Behrmann, Jan Hinrich

Flemings, P. B.

IODP Expedition 308 Shipboard Scientific Party

John, C. M.

Locat, J.

Urgeles, R.

English

OceanRep

Geophysical Research Abstracts, Vol. 9, 00457, 2007SRef-ID: 1607-7962/gra/EGU2007-A-00457© European Geosciences Union 2007Mechanisms leading to overpressure and slopeinstability in the Gulf of Mexico continental slopeR. Urgeles (1), J. Locat (2), P.B. Flemings (3), J. Behrmann (4), C.M. John (5), andthe Expedition 308 Shipboard Scientific Party *(1) Dept. of Stratigraphy, Paleontology and Marine Geosciences, University of Barcelona,Barcelona, Spain, urgeles@ub.edu, (2) Dept. of Geology and Geological Engineering, LavalUniversity, Ste. Foy QC, Canada, (3) Dept. of Geosciences, Penn State University, UniversityPark PA, USA, (4) Dept. of Marine Geodynamics, IFM-GEOMAR, Kiel, Germany, (5)Integrated Ocean Drilling Program, Texas A&M University, College Station TX, USASeismic and multibeam data have shown the occurrence of fossil large-scale MassTransport Deposits (MTD) and Recent failure events in connection with fluid es-cape structures in Ursa Basin at ∼1000 m depth in the eastern levee of the Missis-sippi Canyon, northeastern Gulf of Mexico. Duirng IODP Expedition 308 three Sites(U1322, U1323 and U1324) were drilled adjacent to the Recent failures and throughseveral MTD of Holocene and Pleistocene age. At these sites a complete suite of log-ging data and direct measurements of moisture and density and geotechnical data wereacquired that will allow to illuminate the factors controlling initiation of past sedimentfailures and to characterize the hazard from future slope instabilities. Results indicatethat Ursa Basin has very high sedimentation rates, at least 10m/ky with peaks up to 25m/ky, which resulted in a particular porosity profile, with relatively high values com-pared to overburden stress. Fluid overpressure estimated from a variety of direct andindirect methods indicates that the vertical effective stress is 50 to 70 % lower thanif hydrostatic conditions existed. The trends in density and undrained shear strengthare relatively smoother at Site U1324 compared to Site U1322. At Site U1322 den-sity and strength measurements show significant increases (up to 0.1 g/cm3 and 50kPa respectively) associated with MTDs. This may indicate higher consolidation ofMTD, which probably results from shearing and dewatering of the sediments duringthe landslide process. High sedimentation rates are a crucial factor leading to over-pressure and slope instability at Ursa. The location, depth, thickness and amount ofshearing in MTDs will further influence slope stability.* Expedition 308 Shipboard Scientific Party: P.B. Flemings (co-chief sci.), J.H.Behrmann (co-chief sci.), C.M. John (staff sci.), Y. Aizawa, N.T.T. Binh, N. De Silva,B. Dugan, T.M. Edeskär, C. Franke, A. Gay, W.P. Gilhooly III, J. Gutierrez-Pastor, G.J.Iturrino, S.Y. Jiang, H. Long, J.C. Moore, T. Nonoura, C. Pirmez, M. Reichow, D.E.Sawyer, J. Schneider, A.V. Shumnyk, T. Suzuki, Y. Takano, R. Urgeles, Y. Yamamoto,V. Zampetti

Mechanisms leading to overpressure and slope instability in the Gulf of Mexico continental slope

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