Vast fields of hydrocarbon-derived carbonate chimneys related to the accretionary wedge/olistostrome of the Gulf of Cádiz



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Díaz del Río, Víctor and Somoza Losada, Luis and Martínez Frías, Jesús and Mata, M. Pilar and Delgado Huertas, Antonio and Hernández Molina, F.J. and Lunar Hernández, Rosario and Martín Rubí, Juan Antonio and Maestro, Adolfo and Fernández Puga, Mª Carmen and León Buendía, Ricardo and Llave, E. and Medialdea, Teresa and Vázquez, Juan Tomás (2003) Vast fields of hydrocarbon-derived carbonate chimneys related to the accretionary wedge/olistostrome of the Gulf of Cádiz. Marine geology, 195 . pp. 177-200. ISSN 0025-3227

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We report the first discovery and sampling of vast fields of hydrocarbon-derived carbonate chimneys along the Gulf of Ca¤diz continental slope, at depths between 500 and 1200 m. A large variety of carbonate chimneys (more than 200 samples) were recovered from four different areas, named the DIASOM, TASYO, GBF (Guadalquivir Basin) and ESF (East Moroccan) fields. Observations from an underwater camera revealed a spectacular high density of pipe-like chimneys, some of them longer than 2 m, lying over the sea floor, and some protruding from muddy sediment. Local fissures and alignment of isolated chimneys were also observed, suggesting that their distribution is controlled by fault planes. Chimneys collected show a wide range of morphological types (spiral, cylindrical, conical, mushroom-like and mounded) with numerous nodule protuberances and ramified fluid channelways. The chimneys are mainly composed of authigenic carbonates (ankerite, Fe-bearing dolomite and calcite) with abundance of iron oxides, forming agglomerates of pseudo-pyrite framboids. N18O isotopic values vary from 0.7 to 5.5x whereas N13C values indicate that chimney carbonates are moderately depleted in 13C, ranging from 346xto 320xPDB, interpreted as formed from a mixture of deep thermogenic hydrocarbons and shallow biogenic methane. These vast fields of carbonate chimneys imply new considerations on the importance of hydrocarbon fluid venting in the Gulf of Ca¤diz and, moreover, on the active role of the olistostrome/accretionary wedge of the Gibraltar arc.

Item Type:Article
Uncontrolled Keywords:Carbonate chimneys; Mounds; Hydrocarbon seeps; Microbial chemosynthesis; Accretionary wedges, Gulf of Cádiz
Subjects:Sciences > Geology > Petrology
ID Code:70932
Deposited On:03 Mar 2022 09:02
Last Modified:03 Mar 2022 09:09

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