Few detailed records of the high-resolution variations in climate regimes that likely accompanied the evolution of Pangean monsoonal circulation during the Permian exist. Moreover, geologic climate indicators and numeric models for Pangea suggest that megamonsoon development was accompanied by increased global warming possibly brought on by increased pCO2 levels in Permian atmospheres. Paleosols are a sensitive source of paleoenvironmental and paleoclimate information by offering multiple proxies of paleohydrology, precipitation levels, and seasonality that collectively reflect regional paleoclimatic conditions. In addition, pedogenic carbonates in the same paleosols can provide a direct record of paleo-pCO2 and associated changes in global temperature that is independent from the record provided by other paleosol proxies. Our collaborative research team proposes to define the first detailed paleoclimate reconstruction and paleo-pCO2 record for western equatorial Pangea by carrying out an integrated sedimentologic, petrologic, geochemical, magnetostratigraphic, and geochronologic analysis of Permian paleosols in the terrestrial successions of Texas and Oklahoma.
This research is directed by three main objectives: (1) to carry out a comprehensive field and laboratory study of paleosols in order to identify those sedimentologic, mineralogic, geochemical, and biologic proxies that most accurately record temporal changes in regional climate. (2) To reconstruct the evolution of atmospheric pCO2 throughout Permian time by carrying out a stable isotope analysis of pedogenic carbonates and associated vertebrate tooth enamel, as well as compound-specific stable isotope analysis of terrestrial organic matter from the same paleosols. (3) To develop a significantly improved temporal framework for calibration of the detailed paleoclimate and paleo-pCO2 records by applying the following techniques to the Texas and Oklahoma terrestrial successions: a) 40Ar/39Ar dating of volcanic sanidines, pedogenic Fe-sulfates (natrojarosite), and evaporitic minerals (langbeinite), b) U-Pb dating of pedogenic carbonates, c) Rb-Sr dating of Mg-rich authigenic clays encapsulated within evaporites, and d) detailed magnetostratigraphic study of the Late Permian terrestrial successions.
The resulting paleoclimate and paleo-pCO2 records should (1) provide significantly enhanced temporal constraints on megamonsoon development and associated evolution of the climate system, (2) contribute toward constraining the timing of deglaciation that would have been brought on by increased atmospheric pCO2 levels, (3) provide detailed and calibrated paleoclimate/paleo-pCO2 records for testing and constraining numeric model results, (4) greatly facilitate the correlation of our terrestrial records to climate records derived from other terrestrial deposits as well as to marine paleoclimate records, and (5) 'set the stage' for better understanding the paleoenvironmental stresses that may have contributed to the massive end-Permian extinction.
