Abstract
About 2000 large sediment samples were collected during the early 1960s throughout the continental shelf off the Atlantic coast of the United States to establish and map sediment types including sediments relict from times of glacially low (and subsequently higher) sea levels. In about 510 of these samples we found fossil shells of mollusks remaining from environmental conditions different from those at present. Publications and collections by others contain about 70 additional samples having relict mollusks. Some of these shells indicate lower sea levels, others colder water, and still others warmer water than is now present. Radiocarbon measurements from earlier studies by us and others established the dates of colder water (late Pleistocene), and we made additional measurements to learn the dates of warmer water (about 1000 to 2000 yr B.P.). The results show reasonably enough that continental shelves are the sites of relict faunas as well as of sediments that indicate changed and complex environmental histories.
Highlights
Glacial advances during the Pleistocene Epoch were accompanied by widely recognized lowerings of sea level and by equatorward shifts of climatic belts
Least well known is the fossil evidence from the transitional margin, the subject of this study, which is based upon investigations of bottom samples from the Atlantic continental shelf and upper slope off the eastern coast of the United States
Shipboard and laboratory studies show that relict sediments of the continental shelf of the Middle Atlantic Bight contain many relict mollusk shells that denote changes in the environment during the past 15,000 yr. These are intermixed with far more numerous mollusks that live in harmony with present water depths, temperatures, and other environmental parameters
Summary
Glacial advances during the Pleistocene Epoch were accompanied by widely recognized lowerings of sea level (the latest major one reaching perhaps 130 m below the present level) and by equatorward shifts of climatic belts. Especially of the larger and more common species, were found in a subsequent series of sediment samples collected during cruises aboard R/ V GosnoEd (Woods Hole Oceanographic Institution) between 1963 and 1970 (Emery and Schlee, 1963; Hathaway, 1971) These samples (volumes to 0.2 m3) were obtained with a Campbell clam-shell grab (Emery et al, 1965) in a IO- to 15-min (latitude and longitude) grid across the entire continental shelf and upper slope from eastern Nova Scotia to southern Florida. The more than 2000 large bottom samples that have been collected from the shelf and upper slope contain abundant living and fossil remains of mollusk species that have identical habitats (same depth, latitude, and substrate). Fossil shells were taken at three stations off Long Island, NY, to Cape Hatteras, NC, in present water depths of 55 to 84 m.
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