Abstract

Acoustic 3.5-kHz records from the Ontong-Java Plateau indicate that calcareous sediments in shallow-water areas (< 2,800 m) are characterized by a strong surface reflection. Uppermost calcarious sediments in intermediate water depths (2,800 to 5,000 m) show numerous closely spaced reflectors, whereas such sediments in great water depths (> 5,000 m) typically show an acoustically transparent layer. The levels at which these transitions occur roughly correlate with the present lysocline and the calcite compensation depth, which correspond to water depths at which the facies of the surface sediments changes markedly. Such facies boundaries can migrate rapidly through large depth intervals in response to changes in the rate of calcite dissolution (dissolution cycles). One might expect that a migration of facies boundaries could precondition concurrently deposited calcareous sediments for making reflectors after burial. However, this simple hypothesis cannot explain all the observations, and several alternatives need to be tested.

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