Abstract

The upper, and sometimes lower, boundaries of deep-sea disconformities, recognized as sedimentary hiatuses at ocean drilling sites, are shown to be diachronous. The age-depth relationships of these hiatuses are used, in conjunction with the geographical location of sites relative to individual water masses, in order to explain the formation of hiatuses as the product of interaction between fluctuating oceanic water masses and the sea floor. The fluctuations in the water masses are related to the glacial history of Antarctica. The method used is a departure from a traditional approach in which deep-sea hiatuses were considered to have no diachronous component and were viewed as the products of instantaneous regional or global events.

Sedimentary hiatuses have commonly been identified in deep sea cores recovered by the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP). The disconformity associated with a hiatus has three components: firstly, an upper boundary which represents a point in time when sedimentation recommenced; secondly, a lower boundary that is the product of either erosion (i.e. of no temporal significance), or non-deposition (i.e. of potential temporal significance); and thirdly, the time interval between these two boundaries (termed intra-hiatus in this paper). Earlier studies of hiatuses and hiatus-forming events have been used to infer the influence of climatic (e.g. Keller & Barron 1987) and/or tectonic (e.g. Watkins & Kennett 1972) changes on the development of erosive oceanic watermasses. Hiatus distributions have been interpreted as having ocean-wide (e.g. Davies et al. 1977; Keller & Barron 1987) or, even,

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