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Authigenic carbonates from the Darwin Mud Volcano, Gulf of Cadiz: A record of palaeo-seepage of hydrocarbon bearing fluids

Authigenic carbonates from the Darwin Mud Volcano, Gulf of Cadiz: A record of palaeo-seepage of hydrocarbon bearing fluids
Authigenic carbonates from the Darwin Mud Volcano, Gulf of Cadiz: A record of palaeo-seepage of hydrocarbon bearing fluids
of the oceans, but little is known about the long-term variation in fluid fluxes at MVs. The Darwin MV is one of more than 40 MVs located in the Gulf of Cadiz, but it is unique in that its summit is covered by a thick carbonate crust that has the potential to provide a temporal record of seepage activity. In order to test this idea, we have conducted petrographic, chemical and isotopic analyses of the carbonate crust. In addition a 1-D transport-reaction model was applied to pore fluid data to assess fluid flow and carbonate precipitation at present. The carbonate crusts mainly comprise of aragonite, with a chaotic fabric exhibiting different generations of cementation and brecciation. The crusts consist of bioclasts and lithoclasts (peloids, intraclasts and extraclasts) immersed in a micrite matrix and in a variety of cement types (microsparite, botryoidal, isopachous acicular, radial and splayed fibrous). The carbonates are moderately depleted in 13C (?13C = ? 8.1 to ? 27.9‰) as are the pore fluids (?13C = ? 19.1 to ? 28.7‰), which suggests that their carbon originated from the oxidation of methane and higher hydrocarbons, like the gases that seep from the MV today. The carbonate ?18O values are as high as 5.1‰, and it is most likely that the crusts formed from 18O-rich fluids derived from dehydration of clay minerals at depth. Pore fluid modelling results indicate that the Darwin MV is currently in a nearly dormant phase (seepage velocities are < 0.09 cm yr? 1). Thus, the thick carbonate crust must have formed during past episodes of high fluid flow, alternating with phases of mud extrusion and uplift.
Authigenic carbonate, Mud volcano, Gulf of Cadiz, Fluid seepage, Methane
0009-2541
24-39
Vanneste, Heleen
09098953-c28c-4d59-aa6d-8789f17220d1
Kastner, Miriam
c88b7331-83d2-49b4-acaf-c321fd1bf314
James, Rachael H.
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Connelly, Douglas P.
d49131bb-af38-4768-9953-7ae0b43e33c8
Fisher, Rebecca E.
7ebc6bb2-2ad7-4481-9513-3ab490d0c43d
Kelly-Gerreyn, Boris A.
0774749f-e27b-44e9-bad9-6c68391c060e
Heeschen, Katja
4ab1f404-78d1-4c16-a982-54d13abc8f18
Haeckel, Matthias
8b05c8db-8426-4270-88e1-80d3bd38df76
Mills, Rachel A.
a664f299-1a34-4b63-9988-1e599b756706
Vanneste, Heleen
09098953-c28c-4d59-aa6d-8789f17220d1
Kastner, Miriam
c88b7331-83d2-49b4-acaf-c321fd1bf314
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Connelly, Douglas P.
d49131bb-af38-4768-9953-7ae0b43e33c8
Fisher, Rebecca E.
7ebc6bb2-2ad7-4481-9513-3ab490d0c43d
Kelly-Gerreyn, Boris A.
0774749f-e27b-44e9-bad9-6c68391c060e
Heeschen, Katja
4ab1f404-78d1-4c16-a982-54d13abc8f18
Haeckel, Matthias
8b05c8db-8426-4270-88e1-80d3bd38df76
Mills, Rachel A.
a664f299-1a34-4b63-9988-1e599b756706

Vanneste, Heleen, Kastner, Miriam, James, Rachael H., Connelly, Douglas P., Fisher, Rebecca E., Kelly-Gerreyn, Boris A., Heeschen, Katja, Haeckel, Matthias and Mills, Rachel A. (2012) Authigenic carbonates from the Darwin Mud Volcano, Gulf of Cadiz: A record of palaeo-seepage of hydrocarbon bearing fluids. Chemical Geology, 300-301, 24-39. (doi:10.1016/j.chemgeo.2012.01.006).

Record type: Article

Abstract

of the oceans, but little is known about the long-term variation in fluid fluxes at MVs. The Darwin MV is one of more than 40 MVs located in the Gulf of Cadiz, but it is unique in that its summit is covered by a thick carbonate crust that has the potential to provide a temporal record of seepage activity. In order to test this idea, we have conducted petrographic, chemical and isotopic analyses of the carbonate crust. In addition a 1-D transport-reaction model was applied to pore fluid data to assess fluid flow and carbonate precipitation at present. The carbonate crusts mainly comprise of aragonite, with a chaotic fabric exhibiting different generations of cementation and brecciation. The crusts consist of bioclasts and lithoclasts (peloids, intraclasts and extraclasts) immersed in a micrite matrix and in a variety of cement types (microsparite, botryoidal, isopachous acicular, radial and splayed fibrous). The carbonates are moderately depleted in 13C (?13C = ? 8.1 to ? 27.9‰) as are the pore fluids (?13C = ? 19.1 to ? 28.7‰), which suggests that their carbon originated from the oxidation of methane and higher hydrocarbons, like the gases that seep from the MV today. The carbonate ?18O values are as high as 5.1‰, and it is most likely that the crusts formed from 18O-rich fluids derived from dehydration of clay minerals at depth. Pore fluid modelling results indicate that the Darwin MV is currently in a nearly dormant phase (seepage velocities are < 0.09 cm yr? 1). Thus, the thick carbonate crust must have formed during past episodes of high fluid flow, alternating with phases of mud extrusion and uplift.

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More information

Published date: 2012
Keywords: Authigenic carbonate, Mud volcano, Gulf of Cadiz, Fluid seepage, Methane
Organisations: Geochemistry, Marine Geoscience

Identifiers

Local EPrints ID: 347416
URI: http://eprints.soton.ac.uk/id/eprint/347416
ISSN: 0009-2541
PURE UUID: 94309edd-eab4-4140-96f0-3bc402446c5b
ORCID for Rachel A. Mills: ORCID iD orcid.org/0000-0002-9811-246X

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Date deposited: 21 Jan 2013 17:14
Last modified: 22 Oct 2019 00:54

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Contributors

Author: Heleen Vanneste
Author: Miriam Kastner
Author: Douglas P. Connelly
Author: Rebecca E. Fisher
Author: Boris A. Kelly-Gerreyn
Author: Katja Heeschen
Author: Matthias Haeckel
Author: Rachel A. Mills ORCID iD

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