The El Arraiche mud volcano field at the Moroccan Atlantic slope,Gulf of Cadiz |
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| Institution: | 1. Renard Centre of Marine Geology, Ghent University, Krijgslaan 281-S8, 9000 Ghent, Belgium;2. IFREMER, Brest, France;3. UNESCO-MSU Centre for Marine Geoscience, Moscow State University, Moscow, Russia;4. Mohamed V University, Rabat, Morocco;5. Departamento de Geosciências, Universidade de Aveiro, Aveiro, Portugal;6. Departamento de Biologia, Universidade de Aveiro, Aveiro, Portugal;1. Zoological Museum Hamburg, Center of Natural History, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany;2. Senckenberg Research Institute and Natural History Museum, Department Marine Zoology, Section Crustacea, Senckenberganlage 25, 60325 Frankfurt, Germany;3. German Centre for Marine Biodiversity Research, c/o University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany;4. A.V. Zhirmunsky Institute of Marine Biology, FEB RAS, Palchevskogo 17, 690041, Russia;5. Far East Federal University, Oktiabrskaya Str, 29, 690600 Vladivostok, Russia;6. Bavarian State Collection of Zoology, Münchhausenstrasse 21, 81247 München, Germany;7. Universtiy of Alaska Fairbanks, College of Fisheries and Ocean Sciences, 905 N. Koyukuk Drive, 245 O′Neill Bldg., 99775 Fairbanks, AK, USA;8. British Antarctic Survey, High Cross, Mandingley Road, Cambridge CBE 0ET, United Kingdom;1. Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. University of Oxford, Department of Earth Sciences, Oxford OX1 3AN, England, UK;3. Shenzhen Branch of CNOOC Ltd., Guangzhou, China;4. PetroChina Hangzhou Institute of Geology, Hangzhou 310023, China;1. CSIR-National Geophysical Research Institute (NGRI), Uppal Road, Hyderabad, India;2. Academy of Scientific and Innovative Research of CSIR at NGRI, Uppal Road, Hyderabad, India;3. The Research Centre for Arctic Petroleum Exploration, Norwegian University of Science and Technology, Trondheim, Norway;4. Oasis Geoconsulting Limited, Ogun State, Nigeria;1. Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China;2. College of Marine Science and Technology, China University of Geosciences, Wuhan 430074, China;3. China National Offshore Oil Corporation Ltd., Shenzhen 518054, China |
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| Abstract: | The El Arraiche field is a new mud volcano field discovered near the Moroccan shelf edge in the Gulf of Cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m. The largest mud volcano in the field (Al Idrissi mud volcano) is 255 m high and 5.4 km wide. The cluster was discovered during a survey with the RV Belgica and studied further during Leg 2 of the TTR 12 survey onboard the R/V Prof Logachev. The 2002 surveys yielded detailed multibeam bathymetry over a 700 km2 study area, dense grids of high-resolution seismic data, deep-tow sub bottom profiles, sidescan sonar mosaics over the major structures. Selected video imagery lines, video guided grab samples, dredge samples, gravity cores, and box cores were collected for groundtruthing purposes. Eight mud volcanoes in water depths from 200 to 700 m cluster around two, sub-parallel anticlines and associated active extensional faults. Rock clasts and regional seismic data locate the El Arraiche field over a Late Miocene–Pliocene extensional basin. The onset of mud volcanic activity is estimated at about 2.4 Ma and probably roots in the Cretaceous–Miocene accretionary wedge. Stacked outflows are visible up to a depth of about 500 m below the sea floor. The occurrence of long-lived mud volcanoes bear witness to continued overpressure generation at depth, either by in situ oil and gas generation or by focussed flow and accumulation in the area. Geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes. The activity of the mud volcanoes is indicated by the thickness of hemi-pelagic sediments covering extruded mud breccia, the occurrence of seep-typical fauna, the degree of mixing between thermogenic and biogenic hydrocarbon processes, or the depth to the base of the sulphate reduction zone. Given its structural setting and the evidence of thermogenic and biogenic hydrocarbons, the area has promising hydrocarbon potential but remains untested. |
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