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Title	Jurassic history and stratigraphy of Colorado
Publication Type	thesis
School or College	College of Social & Behavioral Science
Department	Geology
Author	Holmes, Clifford N.
Date	1960
Description	At the beginning of the Jurassic period western Colorado was a relatively low-lying, flat plain with the Ancestral Rockies reduced to low relief The Chino formation, on which the rocks of the Glen Canyon group rest, thins gradually from west to east and disappears completely before reaching the axes of the ancestral Uncompahgre and Colorado Range positive elements 0 The first rocks deposited, assigned to the Glen Canyon group, consist of the Wingate sandstone, Kayenta formation and Navajo sandstone, in ascending order. These formations were deposited in an immense desert basin. The Wingate sandstone pinches out rapidly within a belt that cuts diagonally across the western edge of the Uncompahgre high before reaching the axis of the positive element. No Wingate is known in or east of the central Colorado basin. The Kayenta formation has approximately the same distribution as the Wingate sandstone, but of flaps its outer boundaries. The Navajo and its equivalent the Nugget extend southeastward across northwestern Colorado into the central Colorado basin as far as Rifle Rocks of the San Rafael group are also present in Colorado although their marine origin is less evident here than in central Utah. The Carmel formation extends eastward only a few miles into Colorado before it disappears 0 The widespread Entrada sandstone transgresses all older formations before pinching out against the Ancestral Rockies in southwestern and north central Colorado In these areas the basal part of the Entrada contains fragments of igneous and metamorphic rocks where it rests on the Precambrian roc􁪽s of the positive elements. The Entrada is correlative with local units such as the Garo sandstone, Exeter sandstone, Dr. Bond sandstone, and the lower Stance The marine Curtis formation covers northwestern Colorado and extends southeastward in a fairly well-defined lobe as far as Aspen in the Central Basin Thin-bedded sandstone and shale beds that may correlate with the marine Curtis formation extend southward from Wyoming along the Front Range to the vicinity of Boulder. Th􁪽se have not yielded diagnostic fossils A gypsum deposit over 200 feet thick was formed in a restricted part of the Curtis sea, both to the southeast of the Colorado uplift and to the southwest of the Uncompahgre uplift In southwestern Colorado the gypsum deposit passes laterally into the Bilk Creek sandstone member of the Wanaka formation and the Moab tongue of the Entrada sandstone to the west. The Wanaka formation and the Tidily limestone are confined to the gypsum basin southwest of the Uncompahgre uplift The Wanaka formation passes laterally into the typical Summerville formation of western Colorado.
Type	Text
Publisher	University of Utah
Dissertation Name	Doctor of Philosophy
Language	eng
Rights Management	© Clifford No Holmes
Format	application/pdf
Format Medium	application/pdf
ARK	ark:/87278/s6d19tx4
Setname	ir_etd
ID	2206252
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6d19tx4

Page Metadata

Title	Page 141
Format	application/pdf
Setname	ir_etd
ID	2206393
OCR Text	Show 9.8 LOWER PIEDRA RIVER SECTION Archuleta County, Colorado T. 34 No, R. 4 Wo Section 6 May, 1950 (Measured by C. N. Holmes & To Eo Mullens) Todilto formation: Limestone; Limstone; dark gray, dark gray, massive, denseo.o.ooo thin-beddedo ... ooooo •.........•...... RIDGEWAY SECTION Ouray.County, Colorado To 45 No, Ro 8 Wo Section 5 November ,_ 1949 (Measured by Todilto Holmes) C. No formation: Sandstone; gypsiferous, medium fine-,grained, quartz grains well-rounded scattered in gypsum, red accessory, scattered fine black accessory, friableoooooooooooooooooooo04 Gyp S1lJ1l; whi t e , impure Gypsum; impure, scattered black shale fragments, thin-bedded 0 0 0 0 0 2.8 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 •• 0 0 0 0 0 0.5 5508 5300 •• 0 .. 0 0 0 0 0 ••• 0 •• 0 • 0 0 0 0 0 0 0 0 0 0 0 204 5205 LO 5001 0 0 0 Sandstone; gypsiferous, medium fine-grained, scat tered quartz grains in gypsum, very fine black accessoriesooooooooooooooooooooooooooooo Sandy shale; olive gray, slightly fissile, abun dant veinlets of gypsum, thin-beddedoooooooooo 605 4901 Sandy gypsum; scattered quartz grainsoooooooooooooo Shale; black, abundant coarse perfectly rounded 0' e quartz grains. black accessories, fine Sandstone, gypsiferous, 2.6 4206 006 40.0 307 3.4 39.4 3507 500 003 3204 104 2701 507 25.7 2000 2000 0 0 0 0 •••••• 0 even-bedded Gypsum ; white 0 0 0 0 0 0 0 0 0 0 0 0 • 0 • 0 0 •••• 0 ••• 0 0 0 0 0 0 0 0 0 0 0 ••••••••••• 0 ••• 0 0 0 0 0 • 0 • 0 0 0 0 0 • 0 0 •••••• 0 0 0 0 0 0 0 0 0 0 0 0 ••• 0 0 0 0 Sandstone; white, very gypsiferous, scattered rounded quartz grains Shale; black, fi ssile Sandy gypsum; pure gypsum to ,sandstone along strike, very light gray Gypsum; sandy; white, wavy irregular contact, some reddish coloring in top 1.5v.oooooooooo Sandstone; whi t.e, medium fine, gypsiferous sand, well-rounded scattered quartz grains, friable, .... .. 0 0 0 0 0 0 0 0 0 0 0 0 0 • .00 0 0 • 0 0 0 0 0 • 0 • 0 • 0 0 • 000 •• 0 •• 0 • 0 • 0 .0 • 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 • .. ooooo 27.4 scattered rounded red accessory (chert?) occasional black accessory coarse to very fine-grained, gypsum concentrated and dis- seminated, Sample gg-#l.oooooooooooooooooooooo
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6d19tx4/2206393