The Albian-Cenomanian Dakota Formation and Mowry Shale of the Uinta Basin consist of an overall transgressive sequence of continental and marine strata that were deposited in the medial part of the Cordilleran foreland-basin system. However, complex stratigraphic relationships within the Dakota Formation and Mowry Shale, as well as complexities between both older and younger strata, have led to different interpretations regarding the large-scale stratigraphic architecture of the basin. In order to provide a better understanding of the overall stratigraphic relationships between the Albian-Cenomanian rocks of the region, palynological samples from the Dakota Formation, Mowry Shale, and overlying units were collected from the northern and southern margins of the Uinta Basin. When combined with preexisting biostratigraphic studies and regional stratigraphic correlations of the Dakota-Mowry interval, this data can be used to construct a unifying stratigraphic model for Dakota and Mowry deposition.
Results of this study indicate that Dakota Formation contains three, unconformity-bound depositional sequences. The first Dakota sequence is late Albian in age and was deposited above a regional unconformity that can be traced throughout the Uinta Basin. The second Dakota sequence was deposited above a second regional unconformity that formed during latest Albian time. In the northern part of the Uinta Basin, nonmarine deposition of second Dakota sequence was confined to the late Albian. Early Cenomanian-aged marine deposits of the overlying Mowry Shale comprise the upper parts of the sequence. In the southern part of the basin, the second Dakota sequence is entirely nonmarine. A regional decrease in relative sea level at the end of early Cenomanian time resulted in the development of a regional unconformity throughout the study area. In the southern Uinta Basin, incised fluvial channel complexes of the third Dakota sequence lie above the unconformity. The third Dakota sequence in this region is capped by the middle Cenomanian-Turonian Tununk Member of the Mancos Shale In the northern part of the basin, nonmarine deposits of the third Dakota sequence are absent. In this region the unconformity is situated at the erosional contact between the Mowry Shale and the middle Turonian Tununk Member.