RAPID ENVIRONMENTAL AND CLIMATIC CHANGES IN THE CRETACEOUS: WESTERN INTERIOR SEAWAY OVERVIEW AND UPDATE

Cretaceous strata preserve one of the most valuable archives of geologic history, not only because they record a time of elevated CO₂ levels and peak global warmth. Superimposed upon a greenhouse background, geologically brief global environmental and climatic perturbations took place during the Cretaceous. Studies of the rates and magnitudes of geological processes during these events, and their manifestations in atmospheric, terrestrial, and marine environments, as sensed through a variety of proxy records, provide critical information for defining the full spectrum of Earth System behavior. The Western Interior basin has long been a rich source of information on Cretaceous environmental and climate change, in large part due to near-continuous accommodation of marine sediments from Albian through Maastrichtian time, as well as a highly resolved chronostratigraphic framework based on detailed macro- and microfossil biostratigraphy, radioisotopic age dating of volcanic ash beds, and the development of floating astronomical time scales in rhythmic carbonate-rich facies. Lessons learned from studies of the Western Interior may help guide future study of other Cretaceous archives, such as the Songliao Basin in China. This talk will provide an overview of advances in Western Interior geoscience focused on five major issues: 1) tectonic context – new ideas about why the long-term pattern of accommodation is inconsistent with the classic foreland model; 2) sea level history – updated estimates of paleobathymetry based on sedimentological observations; 3) redox history and organic carbon burial – role of shallow epeiric seas in the global carbon cycle; 4) climate history – sedimentary cyclicity and the relationship between marine biogeochemical cycles and atmospheric CO₂ levels, the analysis of which is greatly improved by linkage of terrestrial and marine records; and 5) nature of epicontinental archives – to what extent do basins like the Western Interior preserve global environmental signals?