Taphonomic Signature of Shell Accumulations in Cores: An Indicator of Depositional Environments in Holocene Nearshore Sediments, West-Central Florida
CUFFE, C. KELLY, ANN E. GIBBS, and WARREN D. ALLMON, University of South Florida, Tampa, FL
Taphonomic signature is the cumulative effect of physical and biological processes that have acted upon biogenic hardparts before and during deposition and prior to lithification. Description of orientation, fragmentation, angularity, abrasion, bioerosion, and dissolution of shell material can be used to understand depositional energy of the environment. Modern sedimentary environments can be defined using this technique and the results applied to the rock record. In modern paralic environments, however, these data often are available only from cores. Core descriptions, epoxy peels, and direct sediment analysis comprise the data base.
Vibracores taken along the barrier island coastline of west-central Florida display distinct lithofacies characterized by unique taphonomic signatures. High-energy lithofacies include both current- and storm-generated shell accumulations. Storm-generated accumulations can be divided into pulse (washover) and agitated (continuous storm surge) types. Pulse types are characterized by general lack of orientation and upward grading with whole or angular fragmented shells. Rare rounded shells may be the result of previous corrosion. Agitated types are characterized by mixed and concave-up orientations, are more densely packed, and have rounded to subangular shells. Current-generated accumulations have concave-down orientations of larger whole shells; fine shell fragments may remain, protect d by these larger shell armors. Degree of rounding is high. Low-energy lithofacies (coastal bays, back-barrier) can be identified primarily by relatively sparse concentrations of thin-shell species scattered throughout the unit. Shells are preserved whole or are fragmented due to predation.
AAPG Search and Discovery Article #91006 © 1991 GCAGS and GC-SEPM Meeting, Houston, Texas, October 16-18, 1991 (2009)