Modern sediment facies and dynamics of the Dry Tortugas, south Florida, USA: an isolated carbonate ramp

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The Dry Tortugas are a 250 km2 remote carbonate shoal area with coral reefs and islands located at the southwestern boundary of the Florida shelf. The Tortugas platform is unique in that it may be classified as an isolated carbonate ramp, lacking continuous marginal reefs and surrounding deep water. It is planned to collect ca. 150 sediment samples along five east-west traverses across the platform, and to perform textural, compositional, and taphonomic analyses. This project has three objectives. (1) The compilation a of high-resolution facies map of the Dry Tortugas isolated ramp based on the quantitative analysis of sediment composition and texture, and bottom observations. (2) The estimation of spatial variability in taphonomic and early diagenetic signatures of sediment particles such as abrasion, fragmentation, boring, recrystallization, cementation, and dissolution. (3) The comparison of sediment composition and texture with previous datasets of 1908-15 (Thorp 1936) and 1967-69 (Jindrich 1972; Multer unpubl.) will open the unique opportunity to record temporal variation in sediment distribution over a century. The influence of biotic changes in carbonate-producing organisms and physical disturbances (e.g., major storms; cold events) may be evaluated. Preliminary facies maps put together by the applicant based on the previous datasets result in a mosaic of facies rather than larger, continuous facies areas. This is presumably a consequence of the unique, ramp-like geomorphology of the Tortugas lacking a continuous platform margin with sand aprons, steep outer flanks, and a deep platform interior, in combination with high local variability in carbonate prodution.