Molluscan Taphofacies in Recent Carbonate Reef/Lagoon Systems and their Application to Sub-Fossil Samples from Reef Cores


Modern taphofacies analyses have been worked out for different mixed carbonate and siliciclastic sedimentary environments using molluscan faunas. Studies of how the combined effect of the physical, chemical, and biological characteristics of the environment of deposition results in a particular taphonomic signature on fossilizable remains must be done on Recent assemblages to understand taphonomic signatures of ancient faunas. Studies have defined modern taphofacies by erecting broad damage categories to which each sample is assigned. Others graphically characterize environments based on individual taphonomic indices (e.g., fragmentation, abrasion), rely on presence-absence data, or construct ternary taphograms for each taphonomic characteristic. This study defines taphofacies based on a statistical treatment of the entire taphonomic signature of molluscs from several carbonate reef and lagoon systems in the northeastern Caribbean. The method uses non-metric multidimensional scaling ordination to test whether the combined taphonomic signature is recognizable across closely associated shallow carbonate environments. Results show that a statistical technique combining many taphonomic factors is a reliable method for deciphering taphonomic signature. It is most important, however, to test whether taphofacies defined using modern shells can be applied to the fossil record. Taphonomic traits from mollusc shells obtained from reef cores were added to the same statistical routine and assigned environments of deposition based on their taphonomic signature. Molluscs from within the cores suggest that the shelf and patch-reef environments on the SW coast of Puerto Rico have remained fairly stable up to at least 7,000 ybp. Shells were recovered that had distinct reef and open-shelf taphonomic signatures. Shells from cores from Buck Island, U.S. Virgin Islands had signatures that suggested migration of the reef over seagrass areas of the shelf, and/or landward into the lagoon behind Buck Island reef. Thus, not only does the total taphonomic signature mirror the environment of deposition, but the taphonomic signature is likely to be preserved well enough to be useful in making paleoenvironmental interpretations of fossil material.


Society for Sedimentary Geology

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Taphonomic signature, Bivalve taphonomy, Environment, Shells, Predation