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Onshore–offshore gradient in reductive early diagenesis in coastal marine sediments of the Ria de Vigo, Northwest Iberian Peninsula

Onshore–offshore gradient in reductive early diagenesis in coastal marine sediments of the Ria de Vigo, Northwest Iberian Peninsula
Onshore–offshore gradient in reductive early diagenesis in coastal marine sediments of the Ria de Vigo, Northwest Iberian Peninsula
Early diagenetic modification of magnetic properties is an important process in marine sediments, but temporal and spatial variability of diagenetic processes have rarely been reported for recent coastal sediments. The magnetic properties of sediments from the Ria de Vigo (NW Spain) define a marked three-part zonation with depth. The uppermost zone is magnetically dominated by (titano-)magnetite. In the intermediate zone, rapid down-core dissolution of (titano-)magnetite increases the relative influence of high-coercivity magnetic minerals, which react more slowly during reductive dissolution than (titano-)magnetite. This zone is characterized by the ubiquitous occurrence of framboidal iron sulphides. Pyrite is the dominant iron sulphide, but framboidal ferrimagnetic greigite is also frequently observed in association with pyrite. The lowermost zone is characterized by an almost complete depletion of magnetic minerals associated with progressive reduction of detrital iron oxides with depth. This zonation is controlled by organic matter diagenesis, which varies with water depth and wave-induced sediment resuspension and organic matter reoxidation in the water column. This leads to a shallowing and thinning of each zone with more intense reductive diagenesis toward the interior of the ria. Such a zonation seems to be a common feature in shallow water marine environments. If preserved, the described zonation and its spatial variability provide a potential tool for detecting estuarine-like environments in the geological record. Magnetic detection of current or past reductive conditions also has important implications for assessing paleoenvironmental proxies that are sensitive to diagenetic redox state.
Early diagenesis, Magnetic minerals, Reductive dissolution, Greigite, Coastal sediments, CaCO3-related proxies
0278-4343
433-447
Mohamed, K.J.
5075ea63-42ff-4861-9031-0a311ed710f8
Rey, D.
af003751-7e91-4b7a-bd76-81e70d7f4f0f
Rubio, B.
514c222b-7a2d-4341-aa64-6f0674d61a03
Dekkers, M.J.
bb3d6980-0fb1-4909-931e-e65ababce5d5
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Vilas, F.
c6ec8943-65f1-4787-a573-6de276a928ae
Mohamed, K.J.
5075ea63-42ff-4861-9031-0a311ed710f8
Rey, D.
af003751-7e91-4b7a-bd76-81e70d7f4f0f
Rubio, B.
514c222b-7a2d-4341-aa64-6f0674d61a03
Dekkers, M.J.
bb3d6980-0fb1-4909-931e-e65ababce5d5
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Vilas, F.
c6ec8943-65f1-4787-a573-6de276a928ae

Mohamed, K.J., Rey, D., Rubio, B., Dekkers, M.J., Roberts, A.P. and Vilas, F. (2011) Onshore–offshore gradient in reductive early diagenesis in coastal marine sediments of the Ria de Vigo, Northwest Iberian Peninsula. Continental Shelf Research, 31 (5), 433-447. (doi:10.1016/j.csr.2010.06.006).

Record type: Article

Abstract

Early diagenetic modification of magnetic properties is an important process in marine sediments, but temporal and spatial variability of diagenetic processes have rarely been reported for recent coastal sediments. The magnetic properties of sediments from the Ria de Vigo (NW Spain) define a marked three-part zonation with depth. The uppermost zone is magnetically dominated by (titano-)magnetite. In the intermediate zone, rapid down-core dissolution of (titano-)magnetite increases the relative influence of high-coercivity magnetic minerals, which react more slowly during reductive dissolution than (titano-)magnetite. This zone is characterized by the ubiquitous occurrence of framboidal iron sulphides. Pyrite is the dominant iron sulphide, but framboidal ferrimagnetic greigite is also frequently observed in association with pyrite. The lowermost zone is characterized by an almost complete depletion of magnetic minerals associated with progressive reduction of detrital iron oxides with depth. This zonation is controlled by organic matter diagenesis, which varies with water depth and wave-induced sediment resuspension and organic matter reoxidation in the water column. This leads to a shallowing and thinning of each zone with more intense reductive diagenesis toward the interior of the ria. Such a zonation seems to be a common feature in shallow water marine environments. If preserved, the described zonation and its spatial variability provide a potential tool for detecting estuarine-like environments in the geological record. Magnetic detection of current or past reductive conditions also has important implications for assessing paleoenvironmental proxies that are sensitive to diagenetic redox state.

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More information

Published date: 1 April 2011
Keywords: Early diagenesis, Magnetic minerals, Reductive dissolution, Greigite, Coastal sediments, CaCO3-related proxies

Identifiers

Local EPrints ID: 180763
URI: http://eprints.soton.ac.uk/id/eprint/180763
ISSN: 0278-4343
PURE UUID: dd94f700-38dd-471b-9b71-7ea399df0d95

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Date deposited: 11 Apr 2011 13:30
Last modified: 16 Jul 2019 23:42

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