A PERSPECTIVE ON THE MID-CRETACEOUS FROM A DINOSAURIAN HIGH LATITUDE GREENHOUSE ECOSYSTEM, NORTH SLOPE, ALASKA

The Albian-Cenomanian Nanushuk Formation crops out over much of the central and western North Slope of Alaska, and varies in thickness from ~1500 m in the west to ~250 m in the northeast. The Nanushuk Formation records a succession of complexly inter-tonguing marine and nonmarine strata. Facies associations included shallow marine deposits, tidal flats, distributary channels and interdistributary bays and bayfills, as well as fluvial channels, floodplains, and coal swamps. These facies associations indicate lower delta plain and upper delta plain environments that prograded from west to east along the axis of the Colville foreland basin with an additional south to north component in the area that now makes up the east-central Brooks Range foothills.

Paleobotanical work in the western region of the North Slope of Alaska, within the nonmarine facies has shown floral heterogeneity across this ancient landscape. Such a landscape reconstruction suggests that the fossil vertebrate record should similarly have patterns of heterogeneity. Preliminary reconnaissance in the western and central regions of the North Slope of Alaska have produced approximately 75 isolated discoveries of both body fossils and trace fossils attributable to dinosaurs from fluvial, alluvial, and deltaic settings. More specifically, the ichnological remains are attributed to large and small theropods, avian theropods, bipedal and quadrupedal ornithischians, while skeletal elements are attributed to ornithopods. Preliminary precipitation data are consistent with the increased hydrologic cycle predicted for this time. These reconnaissance discoveries from nonmarine sections illustrate the great potential of the Nanushuk Formation to produce valuable insights into the structure, dynamics and climate of an ancient high-latitude greenhouse terrestrial ecosystem across the North Slope coastal plain.