. are. The other The specific MRF's ccould be definitely s p e c i f i c rrock o c k types t y p e s of of MRF's o u l d nnot o t be d e f i n i t e l y determined determined b e c a u s e of of their t h e i r extremely e x t r e m e l y ffine-grained i n e - g r a i n e d nnature; a t u r e ; however, h o w e v e r , they they because pprobably r o b a b l y are a r e either e i t h e r pphyllite, h y l l i t e , slate s l a t e oorr argillite. argillite. Positive P o s i t i v e identification i d e n t i f i c a t i o n of of micl~ocrystalline m i c r o c r y s t a l l i n e chert c h e r t versus versus of distinctive fine-grained f i n e - g r a i n e d MRF's iis s difficult d i f f i c u l t bbecause e c a u s e of of a a llack a c k of distinctive petrographi p e t r o g r a p h i cc criteri c r i t e r i aa (Folk, ( F o l k , 1952). 1952). Few MRF' MRF'ss exhi e x h i bit b i t fol f o l iiaati t i oon n or or s c h i s t o s i t y and rrarely a r e l y can c a n other o t h e r minerals m i n e r a l s such s u c h as a s mica l a k e s or or schistosity mica fflakes f e l d s p a r be seen. seen. feldspar i n most m o s t MRF's. in D e t r i t a l quartz q u a r t z ggrains, r a i n s , hhowever, o w e v e r , are are Detrital present present O c c a s i o n a l l y ffaint a i n t evidence e v i d e n c e of r e f e r r e d orientation orientation Occasionally of ppreferred o f clay c l a y minerals m i n e r a l s is i s seen s e e n in i n the the M RF's. of t'1RF's. B e c a u s e oof f this t h i s difficulty, difficulty, Because r o c k ffragments r a g m e n t s from from each e a c h tthin h i n section section w e r e rrecounted e c o u n t e d and re-examined re-examined rock were i n an attempt a t t e m p t tto o eestablish s t a b l i s h ppetrographic e t r o g r a p h i c criteria c r i t e r i a useful u s e f u l iin n distinguishdistinguish in i n g m i c r o c r y s t a l l i n e chert c h e r t from from ffine-grained i n e - g r a i n e d MRF's. ing'microcrystalline MRF's. a r e shown in i n table t a b l e 5. 5. are results The results O c c a s i o n a l l y rock r o c k ffrngments ragments w e r e encountered encountered Occasionally were 5: TABLE 5: C h a r a c t e r i s t i c s of o f rrock o c k , fragments fragments ~haracteristics Sedim e n t a r y Rock Fragrrents Fragments Sedi mentary ______________~(_ex_c_l_u_d_i_ng~_c_h_e_r_t)~ ( e x c l u d i n g c h e r t ) ______________C_h_e~r_t C h e r t __________________~M~e~t.~am~o~r~p~h~i~c~Ro~c~k~F~r~a~gm~e~n~t~s M e t a m o r p h i c Rock F r a g m e n t s___ Color Color reddi r e d d i ssh h brown gray g r a y to t o dark d a r k gray gray ggray r a y tto o black black Texture Texture quite q u i t e va v ari r i ab a b1l e tends homogeneous with t e n d s to t o be homogeneous with some vvariation a r i a t i o n in i n crystal c r y s t a l size size vvariable a r i a b l e (often ( o f t e n resembles resembles chert chert Grai G r a i nn boundar; b o u n d a r i ees s extremely e x t r e m e l y deformed,especially deformed,especially if i f relatively r e l a t i v e l y large l a r g e fragment fragment smooth; s m o o t h ; may hhave a v e vvery e r y minor minor indentations indentations minor m i n o r iindentations n d e n t a t i o n s to to si s i ggni n i ffii ccantly a n t l y deformed deformed Inclusions Inclusions detrital d e t r i t a l quartz q u a r t z grains; g r a i n s ; mica mica fl fl akes akes carbonate c a r b o n a t e rrhombs, h o m b s , mi m icrocroffossils, o s s i l s , detrital d e t r i t a l quartz quartz detrital d e t r i t a l quartz q u a r t z ggrains r a i n s mica mica fl akes akes Grain G r a i n sizes sizes clay with c l a y matrix matrix w i t h detrital detrital quarts quarts ttypical y p i c a l chert c h e r t size s i z e crystals crystals (4-20 microns) with ( 4 - 2 0 m i c r o n s ) w i t h some larger l a r g e r void-filling v o i d - f i l l i n g crystals crystals aphanitic matri aphanitic m a t r i xx with w i t h very very f i n e grained g r a i n e d tto o silt-sized silt-sized fine qqua u a rrtz t z grai g r a i nnss Size Sue pebble p e b b l e size s i z e aand n d smaller smaller ppebble e b b l e to t o vvery e r y fine f i n e grained grained ppebble e b b l e tto o vvery e r y fine f i n e grained grained P referred Preferred o r i eentati n t a t i oon n or"i o f matri matrix of often often nnone one occasionally occasionally Mica where rrare; are; w h e r e ppresent r e s e n t extremely extremely f i nne e grai g r a i nned ed fi nnone one rare; r a r e ; when ppresent r e s e n t extremely extremely f i n e grained grained fine Fragment Fragment Shape Shape hi h i gghly h l y i rrregul r e g u l aar r due to to compaction compaction similar s i m i l a r to t o quartz q u a r t z grains grains or o r elongate elongate similar s i m i l a r to t o quartz q u a r t z grains, grains, elongate e l o n g a t e grains g r a i n s rare rare Location Location channel channel 1 l aag g deposits deposits anywhere anywhere anywhere anywhere Fraqment Fragment U1 o 51 that be positively MRF as t h a t could c o u l d not n o t be p o s i t i v e l y identified i d e n t i f i e d as a s either e i t h e r chert c h e r t or o r MRF as described d e s c r i b e d in i n ttable a b l e 5. 5. This T h i s indicates i n d i c a t e s the t h e table's t a b l e ' s llimited i m i t e d accuracy accuracy and t h a t some of of the t h e characteristics c h a r a c t e r i s t i c s can c a n apply a p p l y tto o bboth o t h rock rock and shows that types. types. Petrographic P e t r o g r a p h i c Comparisons C o m p a r i s o n s of of Sandstone S a n d s t o n e and Siltstone Siltstone Limited L i m i t e d petrographic p e t r o g r a p h i c differences d i f f e r e n c e s are a r e present p r e s e n t among sandstone sandstone and siltstone s i l t s t o n e deposited d e p o s i t e d in i n the t h e large l a r g e meandering m e a n d e r i n g stream s t r e a m ssystems, y s t e m s , in in alluvial a l l u v i a l pplain l a i n stream s t r e a m systems, s y s t e m s , and in i n overbank o v e r b a n k areas. areas. The most The most o b v i o u s petrographic p e t r o g r a p h i c differences d i f f e r e n c e s are a r e even present p r e s e n t iin n sandstone s a n d s t o n e that that obvious d e p o s i t e d in i n different d i f f e r e n t parts p a r t s of of the t h e large l a r g e meandering m e a n d e r i n g streams streams was deposited u n d e r different d i f f e r e n t flow f l o w conditions. conditions. under ~nd Figure F i g u r e 18 is i s a classification c l a s s i f i c a t i o n diagram d i a g r a m of of sandstone s a n d s t o n e and siltstone siltstone from from the t h e large l a r g e meandering m e a n d e r i n g stream s t r e a m system, s y s t e m , the t h e alluvial a l l u v i a l pplain l a i n stream stream s y s t e m , and the t h e overbank o v e r b a n k deposits. deposits. system, A l l of o f the t h e sandstone s a n d s t o n e from from the the All large l a r g e meandering m e a n d e r i n g stream s t r e a m system s y s t e m is i s quartzarenite q u a r t z a r e n i t e and sublitharenite. sublitharenite. One of of tthe h e aalluvial l l u v i a l plain p l a i n sandstone s a n d s t o n e is is a a subarkose, s u b a r k o s e , tthe h e oother t h e r iis s a quartzarenite. quartzarenite. T h r e e of of the t h e four f o u r overbank o v e r b a n k sandstones s a n d s t o n e s aare r e subarkose subarkose Three in i n composition. composition. The fourth f o u r t h one is i s on the t h e border b o r d e r bbetween e t w e e n subarkose s u b a r k o s e and sublitharenite. sublitharenite. The overbank o v e r b a n k sandstone s a n d s t o n e is i s the t h e only o n l y type t y p e that that contains contains a a significant s i g n i f i c a n t amount amount of of feldspar. feldspar. Figure of tthe F i g u r e 19 is i s a grains-matrix-cement g r a i n s - m a t r i x - c e m e n t ternary t e r n a r y pplot l o t of h e same sandstone s a n d s t o n e and siltstone s i l t s t o n e shown iin n figure f i g u r e 18. 18. No clear No c l e a r grouping g r o u p i n g can can be seen s e e n from from this t h i s comparison. comparison. To clarify c l a r i f y further f u r t h e r petrographic p e t r o g r a p h i c comparisons c o m p a r i s o n s of of tthe h e tthree h r e e groups groups of sandstones s a n d s t o n e s and stilstones, s t i l s t o n e s , those t h o s e of t h e large large m e a n d e r i n g stream stream of of the meandering s y s t e m are a r e ddiscussed i s c u s s e d separately. separately. system T h o s e of of the t h e alluvial alluvial Those plain plain 52 Quartz Q uartz FFii gg.. 18 18 Modal n a l y s i s oof f ssandstone a n d s t o n e and siltstone Modal aanalysis and siltstone Mode of of deposition Mode deposition • — . l a r g e meandering stream «— alluvial plain stream A — overbank deposits .