RECONSTRUCTING HOLOCENE SHORELINE TRANSGRESSION AND STORM HISTORY IN HORSESHOE COVE ON THE NORTHERN GULF COAST OF FLORIDA

Geoarchaeological research in the Horseshoe Cove area of the northern Gulf Coast of Florida seeks to understand how the pre-Columbian inhabitants responded to environmental change along the coast during the late Holocene. The goal of the project is to reconstruct a relative sea-level curve in fine-grained coastal sediments that can be directly related to the archaeological record in this area and preliminary results of the study are presented here. Horseshoe Cove is a low-energy estuarine and tidal flat environment that contains a grouping of small islands, the remnants of a large relict Pleistocene parabolic dune that has been isolated from the mainland by sea-level rise. Fifteen marine sediment cores were collected with a vibracore along a 2-km-long transect through this island group and sediment samples were collected from the profile of an archaeological unit on one of the small islands. Despite the thin Holocene sediment cover in this region, evidence of shoreline transgression is preserved in this relatively protected area. Analysis includes core lithology, sediment texture, percentage of organic matter and carbonate, and identification of marine microfossils, along with radiocarbon dates of organic materials. A bulk date from just above the transition from fine-grained, degraded subareal limestone to siliciclastic sediments indicative of marsh deposits in one core suggest the study area was flooded around 4420 to 4240 cal yr bp, which is consistent with other studies along the Gulf Coast of Florida, and places the shoreline near its modern location. There is evidence of a high-energy storm event sometime prior to 2840-2750 cal yr bp that likely scoured seaward marsh sediments and deposited them atop archaeological deposits on the highest elevation of the island, creating a culturally sterile sand layer between two discrete midden deposits. A temporal gap of nearly two thousand years between the lower and upper midden deposits on the island suggests some archaeological materials may have been scoured from the upper portions of the island while a lack of intact archaeological deposits at lower elevations suggest significant disturbance and reworking of deposits during this and subsequent high-energy storms.