Geotechnical characterization and strain analyses of sediment in the Mauritania Slide Complex, NW-Africa.

Förster, A., Ellis, R. G., Henrich, R., Krastel, Sebastian and Kopf, A. J. (2010) Geotechnical characterization and strain analyses of sediment in the Mauritania Slide Complex, NW-Africa. Marine and Petroleum Geology, 27 (6). pp. 1175-1189. DOI 10.1016/j.marpetgeo.2010.02.013.

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Mass wasting processes are a common phenomenon along the continental margin of NW-Africa. Located on the high-upwelling regime off the Mauritanian coastline, the Mauritania Slide Complex (MSC) is one of the largest events known on the Atlantic margin with an affected area of not, vert, similar30 000 km2. Understanding previous failure events as well as its current hazard potential are crucial for risk assessment with respect to offshore installations and tsunamis. We present the results of geotechnical measurements and strain analyses on sediment cores taken from both the stable and the failed part of the MSC and compare them to previously published geophysical and sedimentological data. The material originates from water depths of 1500–3000 m and consists of detached slide deposits separated by undisturbed hemipelagic sediments. While the hemipelagites are characterized by normal consolidation with a downward increase in bulk density and shear strength (from 1.68 to 1.8 g/cm3, 2–10 kPa), the slid deposits of the uppermost debris flow event preserve constant bulk density values (1.75 and 1.8 g/cm3) with incisions marking different flow events. These slid sediments comprise three different matrix types, with normal consolidation at the base (OCR = 1.04), strong overconsolidation (OCR = 3.96) in the middle and normal consolidation to slight overconsolidation at the top (OCR = 0.91–1.28). However, the hemipelagic sediments underlying the debris flow units, which have been 14C dated at <24 ka BP, show strong to slight underconsolidation (OCR = 0.65–0.79) with low friction coefficients of μ = 0.18. Fabric analyses show deformation intensities R ≥ 4 (ratio σ1/σ3) in several of the remobilized sediments. Such high deformation is also attested by observed disintegrated clasts from the underlying unit in the youngest debrites (14C-age of 10.5–10.9 ka BP). These clasts show strong consolidation and intense deformation, implying a pre-slide origin and amalgamation into the mass transport deposits. While previous studies propose an emplacement by retrogressive failure for thick slide deposits separated by undisturbed units, our new data on geotechnical properties, strain and age infer at least two different source areas with a sequential failure mechanism as the origin for the different mass wasting events.

Document Type: Article
Keywords: Meeresgeologie; Geodynamics; Landslides; Geotechnical characterization; Fabric analyses; Debris flow; NW-Africa continental margin; RV Meteor, M65/2, M58/1
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-JRG-B4 Submarine Hazards
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.marpetgeo.2010.02.013
ISSN: 0264-8172
Date Deposited: 29 Nov 2010 10:42
Last Modified: 26 Jul 2017 07:27

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