Print this pageAbstract: Stratigraphy of Cedar Mountain and Dakota Formations (Early Cretaceous), Northwestern Colorado
The Lower Cretaceous Cedar Mountain and Dakota Formations are exposed along the south, east, and north flanks of the Uinta uplift in northwest Colorado. Subsurface information allows limited projection of lithologies southward and eastward into the Piceance Creek basin.
No sedimentologic evidence exists in the study area to indicate a break between deposition of the Morrison Formation and deposition of the overlying Cedar Mountain Formation.
The Buckhorn Conglomeratic Member, where present, has been utilized on the surface and in the subsurface as the base of the Cedar Mountain Formation. The Buckhorn Member is a product of braided fluvial deposition.
The upper part of the Cedar Mountain Formation is primarily gray-green bentonitic mudstone, with thin, lenticular interbeds of sandy to silty calcareous mudstone, and pebbly sandstone. The sandstones and mudstones are fluvial deposits and the calcareous mudstones represent lacustrine and marginal-lacustrine deposits. The relative predominance of marginal-lacustrine deposits indicates a relatively dry climate in the region at the time of deposition.
A regional unconformity separates the Dakota Formation from the underlying Cedar Mountain Formation. On the basis of primary sedimentary structures the Dakota Formation is divisible into two parts: a lower fluvial part and an upper tidal part. Sediment transportation directions indicate deflection around an ancestral Uinta uplift.
AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah