Atlantic Deep-Sea Sediment Cores
Studies of lithology, particle-size distributions, and micropaleontology and chemical analyses o f 221 Atlantic and Caribbean deep-sea cores lead to new conceptions of processes of sedimentation, rates of sediment accumulation, Pleistocene chronology, and pre-Pleistocene history of the Atlantic Basin.
Anomalous layers of sand, silt, and lutite occur widely in the deep basins of the Atlantic. Evidence for deposition of these layers by turbidity currents is as follows: (1) the layers occur in submarine canyons, in deltalike features at the terminal ends of canyons, in basins and depressions, never on isolated rises; (2) they are interbedded with late Pleistocene sediments of abyssal facies; (3) they are well-sorted and commonly graded; and (4) they commonly contain organic remains of.shallow-water origin.
Late Pleistocene slumping of compacted Neogene sediments along the banks of the Hudson submarine Canyon at depths exceeding 3000m indicates deepening of the canyon by erosion by turbidity currents
Variatiohs in the planktonic Foraminifera in 108 of the cores and extrapolation of rates of sediment accumulation determined by 37° radiocarbon dates-in 10 cores show that the last period of climate comparable with the present ended about 60,000 years, ago. A faunal flange indicating climatic amelioration probably corresponding to the beginning of postglacial time, occurred about 11,000 years ago. Cross-correlations by microipaleontological methods establish the ontinuity of the climatic record deduced from the planktonic Foraminifera. Study of variation in the Planktonic Foraminifera kads to a different, Pleistocene chronology from that proposed by Emiliani (1955).
Cross-correlations of faunal zones and radiocarbon dates show that rates of continuous sediment accumulation as opposed to turbidity current deposition range from 0.5cm to 27.4cm in 1000years, depending upon bottom configuration. Cross correlations by means of changes in coiling direction of planktonic Foraminifera give relative rates of sediment accumulation beyond the range of the radiocarbon method of dating.
Forty one of the cores contain pre-Pleistocene sediments. The oldest sediment is Upper Cretaceous. Foraminifera and discoasters indicate the ages. Absence of sediment older than Late Cretaceous and thickness, 800-1000m, of sediment in the Atlantic Basin, as determined by seismic methods-suggest that a large-scale reorganization of the Atlantic Basin took place in the Mesozoic.
Figures & Tables
Edited by Peter A. Roma and published in 1976, Mid-Atlantic Ridge contains a collection of related articles reprinted from other Geological Society of America publications as well as a brief review of exploration of the Mid-Atlantic Ridge from 1960 to 1975.