- deposits deposits Feldspar Rock Fragments Fragments Grains Grains \\ •• • •• • F i g . 19 19 Fig. Grains-matrix--cement ternary plot Grains-matrix-cement ternary plot of sandstone and siltstone of s a n d s t o n e and s i l t s t o n e • • Cement Cement \ "\50% 50% Matrix Matrix ~ 553 3 stream system and the overbank deposits are discussed together. s t r e a m s y s t e m and t h e o v e r b a n k d e p o s i t s a r e d i s c u s s e d The together. The same type of comparisons are made for all three groups, \'Jhich are same t y p e of c o m p a r i s o n s a r e made f o r a l l t h r e e g r o u p s , which are modeled after studies by Picard, 1971; Picard and High, 1970, 1972. modeled a f t e r s t u d i e s by P i c a r d , 1 9 7 1 ; P i c a r d and H i g h , 1 9 7 0 , 1972. Pronounced petrographic variations were noted in sandstone Pronounced p e t r o g r a p h i c v a r i a t i o n s were noted i n that was de~osited t h a t was d e p o s i t e d sandstone in different flow conditions within the large in d i f f e r e n t flow c o n d i t i o n s w i t h i n t h e large meandering stream system. This is best der.lOnstrated by comparing samples of sections QA and S~-B. meandering stream system. This i s b e s t demonstrated by c o m p a r i n g Section SM-8 represents deposition s a m p l e s of s e c t i o n s QA and SM-B. S e c t i o n SM-B r e p r e s e n t s deposition in the main stream channel as indicated by trough and planar crossi n t h e main s t r e a m c h a n n e l as i n d i c a t e d by t r o u g h and p l a n a r cross- stratification, point bar deposits and its relatively large thickstratification, p o i n t b a r d e p o s i t s and i t s r e l a t i v e l y ness (112 feet). ness (112 f e e t ) . large thick­ Section QA represents deposition at or near bank S e c t i o n OA r e p r e s e n t s d e p o s i t i o n a t o r n e a r bank full conditions as indicated by abundant horizontal stratification, full c o n d i t i o n s as i n d i c a t e d by a b u n d a n t h o r i z o n t a l stratification, its high stratigraphic position relative to the main channel, and i t s high s t r a t i g r a p h i c position relative its relative thinness (G7 feet). its relative thinness t o t h e main c h a n n e l , Figure 20 is a (67 f e e t ) . F i g u r e 20 i s a plot of the samples from these two sections. p l o t o f t h e s a m p l e s from t h e s e two s e c t i o n s . about the same in both cases. a b o u t t h e same i n b o t h c a s e s . of cement and matrix. of c e m e n t and m a t r i x . than SM-B samples. t h a n SM-B s a m p l e s . and gi~ain-matl'ix-cement grain-matrix-cement The percent grains is The p e r c e n t g r a i n s is The main difference is in the precent The main d i f f e r e n c e i s in the precent QA samples contain more cement and less matrix QA s a m p l e s c o n t a i n more c e m e n t and l e s s matrix Even though sections QA and SM-8 are not part Even t h o u g h s e c t i o n s QA and SM-B a r e n o t part of the same channel, they probably are indicative of petrographic of t h e same c h a n n e l , t h e y p r o b a b l y a r e i n d i c a t i v e of petrographic changes within the large meandering stream deposits. The differences changes w i t h i n the l a r g e meandering stream d e p o s i t s . The differences in the matrix content imply that at least some of the matrix is i n t h e m a t r i x c o n t e n t i m p l y t h a t a t l e a s t some of t h e m a t r i x is detrital and that lesser amounts of it are deposited in sections detrital and t h a t l e s s e r a m o u n t s of i t a r e d e p o s i t e d in sections sirr:ilar to QA because of higher velocity flow conditions. s i m i l a r t o QA b e c a u s e of h i g h e r v e l o c i t y f l o w c o n d i t i o n s . There There also is an inverse relationship between the contents of matrix and a l s o i s an i n v e r s e r e l a t i o n s h i p cement. cement. SM~B b e t w e e n t h e c o n t e n t s of m a t r i x and samples have relatively high matrix percentages and SM-B s a m p l e s h a v e r e l a t i v e l y low cement percentages. low c e m e n t p e r c e n t a g e s . high m a t r i x p e r c e n t a g e s and QA sandstones have relatively low matrix QA s a n d s t o n e s h a v e r e l a t i v e l y percentages and high cement percentages. p e r c e n t a g e s and h i g h c e m e n t p e r c e n t a g e s . low m a t r i x Figure 21 further illustrates F i g u r e 21 f u r t h e r the matrix-cement relationship for QA and SM-8 sandstones. t h e m a t r i x - c e m e n t r e l a t i o n s h i p for QA and SM-B s a n d s t o n e s . illustrates The The 54 G r a i nns s Grai . . .. 75% ----- --- ,, ,, • .. , ,, ,/ • ., ,, • ,, • ,, ,, ,, , 75% . ,,---- 50% 50% . ~1atri Cement Cement I .- — ssection' e c t i o n SM-B SH-B e c t i o n QA .. - - ssection QA G r a i n s -- m a t r i xx -- cement cement Grains matri tternary e r n a r y pplot l o t of s a m p l e s from l a rge rge of samples from la m e a n d e r i n g sstream t r e a m deposits deposits mzandering FFig i g .. 20 x 55 Scatter S c a t t e r Plot P l o t of of Authigenic A u t h i g e n i c Cement Cement Versus V e r s u s Matrix Matrix 30 ! r T—i—i—i—i—i—i—i—i—i—i—i—r -i 1 1 r- • ... , x',, 25 x \ I I I I I I X I I I 20 x X Or$.. ..., r:> ..., ~-: I I I I I 15 x s::: OJ u x X \ I I I SO) C\.. 10 , ,.------- ......... (e • " ... , I Ri I x XX I X xl/I / X I/ I/ I I I I I I I X ,,' ' 5 I I I I :. - A • ,, , \ \ \ \ • \ \ • ....A. • I I I I _i - L1 L I I I I l_ _1_J_ 10 5 I 0 , \ \ I \ I \ I Il:l . . 1 ~. _'-L-_~ j i I < • • • Ii • • i_ i L 25 15 20 I I .L-- 30 Percent P e r c e n t Cement QA samples samples • - QA ~ • -- alluvial a l l u v i a l plain p l a i n samples samples - overbank o v e r b a n k samples samples SM-B samples samples xx - 5r·1-·8 ~ A Fi F i ggo. 21 56 dotted two groups. d o t t e d lines l i n e s demonstrate d e m o n s t r a t e the t h e ggraphical r a p h i c a l separation s e p a r a t i o n of of these t h e s e two groups Note tthat h a t samples s a m p l e s from from tthe h e other o t h e r two groups g r o u p s pplot l o t iin n tthe h e same area area o f the t h e graph g r a p h as a s QA. of F i g u r e s 22 and 23 show the t h e rrelationship e l a t i o n s h i p of of Figures matrix m a t r i x and cement c e m e n t to t o quartz q u a r t z for f o r these t h e s e same deposits. deposits. t h e two groups, g r o u p s , QA QA and and SM-B, cluster w ell S1'1-8, c1uster well the In each In e a c h case case ggraphically~ r a p h i c a l l y , as a s shown by t h e dotted d o t t e d lines. 1ines. the The same ppetrographic e t r o g r a p h i c comparisons c o m p a r i s o n s that t h a t were w e r e made oof f sections sections QA e r e appiied a p p l i e d to t o sandstone s a n d s t o n e of of alluvial a l l u v i a l pplain l a i n stream stream QA and SM-B S~'-B w were d e p o s i t s and overbank o v e r b a n k deposits. deposits. deposits A l l u v i a l pplain l a i n stream s t r e a m deposits deposits Alluvial a r e t'epresented r e p r e s e n t e d by secti s e c t i oons n s DC DC and C. are s e n t e d by section section sented GM. Gr~. Overbank deposits d e p o s i t s are a r e reprerepre­ Overbank P e t r o g r a p h i c a l l y , tllese t h e s e tvJO two ggroups r o u p s of Petrographically, s a n d s t o n e are a r e similar s i m i l a r tto o each e a c h other o t h e r as a s shown in i n figures f i g u r e s 21, 2 1 , 22 and 23. 