Continental Shelf Sediments off Eastern Newfoundland: A Preliminary Investigation

Abstract

Surficial sediment samples from the continental shelf off eastern Newfoundland were analyzed for grain-size distribution (302 samples) and CaCO3 content (257 samples). The results were compared with those of previous investigations.Gravel covers the inner Grand Banks. Clean, well-sorted sand covers most of the outer banks, but significant quantities of gravel (greater than 10%) are present locally. Biogenic carbonate sand is irregularly distributed on the Grand Banks.The presence of gravel as far seaward as the shelf break indicates the Pleistocene ice sheet once extended across the Grand Banks and the sediments are relict. Other lines of evidence that indicate the sediments are relict include: a radiocarbon date of 17 000 yrs. B.P. on biogenic sand, the occurrence on parts of the shelf of littoral sand now in 90 m of water as well as glacially derived residual sediments, the presence of moraines and a Quaternary shelf sedimentary section 20–200 m thick, and the presence of relict sediments on continental shelves both north and south of the Newfoundland shelf. It is concluded that gravel on the inner Grand Banks is reworked glacial or glacio-fluvial sediment that was deposited during Pleistocene lower stands of sea level and that sand on the outer banks probably was derived by in situ reworking of the Pleistocene substrate during the Holocene transgression.It has previously been suggested that the gravel–sand boundary, which occurs more than 150 km from shore, defines the seaward limit of the Wisconsin ice sheet. This possibility cannot be discounted, however, the presence on the shelf of a transgressive sand sheet, and relict biogenic carbonate sand near this boundary and intermixed with gravel, as well as the Wisconsin glacial history of eastern Newfoundland and Nova Scotia, which suggests late-Wisconsin ice didn't extend offshore a distance of 150 km, all indicate the gravel–sand boundary does not define the seaward limit of Wisconsin ice. The late-Wisconsin ice limit may have been further shoreward.On the North Newfoundland Bank (Ritu Bank) and adjacent areas of the northeast Newfoundland shelf, post-depositional winnowing probably has size-sorted residual sediment according to water depth.