POST-GLACIAL STRATIGRAPHY AND SEDIMENT ACCUMULATION IN THE NORWALK AND SAUGATUCK RIVER ESTUARIES, WESTERN LONG ISLAND SOUND

Estuaries along coastal Connecticut preserve stratigraphic records reflecting late Pleistocene glaciation, Holocene sea-level rise, and the influence of human activities from pre-European settlement to the present. This project is focused on interpreting post-glacial stratigraphy and sediment accumulation observed in sediment cores collected in the Norwalk and Saugatuck River estuaries in western Long Island Sound. In total, we collected 23 intertidal vibracores and 37 terrestrial geoprobes at the Norwalk site, and 17 intertidal vibracores at the Saugatuck site. Sediment cores at Norwalk reach as deep as ~36ft and ¹⁴C dates range from 115 years BP to ~6300 years BP. Sediment cores at Saugatuck are shallower (<15 ft) and ¹⁴C dates are younger, ranging from 115 years BP to ~2000 years BP. The uppermost unit within the vibracores ranges from 20 to 200 cm in thickness and consists of fine silt and sand interspersed with organic material, brick pieces, glass, and coal. This unit also has high concentrations of Pb, Zn, Cu, and Hg indicative of anthropogenic influences on sedimentation due to various industrial activities over the last 150 years. Below the upper unit, cores typically consist of 1-4 m of fine grained silt/sand mixed with shell, oyster, coarse sand, and organic layers. We interpret this middle unit to be estuary sediment accumulation associated with Holocene sea level rise. The bottom units, when preserved, are either glacial materials or soils developed on older deposits. Ongoing work is focused on reconstructing the patterns of these units in fence diagrams across the Norwalk and Saugatuck sites to understand the paleogeomorphology of both river systems. One preliminary observation is that glacial deposits at both sites have likely constrained the position of the river and have not allowed for meandering over the last 15,000 years.