New ichnological, paleobotanical and detrital zircon data from an unnamed rock unit in Yukon-Charley Rivers National Preserve (Cretaceous: Alaska): stratigraphic implications for the region.

A paleontological reconnaissance survey on Cretaceous and Tertiary terrestrial units along the Yukon River drainage through much of east-central Alaska has provided new chronostratigraphic constraints for the units, paleoclimatological data, and the first information on the local biodiversity within an ancient, high latitude ecosystem. The studied unnamed rock unit is most notable for its historic economic gold placer deposits but our survey documents its relevance as a source-rock for Mesozoic terrestrial vertebrates, invertebrates and associated flora. Specifically, new U-Pb ages from detrital zircons combined with ichnological data are indicative of a Late Cretaceous age for at least the lower section of the studied rock unit, previously considered to be representative of nearly exclusively Tertiary deposition. Further, the results of our survey show that this sedimentary rock unit preserves the first record of dinosaurs in the vast east-central Alaska region. Lastly, paleobotanical data when compared to correlative rock units support previous interpretation that the Late Cretaceous continental ecosystem of Alaska was heterogeneous in nature and seasonal.