INTEGRATED PALEOBIOLOGICAL AND GEOCHEMICAL ASSESSMENT OF CARBON CYCLE PERTURBATIONS AND CLIMATE CHANGE DURING CENOMANIAN-TURONIAN OAE II, NORTH AMERICA

The Late Cenomanian-Early Turonian (C-T) deposits of the Western Interior basin (Late Cretaceous) record an important natural climate experiment that provides a potential model for future greenhouse conditions. In the marine geologic record, the C-T interval is characterized by a positive excursion of the stable carbon isotopic composition of carbonate and organic carbon.  This is interpreted to result from a short-term global increase in primary productivity and enhanced burial flux of organic matter to sediments.  It has been suggested that this event, termed Oceanic Anoxic Event II (OAE II), produced an oscillation in atmospheric CO₂ in response to widespread burial of the ¹³C-depleted organic carbon.  Based on correlation of the marine record of this event to coeval terrestrial deposits within a high-resolution temporal and stratigraphic framework, and the preservation of plant cuticular material within these deposits, OAE II provides an excellent opportunity to employ and evaluate the stomatal index proxy for atmospheric pCO₂ estimation.  In this talk, a preliminary dataset of stomatal index and d¹³C values from dispersed fossil cuticle, coal and charcoal collected from marginal marine deposits spanning the C-T boundary in SW Utah will be presented.  The data show that the C-T carbon isotopic shift and associated CO₂ oscillation are well-recorded in the fossil plant material, providing an independent pCO₂ proxy from the terrestrial realm.  This offers a unique opportunity to examine how patterns in fossil plant ecology and evolution may have responded to environmental changes across the C-T, a period known for rapidly increasing angiosperm diversity and abundance at the expense of older gymnosperm and pteridophyte clades.  Analysis of plant ecology will be accomplished with cuticlular morphotyping of dispersed cuticles collected at high resolution from C-T sections in Utah, which will provide a basis for taxonomic identification.  This study is the first of its kind to integrate a high-resolution temporal and stratigraphic framework with detailed paleobotanical and geochemical analyses and to link terrestrial and marine records during the natural climate experiment of the C-T OAE II.