LARGE BENTHIC FORAMINIFERA OF THE FORE-REEF ZONE, SAN SALVADOR, BAHAMAS

San Salvador Island, one of the outermost islands of the Bahamas, is an excellent modern analog for some important ancient carbonate environments, including those in the lagoon, bank barrier reef, and fore-reef zones. In studies of ancient carbonate environments, benthic foraminifera are important in understanding paleoecology and paleobathymetry. In contrast to the lagoon, the fore-reef zone, located oceanward of the bank barrier reef (~5m depth) and including the platform-margin reef (~15m and deeper), is a relatively unstudied zone with regard to benthic foraminifera.

This study examines the nature of modern assemblages of large benthic foraminifera from the fore-reef zone for actualistic purposes. Samples were collected by SCUBA diving and consisted of 200-ml sediment samples taken at the sediment-water interface, separate sediment samples for grain-size analysis, and water samples. Observations of associated benthic organisms and environmental parameters such as water depth and temperature were recorded as well.

Previous foraminiferal studies on San Salvador have shown that the soritids Archaias angulatus and Cyclorbiculina compressa along with the textulariine Valvulina oviedoiana dominate sediment assemblages in shallow lagoonal grass beds, and that the additional presence of the rotaliine Homotrema rubrum signals lagoonal patch reefs. In contrast, the foraminiferal assemblage of the fore-reef zone is much more diverse, consisting of sub-equal amounts of textulariina, miliolina, and rotaliina species. Reef to shelf-edge transects show a decline of the large miliolids that are so common in the lagoons, as they become replaced by Amphistigina in deeper water. Large textulariines such as Dusenburyina sp. and Placopsilina sp. are important fore-reef indicators at some localities, and may be depth zoned. The abundance of Homotrema rubrum, even at considerable depths, distinguishes the windward side of the island. Thus, fore-reef foraminifera not only allow this zone to be distinguished easily from lagoonal environments, but provide additional paleoenvironmental insights.