John McGregor Stewart

Seven sediment cores, ranging in length from 90 to 1290 cm, were collected from sediment filled valleys of the Mid-Atlantic Ridge at 45^oN. The valleys are located from 55 to 110 km west of the Median Valley, in an area where ridge and basin topography of up to 1500 m relief exists. The cores were sampled at 10 cm intervals and the samples sieve-separated into +62 micron and -62 micron fractions. The carbonate content of the -62 micron fraction was determined. The percentage of Foraminifera and the distribution of temperature sensitive Foraminifera in the +62 micron fraction was determined. The cored strata which are widely correlative in the area of study, represent the glacial/interglacial climatic sequence of the Late Pleistocene. Glacial marine sediments in the cores are typified by a relatively low carbonate content (a high clay content), a cool water faunal assemblage and an abundance of ice-rafted sand and gravel. The interglacial sediments are typified by a high carbonate content (low clay content), warm water fauna and an absence of ice-rafted detritus. Isotopic dates at several points in the cores were obtained and indicate that the oldest penetrated strata are Sangamon in age. The succession was compared with the Late Pleistocene time scale of glacial and interglacial events and significant correlation found between the established time/temperature scale of the Wisconsin and Late Sangamon periods, and the climatic sequence in the cores. Correlation of the stratigraphic sequence encountered in the cores was substantiated within individual basins, where two or more cores were retrieved, and between separate basins. Since individual strata are correlative from basin to basin and are very similar in thickness regionally, and since strata possessing the sedimentary characteristics of turbidites are rare, it is concluded that particle-by-particle sedimentation is the dominant mode of sediment accumulation.

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Pages:180
Supervisors: M. J. Keen / R. A. Gees