Reconstructing Submerged Paleoenvironments: Mud Hole, RI Sound and Greenwich Bay, RI

Abstract

Interpretations of high-resolution geophysical data and analysis of the physical properties of vibracores from separate, but closely related study sites have contributed to our understanding of the Late Quaternary paleoenvironments of southern New England. Two submerged areas, Cedar Tree Beach located in the northwest corner of Greenwich Bay and the Mud Hole, a deep bathymetric depression located at the southern edge of the Rhode Island Sound have been designated as study sites for the Bureau of Ocean Energy Management (BOEM) Paleocultural study, which seeks to develop best practices methodology when developing the continental shelf for renewable energy projects. Reconstructions of a post­‐glacial, pre-marine inundation paleoenvironment is a critical step in the development of an archaeological predictive model to better understand potential for habitability and preservation of cultural material. The first chapter is focused on interpreting post­‐glacial depositional environments of the Mud Hole study area. High‐resolution geophysical data consisting of 37 survey lines with 500 m spacing and covering ~130 km2 including CHIRP seismic reflection and interferometric side­‐scan and swath bathymetry data were collected in 2012. Side‐scan imagery was inspected for sedimentary features. Megaripples were interpreted as areas of modern sediment reworking due to storm‐induced bottom currents. Erosional outliers and scour depressions were interpreted as net-erosional sedimentary environments. Featureless, low backscatter areas were interpreted as non­‐erosional or depositional. Several seismic reflectors were identified in the processed seismic reflection lines, representing changes in depositional environments. Identified reflectors and seismic units were correlated with the regional seismic stratigraphic framework of Rhode Island Sound. Five depositional environments were interpreted based on the seismic stratigraphy. A highly eroded Atlantic coastal plain remnant underlies the study area. Glacial deposits ranging from glacial moraine to glaciolacustrine depositional environments unconformably overlie the coastal plain. The draining of pro­‐glacial lake Rhode Island eroded two distinct channels to depths of 60 m below present sea level. Sea level is constrained to have inundated the study area between 12.8­‐10.7 kyBP. Topographic tidal constriction by adjacent moraine deposits may have intensified tidal scour, removing up to 10 m of sediment. A prominent ravinement surface truncates glacial deposits, and Holocene marine sediments drape much of the deeper (>40 m) portions of the study area. Preliminary analysis of two vibracores collected August 2015 indicate lithological agreement with interpreted seismic reflection profiles. Chapter 2 details ongoing investigations of a submerged paleocultural site at Cedar Tree Beach. Approximately 400 artifacts spanning nearly 10,000 years have been