Processes and Sediment Dynamics
Because the shelfedge bridges shallow and deep ocean environments, sedimentary processes characteristic of each of these provinces interact at the shelfbreak to influence sediment transport in the benthic boundary layer. Processes at the shelfedge and mechanics of sediment transport have been inferred from data gathered in many regional shipboard sampling and surveying investigations. Grouping these processes into two major categories—geologic factors and oceanic factors—aids in conceptualizing the complex system of sediment dynamics at the shelfedge. Geologic factors include tectonism, sediment supply, sediment size, shelf width, depth of the break below sealevel, gradient of the upper slope, and bathymetric irregularities. Oceanic factors include fronts between water masses, boundary currents, meteorologically-induced currents, tides, internal waves, and surface waves. Although any of these factors may operate simultaneously on any continental margin, their relative importance varies with time and space; i.e., one, two, or several of these factors may dominate shelfedge sediment transport on a given continental margin or at any given time.
Few investigators have actually measured the water and sediment motions in the benthic boundary layer at the shelfedge. Regional sediment-transport data are of limited value as long as the various factors of the forcing mechanisms have not been properly studied and correlated with the flow field and sediment activity at the bottom. Sophisticated instruments deployed for long periods of time are necessary to acquire data adequate for an assessment of the forcing mechanisms that control sediment transport. The few existing measurements of this type support the concept that shelfedge processes differ with place and time among continental margins and on any given continental margin. It follows that caution should be exercised when one attempts to generalize about the shelfedge transport system.
Figures & Tables
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.