Evidence of pleistocene events in the structure of the continental shelf off the northeastern United States

Abstract

In 1958 and 1959 a seismic reflection reconnaissance was made of three regions of the continental shelf off northeastern United States: the outer shelf off New Jersey and Long Island, the shelf south of Martha's Vineyard, and Georges Bank. Broadband high resolution techniques, including the first use of arrays of underwater spark sources, permitted the delineation of reflectors as little as 4–6 m apart to depths of 100–300 m beneath the seafloor. Profiles of the outer shelf off the New Jersey coast and Long Island suggest that the major events of the Pleistocene age can be traced in a complex series of five sedimentary sequences separated by well developed unconformities. These sedimentary sequences and the erosional surfaces separating them appear to be the products of fluvial and marine processes during regressions and transgressions of the sea. Thirty kilometers south of Martha's Vineyard folded and overthrust plates of layered sediments found along a lobate front are apparently the result of ice pressure. The shelf edge south of Martha's Vineyard was built up and out apparently without enduring the heavy erosion found off New Jersey. A strong reflector that post-dates the time when the layered sediments were disturbed south of Martha's Vineyard is overlain by more than 200 m of sediments at this shelf edge. At the northern edge of Georges Bank both the layered base-rock and the more recent sediments are cut by filled channels which drained north towards the Gulf of Maine. The southern surface of the bank is built up more than 70 m by several successive deposits. Within these deposits there are filled channels. This and other evidence suggests that glaciers overrode the northern part of the bank, and that these successive deposits are a result of glacial depositions, modified by marine reworking during successive regressions and transgressions of the sea in Pleistocene time.