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Depositional environments, palynology, and age of the Dakota Formation, south-central Utah

By
Barbara A. am Ende
Barbara A. am Ende
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Published:
January 01, 1991

The Dakota Formation of south-central Utah was deposited in the foreland basin to the east of the Sevier orogenic belt. During the early Late Cretaceous, clastics shed from the west accumulated in valleys cut into Jurassic rocks along the western margin of the Western Interior Seaway.

Braided stream deposits of horizontal and planar-tabular cross-bedded sand and gravel were the first sediments laid down on the erosional surface. Associated with a transgression of the seaway, anastomosed stream channel sands encased in fine-grained overbank sediments were the next to be deposited. Marine-influenced clastics overlie the fluvial sediments. Initially, these were lagoonal or estuarine beds of fine-grained material with a brackish fauna. The overlying lower shoreface sediments that are similar in appearance are differentiated by an open marine fauna and minor bedding characteristics. Tidal channel deposits of bimodally cross-bedded sandstone provide evidence for a barrier bar system. The final transgression that destroyed the topographically positive features of the barrier bar system is represented by a locally present ravinement deposit and the overlying open marine Tropic Shale.

There are approximately equal percentages of spores, gymnosperm pollen, and angiosperm pollen in the Dakota Formation. Among angiosperm pollen, tricolpate forms are the principal types. There are very few coniferous pollen grains; the gymnosperm pollen content is almost entirely composed of the Araucariaceae and the Taxodiacaeae. A variety of fern and bryophyte spores was identified, plus an acritarch. The assemblage of pollen and spores suggests a warm temperate to subtropical climate.

Palynomorphs, particularly the presence of psilate and reticulate tricolporate pollen, indicate the Dakota Formation is no older than Cenomanian in age. Just above the Dakota Formation in the Tropic Shale the Sciponoceras gracile ammonite zone indicates that the Dakota Formation is no younger than Cenomanian.

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GSA Special Papers

Stratigraphy, depositional environments; and sedimentary tectonics of the western margin, Cretaceous Western Interior Seaway

J. Dale Nations
J. Dale Nations
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Jeffrey G. Eaton
Jeffrey G. Eaton
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Geological Society of America
Volume
260
ISBN print:
9780813722603
Publication date:
January 01, 1991

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