TAPHONOMY AND PALEOENVIRONMENT OF 2 TURRITELLID-GASTROPOD RICH BEDS, PLIOCENE OF FLORIDA

Two beds containing large numbers of turritellid gastropods (Family Tu rritellidae) occurring in the densely fossiliferous Upper Pliocene Pin ecrest Sand of Florida formed as a result of upwelling and consequent high biological productivity, together with some degree of physically mediated time averaging. Analyses of size-frequency distribution and s hell surface condition, combined with isotopic data on chronological a ge of individual shells, water temperature and upwelling intensity, su ggest that both beds formed relatively quickly, probably in less than 100-200 years. The upper bed, occurring within Petuch's (1982) unit 2 (2.5-2.0 Ma) and containing abundant Turritella apicalis Heilprin, app ears to have formed largely as a result of upwelling; the lower bed, o ccurring in upper unit 6/7 (3.5-2.5 Ma) and containing abundant Turrit ella gladeensis Mansfield appears to have formed over a longer period, as a result of upwelling, increased time-averaging, and perhaps coole r overall water temperatures. This study highlights the potential to i solate and examine separately some of the biological and physical fact ors affecting shell bed formation, and especially to address the role of biological productivity in this process.