Recent Calcium Carbonate Facies of the Great Bahama Bank. 2. Sedimentary Facies

Abstract

Statistical analysis of the constituent composition and grain-size data accumulated for 218 Bahamian sediment samples resulted in the delineation of the following five facies: (1) coralgal facies-characterized by a relative abundance of skeletal grains, particularly coral and calcareous algae fragments; (2) oölitic facies-characterized by an abundance of oölitically coated grains; (3) grapestone facies-typified by an abundance of grapestone and cryptocrystalline grains; (4) pellet-mud facies-characterized by an abundance of fecal pellets and particles smaller than 1/8 mm.; and (5) mud facies-typified by an abundance of particles smaller than 1/8 mm. and a relative paucity of indurated fecal pellets. The coralgal facies owes its distinctiveness to a relative lack of non-skeletal calcium carbonate precipitation and to the large areas of rock bottom that characterize this depositional environment. In contrast, differences among three of the other four facies are considered to be primarily the product of differential current strength, with current velocities progressively decreasing in intensity from the oölitic to the pellet-mud facies. The contrast between pellet-mud and mud deposits appears to be due largely to a decreased rate of formation and/or induration of fecal pellets in the mud environment. Ideally one might expect Bahamian facies to be distributed in a series of five concentric bands parallel to the bank's margin. The karst surface of the submerged Pleistocene basement rock, however, creates local current conditions that cause the development of a somewhat patchlike facies pattern.