|Title:||Variations of methane induced pyrite formation in the accretionary wedge sediments offshore southwestern Taiwan||Authors:||Lim, Yee Cheng
Yang, Tsanyao Frank
|Keywords:||Anaerobic methane oxidation; Gas hydrate; Methane; Pyrite; Sulfate reduction||Issue Date:||2011||Journal Volume:||28||Journal Issue:||10||Start page/Pages:||1829-1837||Source:||Marine and Petroleum Geology||Abstract:||
The accretionary wedge of offshore southwestern Taiwan contains abundant deposits of gas hydrate beneath the sea floor. High concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available. To understand temporal variation of methane venting in sediments over geologic time, a 23-m-long Calypso piston core (MD05-2911) was collected on the flank of the Yung-An Ridge. Pore water sulfate, dissolved sulfide, dissolved iron, methane, sedimentary pyrite, acid volatile sulfide, reactive iron, organic carbon and nitrogen as well as carbonate δ13C were analyzed.Three zones with markedly different pyrite concentration were found at the study site. Unit I sediments (>20 mbsf) were characterized with a high amount of pyrite (251-380 μmol/g) and a δ13C-depleted carbonate, Unit II sediments (15-20 mbsf) with a low pyrite (15-43 μmol/g) and a high content of iron oxide mineral and Unit III sediments (<10 mbsf) by a present-day sulfate-methane interface (SMI) at 5 m with a high amount of pyrite (84-221 μmol/g) and a high concentration of dissolved sulfide.The oscillation records of pyrite concentrations are controlled by temporal variations of methane flux. With an abundant supply of methane to Unit I and III, anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation. No AOM signal was found in Unit II, characterized by typical organically-limited normal marine sediments with little pyrite formation. The AOM induced pyrite formation near the SMI generates a marked pyrite signature, rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment. © 2011 Elsevier Ltd.
|DOI:||10.1016/j.marpetgeo.2011.04.004||SDG/Keyword:||Accretionary wedge; Accretionary wedge sediments; Acid volatile sulfides; Anaerobic methane oxidations; Carbon and nitrogen; Diagenetics; Dissolved iron; Dissolved sulfide; High concentration; High-content; Marine sediments; Methane fluxes; Methane venting; Piston cores; Pore waters; Pyrite concentration; Pyrite formation; Sea floor; Study sites; Sulfate reduction; Temporal variation; Anoxic sediments; Dissolution; Hydration; Iron; Iron oxides; Methane; Organic carbon; Oxide minerals; Pyrites; Sedimentology; Submarine geology; Sulfur compounds; Water; Gas hydrates; accretionary prism; anoxic conditions; concentration (composition); gas hydrate; iron oxide; marine sediment; methane; oxidation; porewater; pyrite; seafloor; sulfate; sulfide; temporal variation; venting; Taiwan
|Appears in Collections:||海洋研究所|
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