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Title: Evidence for excess pore pressures in southwest Indian Ocean sediments

Abstract

Brown clay cores from the Madagascar and Crozet basins show the following evidence of excess pore pressures: large amounts of flow-in, increasing average sedimentation rate with age, and nonlinear temperature gradients. Additionally, many hilltops in these basins have no visible sediment cover. The bare hilltops may result from periodic slumping caused by excess pore pressures. Calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using Darcy's law. Since pore pressures which exceed the overburden pressure are unreasonable, we attribute this discrepancy to laboratory measures which underestimate the in situ permeability. The widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay-sized particles. This mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident. Carbonate-rich sediments from the Madagascar Ridge, the Mozambique Ridge, and the Agulhas Plateau had almost no flow-in and occurred in areas where all topography was thickly draped with sediment, Since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement, wemore » attribute these differences between the brown clay and the carbonate-rich material to an absence of significant excess pore pressures in the plateau and ridge sediments.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964
OSTI Identifier:
6767918
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Geophys. Res.; (United States); Journal Volume: 86:B3
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; INDIAN OCEAN; SEDIMENTS; CLAYS; MADAGASCAR; OVERBURDEN; POROSITY; PRESSURIZING; AFRICA; DEVELOPING COUNTRIES; ISLANDS; MINERALS; SEAS; SURFACE WATERS 580500* -- Oceanography-- (1980-1989)

Citation Formats

Abbott, D., Menke, W., Hobart, M., and Anderson, R. Evidence for excess pore pressures in southwest Indian Ocean sediments. United States: N. p., 1981. Web. doi:10.1029/JB086iB03p01813.
Abbott, D., Menke, W., Hobart, M., & Anderson, R. Evidence for excess pore pressures in southwest Indian Ocean sediments. United States. doi:10.1029/JB086iB03p01813.
Abbott, D., Menke, W., Hobart, M., and Anderson, R. 1981. "Evidence for excess pore pressures in southwest Indian Ocean sediments". United States. doi:10.1029/JB086iB03p01813.
@article{osti_6767918,
title = {Evidence for excess pore pressures in southwest Indian Ocean sediments},
author = {Abbott, D. and Menke, W. and Hobart, M. and Anderson, R.},
abstractNote = {Brown clay cores from the Madagascar and Crozet basins show the following evidence of excess pore pressures: large amounts of flow-in, increasing average sedimentation rate with age, and nonlinear temperature gradients. Additionally, many hilltops in these basins have no visible sediment cover. The bare hilltops may result from periodic slumping caused by excess pore pressures. Calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using Darcy's law. Since pore pressures which exceed the overburden pressure are unreasonable, we attribute this discrepancy to laboratory measures which underestimate the in situ permeability. The widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay-sized particles. This mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident. Carbonate-rich sediments from the Madagascar Ridge, the Mozambique Ridge, and the Agulhas Plateau had almost no flow-in and occurred in areas where all topography was thickly draped with sediment, Since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement, we attribute these differences between the brown clay and the carbonate-rich material to an absence of significant excess pore pressures in the plateau and ridge sediments.},
doi = {10.1029/JB086iB03p01813},
journal = {J. Geophys. Res.; (United States)},
number = ,
volume = 86:B3,
place = {United States},
year = 1981,
month = 3
}
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