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Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems

Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems
Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems
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.

mineral magnetism, greigite, pyrrhotite, iron sulphide, siderite, diagenesis, sulphate reduction, methane, anaerobic oxidation of methane, gas hydrate, marine sediments
0012-821X
350-366
Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Musgrave, R.J.
f5eeae5c-9e51-4018-b9b3-82b6bb89e961
Gracia, E.
f9e61943-c032-4be7-9c37-c5199fc8950e
Pinero, E.
ffeaf3a4-3289-4ad5-97df-78a2557a09c9
Vega, M.
6fa4b9a3-b817-4a0f-94be-816d43e34ed4
Martinez-Ruiz, F.
80789053-90ec-429d-ad62-0956340f503a
Larrasoana, J.C.
9201c9da-a9fc-4f3b-86a8-83fda450084e
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Musgrave, R.J.
f5eeae5c-9e51-4018-b9b3-82b6bb89e961
Gracia, E.
f9e61943-c032-4be7-9c37-c5199fc8950e
Pinero, E.
ffeaf3a4-3289-4ad5-97df-78a2557a09c9
Vega, M.
6fa4b9a3-b817-4a0f-94be-816d43e34ed4
Martinez-Ruiz, F.
80789053-90ec-429d-ad62-0956340f503a

Larrasoana, J.C., Roberts, A.P., Musgrave, R.J., Gracia, E., Pinero, E., Vega, M. and Martinez-Ruiz, F. (2007) Diagenetic formation of greigite and pyrrhotite in gas hydrate marine sedimentary systems. Earth and Planetary Science Letters, 261 (3-4), 350-366. (doi:10.1016/j.epsl.2007.06.032).

Record type: Article

Abstract

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.

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More information

Published date: 30 September 2007
Keywords: mineral magnetism, greigite, pyrrhotite, iron sulphide, siderite, diagenesis, sulphate reduction, methane, anaerobic oxidation of methane, gas hydrate, marine sediments

Identifiers

Local EPrints ID: 48844
URI: http://eprints.soton.ac.uk/id/eprint/48844
ISSN: 0012-821X
PURE UUID: f45d116c-3e80-4087-98cc-c81bbee50f38

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Date deposited: 15 Oct 2007
Last modified: 15 Mar 2024 09:50

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Contributors

Author: J.C. Larrasoana
Author: A.P. Roberts
Author: R.J. Musgrave
Author: E. Gracia
Author: E. Pinero
Author: M. Vega
Author: F. Martinez-Ruiz

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