Faunal and Organic Matter Distribution
Using all published data from the Atlantic continental margin and the Gulf of Mexico, the distribution of species occurrence was examined in the vicinity of the shelfbreak. Forarainiferal provinces defined by cluster analyses of occurrence data indicate that the termination of inner shelf provinces, in general, coincides with the approximate position of the shelfbreak. The distribution of species occurrence of 30 selected species from the Atlantic continental margin and 30 from the Gulf of Mexico also indicate that the shelfbreak is an important boundary for benthic foraminifera. Most selected species that occur most often at depths of less than 100 m occur occasionally deeper than 100 m. Likewise, most species that usually occur at depths of more than 100 m occur occasionally at shallower depths. Consequently, for these species the upper depth limit cannot be given more weight than the lower depth limit. In general, the frequency of occurrence is a more useful measure than the observed range.
The depth distribution of some species is different in the two areas studied. Consequently, recognition of provincial differences is important when attempting paleoenvironmental analyses. The shelfbreak has been recognized previously as an important boundary for benthic foraminifera through analyses of species abundance and occurrence. In the present study, only species occurrence was used and no distinction was made between live or dead, Pleistocene or Holocene, in place or transported. Evidently, large-scale patterns are recognizable even when possible sources of error are not taken into account. This is encouraging because much of the literature on fossil and modern localities contains only species lists.
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.