Mud volcano gas hydrates in the Gulf of Cadiz

Abstract

This paper presents new geochemical data on gas-hydratebearing mud volcanoes discovered for the first time in the Gulf of Cadiz during cruises TTR9 and TTR10 of the R ⁄ V Professor Logachev in 1999-2000. The estimated gas hydrate content is 3-16% of sediment volume and 5-31% of pore space volume. Estimated values of the water isotopic composition for the Ginsburg mud volcano are very heavy for d 18 O (up to +53‰) and light for dD (up to ) 210‰). Gas released from the hydrates contains 81% of C 1 and 19% of C 2+ . The inferred source of the gas in the hydrates is enriched in C 2 -C 6 (£ 5%), indicating that the gas has a thermogenic origin. Gas hydrate of cubic structure II should be formed from a gas of such composition. It is interpreted that the composition of the mud volcano fluid corresponds to deep oil basins below the Gulf of Cadiz.

A predictive numerical model for potential mapping of the gas hydrate stability zone in the Gulf of Cadiz

“…In the NE sector of the Gulf of Cadiz, several NE-SW oriented diapiric mud ridges occur, topped by carbonate chimneys and crusts Somoza et al, 2003;Fernán-dez-Puga, 2004). Gas hydrates have been sampled in mud volcanoes (Mazurenko et al, 2002;Pinheiro et al, 2003) and have been detected geophysically as BSR-like reflectors (Casas et al, 2003;Depreiter et al, 2005) (Fig. 1).…”

“…3A). The thermogenic-type group has very high concentrations of saturated hydrocarbon gases, particularly ethane through normal pentane (CrC s ), and also a high content of C 4 and C s (Stadnitskaia et al, 2000;Kozlova et al, 2000;Blinova and Stadnitskaia, 2001;Mazurenko et al, 2002 ). The HSF of this group cover a broader spectrum (Fig.…”

“…A large number of pockmark-like structures (Baraza and Ercilla, 1996;Somoza et al, 2000Somoza et al, , 2003León et al, 2001León et al, , 2006, mud volcanoes bearing gas hydrates Somoza et al, 2000Somoza et al, , 2003Standnitskaia et al, 2001;Mazurenko et al, 2002), and authigenic carbonate crusts and slabs have been reported along the continental sIope Magalhaes et al, 2004;Mata et al, 2005) and have revealed the intense activity of hydrocarbon seeps in the Gulf of Cadiz on both the Iberian and African margins Somoza et al, 2000;Gardner, 2001). These hydrocarbon seepage structures are especially frequent in an area named the Tasyo Field , which is warmed by the Mediterranean outflow water (MOW).…”

Sedimentary sources of the mud-breccia and mud volcanic activity in the Western Alboran Basin

“…Mud volcanoes active over the last 3 Ma were recently discovered along the off-shore Calabrian Arc, at the tip of the Apenninic-Maghrebide accretionary system (Praeg et al, 2009). Occurrence of mud volcanism and diapirism in the Eastern Mediterranean is also recorded in an extensional setting: the Nile Deep Sea Fan (e.g., Loncke et al, 2004;Dupré et al, 2007) Mud volcanoes are well known west of the Gibraltar Strait, in the Gulf of Cadiz, along the Atlantic counterpart of the Alboran Basin in the Gibraltar Arc System (GAS; e.g., Pinheiro et al, 2003;Fernández-Puga et al, 2007) where the related phenomena such as cold seepage, pockmarks, hydrocarbon venting, methanederived authigenic carbonates and gas hydrates have been investigated since 1996 (Baraza and Ercilla, 1996;Baraza et al, 1999;Ivanov et al, , 2001Kenyon et al, 2000;Somoza et al, 2000Somoza et al, , 2003Gardner, 2001;Mazurenko et al, 2002;Pinheiro et al, 2003Pinheiro et al, , 2006Magalhães et al, 2012). Their origin is associated with recent compressive tectonics on shale and salt deposits of the olistostrome/accretionary complex units, emplaced as an allochthonous unit in the Late Miocene as a result of Africa-Eurasia convergence (Maldonado et al, 1999;Somoza et al, 2003).…”

Growth and demise of cold-water coral ecosystems on mud volcanoes in the West Alboran Sea: The messages from the planktonic and benthic foraminifera

“…Mud volcanism and associated phenomena such as cold seepage, hydrocarbon venting and gas hydrates in the Gulf of Cadiz have been investigated since 1996 (Baraza and Ercilla, 1996;Baraza et al, 1999;Ivanov et al, 2000Ivanov et al, , 2001Somoza et al, 2000;Gardner, 2001;Kenyon et al, 2001;Mazurenko et al, 2002;Pinheiro et al, 2003). An exploratory cruise of R/V Belgica in 2002 on an accretionary setting in the Gulf of Cadiz (Gutscher et al, 2002) off Larache (Morocco), led to the discovery of a cluster of nine mud volcanoes: the El Arraiche mud volcanoes field (Van Rensbergen et al, 2005).…”