PALEOENVIRONMENTAL RECONSTRUCTION OF CRETACEOUS TERRESTRIAL FORMATIONS OF TEXAS AND OKLAHOMA USING PEDOGENIC MINERALS

Analysis of pedogenic minerals from paleosols in north central Texas and southern Oklahoma are used to test hypothesized climate change across the Early to Late Cretaceous boundary of the Western Interior of North America as indicated by previous sedimentological and paleontological proxies and climate models. The analysis also provides contextual information for fossils found within the formations and identifies possible factors contributing to shifts in fauna and flora across the Early to Late Cretaceous boundary including the shift from gymnosperm to angiosperm dominated landscapes. Mineralogical analysis of the <0.2µm size phyllosilicate fraction from the paleosols revealed down-profile trends consistent with modern weathering profiles suggesting a dominantly pedogenic origin. Paleosols from the Early Cretaceous Twin Mountains (Aptian) and Antlers Formation (Aptian-Albian) were identified as calcic vertisols and are dominated by smectite and hydroxy-interlayered 2:1 phyllosilicates indicating semi-arid environments. Paleosols from the Late Cretaceous Woodbine Formation (Cenomanian) were identified as gleyed vertisols and are dominated by kaolinite indicating a more humid environment. Both qualitative and quantitative methods support an increase in soil weathering due to an increase in soil moisture across the Early to Late Cretaceous boundary of Texas. This is consistent with sedimentological and paleontological evidence across the Western Interior of North America suggesting a regional climatic shift from semi-arid to humid environments across the Early to Late Cretaceous boundary.