23 sandstone T h e r e f o r e , it i t would aappear p p e a r to t o be difficult d i f f i c u l t tto o ddistinguish i s t i n g u i s h them them Theref01~e. ppetrographically. etrographically. A l s o , tthese h e s e ppetrograpllic e t r o g r a p h i c comparisons c o m p a r i s o n s show that that Also, s a n d s t o n e from from the t h e alluvia.l a l l u v i a l pplain l a i n stream s t r e a m system s y s t e m and overbank o v e r b a n k at'eas areas sandstone r e s e m b l e s sandstone s a n d s t o n e of of section s e c t i o n QA. resembles i t appears a p p e a r s that t h a t ppetrographic e t r o g r a p h i c analysis a n a l y s i s is i s nnot ot a In summary, it s t r o n g indicator i n d i c a t o r of of the t h e different d i f f e r e n t modes of fluvial f l u v i a l deposition d e p o s i t i o n that that modes of strong have been been discussed. discussed. All A l l tne t n e sandstone s a n d s t o n e and siltstone s i l t s t o n e is is similar similar ppetrograp!lically e t r o g r a p h i c a l l y except e x c e p t for f o r sandstone s a n d s t o n e deposited d e p o s i t e d in i n or o r nnear e a r tthe h e main channel by section c h a n n e l of of the t h e large l a r g e meandering m e a n d e r i n g streams s t r e a m s as a s rrepresented e p r e s e n t e d by section St(1-B. SM-B. Diagenesis Diage.nesis The ppt~inciple r i n c i p l e ddia~Jenetic i a g e n e t i c effect e f f e c t on tthe h e Dakota s e d i m e n t s iis s the the Dakota sediments formation f o r m a t i o n of of clay c l a y minerals. minerals. They form m most o s t of of tthe h e matrix m a t r i x material material a r e tile t h e ppl'"imary r i m a r y bbonding o n d i n g agent a g e n t of of the t h e coarse-grained c o a r s e - g r a i n e d facies. facies. and are 57 Scatter of QQuartz Versus S c a t t e r PPlot l o t of uartz V e r s u s Matrix Matrix 100 r -i r - 80 ~ 70 /. t m / BS -/ A V® A \ <* 60 CY 50 i i 1 1 1 7 r —— | —| i i i | i | ' n N. 1 1 ' . 1 . . . - ~" ~" ~" — - _ ** x N (\ v »> \ s\ X x 6 x s © ^ * X -- X X x A X m ::s +l ]i 1 ..— 90 N +l S- T \ \ A X _ c.: (I) u S(I) 0.. 40 - 30 - - 20 - - 10 - o I- 1 ' ' L_JI 1 1 1 1 I1 1 1 1 1 I1 1 1 " 5 "10 10 20 15 Percent Percent QA samples samples •© - QA SM-B samples samples x - St~-B J1 . 1 . 1~ . i . . . 25 30 30 ~latri M a t r ix •• -- alluvial a l l u v i a l plain p l a i n samples samples A A - overbank overbank Fig. F i g . 22 samples samples 58 SScatter c a t t e r PPlot l o t of uartz V e r s u s Cement of QQuartz Versus Cement 100 100i—'—i—'—i—i—i—i— — —i—•—i—'— —i— — I I I 1 f- 80 ~---, I N 60 - oj..) 50 - I III Ji. , I x: \. \ , ,, -- -. " , ... ... I X !:, X x iI , :::::l 0" 1 r I I -i—i—i—i—|—i 1 1—r - .............. f "- X SItS '- " f xxx\ X " I I \ ,:X XXX1, w • , \ X , .. - ...... - f f f X '.\I V\ \ oj..) 1 - 90 70 1 A. -'- " " - .... • • II ... '\\ • \ \ \ \ I f f •9 ,' , _----- ~~ --~ - I II - s:: QJ U S- QJ 0- 40 - - 30 I- - 20 ~ - 10 I- I ' II I I I • I1 I I I I I 1 I1 I 1 I 1 I ! I 1—II I 1 1—J I"—L 0 5 10 10 20 20 15 15 25 25 30 30 Percent P e r c e n t Cement Cement •© -- QA QA ssamp a m p1les es xx -- SM-B SM-B samples samples m -A Fig. F i g . 23 23 ~•- a l l u v i a l plain p l a i n samples samples alluvial o v e r b a n k samples samples overbank Kaolinite is the most abundant clay mineral. Lesser amounts of K a o l i n i t e i s the most abundant c l a y m i n e r a l . L e s s e r amounts 59 59 of illite, montmorillonite and chlorite are also present. Thin-section i l l i t e , m o n t m o r i l l o n i t e and c h l o r i t e a r e a l s o p r e s e n t . Thin-section examination precludes the origin of the clays from the alteration of e x a m i n a t i o n p r e c l u d e s t h e o r i g i n of t h e c l a y s from t h e a l t e r a t i o n original constitutents. Such an origin could account for only a original Such an o r i g i n c o u l d a c c o u n t f o r o n l y a constitutents. of minor portion of the authigenic material because feldspar and m i n o r p o r t i o n of t h e a u t h i g e n i c m a t e r i a l because f e l d s p a r and mica are the only minerals in the coarse-grained facies that could mica a r e t h e o n l y m i n e r a l s i n t h e c o a r s e - g r a i n e d facies that could alter into clay minerals, and they are present only in trace amounts alter i n t o c l a y m i n e r a l s , and t h e y a r e p r e s e n t o n l y i n t r a c e amounts (Carrigy and Mellon, 1964). From thin-sections it was determined that ( C a r r i g y and M e l l o n , 1 9 6 4 ) . From t h i n - s e c t i o n s i t was d e t e r m i n e d that the authigenic clays must have been derived from another source. t h e a u t h i g e n i c c l a y s m u s t h a v e b e e n d e r i v e d from a n o t h e r source. The most likely source is from water that was expelled from the The m o s t l i k e l y s o u r c e i s from w a t e r t h a t was e x p e l l e d from overlyi~g Mowry Formation. o v e r l y i n g Mowry F o r m a t i o n . the These waters must have moved through T h e s e w a t e r s m u s t h a v e moved through the interstices of the Dakota sediments and precipit2ted the clay the i n t e r s t i c e s of t h e Dakota s e d i m e n t s and p r e c i p i t a t e d the clay minerals. The silica cement probably originated from the r"lovll'y as minerals. The s i l i c a c e m e n t p r o b a b l y o r i g i n a t e d from t h e Mowry a s well. Chronologically, precipitation of the silica preceded that of well. Chronologically, precipitation of t h e s i l i c a preceded t h a t of the clays. the clays. It should be noted that fresh sru~ples I t s h o u l d be n o t e d t h a t f r e s h samples are d i f f i c u l t are difficult to obtain. to obtain. It is likely that fresh samples contain less kaolinite and more I t is l i k e l y t h a t fresh s a m p l e s c o n t a i n l e s s k a o l i n i t e and more carbonate cement than the weathered samples (Potter and Glass 9 1958, c a r b o n a t e cement than t h e weathered samples ( P o t t e r and G l a s s , 1958, p. 35-43). Carbonate cement is almost non-existent in the weathered p. Carbonate cement i s a l m o s t n o n - e x i s t e n t in t h e 35-43). samples. samples. weathered PALEOCURRENTS PALEOCURRENTS Paleocurrent P a l e o c u r r e n t directions d i r e c t i o n s were w e r e determined d e t e r m i n e d from sedimentary sedimentary s t r u c t u r e s at a t each e a c h measured m e a s u r e d section. section. structures A t o t a l of o f 349 measurements measurements A total were w e r e made, m a d e , mainly m a i n l y from smalls m a l l - and medium-scale m e d i u m - s c a l e trough t r o u g h and planar planar c r o s s - s t r a t i ffi i ccati a t i oon. n. cross-strati o f measurements m e a s u r e m e n t s at a t each e a c h local l o c a lii ty ty The number of r a n g e d from from 10 to t o 64 and averaged a v e r a g e d 34.9 3 4 . 9 per p e r locality. locality. ranged Paleocurrent Paleocurrent m e a s u r e m e n t s were w e r e corrected c o r r e c t e d for f o r ttectonic e c t o n i c tilt t i l t whenever w h e n e v e r tthe h e formaforma­ measurements t i o n dipped d i p p e d over o v e r 15 degrees d e g r e e s (Potter ( P o t t e r and Pettijohn, P e t t i J o h n , 1963, 1 9 6 3 , pp.. 260). 260). tion fYjethods Methods Paleocurrent ways. P a l e o c u r r e n t ddata a t a vias was processed p r o c e s s e d in i n two different different w ays. First, First, the modal vectors t h e data d a t a was was evaluated e v a l u a t e d in i n terms t e r m s of of modal v e c t o r s as a s described described by Tanner T a n n e r (1959). (1959). T h i s ,method m e t h o d was slightly s l i g h t l y mod·/fied m o d i f i e d by ddividing ividing a This d i a g r a m into i n t o twelve t w e l v e 30 degree d e g r e e arcs a r c s instead i n s t e a d oof f eeight i g h t 45 degree compass diagram 45 degree arcs. arcs. T h i s method established e s t a b l i s h e d the t h e modal direction d i r e c t i o n oof f ssediment e d i m e n t transtrans­ This pport o r t for f o r various v a r i o u s groups g r o u p s of o f data. data. H o w e v e r , since s i n c e most most of o f tthe h e paleopaleo­ However, current m e a s u r e m e n t s were w e r e essent-j e s s e n t i aally l l y uni unim odal, a a more info i n f o rillati r m a t i vvee current measurements modal. method ( P o t t e r and Pettijohn. P e t t i J o h n , 1963, 1 9 6 3 , p. p . 