Reefs, Bioherms, and Banks: A Semantic and Genetic Continuum

Randolph B. Burke, Lee C. Gerhard

Recent literature has restated old concepts of a one-to-one relationship between frameworks and reefs. It is important to revise reef definitions to fit natural systems into generic models of reef complexes rather than to force artificial models on natural systems.

St. Croix, U.S. Virgin Islands, has a variety of reef types including classical framework reefs (i.e., algal ridges nearest shore), extensive bank barrier reefs on the shelf farther offshore, and submerged shelf-edge reefs. Reef architecture demonstrates the balanced roles of framework growth, skeletal degradation, hydrodynamic transport of degradation products, and marine cementation. Reef fabrics provide a record of the processes that produced these reef architectures. Because the processes result in a characteristic fabric, process/fabric relationships can be plotted on a tetrahedral diagram where the processes are used as end members. Thus, a classification evolves that is descriptive, with architectural end members resulting from whichever process dominates. Reefs can be classifi d either quantitatively, or qualitatively, on any scale, outcrop or thin section, modern or ancient, in addition to being independent from organism evolution. A flexible classification scheme such as this is required because reefs are the synergistic product of the various processes acting in concert to produce the continuum of reef types and fabrics observed. Framework reefs probably represent a minority of reefs, as would each architectural end member.

Framework reefs, because they tend to be more mineralogically homogeneous, typically have less effective permeability after early and intermediate diagenesis than non-framework reefs. Where porosity is developed in a framework system, however, it is likely to be very effective.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.