COMBINING PALEOSOL PROXIES TO PROVIDE INSIGHT ON INTERACTIONS BETWEEN CLIMATIC, BIOTIC, AND ATMOSPHERIC PROCESSES DURING THE MID-CRETACEOUS IN TEXAS AND OKLAHOMA

Chemical, mineralogical, and stable isotopic proxies are applied to reconstruct paleoclimatic and paleoatmospheric conditions during the Mid-Cretaceous (Aptian-Cenomanian) using paleosols from fossil localities in north-central Texas and southern Oklahoma. These results in conjunction with analyses of the δ¹³C of plant organic material at each locality were then compared to investigate interactions between biotic responses in plant organic matter to changes in paleoprecipitation and paleoatmospheric pCO². Results show a strong correlation between mean annual precipitation (MAP) and the δ¹³C of plant organic matter. Localities reporting low paleoprecipitation estimates correlate with more positive δ¹³C organic matter values, consistent with modern observations. Less understood and constrained is the influence of changes in pCO₂ levels on the δ¹³C of plant organic matter. Using paleosol carbonates we show an estimated pCO₂ effect of -0.4‰ to -1.4‰ per 100 ppmV on the δ¹³C values of organic matter collected from two localities with similar paleoprecipitation estimates. Furthermore U-Pb dating of detrital zircons collected from the Jones Ranch Quarry indicate a maximum depositional age of 113.1 ± 1.5 Ma (n=4). This provides the first reported absolute age dating for the Twin Mountains Formation and is a valuable time constraint for the reported increase in atmospheric pCO² occurring at the Aptian/Albian boundary and within the OAE1b interval. This data exhibit how deep time proxies from terrestrial deposits can contribute to our knowledge and understanding of interactions between biotic, climatic, and atmospheric processes while also providing crucial paleoclimatic and paleoatmospheric data for periods of greenhouse climate conditions.