Structural and Stratigraphic Framework
This study focuses on the origin of prograding shelfbreaks on passive margins, using as examples selected seismic sections recorded on Iberian Atlantic and Western Mediterranean margins. Five main factors appear to control shelf progradation: (1) the amount and nature of sediment contributed to the outer shelf; (2) the equilibrium depth H at which sedimentary particles come to rest, a factor depending on grain-size distribution and specific hydrodynamic conditions at the depositional site (according to the models presented herein, H is the shelfbreak depth); (3) the morphology of the margin, i.e. the shelfbreak is significantly prograding only where the shelf forms on a slightly inclined slope or a marginal plateau; (4) the geological activity of the margin, i.e. prograding shelves have a sigmoid configuration on young subsiding margins, and an oblique configuration on mature, slowly subsiding margins; (5) the eustatic sealevel changes, i.e. the shelfbreak is eroded during periods of low sealevel and is built-up and progrades during periods of high sealevel. In sum, the prograding outeredge of shelves provides a fairly reliable record of Quaternary sealevel changes and of the geological evolution of margins, of which they are an integral part.
Figures & Tables
The Shelfbreak: Critical Interface on Continental Margins
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.