Paleoenvironmental and paleolandscape reconstructions of Greenwich Bay region, RI

A paleoenvironmental and paleolandscape reconstruction of two separate sites in the Greenwich Bay region of RI was completed for use in the Paleocultural Landscapes Project. Investigations of a lacustrine sediment record in Warwick, RI were completed in order to develop a regional paleoenvironmental reference record. Investigations of the acoustic sub-bottom record in Greenwich Bay, RI were completed in order to develop paleolandscape reconstructions of the observed depositional environments for future use in an archaeological site prediction model.;For Chapter one, we took a single sediment core from Gorton Pond, Warwick, RI in the summer of 2013 for the purpose of developing a regional paleoenvironmental reference record. The core was dated using both AMS-radiocarbon dating of four terrestrial macrofossil samples, and correlations with a radiometric/pollen age model from a surface core taken from Gorton Pond for a previous study. The oldest terrestrial macrofossil was a spruce cone dated to ~12,100 calendar years BP, but an estimated 18,000 years of sediment is in the Gorton Pond record, based on bracketing ages from dated recessional moraines in the region. However, we only sampled an estimated 16,000 years, based on a Younger Dryas transition of 13,000 BP.;Physical, magnetic, and elemental/isotopic (C, N, S, D/H) proxy measurements were made, and six distinct environmental zones were interpreted. The Gorton Pond record indicates significant changes in lake productivity and temperature. The Late Pleistocene Deglacial Period (16.0-13.0 ky BP) is indicated by low OC%, high concentrations of magnetic material, and terrestrially-sourced organic matter. The Younger Dryas chronozone was observed (13.0-11.8 kyr BP) as large decreases in deltal13C, OC%, and deltaDBA, indicating cold conditions. A transition from the Late Pleistocene to Early Holocene (11.8-9.6 ky BP) was observed by rapid warming and increased aquatic productivity. The Middle Holocene (9.6-3.6 ky BP) was characterized by depleted deltaD BA of behenic acid ratios, which may suggest Gorton Pond is sensitive to changes in air mass/moisture sources, but other local effects are being investigated.;In chapter two, a geophysical survey was conducted using acoustic sub-bottom (CHIRP) seismic reflection techniques, and 24 lines covering 40 km were processed and interpreted. Four distinct seismic units were interpreted, spanning from the Pleistocene-aged deglacial sediments to modern day estuarine sediments. A basal till/bedrock surface marks the limit of seismic penetration, and overlying thick (up to 42 m) varved proglacial lake sediments suggest that the area was part of Glacial Lake Narragansett (GLN). Paleochannel stream cuts unconformably lie above the proglacial lake sediments, indicating a draining of GLN and a period of subaerial exposure in which an organized tributary system existed in Greenwich Bay. A GIS-based Local Polynomial Interpolation model was used to create a representative surface of the stream-dissected paleolandscape that existed prior to marine inundation. While useful, denser CHIRP coverage (100 m line spacing minimum) is recommended in order to take stress off of the interpolation. The proximity of channels to archaeological finds at Cedar Tree Beach would suggest that they might have been important resources for ancient inhabitants. Comparisons to the USGS East Greenwich Quadrangle Surficial Geology Map (Smith, 1955) shows significant kame terrace and other glacial meltwater deposits that may indicate a paleo-drainage of the modern day Pawtuxet river into the paleolandscape observed in the Greenwich Bay seismic record.