Southeastern Section - 68th Annual Meeting - 2019

Paper No. 1-7
Presentation Time: 10:15 AM


DALEY, Gwen M., Winthrop University, Rock Hill, SC 29732; Winthrop University, Rock Hill, SC 29732, BECKHAM, Tira, Department of Chemistry, Physics, and Geology, Winthrop University, Rock Hill, SC 29732 and MOORE, Sarah Catherine, Winthrop University, Rock Hill, SC 29732

Ichnology and taphonomy are intimately intertwined studies of how organismal behavior affects the sedimentary environment and how the sedimentary environment affects the post-mortem history of fossils, respectively. Such behaviors as bioturbation and pagurization can destroy trace fossils and transport shells and other potential fossils; clionid sponges can turn robust shell material into shell cheese holding the clionid trace fossil.

Boring predatory marine gastropods are a favorite of ichnologists because they bore holes with distinct characteristics that allow the predator to be identified while also preserving enough of the prey species shell that it may also be identified. While still identifiable, the bored valve of the bivalve may act differently than its unbored counterpart. The bored valve is missing shell material, making it less robust. If bored valves are preferentially destroyed, predatory boring rates based on counts of bored and unbored valves would be lower than if all valves were equally preservable. Decades of actuotaphonomic experiments have shown that differential transport of the two valves in a bivalve shell is characteristic in energetic environments.

On September 10th, 2017, Hurricane Irma moved through the Tampa Bay area with greater than 100 km/h sustained winds. A WeatherFlow station on Egmont Key recorded a 79 knot (146 km/h) wind gust during Irma and there was significant damage to human buildings on many of the smaller islands in the region. Based on published estimates of the age of subfossil shell material found on beaches and shallow subtidal areas, it seems likely that many of the subfossil bivalves collected from the beach on December 28th, 2017 were affected by the passage of Irma.

The bivalves on Egmont Key took the brunt of a hurricane which produced powerful winds, storm surge, and rip currents. We examined 178 complete subfossil valves of the abundant bivalve Spisula raveneli, a large mactrid clam that is frequently found on Gulf of Mexico beaches. We collected along an approximately 1 kilometer stretch of beach on the northwestern shoreline of Egmont Key. We specifically examined the left/right sorting of valves, the taphonomic condition of the valves, and damage to the valves associated with bore holes, to see if there were quantifiable patterns in these subfossil remains.