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Martin Grecula1, Peter Sixsmith1, Graham Potts1, Stephen Flint1, DeVille Wickens2
(1) University of Liverpool, Liverpool, United Kingdom
(2) University of Stellenbosch, South Africa

Abstract: Influence of the punctuated growth of basinal structures on the stacking patterns of basin floor and slope turbidite fans: Laingsburg Formation, Karoo Basin, South Africa

The Laingsburg sub-basin is a part of the Karoo retro-arc foreland basin. Initial deposition during the Permian recorded early Cape Fold Belt (CFB) tectonism. CFB deformation led to the creation of several basin floor highs prior to and during deposition of the Laingsburg Formation, an 800 m thick succession of six turbidite fans, A-F. The fans represent a gradual evolution from basin floor to slope setting. Fan A comprises seven sub-units separated by condensed intervals. Along depositional strike, sand bodies are observed to onlap a structural high, the Hexrivier antiform, which is interpreted to have been growing during turbidite deposition. This high generated enough elevation to cause slump zones 30 m thick and ~7 km long and also inhibited the transport of sand northwards. There is no evidence of the active fold growth during the sedimentation of fan B. However, routing of the initial channels and the overall extent of channelised elements was affected by residual topography. Deposition of the overlying fans C-F experienced renewed fold growth causing creation of localised depocentres and highly discontinuous, laterally very variable character of the systems. Paleocurrent analysis has identified saddles in the highs, reflecting changing plunges of the growth folds. These syn-depositional lows allowed the northerly flow of turbidity currents across the east-west trending structures in specific locations. High-resolution structural and stratigraphic reconstruction of the systems enabled better understanding of the influence of syn-sedimentary fold activity on the patterns of turbidite deposition.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana