ANALYSIS OF SUBMERGED FOSSILIFEROUS 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 including shark teeth, such as those belonging to megatoothed sharks. Many of these vertebrate fossils derive from submerged exposures of the Miocene-Pliocene Peace River Formation in ≤10 m of seawater and within 4.5 km of the present shoreline. Fossil concentrations initially formed during the deposition of the Peace River Formation from wave- and current-driven bottom erosion and hydrodynamic sorting in response to storm events and changes in sea level. These same processes are currently re-exhuming and enriching sediments with fossil remains on the modern seafloor. Bulk sampling of these vertebrate fossil concentrations by SCUBA diving for the first time reveals that: 1) the most abundant and identifiable fossil remains are those from elasmobranchs (i.e., shark and ray teeth); 2) fossil remains are most abundant in the granule to small pebble grain size class (~6-3mm); 3) fine sand-silt sediment comprises most of the bulk samples and is consistent with the lithologic description of the Peace River Formation; and 4) phosphate is present in all sediment grain size classes, but is most abundant as granules and sand. As such, the unique geologic setting of the shallow Venice shelf and active reworking of fossiliferous exposures of the Peace River Formation provides a means to further understand the taphonomy of lag deposit fossil concentrations. The active reworking of Miocene-Pliocene lag deposits on the modern seafloor further demonstrates that these fossil concentrations form over thousands to millions of years of time. Moreover, observations and data gained from this analysis can provide valuable insights on field prospecting and sampling of similar shallow marine, Mesozoic and Cenozoic lag deposits elsewhere globally.