Studies of lithology, particle-size distributions, and micropaleontology and chemical analyses of 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 3000 m indicates deepening of the canyon by erosion by turbidity currents.

Variations 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 change indicating climatic amelioration, probably corresponding to the beginning of postglacial time, occurred about 11,000 years ago. Cross-correlations by micropaleontological methods establish the continuity of the climatic record deduced from the planktonic Foraminifera. Study of variation in the Planktonic Foraminifera leads to a different Pleistocene chronology from that proposed by Emiliani (1955).

Cross-correlations of faunal zones and radio-carbon dates show that rates of continuous sediment accumulation, as opposed to turbidity-current deposition, range from 0.5 cm to 274.4 cm in 1000 years, 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, 800–1000 m, 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.

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