| This thesis presents mineralogical, chemical, and stable isotope compositions of pedogenic clay minerals from the Upper Paleozoic strata of the southwestern United States (Texas, Oklahoma, New Mexico, Arizona, Utah, and Colorado), the Lower Mesozoic, Upper Triassic, strata of northern Argentina, Eocene strata of northern California, and several modern soil profiles from northern California. The clay minerals of interest include 1:1 phyllosilicates, such as kaolinite, 2:1 phyllosilicates, such as smectite, hydroxy-interlayered minerals and illite, iron (oxyhydr)oxides, including goethite and hematite, and calcite. These minerals were analyzed for there stable oxygen and hydrogen isotope compositions. In addition, this work includes carbon isotope analyses of pedogenic calcites, organic matter, and goethite.; Paleoclimate reconstructions are a key component to our understanding of ancient geologic systems, including major plant and animal extinctions, icehouse to greenhouse transitions, and major orogenic events. As we further our ability to accurately reconstruct (“retrodict”) ancient paleoclimate conditions with improved geologic data for energy balance models (EBM) and General Circulation Models (GCM) we are able to provide predictions of future climates with more accuracy and confidence.; Almost all minerals at the surface of the Earth form in, or very near, oxygen and hydrogen isotopic equilibrium with meteoric water. Therefore, it is expected that the oxygen and hydrogen isotopic composition of clay minerals that form in soils will plot in an array that is roughly parallel to the meteoric water line defined by Craig (1961). Furthermore, the scatter in the oxygen and hydrogen isotopic array of naturally occurring soil clay minerals will be related to the different temperatures of formation. This thesis applies that array to reconstruct ancient soil conditions, including the isotopic composition of ancient soil waters and soil temperature. Furthermore, reconstructed oxygen and hydrogen isotope compositions of the ancient soil waters are used to reconstruct regional atmospheric circulation patterns at the time of mineral formation. |
