Geochemical and Stable Isotopic Study of the Corg-S-Fe-Mn inAnoxic Paleoenvironments

利用新的中新世蒙特雷组和中白垩世格林霍恩组的地球化学和稳定同位素资料，研究低氧-缺氧海相沉积物中碳、硫、铁和锰的早期成岩再分配作用。我们的目标是：1)从沉积和早期成岩条件解释COG-S-Fe-Mn体系的相互关系；2)重建硫从溶解的和固体的无机硫形态向沥青和干酪根中的有机硫化合物转移的途径。有机硫和无机硫的分离将采用一步一步的程序，该程序将产生七个硫组份(硫酸盐、元素、沥青、酸挥发性、二硫化物、重晶石和干酪根)。根据不同硫馏分的同位素组成以及铁和锰的分布，可以推断出与硫进入有机质有关的黄铁矿形成的深度和时间。蒙特利和格林霍恩都含有互层、层状和生物扰动岩相，这将使我们能够对广泛的古环境和早期成岩环境进行采样。有机、无机硫数据与锰、铁数据的结合，将为解释古低氧-缺氧盆地提供新的依据。为这项研究选择的地质单位将可以比较现代和中新世海岸上升流以及现代大洋和白垩纪陆缘环境中的沉积地层。

Early diagenetic repartitioning of carbon, sulfur, iron, and manganese in poorly oxygenated to anoxic marine deposits will be studied using new geochemical and stable isotopic data on the Miocene Monterey Formation and the mid-Cretaceous Greenhorn Formation. Our objectives will be 1) to interpret interrela- tionships in the Corg-S-Fe-Mn system in terms of depositional and early diagenetic conditions and 2) to reconstruct the pathways for transfer of sulfur from dissolved and solid inorganic-sulfur species to organic-sulfur compounds in bitumen and kerogen. Organic and inorganic sulfur species will be isolated using a step-wise procedure that will yield seven sulfur fractions (sulphate, elemental, bitumen, acid-volatile, disulfide, barite, and kerogen). Depth and timing of pyrite formation relative to incorporation of sulfur into organic matter will be inferred from the isotopic compositions of the various sulfur fractions in conjunction with the distribution of iron and manganese. The Monterey and Greenhorn both contain interbedded laminated and bioturbated lithofacies that will enable us to sample a wide range of paleoenvironmental and early diagenetic settings. Integration of organic and inorganic sulfur data with manganese and iron data will provide a new basis for interpreting ancient poorly oxygenated to anoxic basins. The geological units selected for this study will permit comparison of sedimentary strata in modern and Miocene coastal upwellings and in modern oceanic and Cretaceous epicontinental settings.