Ancient Atmospheric Carbon Dioxide, Paleoclimates, and the Stable Isotope Geochemistry of Low Temperature Iron (III) Oxides

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EAR-0606257Crayton J. YappAbstractAncient Atmospheric CO2, Paleoclimates, and the Stable Isotope Geochemistry of Low Temperature Iron (III) OxidesThe geologic record has revealed that climate change on Earth occurs on a wide range oftemporal and spatial scales. As a result, the search for answers to questions about causality in climate change has become more complex. Development of a deep understanding of the mechanisms by which natural systems were (and are) linked through the Earth's fluid spheres(the atmosphere and hydrosphere) requires new sources of information on both modern and ancient environments. Among the requirements are data on the composition of ancient atmospheres, surficial temperatures and the behavior of the hydrologic cycle.Studies of the oxygen and hydrogen isotope systematics of the common, low-temperatureiron oxyhydroxide, goethite ( -FeOOH), have established its value as a source of information on wet, oxidizing, continental environments such as lateritic soils. Moreover, it was discovered that a small amount of CO2 is istrapped in the crystal structure of goethite as an Fe(CO3 )OH component in solid solution. This Fe(CO3 )OH serves as a proxy for the partial pressure and carbon isotope composition of CO2 present at the time of goethite crystallization. Therefore, goethite from ancient soils can be used to determine the isotopic composition of waters, paleotemperatures, the presence of ancient biological activity, soil CO2 pressures, and, under the right circumstances, the partial pressure of CO2 in the Earth's atmosphere.A continuation of efforts to contribute information on long-term changes in continental climate and atmospheric chemistry during the Phanerozoic is proposed here. Two paleosols (Late Paleocene and Middle Eocene laterites) that bracket the Early Tertiary thermal maximum have been identified as promising candidates for study. Carbon,hydrogen and oxygen isotope, chemical, XRD and petrographic data would be obtained from multiple samples of these highly leached soils. These data should provide information on atmospheric CO2 pressures, climatic temperatures, isotopic compositions of waters and biological activity.