USING FORAMINIFERA TO RECONSTRUCT PALEODEPTHS OF SOUTHERN FLORIDA'S PLIOCENE SHELL BEDS

Florida’s marine communities suffered a biodiversity crisis roughly 2 Ma, but there is little consensus on the extent of recovery. A central issue is the paleodepth of southern Florida’s Pliocene shell beds. The modern Florida shelf at 30 m has molluscan richness roughly equivalent to that of the Pliocene shell beds, while the modern shelf at 10 m or less is substantially less diverse. Thus, deeper paleodepth reconstructions for fossil units support the hypothesis of rapid faunal recovery, while shallower reconstructions do not. To test these opposing views, we used detrended correspondence analysis (DCA) of foraminifera abundance distributions from Pliocene sediment samples from Tamiami Formation (Pinecrest beds) exposures at SMR Aggregates Quarries, Sarasota and modern coastal, bay and reef habitats ranging in depth from 0 to 90 m. Pliocene samples were dominated by an Ammonia-Elphidium assemblage characteristic of brackish mangrove and estuarine habitats. In DCA analyses, these samples clumped with modern foraminifera from the shallowest parts of northern Florida Bay (<3 m depth) rather than deeper, normal marine assemblages. These results support a shallow paleodepth for the Pliocene shell beds and, more importantly, establish the Pliocene shell beds as a more diverse analog to modern bay or estuarine habitats.