Mineral Deposits at the Shelfbreak1
The shelfbreak, the transitional zone between the outer continental shelf and slope, is a unique environment with respect to some mineral deposits. Physical and chemical processes exert considerable influence over the occurrence of minerals formed in this environment. Most prominent are geochemical deposition of phosphorus, uranium, and other metals, resulting from upwelling and areas of oxygen minima; physical concentrations of heavy minerals such as tin oxides or gold, resulting from eustatic changes, surface and internal waves and geostrophic currents; biological deposits such as limestones, and precious corals associated with coral bioherms, reefs and atolls; and strata-bound deposits of sulfur, salt, or coal, associated with bedded or diapiric structures. While almost any economic mineral deposit of the type found in continental land masses may be located at the shelfbreak, only phosphorite, some heavy mineral placers, and certain precious corals appear to be products of the zone's unique environment. Because of the water depth and distance from land, prospecting might usefully be limited at the present time to these types of deposit. As the zone overlaps the various legal boundaries of national and international jurisdiction, any prospecting activity should include a complete investigation of the legal factors involved.
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.