Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A 60-Kilometer-Long Architectural Transition from Slope Valley to Terminal Lobe: Unit C, Fort Brown Formation, Karoo Basin, South Africa
(1) University of Liverpool, Liverpool, United Kingdom.
(2) University of Camerino, Camerino, Italy.
The Permian Karoo Basin provides a rare opportunity to study an ancient continental margin from deepwater to terrestrial reservoir analogues via seismic-scale continuous outcrops along the limbs of W-E trending post-depositional folds. A depositional dip time window of deposits from mid slope (channel-levee complexes) to distal basin floor (terminal lobe) is provided by Unit C of the Fort Brown Formation. Unit C has been analysed over some 1000 km2 through the measurement of more than 400 detailed sedimentary logs compiled into detailed correlation panels and the construction of sub-unit isopach and sedimentary facies maps. Regionally mapped mudstones within Unit C permit a threefold stratigraphic division (C1, C2 and C3), describing phases of initiation, growth, and retreat of the system. At Unit C time sediment was input to the Karoo Basin through at least two main point sources located to the south. The most significant delivery system is marked by a 4 km wide entrenched slope valley bounded by external levee deposits (C-D ridge). A second axial system is inferred farther to the east based on thickness, sedimentary facies, and palaeocurrent distributions. Down dip the axial systems divide into a series of channel complexes which continue down dip to feed an extensive sand-prone distributive lobe system. Sediment dispersal was to the NE and E, leading to a downdip merging of distributive lobes fed by adjacent supply systems.
Work conducted on Unit C helps bridge the gap between the scale provided by seismic data sets and the detail gained through outcrop work. The dataset provides an exploration scale insight into the distribution of facies associations and depositional environments of an entire slope to basin-floor system.