Turbidite Systems in Deep-Water Basin Margins Classified by Grain Size and Feeder System

Abstract

Depositional systems in deep-water basin margins can be classified on the basis of grain size and feeder system into 12 classes: mud-rich, mud/sand-rich, sand-rich, and gravel-rich point-source submarine fans; mud-rich, mud/sand-rich, sand-rich, and gravel-rich multiple-source submarine ramps; and mud-rich, mud/sand-rich, sand-rich, and gravel-rich linear-source slope aprons. The size and stability of channels and the organization of the depositional sequences decreases toward a linear source as does the length:width ratio of the system. As grain size increases, so does slope gradient, impersistence of channel systems, and tendency for channels to migrate. As grain size diminishes, there is an increase in the size of the source area, the size of the depositional sys em, the downcurrent length, the persistence and size of flows, fan channels, channel-levee systems, and in the tendency to meander and for major slumps and sheet sands to reach the lower fan and basin plain. The exact positioning of any one depositional system within the scheme cannot always be precise, and the position may be altered by changes in tectonics, climate, supply, and sea level. However, the models derived from each system are sufficiently different to significantly affect the nature of petroleum prospectivity and reservoir pattern. Understanding and recognizing this variability is crucial to all elements of the exploration-production chain. In exploration, initial evaluations of prospectivity and commerciality rely on the accurate stratigraphic prediction of reservoir facies architecture, and trapping styles. For field appraisal and reservoir development, a similar appreciation of variability aids reservoir description by capturing the distribution and architecture of reservoir and nonreservoir facies and their impact on reservoir delineation, reservoir behavior, and production performance.