Paleoenvironmental and paleoclimatic reconstruction of Cretaceous (Aptian-Cenomanian) terrestrial formations of Texas and Oklahoma using phyllosilicates

Abstract

Clay mineralogy, chemistry, and stable oxygen and hydrogen-isotope compositions of 11 phyllosilicate samples from Cretaceous paleosol profiles were determined in order to evaluate Early-to-Late Cretaceous paleoenvironments and paleoclimates around north-central Texas and southern Oklahoma. Samples consist of mineralogical mixtures of illite, smectite, and kaolinite. Samples from the Albian Antlers Formation in southern Oklahoma and the Cenomanian Woodbine Formation are dominated by kaolinite, while the remaining samples are dominated by smectite and illite. Major element compositions of paleosol matrix materials are used to calculate CALMAG weathering values that range from 31 to 84 and correspond to Cretaceous paleoprecipitation estimates ranging from 270 to 1490 mm/yr. Paleosol phyllosilicate hydrogen and oxygen stable isotope values range from −50‰ to −67‰ to 18.5‰ to 21.7‰, respectively, and in conjunction with their respective mineral and chemical compositions, correspond to in-situ soil crystallization temperatures ranging from 26 ± 3 °C to 31 ± °C. Paleoprecipitation trends exhibit two marked increases in precipitation from the Early to Late Cretaceous, in the Albian Antlers Formation and Cenomanian Woodbine Formation. Stratigraphic intervals with phyllosilicates that yield cooler temperature estimates coincide with stratigraphic intervals with markedly higher precipitation estimates based on CALMAG values. Importantly, cool, high precipitation intervals correlate with periods of extensive shallow seas upon the North American craton. Comparison of Cretaceous temperature, precipitation and meteoric water estimates to modern analogs supports the presence of climates similar to modern tropical climates during the Cretaceous at subtropical or temperate paleolatitudes in what is now Texas and Oklahoma, consistent with general circulation models and energy balance models suggesting a pervading Cretaceous greenhouse.