Stable isotope analyses of Phanerozoic paleosols: Implications for paleoenvironments

More knowledge regarding the paleoclimate of the Earth is desired. Geochemical studies of fossil materials are of use in constraining aspects of paleoenvironments. Stable carbon isotope analyses of 345 pedogenic calcites are presented and integrated with 404 analyses from the literature, totaling 749 analyses of various ages and global locations. The paleosol CO2 barometer is applied to these data, estimating paleoatmospheric carbon dioxide for those time units represented. Results indicate large variations in pCO2 over the past 400 million years, since plants evolved to form suitable soils for this method. A decline in paleo-pCO2 from the Devonian to the Early Permian is followed by a high amplitude oscillation in the Late Paleozoic. The Mesozoic is dominated by relatively high levels, except for the Early Triassic and Late Cretaceous. Variations in the Cenozoic were of smaller magnitude.;Stable oxygen isotope analyses of 266 pedogenic calcites from paleosols of western North America are presented and integrated with 509 analyses from the literature for a total of 775 analyses from the last 300 million years for which a series of terrestrial sediments is available. Sample locations are recalculated to paleolatitudes during formation. Results indicate a 15‰ oscillation in the Permian and Triassic, when North America was at equatorial latitudes. This oscillation probably relates to disruption (and later reestablishment) of equatorial atmospheric flow by the Appalachians, with development of monsoonal flow in the study area. Highly depleted values from the Late Jurassic to recent correspond to a rain shadow behind the western Cordillera.;Stable carbon and oxygen isotope analyses of 266 samples from the Late Jurassic Morrison Formation are presented. Application of the paleosol barometer indicates a downward revision in pCO2 for the Morrison Formation to approximately 2000 ppmV from previously published values (3180 ppmV). Depleted oxygen isotope values are likely the result of a rain shadow east of a Cordillera along the western margin of the continent. Latitudinal gradients are less than those observed in modern meteoric waters at similar latitudes. A temporal enrichment trend from the Salt Wash member through the middle condensed paleosol zone into the Lower Brushy Basin is observed.