Pore pressure penetrometers document high overpressure near the seafloor where multiple submarine landslides have occurred on the continental slope, offshore Louisiana, Gulf of Mexico

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doi: 10.1016/j.epsl.2007.12.005
Author(s): Flemings, P. B.; Long, H.; Dugan, B.; Germaine, J.; John, C. M.; Behrmann, J. H.; Sawyer, D.
Integrated Ocean Drilling Program, Expedition 308 Scientists
Author Affiliation(s): Primary:
University of Texas at Austin, Austin, TX, United States
Other:
Pennsylvania State University, United States
Rice University, United States
Massachusetts Institute of Technology, United States
Texas A&M University, United States
Universität Kiel, Federal Republic of Germany
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 269(3-4), p.309-324. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplemental information/data is available in the online version of this article. 50 refs.; illus., incl. sect., 1 table, geol. sketch map
Summary: Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (λ* = (u-uh)/(σ'vh) = 0.6) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (1/√t) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced overpressure at depth at Site 1324 suggests suggest lateral flow (drainage) whereas high overpressure at Site 1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta. Abstract Copyright (2008) Elsevier, B.V.
Year of Publication: 2008
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Cenozoic; Continental slope; Expedition 308; Extrapolation; Gulf of Mexico; Hydrostatic pressure; IODP Site U1322; IODP Site U1324; Integrated Ocean Drilling Program; Louisiana; Marine sediments; Mass movements; Mississippi River; North Atlantic; Ocean floors; Offshore; Overpressure; Penetrometers; Permeability; Pleistocene; Pore pressure; Quaternary; Sedimentation rates; Sediments; Slope stability; Slumping; United States
Coordinates: N280000 N281500 W0890000 W0891500
Record ID: 2008103839
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands