Geophysical Evidence of Fluid Seepage on the Tofiño and Xauen Banks, Alboran Sea
Jeffrey Poort, Silvia Ceramicola, Elia D'Acremont, Damien Do Couto,
Christian Gorini, Alain Rabaute, Abdellah Ammar, Gemma Ercilla, Belen Alonso, Juan Tomas Vazquez,
Nieves Lopez-Gonzalez, Bernard Mercier de Lépinay, and Pascal Le Roy
In the Alboran Sea, several NE-SW elongated ridges ("Alboran Line") separate the West from the South basins. While the South Alboran basin contains different Miocene volcanic structures, the West Alboran basin is mostly non-volcanic. The Alboran Line is formed from NE to SW by the Alboran Ridge, the Tofiño Bank and the Xauen Bank. All these features show flat abraded summits topped by mainly calcareous sediments. Where the Alboran Ridge is mainly a volcanic ridge, the Xauen Bank is a fold and thrust belt structure. In between, three summits constitute the Tofiño Bank, located at the intersection with the offshore continuation of the N30°E trending Al Idrissi fault zone. The West Alboran basin is filled with a large Neogene successions (>10 km) and characterised by numerous mud volcanoes sourced by the Burdigalian olistostromes.
We will show evidence of fluid seepage on the Tofiño and Xauen Banks between the West and South Alboran basins based on new geophysical and geological datasets (airgun and sparker seismic reflection, chirp, echosounding, swath-bathymetry, coring and visual observations). These data were collected during the Marlboro 1 and 2 and Eurofleets Saras cruises in 2011 and 2012. Our data reveal that the area is characterised by ancient and active transpressive deformation associated with mass-movement deposits and contourites sedimentation. A preliminary analysis indicates the presence of different fluid seepage features on and near the Tofiño and Xauen Bank. (1) an acoustic flare was detected and free gas escape (bubbles) was observed at the sea surface On top of the central Tofiño summit, at a water depth of only 70m; (2) a mound and a pockmark field were recognized at NE and SW of the Tofiño Bank, respectively; (3) different flares and a an acoustic chimney were imaged near the fault zone offshore Al Hoceima; and (4) chimneys were imaged on the flanks and acoustic flares on top of the Xauen Bank.
These newly imaged fluid seepage features are located in one of the most tectonically active areas of the Alboran Sea, where two major fault zones intersect. It is not clear weather the Tofiño and Xauen Banks are still part of the West Alboran Basin, nor if the Burdigalian olistostromes exist in this zone. Fluid seepage near the Tofiño and Xauen Banks could originate from more shallow overpressured Tortonian shales recognized in the El Jebha well, or linked to very shallow mass transport deposits.
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013