Systematic paleontology, paleoecology, and biostratigraphy of ostracodes and agglutinated foraminifera from the western margin of the Cenomanian-Turonian Western Interior sea, southwest Utah

Sixty-four foraminifera and ostracode taxa are described from estuarine coal-bearing strata in the upper Cenomanian-middle Turonian Dakota, Tropic, Iron Springs, and Straight Cliffs Formations. These taxa comprise 3 Microfossil Assemblage Zones that include: Zone I (late Cenomanian), Zone II (latest Cenomanian), and Zone III (early-late middle Turonian).; Four primary paleoecological assemblages characterize the strata: (1) a proximal estuary comprising the brackish ostracode Fossocytheridea , charophytes, and smooth admetopsid gastropods within coal zones; (2) a central estuary comprising a rich agglutinated foraminiferal population of Trochammina and Verneuilinoides and brackish ostracodes and molluscs in a skeletal shell accumulation; (3) a distal estuary/bay comprising the ostracodes F. posterovata, Cytheromorpha, Looneyella, and Cytheropteron, the foraminifera Trochammina and Ammobaculites, and ornate brackish mollusks in calcareous shelly mudstones; and (4) an estuarine marsh comprising an exclusive population of the foraminifera Trochammina, Miliammina , and Ammobaculites in rooted lignites.; Intermediate flooding surfaces are marked by normal marine taxa that superimpose the prominent marginal marine assemblage. In general, major flooding events approximate lithologic and biostratigraphic boundaries and record basin-wide paleoenvironmental changes with the advancing Greenhorn Sea. Coal zones near the coast correlate to calcium carbonate and planktic foraminiferal maxima in the offshore. The duration of the intermediate cycles are similar to the ammonite biostratigraphic zones and therefore maintain periodicities within the 105 yr bandwidth and suggest a regional and perhaps global sea level mechanism controlled their stratigraphic position. Superimposed on the intermediate cycles are higher frequency cycles that contain short-lived flooding events that often overlie coal seams within coarsening-up bayfill packages. As many as 6 high frequency cycles may overly an intermediate cycle and therefore periodicities fall with the 104–10 5 yr range. The general asymmetry of the packages suggests a combination of oceanographic, climatic, and autogenic processes exerted primary control on stratal architecture.; Both the foraminifera and the ostracode generic population compositions resemble modern marginal marine ecosystems, suggesting that a modern-like brackish biota developed on the western coast of the Western Interior Basin during deposition of the third-order Greenhorn transgressive-regressive marine cycle.