Stratigraphic and Temporal Distribution of Submarine Levee Crevasse Deposits

The traditional model of a distributive deepwater system depicts a lobe fed by a genetically related channel, where down dip lengthening of the channel can lead to the accumulation of characteristic thinning and fining upward external levee successions directly above lobe deposits. However, discontinuous thick-bedded lobe-like sandstone units are encountered as isolated bodies within the extensive external levee units of the Fort Brown Formation, Karoo Basin, South Africa. These bodies are interpreted to have been deposited as crevasse splays by rapidly expanding and decelerating flows that breached the levee crest. The crevasse splay deposits are up to a kilometre in width and a few meters in thickness, often thickening slightly away from the source channel. Typically they are associated with accumulations of slumped levee, but are dominated by rapidly deposited sandstones and sand rich debrites resulting in a deposit that is higher net-to-gross than the host levee. Spatial and stratigraphic relationships drawn from outcrop data suggest that crevasse events occurred preferentially in the more distal parts of the channel-levee system and more frequently late in the constructional history of the levee. Partial infill of relatively low-relief channels during system retreat may cause this as effective confinement to flow is reduced increasing the likelihood of levee breaching. However, if supply to the levee breach is maintained, an erosively confined crevasse channel may develop, exploiting the gradient of the levee surface and open slope accommodation space.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California