Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems
Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems
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DOI：
10.1016/j.epsl.2007.06.032
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发表时间：
2007-09
影响因子：
5.3
通讯作者：
J. Larrasoaña;A. Roberts;R. Musgrave;E. Gràcia;E. Piñero;M. Vega;F. Martínez-Ruiz
中科院分区：
文献类型：
--
作者：
J. Larrasoaña;A. Roberts;R. Musgrave;E. Gràcia;E. Piñero;M. Vega;F. Martínez-Ruiz
海洋钻探计划第204号（俄勒冈州Cascadia边缘1244至1252号地点）在水合物脊南部提取的含天然气水合物海洋沉积物的矿物磁学结果和电子显微镜观察表明，自生灰长岩和磁黄铁矿是硫酸盐、甲烷厌氧氧化（AOM）和甲烷/天然气水合物带中微生物催化的成岩反应的副产品。有利于灰长岩和磁黄铁矿形成和保存的地球化学条件似乎是一个有限的硫化物来源，无论是在硫酸盐带，在AOM带还是在发生AOM的深层沉积物中，微生物驱动的硫酸盐还原，使黄铁矿化反应没有被驱动到完成。我们的研究结果表明，辉长岩和磁黄铁矿的岩石磁识别对于海相沉积记录中的古代天然气水合物系统的探测是有用的，因为它可以快速筛选可能存在甲烷和浸染型天然气水合物的潜在层位。在天然气水合物稳定带内不同深度的自生灰长岩和磁黄铁矿的形成也意味着在不同的时间获得了主沉积物的磁化，这可能会损害含灰长岩和磁黄铁矿的海洋沉积物的古磁学结果。
Mineral magnetic results and electron microscope observations from gas hydrate-bearing marine sediments cored at southern Hydrate Ridge during Ocean Drilling Program Leg 204 (Sites 1244 to 1252, Cascadia Margin, offshore Oregon) demonstrate that authigenic greigite and pyrrhotite formed as a byproduct of microbially-mediated diagenetic reactions in the sulphate, the anaerobic oxidation of methane (AOM), and the methanic/gas hydrate zones. Geochemical conditions favourable for formation and preservation of greigite and pyrrhotite appear to be a limited source of sulphide, whether it derives from microbially-driven sulphate reduction in the sulphate zone, in the AOM zone or in deep sediments undergoing AOM, so that pyritization reactions are not driven to completion. Our results indicate that rock magnetic identification of greigite and pyrrhotite should be useful for detecting ancient gas hydrate systems in the marine sedimentary record, because it can enable rapid screening of ancient sediments for potential horizons where methane and disseminated gas hydrates might have occurred. Formation of authigenic greigite and pyrrhotite at different depths within the gas hydrate stability zone also implies that the magnetization of the host sediments will have been acquired at variable times, which is likely to compromise paleomagnetic results from greigite- and pyrrhotite-bearing marine sediments.