David B. Ericson

Atlantic Deep-Sea Sediment Cores

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.

Coiling Direction of Globigerina pachyderma as a Climatic Index

An interdependence between the geographical distribution of dextral and sinistral populations of the planktonic foraminifer, Globigerina pachyderma, and sea surface-temperatures is demonstrated. It is inferred that changes in dominant coiling direction at lower levels in sediment cores from the North Atlantic record southward shifts of isotherms during the last ice age.

Magnetism of the earth and climatic changes

Abstract Variations in the earths magnetic intensity, fluctuations in atmospheric radiocarbon activity, and climatic changes of the earth surface and of the ocean during the last 7000 yr are correlated. Variations in magnetic intensity, fluctuations in magnetic inclination, and climatic changes in deep-sea sediment cores are correlated for the last 470,000 yr. We tentatively conclude that magnetism may modulate climate.

Pliocene-Pleistocene Boundary in Deep-Sea Sediments: Extinctions and evolutionary changes in microfossils clearly define the abrupt onset of the Pleistocene

For a hundred years students of the Pleistocene have looked for evidence of the climatic change which initiated the Pleistocene epoch. Glacial deposits on the continents have been of little help because of their discontinuity and because of the destructive effect of later glaciations. Hence, Pleistocene geologists have turned to the uplifted Pliocene-Pleistocene marine sediments of the Mediterranean region. In the absence of evidence of a single, clearly defined climatic change in this sedimentary section, they have agreed to define the beginning of the Pleistocene by the first appearance of Anomalina baltica, a species of benthic Foraminifera tolerant of cool water. This definition leaves much to be desired: It rests on a single benthic species whose areal distribution must have been partly determined by local conditions on the sea floor; it is useless outside of the Mediterranean region; and there is no convincing evidence that the first appearance of Anomalina baltica in the Mediterranean coincided with the onset of the first glaciation.

Correlation of six cores from the equatorial Atlantic and the Caribbean

Curves of late Pleistocene climatic variation based on vertical distribution of planktonic Foraminifera in six cores from the Equatorial Atlantic and Caribbean have been satisfactorily correlated. Variation in percentage of material coarser than 74 microns and variation in coiling direction of Globorotalia truncatulinoides have also been used in correlation. Such correlation is construed as evidence that the sediment sections in these cores have accumulated slowly, and without interruption by slumping or turbidity current deposition.

Micropaleontological and isotopic determinations of Pleistocene climates

Climatic curves derived from variations in planktonic foraminifera in three deep-sea cores are compared with isotopic temperature curves drawn by Emiliani on the basis of the same cores. There is close correlation in the upper part of the section, but increasing deviation downward. Micropaleontological and isotopic determinations of Pleistocene climates DAVID B. ERICSON AND GOESTA WOLLIN Lamont Geological Observatory Columbia University Palisades, New York

Further evidence for a turbidity current following the 1929 Grand banks earthquake

Abstract Evidence has been obtained indicating that the uppermost layer of sediment of the abyssal plain south of the Grand Banks consists of silt and sand. The top layers of two piston sediment cores consist of 130 and 70 cm of graded silt and sand overlying foraminiferal clay of abyssal facies. Recent deposition of these graded layers is indicated by absence of abyssal sediment overlying them. At three additional coring stations nothing but a few grains of sand was obtained. The existence of this silt and sand layer constitutes a further line of evidence in support of the hypothesis of Heezen and Ewing (1952) that slumps initiated by the 1929 Grand Banks earthquake were transformed into a turbidity current which swept down slope, broke and carried away the submarine telegraph cables, destroyed bottom life and deposited a large quantity of sediments far out into the ocean basin. The thickness of the graded silt and sand layers in the cores is near to the 40–100 cm thickness predicted by Kuenen (1952). The existence of the layers of silt and sand is also further evidence for the hypothesis that the abyssal plains with their flat gently sloping surface were formed by ponded or otherwise spent turbidity currents.

Climatic changes, magnetic intensity variations and fluctuations of the eccentricity of the earth's orbit during the past 2,000,000 years and a mechanism which may be responsible for the relationship

Abstract Our investigation of deep-sea climatic and magnetic records showing that high eccentricity of the earths orbit, low magnetic field intensity and warm climate occur together indicates the relative importance of eccentricity as perhaps the phenomenon which has most consistently modulated both climate and magnetism for at least the past 2,000,000 years. A speculative hypothesis regarding the mechanism which may be responsible for a relationship between the eccentricity of the earths orbit, geomagnetism, and climate is suggested.

Turbidity Currents and Sediments in North Atlantic

During the past 4 years a large collection of deep-sea cores from the North Atlantic has been brought together at the Lamont Geological Observatory. These cores show that during Pleistocene and Recent time large quantities of sediment of shallow-water origin have been deposited in the deep basins of the North Atlantic. It is inferred that turbidity currents are responsible for the transportation of this material. The effect of such a depression-filling process upon the regional topography is discussed. The effectiveness of turbidity currents as agents of erosion is considered, and it is concluded that erosion by turbidity currents is sufficient to explain the origin of the Hudson Submarine Canyon. In support of the discussion the paper is followed by a list of some of the most important cores, with short lithologic descriptions.

Geophysical and geological investigations in the Gulf of Mexico, Part 1

In 1953 the research vessels VEMA and ATLANTIS spent about three weeks in the Gulf of Mexico. Coring, seismic refraction, and topographic studies were undertaken. The topography in the various physiographic provinces is illustrated by reproductions of precision depth records from the continental shelf, continental slope, continental rise, and abyssal plain areas.Many sediment cores longer than 30 ft were taken in the Gulf. An abrupt change separates approximately three feet of Recent sediments from Wisconsin in all cores taken in depths greater than 1700 fathoms. This change is very similar to one found in many Atlantic and Caribbean cores indicating an abrupt termination of the Wisconsin glacial epoch. Abundant evidence of turbidity current deposition was found in all cores from the abyssal plain and the continental rise. Deposition of sediments in the unusually rough and broad continental slope area is apparently very rapid in the depressions and very slow on the elevations.The seismic results point to the southern half of the Gulf of Mexico as a typical oceanic area, modified by an increased load of sediments. A profound change near the continental slope is required for connecting this structure to typical continental structures.