Abstract

Detailed geological and geophysical studies conducted within a 300 km2 region of the equatorial Pacific (near 07°40′ N., 134°00′ W.), using the deep-towed instrumentation of the Marine Physical Laboratory. Closely spaced sediment cores and near-bottom reflection profiles show a sharp angular unconformity which separates a thin upper layer of Holocene sediment from a chalk bed of Tertiary age. This unconformity is interpreted as a Pleistocene erosion surface which truncates sediments ranging in age from late Eocene to middle Miocene. Bottom currents have evidently eroded and redistributed sediments tens to hundreds of meters in thickness.

Bottom-current measurements in the surveyed area indicate that present current speeds are generally less than 10 cm/sec. It appears likely, therefore, that significant erosion is not taking place today but was perhaps restricted to the glacial stages of the Pleistocene. A schematic model is proposed to suggest how climatic and oceanographic processes may be modified in response to glaciation, and how these processes may interact to create conditions on the sea floor which favor increased sediment erosion and redistribution during glacial stages.

Some of the missing sediment has evidently been redeposited into local topographic depressions. An enclosed basin measuring approximately 15 km × 25 km near the study area contains sediments which are twice as thick as those in the surrounding region. Such sites with anomalously thick accumulations of sediment, however, appear to be relatively rare in the equatorial Pacific. It may be that a substantial fraction of the eroded sediment must be accounted for by chemical dissolution.

The results of this study are comparable with observations obtained in widely separated regions in the central Pacific, suggesting that some of the processes responsible for erosion within this area may have affected a substantial portion of the Pacific Ocean floor.

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