The Record of Terrestrial Organic Matter in the Western Interior Seaway Across the Cenomanian-Turonian Ocean Anoxic Event
Geology & Geophysics, Yale University, New Haven, CT, USA
The Late Cretaceous was one of the warmest times of Earth's past with high concentrations of CO2 and other greenhouse gases. Punctuated throughout this time period are declines in atmospheric CO2 concentrations which correlate with Ocean Anoxic Events (OAEs) defined by thin, laterally extensive and usually globally correlated beds of organic rich marine shales. The Cenomanian-Turonian (C-T) event ~94 Ma (a.k.a. OAE2) is distinguished by a strong (~ 2-6 ‰) positive shift in δ13Corganic, evidence of biological turnover, drawdown of CO2 and ocean acidification. The non-marine record across the OAE2 is less well understood but estimates of Cretaceous CO2 concentrations (GEOCARB II models, stomatal index, etc.), show a correlation between declining CO2 and angiosperm radiations. I will investigate the relationship between CO2 decline and the composition of terrestrial plant communities by looking at the records of organic carbon and angiosperm and gymnosperm organic biomarkers across OAE2 from both the marine stratotype in central Colorado and paralic sediments of southwestern Utah. Looking at the preservation of n-alkanes, δ13Cn-alkanes, and lignin phenols diagnostic of vascular plant type across these two sections we can test whether angiosperms began to dominant terrestrial ecosystems during this time period of declining CO2 concentrations. If the biomarker and δ13Cn-alkane evidence shows greater angiosperm dominance during OAE2, it could support the idea that angiosperms' ability to more rapidly control their stomata gave them a competitive advantage over gymnosperms during periods of lower CO2 concentrations, allowing their adaptive radiation in the Late Cretaceous.
AAPG Search and Discovery Article #90199 © 2014 AAPG Foundation 2014 Grants-in-Aid Projects