--> Abstract: Cannibalisation of a Submarine Channel-Levee System by an Entrenched Submarine Channel System in the Laingsburg Depocentre, Ka; #90063 (2007)

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Cannibalisation of a Submarine Channel-Levee System by an Entrenched Submarine Channel System in the Laingsburg Depocentre, Karoo Basin, South Africa

 

Hodgson, David M.1, Rufus L. Brunt2, Claudio Di Celma1, Stephen Flint1, John. P. Kavanagh1 (1) University of Liverpool, Liverpool, United Kingdom (2) Liverpool University, Liverpool, United Kingdom

 

Kilometres-wide submarine slope channel systems are commonly imaged on seismic and modern datasets. Exposure quality commonly precludes the identification and detailed facies analysis of systems of this scale at outcrop. In the Laingsburg Depocentre, South Africa, however, two juxtaposed >2km-wide and >50m-thick slope channel systems have been identified. Sedimentary logs collected every 20m along a 4km strike transect have helped to document an older channel-levee system (Unit C) that was incised by a deeply entrenched channel system (Unit D).

 

At the axis of the Unit C channel system there is >30m of incision into mudstones. Adjacent thin-bedded and fine-grained deposits thin and fine away from the axis of the channel system, and are interpreted as 8km-wide constructional levees. Mapping and logging demonstrates that the Unit C system is cannibalised by the Unit D system. The fill of the >80m deep, asymmetric composite incision surface is dominated by thin-bedded low net:gross turbidites.

 

In both channel systems, older channel- and channel complex-fills contain slumps and basal mudstone clast conglomerates, whereas younger channel-fills are sand-prone and tabular. The majority of remnant erosion surfaces identified in Unit C and D display a westward stepping trend, such that the westernmost channel complexes represent the last phase of cut-and-fill. This study has led to the detailed assessment of the erosional and depositional history of two different but juxtaposed channel systems. The distribution of channel-fill facies will help to reduce uncertainties in slope channel reservoir exploration and production.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California