Palynostratigraphic framework for the cretaceous (albian‐maestrichtian) of the overthrust belt of Utah and Wyoming

The ranges of twenty selected species of palynomorphs define the palynostratigraphic framework of Cretaceous strata of the central overthrust belt of the Rocky Mountains. The palynostratigraphy is based on local ranges of dinocysts, spores, and pollen determined from more than 300 samples from independently dated outcrop reference sections in Fossil Basin, southwestern Wyoming. The stratigraphic succession in Fossil Basin is essentially continuous from middle Albian to upper Maestrichtian, except for a hiatus in the Campanian, and includes about 4500 meters of marine and nonmarine rocks. The most reliable biostratigraphic zonation for the region is one based on local ranges of palynomorphs. Use of both marine and nonmarine palynomorphs not only permits correlation between facies, but also can refine zonation of the total interval. Ratios of marine to nonmarine palynomorphs in the interval studied show a pattern that represents transgression and regression of the Western Interior Cretaceous seaway overprinted by local depositional events. The dinocyst species, which occur in marine intervals of Albian to earliest Campanian age, are: "Muderongia”; sp. A, Spinidinium vestitum, Cribroperidinium edwardsii, Ovoidinium verrucosum, Alterbia sp. A, Palaeohystrichophora infusorioides, Surculos‐phaeridium sp. cf. S. longifurcatum, Chatangiella sp. cf. C. victoriensis, Dinogymnium sp. A, and Alterbia sp. B. Some of these forms appear to be new species. The spores and pollen, which also include some new species, occur variously throughout the stratigraphic succession in both marine and nonmarine rocks. The species of spores and pollen are: Asteropollis asteroides, Janu‐asporites spiniferus, Appendicisporites unicus, Appendicisporites auritus, Tricolpites sp. A, Quadripollis krempiv; Proteacidites retusus, Pseudoplicapollis nev/manii n. sp. ("Sporopollis laqueaeformis"), Aquilapollenites quadrilobus, and Wodehouseia spinata. Evidence is presented to support our contention that the genus Proteacidites is a guide for the Senonian (Coniacian to Maestrichtian) in the Western Interior and that the "Proteacidites datum”; is early Coniacian.