Linking Intra-Channel to Extra-Channel Facies through Contrasting Styles of Channel Margin in Deepwater Slope Systems, Karoo Basin, South Africa

Rufus L. Brunt, David. M. Hodgson, John. P. Kavanagh, Chris J. Haigh, Jamie K. Pringle, and Stephen S. Flint
University of Liverpool, Liverpool, United Kingdom

Permian deepwater submarine slope channel complexes and spatially adjacent layered sheet deposits are well exposed in the Laingsburg depocenter and represent a range of lower to upper slope profile positions. The 50 meter thick mid-slope Unit C interval, exposed at the perimeter of Laingsburg garbage dump includes most of a channel complex, concentrated within the lower 30 meters of the unit, along a 720 meter east – west trending ridge, oriented sub-perpendicular to the palaeoflow direction. A total of 62 measured sections were collected through the channelised section at approximately 10 meter intervals. Every bed was walked out between logs and complemented by LIDAR scans. A correlation panel built from the measured sections enabled a detailed investigation to be conducted on bed spatial distribution and thickness variation on an individual and package scale. Synthesis of the data has identified five channels within the complex, which have been categorised into three styles of margin and fill: (1) Erosional margin with mud fill. A clear incisional relationship is displayed between margin and channel fill. The channel is passively filled with mud and may represent a phase of abandonment; (2) Erosional margin with sandstone/ heterolith fill. An incisional relationship is displayed between margin and channel fill. Channel is actively filled and shows evidence of sediment bypass; (3) Transitional margin with sandstone/ heterolithic fill and rapid thinning and fining of sandstone beds against a shallow channel margin. Individual beds may be traced over tens of meters from the channel axial region into overbank areas.