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Three-dimensional architecture of submarine slide surfaces and associated soft-sediment deformation in the Lutetian Sobrarbe deltaic complex (Ainsa, Spanish Pyrenees)
Authors:PIERRE CALLOT  FRANCIS ODONNE  ELIE-JEAN DEBROAS  AGNÈS MAILLARD  DAMIEN DHONT†  CHRISTOPHE BASILE‡  GUILHEM HOAREAU
Institution:Universitéde Toulouse;UPS (OMP);LMTG;14 av. Edouard Belin, F-31400 Toulouse, France;
2CNRS;LMTG;F-31400 Toulouse, France;
3IRD;LMTG;F-31400 Toulouse, France (E-mail:;);
MIGP, UMR 5212 CNRS –Total –Universitéde Pau et des Pays de l'Adour, Bat. IPRA, BP 1155, 64013 Pau Cedex, France;
Laboratoire de Géodynamique des Chaînes Alpines, CNRS-UMR 5025, Observatoire des Sciences de l'Univers de Grenoble, UniversitéJoseph Fourier, BP 48, 38041 Grenoble Cedex, France
Associate Editor –George Postma
Abstract:Five successive fossil submarine slides have been mapped and described in the Sobrarbe deltaic complex (Ainsa Basin, Spanish Pyrenees). These slides affect and remove up to 15% of the delta front. The head of the scar surfaces is recognized clearly in the field due to the angular unconformity between the infilling sediments and the underlying layers. Most of the slide scarps trend 55°N with 20° to 40° dips indicating north-westward sliding. Downslope, traces of the sliding surfaces parallel stratification. However, these surfaces can be identified by displaced masses, resedimented sandstones and soft-sediment deformation features such as metre-scale half-grabens, normal faults and tension cracks; all the surfaces indicate a sliding displacement toward the north-west. A three-dimensional model built from topographic data with Earth Vision® software shows the architecture of the slide surfaces and provides an estimation of the volume of each sedimentary body within the limit of the studied area. This study also indicates that: (i) the sediments have been cut and carried away before their lithification; (ii) the sedimentation rate infilling a single slump scar is estimated to be about 8 m per 1000 years, i.e. 10 times higher than in the overall area of the Sobrarbe deltaic complex; (iii) each composite scar progressively develops and infills by retrogressive slumps; (iv) the successive slide surfaces stack vertically in a collapse complex structure and migrate downward to follow the sea-level drop between two successive collapse complex structures; (v) the development of the scars in the Sobrarbe delta is described from a seven-stage conceptual model starting with a regressive event; and (vi) the triggering of the Sobrarbe instabilities is controlled by high values of sedimentation rate, relative sea-level falls mainly controlled by tectonic uplift, and likely seismic activity.
Keywords:3D modelling  Ainsa Basin  fossil submarine slides  sedimentary instabilities  seismite  slope instabilities  soft-sediment deformation  tsunamite
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