264) of of analyzing a n a l y z i n g tthe h e data data method (Potter sed. was uused. c a l c u l a t i o n s for f o r grouped g r o u p e d data d a t a of o f this t h i s llatter a t t e r method method are are The calculations n V = =L X n. cos Xl x, V Il*i ~I 1i =.t 1 w = 1h nr W n . ssin i n x· x.1 I' \ _ i-i X IJJ/V X = = arctan a r c t a n W/V 1 1 2 ~i)~ R R = = (V (V + + w r* 2 2 L :::- (R/n) ( R / n ) 1100 00 ;,- where mean), where X x is i s tthe h e aazimuth z i m u t h of o f tthe h e rresultant e s u l t a n t vvector e c t o r ((vector vector m e a n ) , RR i s the t h e magnitude m a g n i t u d e of o f tthe h e vector v e c t o r mean, and i s tthe h e magnitude m a g n i t u d e of o f the the is and LLis v e c t o r mean iin n tterms e r m s of o f percent. percent. vector L is i s a measure m e a s u r e of o f tthe h e concentration concentration L o f tthe h e azi azim u t h s ; tthe h e greater g r e a t e r tthe he L L the t h e greater g r e a t e r tthe h e con c o ncent c e n trati r a t i on. on. of muths; x For h e purposes p u r p o s e s of o f tthis h i s thesis, t h e s i s , tthe h e important i m p o r t a n t figures f i g u r e s are a r e x and and L. For tthe a p p r o p r i aate t e cal c a l ccul u l aations tions w e r e made w i t h tthe h e ffo o l11 l oov.'i w i nng g three three The appropri vlere VJith objectives: objectives: q u a n t i t a t i v e l y evaluate e v a l u a t e ppaleocurrent a l e o c u r r e n t measurement measurement a) ttoo quantitatively data meandering d a t a of o f ancient ancient m e a n d e r i n g stream s t r e a m deposits, deposits, b) tto b) o compare tthe h e rresults e s u l t s oof f a) tto o tthe h e results r e s u l t s of o f the the anci a n c i eent n t all a l l uuvi v i aall ppll aaii nn stream s t r e a m depos d e p o sits, i t s , and c) c ) tto o determine d e t e r m i n e tthe h e nnet e t regional r e g i o n a l dispersal d i s p e r s a l direction d i r e c t i o n of of tthe h e Dakota Dakota sediments. sediments. T h e s e objectives o b j e c t i v e s were w e r e approached a p p r o a c h e d by calculating c a l c u l a t i n g xx and L L for f o r each each These c y c l e of o f the the cycle m e a n d e r i n g stream s t r e a m deposits. deposits. meandel~ing T h i s established e s t a b l i s h e d the the This d i r e c t i o n of o f sediment s e d i m e n t movement h e concentration c o n c e n t r a t i o n of of azimuths a z i m u t h s in in direction movement and tthe tthe h e channel c h a n n e l pportion o r t i o n of o f each e a c h cycle. cycle. v a r i aati t i oon n of of vari x S e c o n d l y , at a t each e a c h outcrop o u t c r o p the the Secondly, x of o f eeach a c h channel c h a n n e l was observed. vias observed. T h i s shmvs shows tthe h e amount amount This o f change c h a n g e in i n tthe h e direction d i r e c t i o n of o f stream s t r e a m fflow l o w through t h r o u g h ttime i m e at a t that that of outcrop. outcrop. T h i rdly, rdly, Thi xx and L w e r e computed from tthe h e ppal a l eeocurrent o c u r r e n t data data L vlere computed from o f all a l l tthe h e cycles c y c l e s at a t each e a c h outcrop. outcrop. of x From this t h i s ccal a l ccul u l aation, tion, x indicates movement at i n d i c a t e s tthe h e net n e t direction d i r e c t i o n of of sediment s e d i m e n t movement a t each e a c h outcrop outcrop \vhereas through t h r o u g h ttirre, ime, w hereas L L iindicates n d i c a t e s tthe h e vvertical e r t i c a l consistency c o n s i s t e n c y of of paleopaleo­ current c u r r e n t directions d i r e c t i o n s at a t each e a c h outcrop o u t c r o p tthrough h r o u g h ttime. ime. Finally, F i n a l l y , ail all o f tthe h e paleocurrent paleocurrent m e a s u r e m e n t s of of the t h e study s t u d y area area w e r e combined combined of measurements were computed for for and computed X, x , which is i s the t h e ggoal o a l of o f objective o b j e c t i v e c). c). 61 62 Results Results The results r e s u l t s of of tthe h e computations c o m p u t a t i o n s are a r e listed l i s t e d in i n ttable a b l e 6. 6. ConCon­ cerning c e r n i n g objectives o b j e c t i v e s a) a ) and bb), ) , the t h e concentration c o n c e n t r a t i o n of of azimuths a z i m u t h s (L) in of the meandering i n the t h e channels c h a n n e l s of t h e large large m e a n d e r i n g stream s t r e a m ddeposits e p o s i t s average average about a b o u t 73.2 7 3 , 2 ppercent. ercent. 444.5 4 . 5 ppercent. ercent. The outcrops, whole, o u t c r o p s , as as a a w h o l e , hhave a v e an L L of of about about The same comparisons c o m p a r i s o n s for f o r tthe h e ancient a n c i e n t alluvial a l l u v i a l plain plain sstream t r e a m deposits d e p o s i t s are a r e 61.2 6 1 . 2 ppercent e r c e n t and 37.7 3 7 . 7 ppercent e r c e n t respectively. respectively. Data concerning was obtained by computing c o n c e r n i n g tthe h e tthird h i r d oobjective b j e c t i v e was o b t a i n e d by c o m p u t i n g xx from tthe h e total t o t a l number of of ppaleocurrent aleocurrent m e a s u r e m e n t s (349) ( 3 4 9 ) that t h a t were were from measurements ttaken a k e n in i n tthe h e study s t u d y aarea. rea. 0 t h i s case c a s e xx was oriented o r i e n t e d N2.7 N 2 . 7 ° E. E. In this F i g u r e 24 shows tthe h e vvertical e r t i c a l vvariation a r i a t i o n of of x x at a t the t h e outcrop. outcrop. Figure F i g u r e 25 Figure t h e nnet e t direction d i r e c t i o n of of sediment s e d i m e n t movement a t each e a c h studied s t u d i e d locality; locality; shows the movement at f i g u r e 26 shows tthe h e net n e t regional r e g i o n a l dispersal d i s p e r s a l direction d i r e c t i o n of of tthe h e Dakota Dakota figure ssediments. ediments. Interpretation Interpretation The results r e s u l t s of of the t h e ppaleocurrent a l e o c u r r e n t calculations c a l c u l a t i o n s indicate i n d i c a t e that that meandering ppaleocurrent a l e o c u r r e n t azimuths a z i m u t h s of of tthe h e ancient ancient m e a n d e r i n g channel channel deposits deposits of widely o f the t h e Dakota D a k o t a are a r e nnot ot w i d e l y dispersed, d i s p e r s e d , bbut u t fairly f a i r l y well w e l l concentrated concentrated by the as a s shown by t h e 73.2 7 3 . 2 ppercent e r c e n t average a v e r a g e of of L. The combined L of combined total total L all a l l tthe h e cycles c y c l e s of of each e a c h outcrop, o u t c r o p , which w h i c h averages a v e r a g e s 44.5 4 4 . 5 percent, p e r c e n t , indicates indicates tthat h a t the t h e direction d i r e c t i o n of of flow f l o w changed c h a n g e d substantially s u b s t a n t i a l l y through t h r o u g h time, time, w h i c h is i s indicated i n d i c a t e d in i n ffigure i g u r e 24. 24. which from sinuous s i n u o u s streams. streams. from a r i a b l e patterns p a t t e r n s are a r e expected expected The vvariable C o m p a r i s o n of t h e rresults e s u l t s of of paleocurrent paleocurrent Comparison of the c a l c u l a t i o n s show tthat hat x X and L a r e similar s i m i l a r in i n both b o t h stream s t r e a m systems. systems. calculations L are T h i s suggests s u g g e s t s tthat h a t alluvial a l l u v i a l pplain l a i n streams streams w e r e also a l s o meandering. meandering. were This TABLE 6: 6 : Paleocurrent P a l e o c u r r e n t azimuth a z i m u t h concentration c o n c e n t r a t i o n (L) of of Dakota D a k o t a stream s t r e a m depostts deposits Location Location ( Large L a r g e me m ean a nde d er"j r i nng9st s t rre e aam m de d eppas o si its ts) SM-A Fl uvi al al C y c l es es Cycl Combined Comb; ned Total Total 6 5 4 3 2 1 SM-B SM-C SM-D SM-O QA QA S 79.7%(13) 79.7%(13) 70.8%( 7 0 . 8 % ( 77)) 99.4%(7) 99.4%(7) 22.1%(9) 22.1%(9) 20.2%(20) 20.2~(20) 97.0%(4) 97.0%(4) 45.3%(7) 45.3%(7) 96.0%(3) 96.0%(3) 38.9%(56) 38.9%(56) 91 9 1 .3%( . 3 % (14) 14) M 6 6 . 0 % ( 1 3 )) 66.0%(13 96.2%(7) 96.22(7) 97.6%(15) 97.6%(15) 9 1 ..7%(10) 7%(10) 91 7 4 . 5%(15) 74.5%(15) 4 8 . 0 %(11) 48.0%(11) 72.2%(15) 72.2%(15) 99.8%(4) 99.8%(4) 36.5%(20) 36.5%(20) 41.0%(8) 41.0% (8) 73.3%( 7 3 . 3 % ( 88)) cL' .~) 9 8 .• 99% 98 ,? ~( 3 ,J ) 63.3%(12) 63.3%(12) 5 7 . 77% % (12) (12) 57. 99.0%(6) 99.0%(6) 66.5%(6) 66.5%(6) 99.7%(6) 99.7%(6) 70.9%( 7 0 . 9 % ( 77)) !l2.4%(14) 42.4%(14) 36.3%(22) 36.3%(22) 38.1%(64) 38.1%(64) 2. 2 . 221~( % ( 332) 2) 36. (35) 3 6 . 11% %(35) 68.3%(39) 68.3%(39) L L averages a v e r a g e s 73.2% for f o r individual i n d i v i d u a l cycles; c y c l e s ; combined c o m b i n e d totals t o t a l s for f o r each e a c h 1l ocati o c a t i oonn ave 5% a v e rrage a g e 44. 44.5% (Alluvial ( A l l u v i a l plain p l a i n stream s t r e a m deposits) deposits) DC C 75.4%(13} 75.4%(13) 4 3 20.1%(22) 20.1%(22) F l uuvi v i aall Cycl C y c l es es ^ Fl 93. 2 9 3 . 88%{ % ( 112) 2) 1 Combined Combi ned Total Total 32.4%(10) 32.4%(10) 84.4%( 8 4 . 4 % ( 113) 3) 32.4%(10) 32.4%(10) 43.0%(60) 43.0%(60) L a v e r a g e s 61.2% for f o r individual i n d i v i d u a l cycles; c y c l e s ; combined combined totals t o t a l s for f o r each each L averages a v e r a g e 37.7% average location location 0"1 W CO CYCLIC VARIATION OF XX Cycles Location SM-A SM-B --- 4 3 ./' \ '1 '-. C f1 \ 2 t J DC 3 2 1 SM- D I 5 4 SM-C 1 "I I \ \ F Fii gg.. 24 'I '" Gr·j \ QA \ S 1 ---\ ! \ \. ,/ -- N 65 WYO W Y O fv1IN M I N G G 10----- - --~-y~~ . MOUNTAINS UINTA VERNAL • ROOS ROOSEVELT EVELT UINT A UINTA 1 B A S IN IN BAS I RANG ELY, COLO RANGELY, COLO. .