Richey, Jon , Upchurch, Garland .
Inference of pCO2 Levels and Climate in the Late Cretaceous from Fossil Lauraceae.
Botanical estimates of pCO2 for the Late Cretaceous have most commonly used Stomatal Index (SI) in fossil Ginkgo. Recently, SI in fossil Lauraceae has been used to infer changes in pCO2 at the Cenomanian-Turonian boundary, based on the relation between SI and pCO2 in extant Laurus and Hypodaphnis. To provide a broad-scale picture of pCO2 based on fossil Lauraceae, we examined dispersed cuticle of the leaf macrofossil genus Pandemophyllum from: 1) the early to middle Cenomanian of the Potomac Group of Maryland (Maulden Mountain locality, lower Zone III) and 2) the Maastrichtian of southern Colorado (Raton Basin, Starkville South locality). These samples fall within the Late Cretaceous decline in pCO2 inferred from geochemical modeling and other proxies. SI was calculated from fossil cuticle fragments using ImageJ and counts of up to 56,000 cells per sample; pCO2 levels were estimated using the relation between SI and CO2 published for Laurus nobilis and Hypodaphnis zenkeri. Early to middle Cenomanian atmospheric pCO2 is estimated at 473 parts per million (ppm) from the L. Nobilis equation and 418ppm from the H. zenkeri equation (95% confidence interval (CI) = 401-550ppm), while late Maastrichtian pCO2 is estimated at 461ppm from the L. Nobilis equation and 405ppm from the H. zenkeri equation (95% CI = 357-522ppm). The Maastrichtian estimates falls within the range of published estimates from other proxies. The Cenomanian estimate, in contrast, is low relative to other estimates. The 95% confidence intervals of our pCO2 estimates overlap each other and those of other pCO2 estimates for the Late Cretaceous based on Lauraceae, suggesting no significant difference. This could indicate that pCO2 was relatively constant through the Late Cretaceous. Alternatively, it could indicate that Lauraceae show low sensitivity to high CO2, or other modern taxa should be used for inferring pCO2 with Late Cretaceous Lauraceae.
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1 - Texas State University-San Marcos, Biology, 601 University Drive, San Marcos, TX, 78666, USA
2 - Texas State University, Department of Biology, 601 University Drive, San Marcos, TX , 78666, U.S.A.
Presentation Type: Oral Paper:Papers for Sections
Location: Lindell C/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 11:30 AM