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ABSTRACT: Eustatic, Volcanic, and Tectonic Contols on Redeposition of Shallow-Water Carbonate: A Reanalysis of Pacific DSDP Examples

James F. Dolan

On the basis of comparisons between eustatic sea level curves and occurrences of displaced shallow marine carbonate sediment in deep-water Pacific DSDP (Deep Sea Drilling Project) cores, several previous workers have proposed that most displaced neritic carbonate is redeposited in the deep sea during eustatic sea level lowstands in a manner similar to siliciclastic sediment. However, reanalysis of these same DSDP data indicates a much more complex set of controls on redeposition, including eustatic, volcanic, and tectonic effects. Of the 43 occurrences identified in 20 DSDP sites, eight (including all occurrences of true allodapic calcarenites) were deposited either during eustatic highstands or immediately after cessation of island-building volcanism; establishment of a hallow-water source area probably represents the dominant control on this type of deposition. Twenty-three other occurrences contain volcanic detritus mixed with minor amounts of reworked carbonate. Of these occurrences eight contain volcaniclastic sediment and exhibit no clear corellation with sea level, indicating probable redeposition of shelf carbonate during volcanic events as a result of either gravitational or seismic instability of the shelf. In contrast, the 15 other mixed volcanic/carbonate occurrences represent lowstand deposits and contain epiclastic volcanic detritus, suggesting lowstand erosion of mixed volcanic/carbonate shelf sediments. Five other lowstand occurrences contain only reworked carbonate sediment and probably record either continued outer shelf/slope lowstand arbonate deposition or minor mechanical erosion of shelf carbonate. Six occurrences contain only reworked Inoceramus fragments, which are not necessarily indicative of a shelf source area.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990