Theory for a clinoform of permanent form on a continental margin emplaced by weak, dilute muddy turbidity currents

摘要

A clinoform is a prograding sedimentary deposit. Of interest here are the clinoforms that constitute the building blocks of continental margins. A continental margin consists of a continental shelf, i.e. a shallow region near the shore of a continent that gently slopes seaward, followed by a continental slope, i.e. a steeper region that drops off into deep water. In many cases the continental slope itself constitutes a clinoform that progrades into deeper water. In other cases, and especially near river mouths, a given margin may have several coexisting clinoforms. Many margin clinoforms tend to be muddy. Here a theory of clinoform progradation is developed. The clinoform is assumed to be continuous in the along-shelf direction. A wave-current boundary layer is assumed to stir up a dilute suspension of mud, which then moves slowly as a sheet down the shelf slope in the direction of deep water. Near the shelf-slope rollover the turbidity current loses wave agitation, and forms a net-depositional flow that results in clinoform progradation. When simplified to the case of a horizontal deep-water basement, constant sea level and negligible tectonism, the theory allows a solution for a clinoform of permanent form, i.e. one that progrades without changing shape.