AAPG Bulletin, V. 82 (1998), No. 4 (April 1998), P. 569-595.

Siliciclastic Slope and Base-of-Slope Depositional Systems: Component Facies, Stratigraphic Architecture, and Classification¹

W. E. Galloway²

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received January 19, 1996; revised manuscript received January 27, 1997; final acceptance October 22, 1997.
²Department of Geological Sciences C1100, University of Texas at Austin, Austin, Texas 78712.

The synthesis and many of the figures in this paper evolved during successive presentations of a short course sponsored by AAPG during the past five years, and then in the publication of the second edition of Terrigenous Clastic Depositional Systems (Copyright 1996, Springer-Verlag). I am indebted to the geologists who reviewed that draft chapter on slope and base-of-slope deposits: John Damuth, Hans Nelson, and William Ross. Suzanne O’Connell, Glen Caytley, and an anonymous reviewer provided useful critique and improved the use of terminology in the draft of this paper. The figures were drafted by Patrice Porter and Jeff Horowitz. Amanda Masterson edited the manuscript and prepared the references cited. 

ABSTRACT

Subaqueous slope and base-of-slope depositional systems are a major component of most marine and many lacustrine basin fills, and constitute primary targets for hydrocarbon exploration and development. Seven basic facies building blocks comprise slope systems: (1) turbidite channel fills, (2) turbidite lobes, (3) sheet turbidites, (4) slide, slump, and debris-flow sheets, lobes, and tongues, (5) fine-grained turbidite fills and sheets, (6) contourite drifts, and (7) hemipelagic drapes and fills. The grain size of supplied sediment is a primary control on channel and lobe morphologies and on the scale and importance of slump and debris-flow deposits. Two general families of siliciclastic slope systems occur. Constructional (allochthonous) systems, including fans, aprons, and basin-floor channels, are built of sediment supplied from superjacent delta, shore-zone, shelf, or glacial systems. The facies architecture of allochthonous systems is determined jointly by the sediment texture and pattern of supply to the shelf margin. Point sources of supply create fans; line sources create strike-elongate prisms of slope sediment called slope aprons. Shelf-margin deltas provide a particularly common intermediate source geometry, forming offlapping delta-fed aprons. Autochthonous systems, including retrogressive aprons, canyon fills, and megaslump complexes, record slope reworking and resedimentation.