Changes in Paleosol Morphology and Geochemistry Associated with Mid-Paleozoic Afforestation and Decline in Atmospheric pCO2

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9418183 Mora The proposed research investigates changes in paleosol and pedogenic carbonate morphology and geochemistry preserved during the Siluro-Devonian time period, a period of rapid evolution and diversification of terrestrial ecosystems. Land plant evolution led to progressively more robust plant size and deeper rooting capabilities and more widespread afforestation of the land surface. The development and increasing abundance of vascular land plants may have contributed to increased weathering rates and draw down of atmospheric pCO2 from very high levels in the middle Paleozoic to near-present day levels in the Permo-Carboniferous. The proposed research will evaluate the hypothesis that afforestation, increased weathering profiles and also contributed to changes in the stable isotope composition of pedogenic carbonate. The proposed study will emphasize morphological and geochemical analysis of Siluro-Devonian paleosols from ten stratigraphic units (chiefly red-beds) exposed in outcrop in the U.S. and maritime Canada Appalachians. Detailed macro- and micromorphological characterization of the paleosols, estimation of paleosol thickness, mass balance evaluation of soil major and trace element geochemistry and stable isotopic analyses of pedogenic carbonates phases will be combined with existing paleontological information for these units to characterize the "pedological signature" of afforestation of the land surface by vascular plants. The results will permit a detailed evaluation of atmospheric pCO2 during this period of profound change using Cerling's soil carbonate paleobarometer. The results will contribute to our understanding of the distribution and preservation of paleosols and pedogenic carbonate deposits and their usefulness (or limitations) as monitors of paleoenvironments and paleoclimate. The results are relevant to models which predict the response of the Earth's lithosphere and biosphere to significant changes in atmospheric pCO2.