Wave-Base, Marine Profile of Equilibrium, and Wave-Built Terraces: A Critical Appraisal

Abstract

The concept of wave-base and its corollaries, the marine profile of equilibrium and the wave-built terrace, are largely erroneous. They do not dominantly control the development of the continental shelf and slope. The treatment of these concepts in geologic textbooks and sourcebooks needs revision. Wave-base, although a useful concept if applied generally to the surficial zone of the ocean of high-ambient agitation, does not control shelf deposition as the entire shelf is above any wave-base in this sense. Instead, the shelf is a drowned and relict surface, developed by oscillation of sea level and prograding and regressing paralic sediments—and here surf plays the dominant role. Sedimentation on the continental terrace is not controlled by wave-base but chiefly by topography; the continental slope is undergoing erosion rather than prograding, and ultimate deposition occurs on the continental rise. The wave-cut terrace is not cut at wave-base but at surf-base. Wave-built terraces are nonexistent both on a small scale and on a grand scale as an explanation of the continental slope. A marine profile of equilibrium is developed in the nearshore zone and is associated with a migrating lens of sand, but the outer-shelf profile is not a profile of equilibrium.