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Figure 2. Map showing the location of end moraines and submerged ridges in southern New York and New England.

Previous studies have shown that the morphological features and sedimentary deposits of Long Island Sound have been greatly influenced by the region's glacial history (Lewis and DiGiacomo-Cohen, 2000; Sirkin, 1980; Stone and Borns, 1986; Uchupi and others, 2001). About 20,000-22,000 years ago, the Laurentide Ice Sheet reached its southernmost position, marked by the Ronkonkoma-Block Island-Nantucket moraine system (fig. 2; Sirkin, 1980; Stone and Borns, 1986; Uchupi and others, 2001). By about 18,000 years ago, the ice sheet had retreated northward to a position marked by the Harbor Hill-Roanoke Point-Orient Point-Charlestown-Buzzards Bay moraine line, which underlies much of the study area (Uchupi and others, 2001). As the ice sheet continued its northward retreat, meltwater formed glacial lakes that were dammed to the south by the northern moraine system. Glacial Lake Connecticut covered much of present-day Long Island Sound from about 17,500 to 15,500 years ago, leaving deposits about 80 m and up to 150 m thick (Lewis and DiGiacomo-Cohen, 2000; Uchupi and others, 2001). After Glacial Lake Connecticut drained, the area was exposed to subaerial erosion before a rise in sea level and the onset of modern marine conditions (Lewis and DiGiacomo-Cohen, 2000).