Deformation-induced diagenesis and microbial activity in the Nankai accretionary prism

Author(s): Famin, V.; Andreani, Muriel; Boullier, Anne-Marie; Raimbourg, Hugues; Magnin, Valerie
Author Affiliation(s): Primary:
Institut de Physique du Globe de Paris, Paris, France
Université de La Réunion, France
University Claude Bernard-Lyon I, France
Institute of Earth Sciences, France
Institut des Sciences de la Terre d'Orléans, France
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: We performed a microscopic and chemical study of diagenetic reactions in deformation microstructures within deep mud sediments from the Nankai accretionary prism (SW Japan) collected during IODP Expedition 315. Our study reveals that deformation microstructures localize the crystallization of pyrite, a diagenetic reaction also found in large megasplay faults of the prism. Textural observation shows that pyrite crystallization is synchronous of the sediment deformation. The framboidal shape of pyrite crystals, the barium depletion and the strong arsenic enrichment observed in deformation microstructures compared with the sediment matrix, suggest that pyrite crystallization is mediated by the proliferation of anoxic archae. During scientific drilling expeditions IODP 315, 316 and 319, microbial life has been evidenced at depths of up to 800 m below the sea floor by the presence of biogenic methane and sulfate reducers in sediments. We suggest that deformation structures localize microbial proliferation because the fracturing of silicate minerals produces hydrogen, a necessary compound for bacteria under anoxic conditions. Bacteria proliferate as long as active deformation supplies hydrogen, and vanish when the deformation stops. The development of bacteria in deformation structures impacts our mechanical understanding of fault zones in accretionary prisms: Firstly, bacterial activity converts carbon from organic matter and hydrogen into methane and/or water, which may alter the fluid budget of fault zones and the recurrence of dynamic ruptures in megathrusts. Secondly, the abundance of bacteria could be used to recognize active fault zones from inactive ones in drilling cores.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Aliphatic hydrocarbons; Alkanes; Expedition 315; Expedition 316; Expedition 319; Hydrocarbons; Integrated Ocean Drilling Program; Methane; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Organic compounds; Pacific Ocean; Sulfates; West Pacific
Coordinates: N331400 N331800 E1364300 E1363800
Record ID: 2015065161
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