An understanding of turbidite depositional systems is important for both geologic reconstructions of ancient margins and for exploration in clastic deep-water basins. In the last 10 yr, ancient turbidites have been interpreted in terms of modern depositional settings such as submarine fans, slope basins, trenches, and basin plains. However, the lack of common ground between models for modern and ancient turbidite deposits has resulted in a nonuniform application of models, facies distinctions, morphologic criteria, and depositional processes. As a consequence, most ancient turbidite systems are still difficult to frame within models derived from modern settings.

Ancient turbidite systems display a variety of sedimentary patterns. Most commonly, these systems consist of channel-fill sediments that are replaced in a downcurrent direction by nonchannelized deposits. Despite this common overall pattern, turbidite depositional systems differ considerably in terms of size, types of facies and facies associations, and geometry and distribution of sandstone bodies. The volume of gravity flows appears to be the main factor in controlling the distribution pattern of sandstone facies within each system.

Substantial accumulations of turbidite sandstone facies are invariably related to periods of lowstand of sea level and are common in those basins where slope instability is enhanced by tectonic uplift. Most predominantly fine-grained systems, and particularly channel-levee complexes, are conversely deposited during periods of highstand and are generally associated with active seaward progradation of deltas on adjacent shelves.

End_of_Article - Last_Page 1837------------