Methanogenesis and clay minerals diagenesis during the formation of dolomite nodules from the Tortonian marls of southern Spain

Type Article
Date 2015-09
Language English
Author(s) Pierre Catherine1, Rouchy Jean-Marie2, Blanc-Valleron Marie-Madeleine2, Etoubleau Joel3, Fouquet Yves3
Affiliation(s) 1 : Univ Paris 06, Univ Paris 04, LOCEAN, F-75252 Paris 05, France.
2 : Univ Paris 06, CNRS, MNHN, Univ Paris 04,CR2P, F-75005 Paris, France.
3 : IFREMER, Geosci Marines, F-29280 Plouzane, France.
Source Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2015-09 , Vol. 66 , P. 606-615
DOI 10.1016/j.marpetgeo.2015.04.017
WOS© Times Cited 3
Note Carbonate conduits linked to hydrocarbon-enriched fluid escape
Keyword(s) Authigenic dolomite nodules, Elemental geochemistry, Oxygen and carbon isotopes, Methanogenesis, Clay minerals diagenesis
Abstract Dolomite nodules are widespread within the Tortonian marls of Fortuna and Lorca basins in southern Spain. They occur as large bodies of various forms (round, ovoid, tabular) that are parallel or secant relative to the stratification. They are massive and present sometimes internal conduits that are considered as drains used for the migration of fluids.

This study brings new results on the mineralogy and elemental and isotopic geochemistry of these dolomite nodules to better describe the processes that were occurring during their formation. The diagenetic reactions that have driven authigenic dolomite precipitation within the sediments involved on the one hand methanogenesis that produced 13C-poor CH4 and 13C-rich CO2, on the other hand carbonate and silicate weathering by the CO2-rich solutions, that released respectively alkalinity and cations in pore solutions. Moreover, the distribution of the major elements (Si, Al, K, Na, Ca, Mg, Fe) in the marls and dolomite nodules indicates that these elements were redistributed within the sedimentary formation during the diagenetic reactions without external inputs by the circulating fluids. These observations thus confirm the link between authigenic dolomite formation and clay minerals diagenesis in sediments where methanogenesis was active.
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