AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Exploration Scale Analysis of Down Dip and Across Slope Stratigraphic Variations in a Multiple Feeder Deepwater System, Karoo Basin, South Africa
(1) University of Liverpool, Liverpool, United Kingdom.
Modern advances in subsurface imaging have provided high-resolution views of the submerged continental margins, furthering our understanding of the evolutionary stages of submarine slope systems and their architecture. In detail, however, a high level of architectural complexity remains difficult to assess with conventional seismic data. Outcrop analogues can help to improve characterisation of these architectural elements, although multiple exposures at seismic scale through the same stratigraphic unit are rare.
A rare outcrop example of a line sourced slope feeder system that can be mapped and correlated in multiple cross-sections is presented from the Permian Fort Brown Formation, South Africa. Sand-prone units B, C, and D, and subordinate units are continuously exposed along WNW-ESE trending ridges. This enables a detailed understanding of the spatial and temporal pattern of sand supply to the slope along a strike length of >100 km and dip length of >40 km. The depositional architecture is complex, but shows a strong paleocurrent trend to the NE. The multiple sources exert an important predictable control on seal geometries and the distribution of sedimentary facies and architectural elements at reservoir scale.
This regional study also provides an opportunity to describe in detail the changing nature of individual depositional sequences from up-dip entrenched channels to mixed erosional-constructional channel-levee- to distributive lobe system at a similar scale to exploration targets in many ancient subsurface slope systems (e.g. offshore West Africa). This will help in the understanding of how different segments of the slope evolved over time in terms of gradient and morphology, and hence the degree to which sand was stored or bypassed to the basin floor.