MICROFOSSIL ANALYSIS OF SUBMERGED LAG DEPOSITS FROM VENICE, SARASOTA COUNTY, FL, USA

The shallow marine shelf off Venice, Florida has long been known for its abundance of vertebrate fossils, in particular shark teeth, belonging to megatoothed sharks. In addition to these fossils, vertebrate and invertebrate microfossils <1cm also occur but have gone unreported. Concentration of these fossils into residual lag deposits began during the deposition of the Miocene-Pliocene Peace River Formation as a result of wave- and current-driven bottom erosion and hydrodynamic sorting in response to storm events and changes in sea-level. These processes are still actively occurring on the seafloor today, and bulk sediments collected by SCUBA diving reveal that: 1) fossils occur in all sediment grain size classes but identifiable remains are most abundant in the granule to small pebble size class (~6-3mm); 2) the most abundant and identifiable fossil remains are those from elasmobranchs (i.e., shark and ray teeth); 3) fossils within the fine sand-silt sediment (≤1mm) fraction mainly consist of fragmentary, unidentifiable remains; 4) >500 individual fossils were collected from each sediment sample; and 5) on average only ~3.43% of each sediment sample is represented by fossil remains. These analyses resulted in the identification of microteeth belonging to 10 elasmobranch taxa previously unreported from Venice, as well as the remains of marginal marine and terrestrial animals. The overall concentration and biodiversity represented by fossils in these submerged lag deposits attests to extensive periods of time-averaging and mixing of fossils from distinctly different paleoenvironments. Moreover, the abundance of remains from specific taxa reflects species abundance and taphonomic controls on lag deposit formation across the Venice shelf since the Late Cenozoic.