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U.S. Geological Survey Open-File Report 02-002

Geological Framework Data from Long Island Sound, 1981-1990:

A Digital Data Release

CERC Technical Report 81-3

Table 3.


Summary of Quaternary geologic events
(Dates from Newman, 1977)

12,300 to present As sea level rose, Long Island Sound became a tidal estuary and deposition of organic muds and sandy silts occurred.  Sources of these sediments were and continue to be coastal erosion of glacial deposits, rivers draining glacial terrain, and sediment influx from Block Island Sound and the adjacent Continental Shelf.
13,400 Short-term readvance or slowing of retreat of the glaciers that were part of the Port Huron stade.  This led to deposition of the several discontinuous terminal moraine segments (Elmhurst, Madison, Old Saybrook, Six Mile, Ledyard, and Middletown) close to the Connecticut coast on Long Island Sound.
15,000 to 13,400 Damming by the Ronkonkom and Harbor Hill Moraines backed up freshwater and created Lake Flushing that covered much of Long Island and Block Island Sounds.  Very fine grained silt and clay were deposited as seasonal varves filling in and covering the high-relief bedrock surface and glacial deposits.
21,000 to 15,000 Late Wisconsin advance of the glacier resulted in deposition of the Harbor Hill Moraine consisting of till and stratified kame and outwash deposits.  Existing river valleys were deepened and widened.

Department of the Interior > U.S. Geological Survey > Coastal and Marine Geology Program > Long Island Sound Studies
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