Atmospheric pCO(2) Reconstruction of Early Cretaceous Terrestrial Deposits in Texas and Oklahoma Using Pedogenic Carbonate and Occluded Organic Matter

Pedogenic carbonate samples collected from three Lower Cretaceous (Aptian-Albian) fossil localities in Texas and Oklahoma were analyzed to develop paleoatmospheric pCO(2) estimates by measuring the stable carbon isotopes of pedogenic calcite and their co-existing occluded organic matter. Calcite delta C-13 values ranged from -10.9 parts per thousand to -4.4 parts per thousand while occluded organic matter delta C-13 values ranged from -27.3 parts per thousand to -21.1 parts per thousand. These stable carbon isotope measurements combined with temperature (30 degrees C) and soil-respired CO2 concentration (839-6047 ppmV) values provided atmospheric pCO(2) estimates ranging from 67 ppmV to over 1100 ppmV. These estimates show a significant increase in atmospheric pCO(2) during the late Aptian followed by a decrease in atmospheric pCO(2) during the late Aptian to early Albian transition period, roughly correlating with the OEA1b event. Given the lack of chronostratigraphic constraints of the Lower Cretaceous geologic units in the study area, these data provide further evidence for the approximate age of the units as well as pertinent paleoclimate insights into greenhouse climate conditions.