Shelfbreak Physiography: An Overview
The shelfbreak (SB) is a distinct, critical interface of continental margins which delineates the major physiographic boundary between two major submarine provinces, shelf and slope. The shelfbreak is defined as that point of the first major change in gradient at the outermost edge of the continental shelf, and its depth, distance from shore and configuration are highly variable. Although structural framework is a dominant controlling factor, depositional regime and consequent progradational and regradational development generally modifies, substantially, the shelf-to-slope configuration. These depositional considerations include, among others, sediment supplied by rivers, carbonate reef buildup, influence of ice transport at high latitudes, and the interplay of fluid-driven and gravitative processes active in environments at and adjacent to the break. Moreover, the imprint (relict) of earlier eustatic oscillations, particularly low stands when the SB was at or close to the coastline, is still in evidence.
This overview, which incorporates observations in diverse geological and geographic settings, focuses on geomorphological aspects and is an attempt to synthesize shelfbreak type by means of a descriptive-genetic classification which takes into consideration the interaction of the dominant controlling factors. These are: (a) structural framework and rate of substrate motion which are functions of the larger-scale geological evolution of a margin, (b) the overprint of earlier (largely Quaternary) climatic and eustatic events, and (c) sediment supply and processes (reviewed in terms of climatic belts). The interplay of these three large-scale parameters has, of course, varied considerably in time and space, giving rise to a diverse suite of “end-member” break and transitional variants. In summary, we view the shelfbreak as a reworked palimpsest feature which has not yet attained complete equilibrium with presently active processes.
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.