Depositional Patterns, Sequence Stratigraphy and Reservoir Development from a Progradational Deepwater Basin Margin: Karoo Basin, South Africa
A 450 m thick succession containing five 8-100 m thick sand-prone units intercalated with 18-110 m thick hemipelagic claystone units is exposed over 400 km2 in the upper Permian Laingsburg and Fort Brown Formations, Karoo Basin, South Africa. The succession overlies a well documented 800 m thick basin floor fan to middle slope succession and is exposed on the flanks of post-depositional synclines and anticlines providing 20 km of depositional dip and 20 km of strike control. The sandstone units are referred to as Units D/E, E, F, G and H in stratigraphic order. Units E, F and G are each divided into three regionally mappable sub-units, separated by regional “intra-unit” claystones and siltstone units. From base of D/E to base of H each Unit and overlying regional claystone is interpreted as a composite sequence that is composed of a set of 3 sequences (apart from D/E). These composite sequences are arranged in an organised progradational stacking pattern with basal sand-rich intraslope lobes through slope channel-levee systems to a 120 m deep entrenched valley with low net-to-gross fill from D/E to F. The overlying succession to the base of H is dominated by hemipelagic deposition. The architecture, facies associations and depositional pattern of the sandstone complexes from base of D/E to base of H is consistent with a major period of relative sea level fall, lowstand and rise, therefore this succession is interpreted as lowstand (early, middle and late) and transgressive system tracts of a composite sequence set within the 1.25 km thick deepwater to shelf Laingsburg supersequence. Progradational development of the basin margin was achieved in a series of multi-scale increments of slope accretion with reservoir development related to predictable architectural styles of slope deposition.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009