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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 143
Format	application/pdf
Setname	ir_etd
ID	2206395
OCR Text	Show 100 Stratigraphic relations - underlying Entrada sandstone (see Figo 29) stone In 0 is sharp general the The contact of the Todilto with the in the restricted and truncates the cross-bedding evenness suggest an the not very probably eolian great. sand reworking did the adva.ncing The very leveling sea fine-grained Pony Express limestone has over them in much the the wind-blown sandstone where been rferred to present commonly surface of which is either smooth the over manner as Navajo sandstoneo siltstone which overlies the or sandstone member of the Wanakah formation. sandstone, same how are It is believed the watevs advanced and Carmel widespread unconformity; the amount of erosion and the time interval involved ever, the of the sand abrupt change in lithclOgy, very nature of the contact and its This evaporite basin locally (Goldman lies or the Bilk Creek as Spencer, 1941)e and directly undulating. on the brecciaj It was noted that .fine quartz grains do not penetrate the underlying open breccia, which may indicate that solutions of gypsum occurred compaction of the overlying At the Bilk Creek type section gray, fine-grained sandstoneo equivalent Pony Express is a The sandstone is considered to the Moab the west and-north and the darkj dense, limestone overlain by 26 feet of irregularly fractured, as after sandstone beds. gray, writer chiefly tongue is therefore, by light the of the Entrada sandstone to of the Curtis one Equivalents (see Fig. 24)0 It is suggested by laminations, that the deposition composition texture, of the Moab tongue place in quet waters, probably sands blown and the horizontal or onto the Bilk Creek took sunfaces of the
Reference URL	https://collections.lib.utah.edu/ark:/87278/s6d19tx4/2206395