期刊
CHEMICAL GEOLOGY
卷 300, 期 -, 页码 24-39出版社
ELSEVIER
DOI: 10.1016/j.chemgeo.2012.01.006
关键词
Authigenic carbonate; Mud volcano; Gulf of Cadiz; Fluid seepage; Methane
资金
- School of Ocean and Earth Science (University of Southampton. U.K.)
- HERMES of the European Commission (EC) [GOCE-CT-2005-511234]
- Worldwide Universities Network
- NERC [noc010011, bosc01001] Funding Source: UKRI
- Natural Environment Research Council [noc010011, bosc01001] Funding Source: researchfish
Hydrocarbon-rich fluids expelled at mud volcanoes (MVs) may contribute significantly to the carbon budget 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 C-13 (delta C-13 = -8.1 to -27.9%.) as are the pore fluids (delta C-13 = 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 delta O-18 values are as high as 5.1%, and it is most likely that the crusts formed from O-18-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. (C) 2012 Elsevier RV. All rights reserved.
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