--> ABSTRACT: Stratigraphic Distribution of Soft-Sediment Deformation Structures in Clinoform Successions of the Permian Ecca Group, Karoo Basin, South Africa, by Oliveira, Carlos M.; Hodgson, David M.; Flint, Stephen S.; #90135 (2011)

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Stratigraphic Distribution of Soft-Sediment Deformation Structures in Clinoform Successions of the Permian Ecca Group, Karoo Basin, South Africa

Oliveira, Carlos M.1; Hodgson, David M.2; Flint, Stephen S.2
(1)Exploration and Production, Petrobras S. A., Rio de Janeiro, Brazil. (2) School of Environmental Sciences, University of Liverpool, Liverpool, United Kingdom.

The stratigraphic distribution of two groups of soft-sediment deformation structures (SSDS) - detached (dominated by lateral movement forming slides and slump deposits, and debrites) and in situ (dominated by vertical movement forming flame structures, pseudonodules and ball-and-pillow structures) - are compared in two Permian successions in the Tanqua and Laingsburg depocentres of the Karoo Basin. SSDS occur in a series of well-exposed 40 to 55 m thick sedimentary cycles. Cycle thicknesses decrease upwards and the proportion of deformed strata is around 30% in both successions. Each flooding surface-bounded cycle is characterized by a lower unit dominated by thin-bedded turbidites, overlain by an intermediate section dominated by soft-sediment deformed facies, above which are undeformed thick-bedded mouthbar and shoreface sandstones. The upper part of each cycle fines upwards into thin-bedded turbidites, which are overlain by the cycle-bounding flooding surface. The cycles, and the distribution of SSDS, are the response to delta outbuilding and retreat over a clinoform rollover, dominated by in situ SSDS, and onto a clinoform slope, dominated by detached SSDS; in a low gradient and relatively low sediment supply basin margin, without growth faulting. Repeatable trends in the distribution of SSDS during the evolution of clinoforms in both depocentres indicate a level of stratigraphic organisation and predictability in the otherwise complicated record of processes around the clinoform rollover.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.