Archaeo-Tempestites and Coastal Taphonomy of Shell-Bearing Sites: Native American Sites in Florida as a Case Study

Energetic conditions during storms cause major geomorphological changes in coastal environments and drive taphonomic transformations of coastal archaeological sites. Facing the emerging realities of modern climate change and sea-level rise, archaeologists have justifiably focused on erosional processes and the loss of cultural heritage. However, sedimentologists have long recognized that storm-forcing also involves significant (re)depositional processes and the formation of supratidal features. Geoarchaeological research at partially inundated Native American shell mound sites in Tampa Bay, Florida, integrated topobathymetric aerial LiDAR with sub-surface testing to reconstruct complex site-formation histories. These histories include reworking of cultural deposits by contemporary, recent-historical, and ancient storms, forming archaeological tempestites—sediment deposits that have been scoured from and/or deposited within archaeological contexts by storm-forcing. Using sedimentological, zooarchaeological, and radiometric data, as well as post-storm observations, we present methods for recognizing storm-driven redeposition in coastal-estuarine archaeological contexts and demonstrate the potential of archaeo-tempestites for improving archaeological and paleoenvironmental interpretation. Storm-reworking of estuarine shell mounds on the Florida Gulf Coast produces diagnostic signatures in stratigraphy, granulometry, organic content, and mollusk-composition. Ephemeral ground surfaces and overwashed sand-sheets provide suitable loci for radiometric dating of past storm events (¹⁴C and OSL). We discuss inter- and intra-site variation among regional archaeo-tempestites to better understand late-Holocene ecosystem transfer and the long-term effects of shell-bearing sites on inshore-estuarine ecological conditions. We consider the absorption of energetic forcing as part of the life-history or use-life of shell-bearing features and suggest that a broader study of Indigenous coastal terraforming may aid modern coastal protection and management efforts.