A REVIEW OF MASS MOVEMENT PROCESSES, SEDIMENT AND ACOUSTIC CHARACTERISTICS, AND CONTRASTS IN SLOPE AND BASE-OF-SLOPE SYSTEMS VERSUS CANYON-FAN-BASIN FLOOR SYSTEMS.

Abstract

Abstract Slopes comprise 10-15% of the Earth's surface and are a major pathway for sediment movement to the deep ocean floor. Mass movement processes are the dominant modes of mobilization, transport and deposition. A review of the literature shows considerable confusion in application of a variety of terms used to describe mass movement phenomena. A summary of the various approaches has been synthesized into a three-part classification in which the major transport and grain support processes can be grouped according to mechanical behavior. Rockfalls and slides (including glides and slumps) represent elastic transport mechanisms. Mass flows move plastically and include debris flows, mud-flows and inertial grain flows. Viscous fluid behavior is represented by viscous grain flows, liquified flows, fluidized flows, and turbidity currents. There are specific assemblages of sedimentary features which have been assigned to each of these processes. A single deposit may contain imprints of more than one process, however. On a less discriminatory scale, particular seismic-reflection patterns can also be used to infer major gravity processes or process groups. It is evident that much information is needed on the geotechnical properties of slope sediments and the delineation of the variables which define the critical conditions at which incipient failure can occur. Effects of particular triggering forces need examination. Because of the limitations inherent in field geology and in contemporary marine geological approaches it is clear that cooperative studies by both groups in conjunction with experimental data will be required to yield a complete description of the slope process-deposit-facies problem and to develop a slope-apron-ocean floor model comparable in sophistication to the current canyon-fan-ocean floor model. Have we identified the major acoustic facies associated with mass movement? What conditions inhibit the full development of the spectrum of mass movement morphologies in a slope-deep ocean floor system? Refinement of acoustic profiling methods and field surveys to delineate these sequences can improve our understanding of the mass budgets of sediment delivery to basin floor or deep-ocean floor. The papers in this volume provide a variety of insights into these problems and also indicate gaps in our present knowledge that should be filled. It is already clear that the 1970's are the decade of emphasis on mass transport comparable to the decades of the 1950's and 1960's when burgeoning discoveries about turbidity currents and the canyon-fan-basin floor system were made. There is much yet to be known about the complete deep ocean sediment deposition system.