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Title	Stratigraphy and sedimentology of the tidwell member, upper jurassic morrison formation, East-Central Utah
Publication Type	thesis
School or College	College of Mines & Earth Sciences
Department	Geology & Geophysics
Author	Bernier, Julie Christine
Date	2003
Description	The Tidwell Member (Upper Jurassic Morrison Formation) in east-central Utah contains the type specimen of the oldest known sauropod dinosaur from the western United States (Dystrophaeus viaemalae Cope 1877; USNM 2364). Because of its stratigraphic position, this species may be an important evolutionary link between the diverse sauropod faunas of the Upper Jurassic Morrison Formation and their Middle Jurassic ancestors. Some controversial studies recently proposed that the Tidwell Member be included at the top of the Middle Jurassic San Rafael Group on the western Colorado Plateau. However, detailed stratigraphic studies of the Tidwell Member presented here concur with the conventional stratigraphy and constrain the stratigraphic age of the Tidwell Member with the D. viaemalae type specimen to the basal Morrison Formation. The Tidwell Member consists of nine lithofacies in the study area: rippled sandstone; thin-bedded sandstone; gypsiferous mudstone; siltstone; lenticular sandstone; mudstone; micritic limestone; and brecciated limestone. These lithofacies were deposited distal to the Salt Wash Member alluvial complex and are dominated by floodplain deposits with small local streams and ponds. Some fluvial sheet sandstones were likely ephemeral. Petrographic analysis shows that Middle and Upper Jurassic sandstones are typically quartz arenites and subarkosic arenites, but composition alone cannot distinguish different stratigraphic units in the study area. Petrologic composition and paleocurrent data indicate that Tidwell Member sediments were derived from a western recycled orogenic source (Elko highlands and/or early Sevier orogeny thrust belt) and were transported northeastward onto the distal alluvial plain. The D. viaemalae type specimen (USNM 2364) is preserved in a thin fluvial channel sandstone of the lenticular sandstone facies. The partially articulated remains suggest that transport prior to burial was minimal. This rare fossil occurrence in the Tidwell Member may be related to: (1) a scarcity of vertebrate faunas in arid alluvial plain environments; (2) early depositional and diagenetic conditions that were unfavorable to the preservation of organic material; or (3) historical sampling biases related to poor exposure of the slope-forming Tidwell Member. Facies analysis and interpretation of Tidwell Member depositional environments provides a context for future studies investigating early Late Jurassic sauropod paleoecology.
Type	Text
Publisher	University of Utah
Dissertation Name	Master of Science
Language	eng
Rights Management	© Julie Christine Bernier
Format	application/pdf
Format Medium	application/pdf
ARK	ark:/87278/s68d4x9d
Setname	ir_etd
ID	2354140
Reference URL	https://collections.lib.utah.edu/ark:/87278/s68d4x9d

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Title	Page 233
Format	application/pdf
Setname	ir_etd
ID	2354373
OCR Text	Show 224 Dunagan, S.P., 2000a, Lacustrine carbonates of the Morrison Formation (Upper Jurassic, Western Interior), east-central Colorado, U.S.A., in Gierlowski Kordesch, E.H. and Kelts, K.R., eds., Lake basins through space and time: American Association of Petroleum Geologists Studies in Geology, v. 46, p. 181-188. Dunagan, S.P., 2000b, Constraining Late Jurassic paleoclimate within the Morrison ecosystem; insights from e continental carbonate record of the Morrison Formation (Colorado, USA), in Advances in Jurassic research 2000; proceedings of the Fifth international symposium on the Jurassic system: GeoResearch Forum, v. 6, p. 523-531. Dunham, RJ., 1962, Classification of carbonate rocks according to depositional texture, in Ham, W.E., ed., Classification of carbonate rocks: American Association of Petroleum Geologists, Memoir 1, p. 108-121. Eldridge, G.H., 1896, Chapter IT, Mesozoic of the Denver basin in Colorado: geology, in Emmons, et aI., eds., Geology u.S. Geological Survey, Monograph 27, p. 51- 150. Engelmann, G.F., and Fiorillo, A.R, 2000, The taphonomy and paleoecology of the Upper Jurassic Morrison Formation determined from a field study of fossil localities, in Advances in Jurassic research 2000; proceedings of the Fifth international symposium on the Jurassic system: GeoResearch Forum, v. 6, p. 533-540. Eugster, H.P., 1969, Inorganic bedded cherts from the Contributions to Mineral Petrology, v. Magadi area, Kenya: 22, p. 1-31. Foster, J.R., 1998, Aspects of vertebrate paleoecology, taphonomy, and biostratigraphy of the Morrison Formation (Upper Jurassic), Rocky Mountain region, Western United States [Ph.D. thesis]: Boulder, University of Colorado, 405 pp. Foster, J.R, Hamblin, A.H., and Lockley, M.G., 2000, The oldest evidence of a sauropod dinosaur in the western United States and other important vertebrate trackways from Grand Staircase-Escalante National Monument, Utah: Ichnos, v. 7, p. 169-181. Gillette, D.D., 1996a, Origin and early evolution ofthe sauropod dinosaurs of North type locality and stratigraphic position of Dystrophaeus Cope 1877, in Huffman, A.c. Jr., Lund, W.R, and Godwin, L.H., eds., Geology and resources of the Paradox basin: Utah Geological Association America: The viaemalae Guidebook 25, p. 313-324.
Reference URL	https://collections.lib.utah.edu/ark:/87278/s68d4x9d/2354373