Preprints
https://doi.org/10.5194/se-2021-54
https://doi.org/10.5194/se-2021-54

  12 May 2021

12 May 2021

Review status: this preprint is currently under review for the journal SE.

Deformation-enhanced diagenesis and bacterial proliferation in the Nankai accretionary prism

Vincent Famin1,2, Hugues Raimbourg3, Muriel Andréani4, and Anne-Marie Boullier5 Vincent Famin et al.
  • 1Université de La Réunion, Laboratoire GéoSciences Réunion, F-97744 Saint-Denis, France
  • 2Université de Paris, Institut de Physique du Globe de Paris, CNRS, UMR 7154, F-75005 Paris, France
  • 3Institut des Sciences de la Terre d'Orléans, UMR CNRS 6113, Université d'Orléans, Campus Géosciences, 1A, rue de la Férollerie, 45071 Orléans cedex 2, France
  • 4Laboratoire de Géologie de Lyon, École Normale Supérieure de Lyon et Université Claude Bernard Lyon 1, UMR 5276 CNRS, 2 rue Raphaël Dubois, 69622 Villeurbanne cedex, France
  • 5CNRS, ISTerre, Université Grenoble Alpes, F-38041 Grenoble, France

Abstract. Understanding diagenetic reactions in accreted sediments is critical for establishing the balance of fluid sources and sinks in accretionary prisms, which is in turn important for assessing the fluid pressure field and the ability for faults to host seismic slip. For this reason, we studied diagenetic reactions in deformation bands (shear zones and veins) within deep mud sediments from the Nankai accretionary prism (SW Japan) drilled at site C0001 during IODP Expedition 315, by means of microscopic observation, X-ray diffraction, and major-trace element analyses. Deformation bands are not only more compacted than the host sediment, but are also enriched in framboidal pyrite, as observed under microscopy and confirmed by chalcophile element enrichments (Fe, S, Cu, As, Sb, Pb). In tandem, clays in deformation bands undergo a destabilization of smectite or illite/smectite mixed layers, and/or a slight crystallization of illite, which is matched by a correlated increase in B and Li compared to the host sediment.

The two diagenetic reactions of sulfide precipitation and clay transformation are both explained by a combined action of sulfate-reducing and methanogen bacteria, which strongly suggests an increased activity of anaerobic microbial communities localized in deformation bands. This local bacterial proliferation was possibly enhanced by the liberation of hydrogen from strained phyllosilicates. We suggest that the proliferation of anoxic bacteria, boosted by deformation, may participate in the pore water freshening observed at depth in accretionary prisms. Deformation-enhanced metabolic reactions may also explain the illitization observed in major faults of accretionary prisms. Care is therefore needed before interpreting illitization, and other diagenetic reactions as well, as evidence of shear heating, as these might be biogenic instead of thermogenic.

Vincent Famin et al.

Status: open (until 25 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-54', Anonymous Referee #1, 26 May 2021 reply
  • RC2: 'Comment on se-2021-54', Anonymous Referee #2, 31 May 2021 reply

Vincent Famin et al.

Vincent Famin et al.

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Short summary
Sediments accumulated in accretionary prims are deformed by the compression imposed by plate subduction. Here we show that deformation of the sediments transforms some minerals in them. We suggest that these mineral transformations are due to the proliferation of microorganisms boosted by deformation. Deformation-enhanced microbial proliferation may change our view of sedimentary and tectonic processes in subduction zones.