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

二氧化碳在地球过去作为一种“温室”气体的实际作用只能从古代大气二氧化碳和相应的气候温度的替代数据中得知。该实验室进行的研究发现，常见矿物针铁矿(a-FEOOH)的氧同位素系统学使其适合作为古温度和古代水源的指示器。此外，我们还发现针铁矿在固溶体中含有明显的Fe(CO3)OH组分，其丰度与古环境PCO2有关。4.4亿年前，天然针铁矿的这些特征被用来推断热带温度和大气二氧化碳压力。计划更广泛地应用针铁矿的这些性质。部分工作包括针铁矿中Al替代Fe的同位素效应的实验研究。这些信息对涉及热带土壤中的针铁矿的同位素古气候研究很重要，在热带土壤中，铝的取代程度可能很高。拟议研究的另一部分将进行针铁矿+磷酸盐的氧同位素系统学研究，作为一种有前途的矿物对氧同位素古温度计。作为研究的第三个方面，土壤的双组分CO2混合模型(如表面针铁矿的Fe(CO3)OH组分所示)将用活动的新生代红土中的针铁矿获得的数据进一步检验。还将对含针铁矿的中生代蚝粒铁矿和红土进行同位素等分析，以评估古代温度、水源和可能的大气二氧化碳压力。

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.