Seafloor Characteristics and Dynamics Affecting Geotechnical Properties at Shelfbreaks
Richard H. Bennett, Terry A. Nelsen, 1983. "Seafloor Characteristics and Dynamics Affecting Geotechnical Properties at Shelfbreaks", The Shelfbreak: Critical Interface on Continental Margins, Daniel Jean Stanley, George T. Moore
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Variable geotechnical and sedimentological properties of sediments on both active and passive continental margins is the rule rather than the exception. Significant variability is observed in the physical, mechanical, and textural properties of sediments from the individual core to the regional level. Sediment properties and soil “state” are determined by the primary depositional properties and post-depositional processes active on and within shelfbreak deposits. Post-depositional processes play an important role in determining the ultimate nature and time-dependent changes in the mass physical and mechanical properties of submarine deposits. Fundamental geotechnical properties such as shear strength and compressibility from several shelfbreak areas are compared and related to eight shelfbreak sediment textural models. Sediment behavior such as resistance to erosion, slumping, consolidation, and liquefaction depend upon: (1) the basic sediment types present at shelfbreaks (textural model), (2) the fundamental geotechnical properties of the particular deposit, and (3) temporally and spacially variable physical and biological processes active in the shelfbreak zone.
Shelfbreak characteristics important to offshore engineering activities and future scientific studies on continental margins include: varied morphology with steep local slopes; rapid changes in physical oceanographic processes; variable erosion and sedimentation rates; variable offshelf sediment transport; onset of significant pelagic sedimentation; rapid textural changes; rapidly changing benthic community; high variability in geotechnical properties; and the onset of creep and mass wasting processes. Shelfbreak sediment types may be predominantly terrigenous, carbonate, or glacio-marine in origin. Although some of these characteristics can be found in other submarine environments, they can be identified as important elements of many passive and active continental margins.
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The shelfbreak is that point where the first major change in gradient occurs on the outermost edge of the continental shelf. Although this environment delimits the boundary between two principal and well-defined provinces, the continental shelf and slope - and thus is of the first order of importance on continental margins - it has received surprisingly little specific attention in either modern oceans or in the rock record. This volume, the first compendium dedicated specifically to the shelfbreak, was derived from an SEPM Research Symposium convened at the joint Annual Meeting of SEPM and AAPG on June 2, 1981. The material is organized in a manner to illustrate examples of the shelfbreak in both modern oceans and the rock record.