SEQUENCE STRATIGRAPHY AND PALYNOLOGY OF THE ALBIAN-CENOMANIAN DAKOTA FORMATION, EASTERN UTAH

The Cretaceous Dakota Formation in eastern Utah is a complex mix of fluvial, tidal, and marine deposits. Based on the architectural arrangement of fluvial sandstones, overbank mudstones, and associated marginal/shallow marine deposits, the formation can be subdivided into upper and lower stratigraphic units that are separated by a sequence-bounding unconformity. Each sequence consists of basal valley-fill deposits that are overlain by carbonaceous overbank/esturarine mudstones, and isolated fluvial/tidal-channel sandstones.

Palynomorphs from the Dakota Formation indicate that the unit is Late Albian-Early Cenomanian in age. In east-central Utah, a Late Albian age for the lower Dakota sequence is based on the occurrence of Concavissimisporites punctatus, Ischyosporites disjunctus, I. punctatus, Klukisporites pseudoreticulatus, K. areolatus, Neoraistrickia robusta, Pilosisporities trichopapillosus, Rouseisporites spp., Trilobosporites marylandensis, T. crassus, T. apiverrucatus, and T. trioreticulosus. An age no older than Late Albian is interpreted based on the presence of Fraxinoipollenites inaequalis, Liliacidites peroreticulatus, L. inaequalis, and Rugubivesiculites rugosus. A Late Albian-Early Cenomanian age for the upper Dakota is defined by Albian taxa from the lower part of the sequence and Middle Cenomanian palynomorphs recovered from the overlying Mancos Shale. Late Albian taxa include K. pseudoreticulatus, K. areolatus, N. robusta, P. trichopapillosus, Rouseisporites spp., T. apiverrucatus, T. crassus, and T. trioreticulosus. Middle Cenomanian taxa from the basal Mancos Shale include Cicatricosisporites crassiterminatus, Cribroperidinium edwardsi, Palaeohystrichophora infusorioides, and Subtilisphaera terrula. In northeast Utah, a Late Albian age for the upper Dakota is defined by the occurrence of Chichaoudinium (Spinidinium) vestitum. The upper sequence in this region is overlain by the Lower Cenomanian Mowry Shale.

These data indicate that the unconformity between the lower and upper Dakota is confined to the Late Albian and that the upper part of the Dakota Formation in east-central Utah can be correlated with the Dakota Formation and Mowry Shale in northeastern Utah.