· ~1~~ o0 10 20 scale s c a l e iin n miles miles Fig. 2255 — --Show of ssedim S h o w ss nnet e t ddirect i r e c t 'jon i o n of e d i m eent n t movement a c h local l o c a l ity ity movement aatt eeach 66 N E T REGIONAL R E G I O N A L PALEOCURRENT P A L E O C U R R E N T NET D I SPERSION S P E R S I O N P A T T E R N DI PATTERN c c ~ E _--'IN 2 u ~ > s N = N' 349 349 x x == N N 2.7°E 2.7°E = L 7.3 % L = 227.3% FFig i g .. 26 26 "COARSE - GRAINED UNIT" Description D escription The " c o a r s e - g r a i n e d unit" u n i t " iis s a a dark d a r k reddish-brown r e d d i s h - b r o w n pebbly p e b b l y sandsand­ The "coarse-grained stone s t o n e and conglomerate c o n g l o m e r a t e (figure ( f i g u r e 27). 27). IIt t iis s uusually s u a l l y situated s i t u a t e d aatt the the ttop o p of o f tthe h e Dakota D a k o t a in i n direct d i r e c t contact c o n t a c t with w i t h the t h e Mowry ormation. t·lm'lry FFormation. iis s ppresent r e s e n t aatt every e v e r y llocality o c a l i t y except e x c e p t GM GM and QA. from 0 0 tto o 40 feet. feet. from It It IIts t s tthickness h i c k n e s s ranges range T h i s unit u n i t is i s ppoorly o o r l y sorted sorted w i t h randomly r a n d o m l y disdis­ This with ttributed r i b u t e d granules g r a n u l e s and pebbles. pebbles. e x c e p t at at a a few localities. localities. except G e n e r a l l y , it i t iis s Generally~ structureless structureless The structures s t r u c t u r e s tthat h a t were w e r e observed observed w e r e studied s t u d i e d iin n an effort e f f o r t to t o ddetermine e t e r m i n e the t h e origin o r i g i n of of this t h i s unit. unit. were The structures s t r u c t u r e s studied s t u d i e d aare r e small-scale s m a l l - s c a l e ripples r i p p l e s in i n sandstone, sandstone, largelarge- s c a l e ripples r i p p l e s in i n conglomerate c o n g l o m e r a t e and medium-scale m e d i u m - s c a l e ttroughs r o u g h s in i n pebbly pebbly scale s a n d s t o n e and conglomerate. conglomerate. sandstone were Ripple R i p p l e iindices ndices w e r e determined d e t e r m i n e d for for a a total t o t a l of of 21 rripple i p p l e sets sets from by Tanner from four f o u r different d i f f e r e n t locations l o c a t i o n s as a s described d e s c r i b e d by T a n n e r (1967). (1967). Determinations D e t e r m i n a t i o n s of of rripple i p p l e iindex n d e x (RI) ( R I ) were w e r e llimited i m i t e d tto o five f i v e sets s e t s because becau measurements be m made. rreliable e l i a b l e rripple i p p l e hheight eight m e a s u r e m e n t s ccoul~ o u l d not n o t always a l w a y s be ade. values v a l u e s obtained o b t a i n e d are a r e 11.7, 1 1 . 7 , 6.3, 6 . 3 , 6.0, 6 . 0 , 5.2 5 . 2 and 3.3. 3.3. RI Corresponding Corresponding ripple r i p p l e symmetry symmetry iindex n d e x (RSI) vvalues a l u e s are a r e 22.0, . 0 , 1.3, 1 . 3 , 1.6, 1 . 6 , 1.3, 1 . 3 , and 2.3. 2.3. RSI values RSI v a l u e s for f o r tthe h e remaining r e m a i n i n g 16 rripple i p p l e sets s e t s range r a n g e from from 1.3 1 . 3 tto o 6.4. 6.4. The five be compared f i v e rripple i p p l e sets s e t s in i n which w h i c h RI versus v e r s u s RSI vvalues a l u e s can c a n be compared s u g g e s t that t h a t they t h e y are are w a v e - f o r m rripples i p p l e s (Tanner, ( T a n n e r , 1967). 1967). suggest wave-form RSI RSI values values for f o r tthe h e other o t h e r 16 cases c a s e s suggest s u g g e s t that t h a t they t h e y are a r e bboth o t h currentc u r r e n t - and 68 68 FFii gg.. 27 - E x p o s u r e of c o a r s e - g r a i n e d uunn i tt"l ' aat t ssection e c t i o n SM-B. t ii s 27 ---Exposure of "Ilcoarse-grained SM- B. IIt tthe h e uupperpper-m o s t uunit n i t tthat h a t ii ss sslightly l i g h t l y more e s i s t a n t tto o eerosion r o s i o n than than most more rresistant tthe h e uunderlying n d e r l y i n g ffluvial l u v i a l sandstone s a n d s t o n e .. 69 wave-formed w a v e - f o r m e d ripples. ripples. Several S e v e r a l vvalues a l u e s of of the t h e latter l a t t e r case c a s e fall f a l l in i n the the indeterminate i n d e t e r m i n a t e rrange a n g e for f o r RSr RSI (1.5-4.0), ( 1 . 5 - 4 , 0 ) , bbut u t bba.sed a s e d on association, association, other o t h e r origins o r i g i n s are a r e unlikely. unlikely. of RSI According A c c o r d i n g to t o Tanner T a n n e r (1967) ( 1 9 6 7 ) genetic g e n e t i c interpretations i n t e r p r e t a t i o n s of values v a l u e s nnot o t in i n the t h e indeterminate i n d e t e r m i n a t e rrange a n g e have a a confidence c o n f i d e n c e llevel e v e l of ercent. 98 ppercent. T h e r e f o r e , the t h e interpretation i n t e r p r e t a t i o n of of the t h e 16 rripple i p p l e sets sets Therefore, in i n 11hich w h i c h RSI values v a l u e s only o n l y were w e r e determined d e t e r m i n e d is i s considered c o n s i d e r e d qquite u i t e reliable. reliabl The genetic RI and g e n e t i c interpretation i n t e r p r e t a t i o n of of 3 3 of of the t h e 5 sets s e t s in i n which w h i c h RI values w e r e made is i s more suspect. suspect. RSI values were t h e others, o t h e r s , are a r e large-scale. large-scale. the to 5 5 feet. feet. to T h e s e rripples, i p p l e s , contrary c o n t r a r y to to These W a v e l e n g t h s rrange a n g e from Wavelengths from 26 26 inches inches R i p p l e height h e i g h t varies v a r i e s from from 5 5 inches i n c h e s to t o 18 iinches. nches. Ripple l i t h o l o g y is i s ppebbly e b b l y sandstone s a n d s t o n e and conglomerate. conglomerate. lithology The previously As previously s t a t e d , tthe h e ripple r i p p l e indices i n d i c e s indicate i n d i c a t e wave-form w a v e - f o r m origin. origin. stated, T h i s is is This d e b a t a b l e bbecause e c a u s e of of the t h e rripple i p p l e magnitude m a g n i t u d e and the t h e coarse-grained coarse-grained debatable lithology. lithology. A l s o the t h e rripple i p p l e indices i n d i c e s and corresponding c o r r e s p o n d i n g oorigins, r i g i n s , as as Also d e t e r m i n e d by Tanner, T a n n e r , are a r e ppresumably r e s u m a b l y for f o r sand-size sand-size m a t e r i a l only. only. material determined T h e s e large-scale l a r g e - s c a l e ripples r i p p l e s are a r e only o n l y found found in i n outcrops o u t c r o p s oof f the t h e large large These m e a n d e r i n g stream s t r e a m deposits d e p o s i t s and apparently a p p a r e n t l y only o n l y in in meandering a r e a s of of the t h e upper u p p e r surface. surface. low areas topographically topographically PROVENANCE PROVENANCE From tthe was ddetermined From h e ppaleocurrent a l e o c u r r e n t ddata, a t a , iit t was e t e r m i n e d tthat h a t tthe h e general general ddirection i r e c t i o n of e d i m e n t ddispersal i s p e r s a l was o tthe h e nnorth; o r t h ; hhence, e n c e , tthe h e source source of ssediment was tto was somewhere somewhere on on tthe aarea r e a pprobably r o b a b l y was h e ssouth. outh. The m most The o s t llikely i k e l y source source was iin west-central and ssouthern Utah and and aadjacent aarea r e a was n w e s t - c e n t r a l and o u t h e r n Utah d j a c e n t pportions o r t i o n s of of Nevada (MacKenzie (MacKenzie and and RRyan, and Young, Young, 1970, eeastern a s t e r n Nevada y a n , 1962, 1 9 6 2 , pp.. 444-61; 4 - 6 1 ; and 1970, pp.. 1147-159). 47-159). This \'/aS ooccupied by tthe T h i s rregion e g i o n was c c u p i e d by h e r~esocordilleran Mesocordilleran Geanticline, from w which G e a n t i c l i n e , aa hhighland i g h l a n d aarea r e a from h i c h tthe h e ddispersal i s p e r s a l ssystem y s t e m transtrans­ and eeast Colorado and Wyoming. pported o r t e d ssediments e d i m e n t s nnorth o r t h and a s t iinto nto C o l o r a d o and In ggeneral, \>Jas ddominated by ssedimentary In e n e r a l , tthe h e ssource o u r c e aarea r e a was o m i n a t e d by e d i m e n t a r y rocks. rocks. E r o s i o n of of pprexisting r e x i s t i n g sandstone s a n d s t o n e and limestone l i m e s t o n e was rresponsible e s p o n s i b l e for for Erosion most m o s t of of the t h e Dakota Dakota sediments. sediments. m i n o r amounts a m o u n t s of of m aterial. minor material. Metamorphic M e t a m o r p h i c source s o u r c e terrains t e r r a i n s contributed contributed s p e c i f i c ttypes y p e s of o f metamorphic m e t a m o r p h i c source source The specific rrocks o c k s could c o u l d nnot o t be determined d e t e r m i n e d although a l t h o u g h most m o s t MRF's are a r e extremely e x t r e m e l y finefine­ g r a i n e d , probably p r o b a b l y pphyllite, h y l l i t e , sslate l a t e or o r argillite. argil!ite. grained, R a r e large large Rare fragments fragments o f quartzite q u a r t z i t e were w e r e noted. noted. of Abundant A b u n d a n t ppetrographic e t r o g r a p h i c criteria c r i t e r i a indicate i n d i c a t e an older o l d e r sedimentary sedimentary source. source. A l l the t h e sandstone s a n d s t o n e of of the t h e Dakota is i s quartz-rich q u a r t z - r i c h and contains contains All l i t t l e , if i f any, a n y , labile l a b i l e constitutents. constitutents. little, A l l are a r e quartzarenite q u a r t z a r e n i t e or o r quartzquartzAll rich r i c h varities v a r i t i e s of of sublitharenite s u b ! i t h a r e n i t e or o r subarkose. subarkose. p r e s e n t only o n l y in i n trace t r a c e amounts. amounts. present p l u t o n i c quartz q u a r t z is i s dominant. dominant. plutonic Feldspars F e l d s p a r s usually u s u a l l y are are Q u a r t z types t y p e s are a r e mixed but b u t nonundulose, nonundulose, Quartz q u a r t z grains g r a i n s apparently a p p a r e n t l y are are Many quartz r e w o r k e d because b e c a u s e some have h a v e good overgrowths o v e r g r o w t h s and others o t h e r s do not. not. re\'ibrked A l s o the t h e nuclei n u c l e i of of the t h e overgrown o v e r g r o w n grains g r a i n s usually u s u a l l y are a r e well w e l l rounded. rounded. Also 71 Chert Dakota and and iiss one one of of tthe most C h e r t iis s uubiquitous b i q u i t o u s iin n tthe h e Dakota he m o s t diagnostic diagnostic of aa ssedimentary ffeatures e a t u r e s of e d i m e n t a r y ssource o u r c e tterrain. errain. t1RF's. aabundant b u n d a n t tthan h a n MRF's. IIt t iis s ggenerally e n e r a l l y more and cconglomerate common and PPebbly e b b l y ssandstone a n d s t o n e and o n g l o m e r a t e iis s common iis s iindicative n d i c a t i v e of e d i m e n t a r y ssource. ource. of aa ssedimentary M e t a m o r p h i c ssource o u r c e rocks rocks Metamorphic f·1RF's. ",ere w e r e eevidently v i d e n t l y ppresent r e s e n t aas s iindicated n d i c a t e d by MRF's. aare r e eextremely x t r e m e l y ffine-grained. ine-grained. Virtually V i r t u a l l y aall l l ~lRF's MRF's O c c a s i o n a l l y aa qquartzite u a r t z i t e ffragment r a g m e n t was Occasionally oobserved b s e r v e d iin n tthe h e cchannel h a n n e l llag a g ddeposits. eposits. IIt t iis s cconceivable, o n c e i v a b l e , however. however, tthat h a t tthe h e MRF's r e aactually c t u a l l y vvery e r y rresistant e s i s t a n t ddetrital e t r i t a l ffragments r a g m e n t s reworked reworked MRF's aare from pprexisting from r e x i s t i n g cclastic l a s t i c sediments. sediments. Many ttextural Many e x t u r a l ffeatures e a t u r e s also a l s o iindicate n d i c a t e ssedimentary e d i m e n t a r y ssource o u r c e rocks. rocks. The h a r a c t e r i z e d by airly w e l l rrounded o u n d e d qquartz u a r t z grains, grains, The Dakota Dakota iiss ccharacterized by ffairly well which have bbeen w h i c h ssuggests u g g e s t s tthat h a t tthey h e y have e e n rrecycled. ecycled. A hhigh A i g h ddegree e g r e e of rrounding o u n d i n g of h e hheavy eavy m i n e r a l s iin n tthe h e Dakota l s o iindicates n d i c a t e s more than than of tthe minerals Dakota aalso e p i s o d e of e r o s i o n and transportation. transportation. one episode of erosion n o t common but b u t are a r e ppresent. resent. not T e x t u r a l inversions i n v e r s i o n s are are Textural y p e s of of ttextural e x t u r a l inversions i n v e r s i o n s observed observed The ttypes w e r e a) a ) fairly f a i r l y well w e l l rounded r o u n d e d ggrains r a i n s that that w e r e nnot ot w e l l sorted, s o r t e d , and were were well b) w e l l - s o r t e d bimodal sediments. well-so~ted bimodal sediments. T h e s e iinversion n v e r s i o n ttypes y p e s probably probably These r e p r e s e n t multiple m u l t i p l e sedimentary s e d i m e n t a r y source s o u r c e rrocks o c k s (Folk, ( F o l k , 1968, 1 9 6 8 , pp.. 106). 106). represent DISPERSAL DISPERSAL SYSTEM SYSTEM The dispersal Dakota d i s p e r s a l system s y s t e m of of the the D a k o t a sediments s e d i m e n t s was pprobably robably a complex by m meandering c o m p l e x fluvial f l u v i a l ssystem y s t e m characterized c h a r a c t e r i z e d by e a n d e r i n g streams s t r e a m s throughout. throughout. This of stream T h i s system s y s t e m evolved e v o l v e d through t h r o u g h tthree h r e e stages s t a g e s of s t r e a m ddevelopment; e v e l o p m e n t ; each each represented r e p r e s e n t e d by characteristic c h a r a c t e r i s t i c deposits. deposits. The tthree h r e e stages s t a g e s are are graphically g r a p h i c a l l y depicted d e p i c t e d iin n figure f i g u r e 28. 28. As ppreviously were r e v i o u s l y discussed) d i s c u s s e d , two bbasic a s i c ttypes y p e s of of streams streams w e r e present present meandering during d u r i n g Dakota Dakota ttime; i m e ; the t h e rrelatively e l a t i v e l y large large m e a n d e r i n g streams s t r e a m s and the the ssmaller m a l l e r alluvial a l l u v i a l pplain l a i n streams. streams. Paleocurrent P a l e o c u r r e n t information i n f o r m a t i o n indicates indicates that meandering well. t h a t alluvial a l l u v i a l pplain l a i n streams s t r e a m s were were m e a n d e r i n g as as w ell. The large The large meandering m e a n d e r i n g streams s t r e a m s evolved e v o l v e d tthrough h r o u g h two stages s t a g e s of of ddevelopment. evelopment. Stage S t a g e I~ I tthe h e earliest, e a r l i e s t , is i s characterized c h a r a c t e r i z e d by s t r e a m s that t h a t apparently a p p a r e n t l y were w e r e quite quite by streams l a r g e as a s iindicated n d i c a t e d by t h e thickness t h i c k n e s s of of ttheir h e i r deposits. deposits. large by the The lower The lower bboundary o u n d a r y surface s u r f a c e is i s undulating u n d u l a t i n g bbecause e c a u s e of of scouring s c o u r i n g action a c t i o n iinto n t o the the Cedar M o u n t a i n Formation. Formation. Cedar Mountain S t a g e II streams, s t r e a m s , therefore, t h e r e f o r e , are a r e degrading degrading Stage sstreams t r e a m s as a s indicated i n d i c a t e d by t h e i r downward erosion. erosion. by their The b a n k s were were The banks pprobably r o b a b l y cohesive c o h e s i v e enough to m i n i m i z e tthe h e amount amount of lateral enough to minimize of lateral migration, migration, w h i c h allowed a l l o w e d time t i m e for f o r substantial s u b s t a n t i a l quantities q u a n t i t i e s of of overbank o v e r b a n k material material which tto o accumulate a c c u m u l a t e and be reserved. be ppreserved. T o p o g r a p h y , ttherefore, herefore, Topography, probably probably ggained a i n e d enough rrelief e l i e f to t o further f u r t h e r iinhibit n h i b i t cchannel hannel m igration. migration. Lateral Lateral movement was was nnot o t totally t o t a l l y eliminated, e l i m i n a t e d , however. however. S t a g e II I I streams s t r e a m s rrepresent e p r e s e n t significant s i g n i f i c a n t changes c h a n g e s in i n the t h e dispersal dispersal Stage system. system. T h e s e I'/ere were m e a n d e r i n g streams s t r e a m s tthat hat w e r e somewhat s m a l l e r than than meander-ing VJere somewhat smaller These tthose h o s e of of Stage S t a g e I. I. o w e r bboundary o u n d a r y is i s nnot o t uundulatory n d u l a t o r y bbut u t iis s smooth The llower 73 ----- S t a g e IIII II Stage Small, alluvial plain streams streams S t a g e II I Stage stage I - -----~ --------- - - Large, meandering streams n (somewhat s m a l l e r t h a n Stage Stage I) Stage I Stage -- -- - -- F i g . 28 Fig. streams 74 and horizontal. This suggests that the streams of Stage II had and h o r i z o n t a l . T h i s s u g g e s t s t h a t t h e s t r e a m s of S t a g e I I had approached "grade" and reach equil i brium with the surroundi ngs. approached " g r a d e " and r e a c h e q u i l i b r i u m w i t h t h e surroundings. Lateral migration of the streams is suggested, whereas downward L a t e r a l m i g r a t i o n of t h e s t r e a m s i s s u g g e s t e d , w h e r e a s erosion was probably negligible. e r o s i o n was p r o b a b l y n e g l i g i b l e . downward The banks of the streams apparently The b a n k s of t h e s t r e a m s apparently were not resistant to lateral erosion, which allowed the streams to were n o t r e s i s t a n t t o l a t e r a l e r o s i o n , which allowed t h e s t r e a m s migrate rapidly back-and forth across the floodplain. m i g r a t e r a p i d l y back-and f o r t h across the floodplain. to This accelerated This accelerated rate of lateral movement did not time for substantial thicknesses r a t e of l a t e r a l movement d i d n o t t i m e f o r s u b s t a n t i a l of overbank material to accumulate on the floodplain. of o v e r b a n k m a t e r i a l t o a c c u m u l a t e on t h e f l o o d p l a i n . thicknesses Frequent Frequent reworking of the floodplain prevented such material from being r e w o r k i n g of t h e f l o o d p l a i n p r e v e n t e d s u c h m a t e r i a l from being preserved and probably produced a flat topography. p r e s e r v e d and p r o b a b l y p r o d u c e d a f l a t topography. These two stages of stream development have produced a sequence T h e s e two s t a g e s of s t r e a m d e v e l o p m e n t h a v e p r o d u c e d a s e q u e n c e of sediments that represent IIfilling-up" of the depositional basin. of s e d i m e n t s t h a t r e p r e s e n t " f i l l i n g - u p " of t h e d e p o s i t i o n a l basin. Stage I streams were in disequilibrium with the tectonic and (or) S t a g e I s t r e a m s w e r e i n d i s e q u i l i b r i u m w i t h t h e t e c t o n i c and climatic setting. (or) These streams then evolved into Stage II streams climatic setting. These s t r e a m s then evolved i n t o Stage II streams that represent continued filling of the basin under graded conditions. t h a t represent continued f i l l i n g of t h e b a s i n u n d e r g r a d e d conditions. All outcrops of the large meandering stream deposits show both All o u t c r o p s of t h e l a r g e m e a n d e r i n g s t r e a m d e p o s i t s show b o t h stages of stream development. s t a g e s of s t r e a m development. The tlli rd type of stream development, Stage II I, is represented The t h i r d t y p e of s t r e a m d e v e l o p m e n t , S t a g e I I I , i s by the alluvial plain stream system. by t h e a l l u v i a l plain stream system. represented Stage III streams I'Jere definitely Stage III streams were definitely formed after those of Stage I and probably simultaneously with those formed a f t e r of Stage II. of S t a g e I I . t h o s e of S t a g e I and p r o b a b l y s i m u l t a n e o u s l y w i t h those This relationship VJas determined from the outcrop at T h i s r e l a t i o n s h i p was d e t e r m i n e d from t h e o u t c r o p a t section M near Manila, Utah. s e c t i o n M near Manila, Utah. At this location Stage III stream At t h i s l o c a t i o n S t a g e I I I deposits overlie Stage I stream deposits. d e p o s i t s o v e r l i e Stage I stream d e p o s i t s . stream Also, Stage III stream Also, Stage I I I stream deposits are in contact with the Mowry Shale as are those of Stage II. d e p o s i t s a r e i n c o n t a c t w i t h t h e Mowry S h a l e a s a r e t h o s e of S t a g e II. Individual channel deposits of Stage III are arranged in an en echelon Individual channel d e p o s i t s of S t a g e I I I a r e a r r a n g e d manner separa ted by overbank rna teri a1 . manner s e p a r a t e d by o v e r b a n k m a t e r i a l . i n an en echelon I n Stage I II depos its VJere In S t a g e I I I d e p o s i t s found the only example of crevasse-splay deposits. found t h e o n l y e x a m p l e of c r e v a s s e - s p l a y d e p o s i t s . were The en enchelon The en e n c h e l o n 75 arrangement is interpreted to represent shifting of the channels arrangement i s i n t e r p r e t e d to represent s h i f t i n g into nearby topographic low areas. into nearby topographic system. system. low a r e a s . Stage rlr of t h e channels probably is an aggrading S t a g e I I I - p r o b a b l y i s an Except for section M, outcrops of Stage rlr aggrading deposits are E x c e p t f o r s e c t i o n M, o u t c r o p s of S t a g e I I I d e p o s i t s are exclusive of deposits of other stages. e x c l u s i v e of d e p o s i t s of o t h e r stages. All of the sandstone bodies of the dispersal system are elongate A l l o f t h e s a n d s t o n e b o d i e s of t h e d i s p e r s a l bodies. bodies. system a r e elongate The specific type is difficult to determine from surface The s p e c i f i c type is d i f f i c u l t t o d e t e r m i n e from surface exposures; but, probably, dendroid and ribbon varieties are all e x p o s u r e s ; b u t , p r o b a b l y , d e n d r o i d and r i b b o n v a r i e t i e s a r e present (Potter, 1962). present (Potter, 1962). all Elongate sand bodies are usually oriented E l o n g a t e sand b o d i e s a r e u s u a l l y oriented perpendicular to the depositional strike and parallel with the perpendicular paleoslope. paleoslope. to the depositional s t r i k e and p a r a l l e l with the DEPOSITIONAL ENVIRmU·lENTS ENVIRONMENTS The Dakota within The Dakota Formation Formation w i t h i n tthe h e study s t u d y area a r e a was deposited d e p o s i t e d in in f l u v i a l environment. environment. aa fluvial T h i s \'Jas was determined d e t e r m i n e d by by observing o b s e r v i n g the t h e erosiona"1 erosional This s u r f a c e at a t the t h e llower o w e r contact c o n t a c t and by s t u d y i n g the t h e sedimentary s e d i m e n t a r y structures, structures, surface by studying textural t e x t u r a l pparameters, a r a m e t e r s , petrography p e t r o g r a p h y and paleocurrents. paleocurrents. Subenvironments Subenvironments were w e r e recognized r e c o g n i z e d as a s channel c h a n n e l and overbank o v e r b a n k deposition. deposition. Each forms f orms a lithologic l i t h o l o g i c facies f a c i e s within w i t h i n the t h e Dakota. Dakota. Specific S p e c i f i c ttypes y p e s of of stl~eam stream deposits d e p o s i t s -include i n c l u d e channel c h a n n e l lag, l a g , ppoint o i n t bbar, a r , llevee e v e e and ppossible o s s i b l e crevassecrevassesp s p l1aay y depos d e p o sits. its. As previously p r e v i o u s l y discussed, d i s c u s s e d , tthe h e tthree h r e e types t y p e s of of streams streams c h a n n e l facies f a c i e s of of the t h e fluvial f l u v i a l environment. environment. channel repl~esent represent, the the The nnature a t u r e of of these these s t r e a m s , as a s iind-icated n d i c a t e d by h e i r deposits, d e p o s i t s , in i n conjunction conjunction w i t h the the by ttheh' v1ith streams, t r a n s g r e s s i v e Mowry sea s e a suggest s u g g e s t tthat h a t tthe h e best b e s t large-scale l a r g e - s c a l e model of transgressive tthe h e depositional d e p o s i t i o n a l environment e n v i r o n m e n t is is a a llow-lying o w - l y i n g pplain, l a i n , pprobably r o b a b l y nnear e a r the the s e a , on which w h i c h sluggish s l u g g i s h meandering m e a n d e r i n g streams s t r e a m s flcwed. flowed. sea, Stage 1 I streams s t r e a m s were w e r e more distant d i s t a n t from from the t h e sea sea Stage S t a t e III, III. and State D e p o s i t s of Deposits ttha~ h a n tthose h o s e of of Stage S t a g e II II T h i s is i s bbecause e c a u s e Stage S t a g e II deoosits d, e .p o s i t s aare r e oldest o l d e s t and that that This tthe h e Mowry d i r e c t l y overl o v e r l iies e s Stages S t a g e s II I I and I'lowry directly III. III. The mode ooff ori o r i gg-ji nn of of the t h e "coarse-gra " c o a r s e - g r a iinned e d uunit" n i t " is is 1 l eess s s certa c e r t a in. in. It I t is i s conceivable c o n c e i v a b l e that t h a t iit t could c o u l d hhave a v e formed formed iin n either either a a fluvial fluvial e n v i r o n m e n t or o r some environment some t r a n s iiti t i oana n a l1 envi e n v i rronment o n m e n t bbeh'/een etween tran~ c o n t i nenta nenta1 l conti or m a r i n e conditions c o n d i t i o n s such s u c h as a s an estuary, e s t u a r y , ttidal i d a l flat f l a t or or a a river r i v e r that t h a t is is or marine s t r o n g l y affected a f f e c t e d by t i d a l cur-rents. currents. str-ongly by tida"1 I t could c o u l d be a r g u e d tthat hat a It be argued s w i f t l y flowing f l o w i n g stream s t r e a m would be nnecessary e c e s s a r y tto o ttransport r a n s p o r t such s u c h coarsecoarseswiftly grained mated':;.l. The grained m a t e r i a l . The m e d i u m - s c a l e t r o u g h s p l u s t h i s u n i t ' s 77 troughs plus this unit's close medium·~sca·le close association with the fluvial rocks of the Dakota support the fluvial association with the fluvial r o c k s of t h e Dakota s u p p o r t t h e fluvial hypothesis. Evidence in favor of deposition in one of the transitional hypothesis. E v i d e n c e i n f a v o r of d e p o s i t i o n i n one of t h e transitional environments is its widespread occurrence, which makes correlation e n v i r o n m e n t s i s i t s w i d e s p r e a d o c c u r r e n c e , w h i c h makes correlation possible over much of the study area. 1\150, in spite of the debatable p o s s i b l e o v e r much of t h e s t u d y a r e a . A l s o , i n s p i t e of t h e debatable origin of the large-scale ripples, they appear likely to have formed o r i g i n of t h e l a r g e - s c a l e ripples, t h e y a p p e a r l i k e l y t o have formed in strong, bimodally opposed currents. The reason for this is that in s t r o n g , The r e a s o n f o r b i m o d a l l y opposed c u r r e n t s . this is that coarse-grained ripples that have originated in unidirectional coarse-grained r i p p l e s t h a t have o r i g i n a t e d in unidirectional fluvial conditions appear to have long wave-lengths, much longer fluvial c o n d i t i o n s a p p e a r t o h a v e l o n g w a v e - l e n g t h s , much longer than the \>Javelength observed in the IIcoarse-grained unitll (Thiel, 1932). than the wavelength observed in the " c o a r s e - g r a i n e d unit" (Thiel, 1932). The contact between the Ilcoarse-grained unit and the underlying ll The c o n t a c t b e t w e e n t h e " c o a r s e - g r a i n e d u n i t " and t h e underlying fluvial deposits is probably unconformable. The writer favors the fluvial The w r i t e r f a v o r s deposits i s probably unconformable. the ; nterpreta t'i on of the IIcoarse-gra i ned unit as representi ng a ll interpretation of t h e " c o a r s e - g r a i n e d u n i t " as r e p r e s e n t i n g transitional environment. It transitional It is therefore gr'ained unit environment. ll grained unit" a is therefore felt that the IIcoarsefelt that the "coarse­ is genetically t'elatc:d to the transgression of the is genetically related to the t r a n s g r e s s i o n of the r·lowry sea and is therefore not part of the Dakota Formation deposiMowry s e a and i s t h e r e f o r e tional environment. tional environment. n o t p a r t of t h e Dakota F o r m a t i o n deposi- CONCLUSIONS CONCLUSIONS In conclusion, Utah is c o n c l u s i o n , the t h e Dakota Dakota Formation F o r m a t i o n in i n nnortheastern o r t h e a s t e r n Utah is a c o n t i n e n t a l ffluvial l u v i a l deposit. deposit. continental l i t h o l o g i c facies; f a c i e s ; aa lithologic I t is i s characterized c h a r a c t e r i z e d by bow two different different It ccoarse~grained o a r s e - g r a i n e d channel c h a n n e l facies f a c i e s and a finefine­ grained g r a i n e d overbank o v e r b a n k facies. facies. The channel by tvJO c h a n n e l facies f a c i e s iis s rrepresented e p r e s e n t e d by two t y p e s of of ooutcrops u t c r o p s tthat h a t indicate indicate a a change c h a n g e in i n tthe h e dispersal d i s p e r s a l system. system. types L a t e r a l accretion a c c r e t i o n is i s responsible r e s p o n s i b l e for f o r vvirtually i r t u a l l y aall l l of o f the t h e deposition deposition Lateral i n thE t h e channel c h a n n e l facies. facies. in form of of point p o i n t bars. bars. form of tthe h e channel c h a n n e l deposition d e p o s i t i o n is i s in i n the the Most of A l s o , tthe h e channel c h a n n e l facies f a c i e s is i s characterized c h a r a c t e r i z e d by by Also, cycles, c y c l e s , each e a c h rrepresenting epresenting a a ssingle i n g l e episode e p i s o d e of of ffluvial l u v i a l deposition. deposition. Certain C e r t a i n ttextural e x t u r a l pparameters, a r a m e t e r s , expecially e x p e c i a l l y grain g r a i n size, s i z e , are are vlh-ich valuable v a l u a b l e in i n indentifying i n d e n t i f y i n g the t h e type t y p e of of stream s t r e a m in in w h i c h tthe h e sediments sediments were w e r e deposited. deposited. Petrographic P e t r o g r a p h i c studies s t u d i e s showed that t h a t the t h e coarse-grained coarse-grained cchannel h a n n e l facies f a c i e s iis s quartz-rich. quartz-rich. other o t h e r main constituents. constituents. Matrix and rrock M a t r i x and o c k fragments f r a g m e n t s are a r e the the Detailed D e t a i l e d ppaleocurrent a l e o c u r r e n t analysis a n a l y s i s demonstrated demonstrated t h a t all a l l of of the t h e Dakota Dakota streams s t r e a m s were w e r e meandering. meandering. that P a l e o c u r r e n t azimuths azimuths Paleocurrent are a r e fairly f a i r l y well w e l l concentrated c o n c e n t r a t e d for f o r single s i n g l e channels c h a n n e l s bbut u t less l e s s concentrated concentrated f o r the t h e outcrop o u t c r o p as as a a whole. whole. for The r e g i o n a l dispersal d i s p e r s a l direction direction The regional is is a l m o s t due d u e north. north. almost The The IIcoarse-grained " c o a r s e - g r a i n e d unit", u n i t " , ppresent r e s e n t at a t the t h e top t o p of of the t h e channel channel facies, f a c i e s , iis s tthought h o u g h t tto o have h a v e originated o r i g i n a t e d in in a a ttransitional r a n s i t i o n a l environment environment between marine b e t w e e n ccontinental o n t i n e n t a l and m a r i n e conditions c o n d i t i o n s as as a a product p r o d u c t of of the the ~'m'll~y sea. ttransgressing r a n s g r e s s i n g Mowry sea. From tthese new upper From h e s e conclusions, conclusions, a a new upper c o n t a c t is i s proposed p r o p o s e d and i t lies l i e s at a t tthe h e bbase a s e of of the t h e "coarse-grained "coarse-grained and it contact 79 uunit." nit." The pprovenance Dakota sediments The r o v e n a n c e area a r e a for f o r tthe h e Dakota s e d i m e n t s vIas was pprobably r o b a b l y in in south-central s o u t h - c e n t r a l Utah Utah and and adjacent a d j a c e n t pportions o r t i o n s of of Nevada. Nevada. The source The source terrane t e r r a n e consisted c o n s i s t e d of o f older o l d e r sedimentary s e d i m e n t a r y reeks r e c k s and llesser e s s e r amounts a m o u n t s of fine-grained f i n e - g r a i n e d metamorphic m e t a m o r p h i c rocks. rocks. The di \'las composed d i sspersal p e r s a l system s y s t e m was composed of of three t h r e e different d i f f e r e n t forms forms of streams. streams. The d i f f e r e n c e s in i n tthe h e streams streams w e r e in i n size, s i z e , degree d e g r e e of The differences were l a t e r a l migration, m i g r a t i o n , presence p r e s e n c e or o r aabsence b s e n c e of of ooverbank v e r b a n k deposits d e p o s i t s and lateral e q u i l i b r i u m or o r disequilibrium d i s e q u i l i b r i u m conditions c o n d i t i o n s with w i t h tthe h e geologic g e o l o g i c and (or) equilibrium and (or) c l i m a t i c setting. setting. climatic The dominant d o m i n a n t environment e n v i r o n m e n t of of deposition d e p o s i t i o n was probably p r o b a b l y variable variable i n terms t e r m s of of distance d i s t a n c e from t h e sea. sea. in from the S t a g e I streams s t r e a m s were w e r e probably probably Stage at a a ggreater r e a t e r d1 d i sstance t a n c e from from tthe h e ssea e a than t h a n strea!ns s t r e a m s of of Stages S t a g e s II I I and II II. II. at The environment e n v i r o n m e n t of of deposition d e p o s i t i o n for f o r Stage S t a g e I deposits d e p o s i t s is i s concluded c o n c l u d e d tto o be f a i r l y large l a r g e stream s t r e a m valley v a l l e y at a t an undetermined u n d e t e r m i n e d distance d i s t a n c e from the t h e sea. sea. a fairly S t a g e s II I I and III I I I represent r e p r e s e n t deposition d e p o s i t i o n on a a low-lying l o w - l y i n g alluvial a l l u v i a l plain plain Stages nnearer e a r e r to t o the t h e sea, s e a , pprobably r o b a b l y a coastal c o a s t a l p1ain. plain. The uultimate The l t i m a t e site s i t e of deposition by Dakota of the d e p o s i t i o n by Dakota streams s t r e a m s was pprobably r o b a b l y nnorth o r t h of t h e study s t u d y area area i n wes w e s tern t e r n Lvyomi Wyoming. in n9. REFERENCES CITED REFERENCES CITED Allen, R. LL., A l l e n , J. J . 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