Abstract

Tests of benthic foraminifera were analyzed quantitatively in 43 surface sediment samples collected along E–W traverses across the modern isolated carbonate platforms of Glovers Reef (N=14), Lighthouse Reef (N=14), and Turneffe Islands (N=15), offshore Belize, Central America. Water depths of sample stations range from 0 m (beach) to 40 m (fore reef). Each sample was sieved in the size classes 2–1, 1–0.5, 0.5–0.25, and 0.25–0.125 mm (ϕ=1–0, 0–1, 1–2, and 2–3, respectively) and 300 foraminiferal identifications were attempted for each sieve fraction (i.e., 1,200 individuals per sample, totaling 46,003 specimens). Cluster analyses of samples characterized platform environments and distinguished four benthic foraminifera associations. Fore reef samples were characterized by abundant Amphistegina gibbosa and the occurrence of Asterigerina carinata, both rotaliids. In high-energy, marginal-reef areas the encrusting rotaliid Homotrema rubrum predominated. Platform-interior environments were marked by a variety of common taxa, the most common of which include Miliolina such as Archaias angulatus, Quinqueloculina sp., and Triloculina sp., as well as the rotaliid Cribroelphidium poeyanum, the latter indicating low-energy or deep-lagoonal regimes. Diversity, expressed as numbers of identified taxa, appears to be a function of relative degree of circulation. The highest number (147) of taxa was found in the shallow, high-energy platform of Lighthouse Reef, followed by Glovers Reef (78), both of which are open to the Caribbean Sea. The lowest number of taxa (66) occurred in Turneffe Islands where large parts of the platform are characterized by the restricted circulation imposed by dense mangrove growth behind platform margins. The occurrence of tests of common foraminiferal species outside their original habitats, coupled with trends towards smaller grain-sizes and better sorting of tests away from original habitats along parts of the sample traverses, indicates sediment transport across platform margins. In the great majority of samples, however, sediment redeposition did not significantly alter characteristic taxonomic compositions. This result has important implications for the use of benthic foraminifera as facies indicators in fossil carbonate platforms.

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