Ancient Atmospheric P(CO2), Paleoclimates and the Stable Isotope Geochemistry of Low Temperature Iron Oxides

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The actual role of CO2 as a "greenhouse" gas in the Earth's past can only be learned from proxy data on ancient atmospheric Pco2 and corresponding climatic temperatures. Research conducted in this laboratory has found that the oxygen isotope systematics of the common mineral goethite (a-FEOOH) make it a suitable indicator of paleotempeatures and ancient sources of water. Furthermore, we have discovered that goethite contains an apparent Fe(CO3)OH component in solid solution whose abundance is related to ancient ambient Pco2. These characteristics of natural goethites have been used to deduce tropical temperatures and atmospheric CO2 pressures 440 million years ago. A broader application of these properties of goethite is planned. Part of the work well involve experimental study of the isotopic effects of substitution of Al for Fe in goethite. Such information is of importance to isotopic paleoclimatic research involving goethites in tropical soils, where degrees of Al substitution can be high. another portion of the proposed research will undertake the study of the oxygen isotope systematics of goethite + phosphate as a promising mineral pair oxygen isotope paleothermometer. The two-component CO2 mixing model for soils (as manifested in the Fe(CO3)OH component of surficial goethite) will be tested further as a third aspect of the research with data obtained from goethite in active Cenozoic laterites. Goethite-bearing Mesozoic oolitic ironstones and laterite will also be isotopically, etc., analyzed to evaluate ancient temperatures, water sources and possibly atmospheric CO2 pressures.