Paper No. 4
Presentation Time: 8:45 AM
LATE CRETACEOUS CLIMATE CHANGES RECORDED IN EASTERN ASIAN LACUSTRINE DEPOSITS AND NORTH AMERICAN EPIERIC SEA STRATA
Cretaceous climate data of the long-lived Cretaceous Songliao Basin (SB) in eastern Asia is correlated and compared with the Western Interior Seaway (WIS) on the North American plate, in order to understand better the dynamics of Earth’s past ‘greenhouse’ climates. Nearly continuous Late Cretaceous terrestrial deposition in the Songliao Basin is represented by two cores totaling 2431 m in length. The Turonian-Maastrichtian age of the section is based on integrated stratigraphy, and is comparable in age with Upper Cretaceous strata in the WIS. Being consistent with that of the global trend, the dynamic Late Cretaceous climates of both the SB and WIS gradually cooled from the warmest Albian-Cenomanian time to the end of the Maastrichtian with several intervening warm periods as did the global climate. However regional differences existed, the Songliao Basin climate was humid to semi-humid, warm temperate-subtropical and the Western Interior Seaway was in the humid, warm temperate zone and experienced only moderate climatic changes. The shifts of oxygen isotope data in the Songliao Basin were frequent and abrupt, whereas the WIS records more gradual change affected mainly by fresh-water runoff mixing with southern Tethyan and northern Arctic waters. Sedimentary cycles of eccentricity, obliquity and precession bands are recorded in both SB and WIS basins. The sedimentary cycles in the WIS and SB are interpreted to be related to variations of the wet/dry runoff cycles, which indicate that orbital forcing played an important role in global climate change in Late Cretaceous. The most favorable condition for organic carbon burial in both the SB and WIS basin was bottom water anoxia regardless of the cause of the anoxia. But organic carbon burial rate was usually much higher in the Songliao Lake than in the WI epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric CO2. In both basins organic-rich deposits formed during rise in water level and incursion of saline waters. The integration of paleoclimate data from Cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the Cretaceous ‘greenhouse’ climate change and may provide insights for a future greenhouse world.