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Submarine slope systems: processes, products and prediction, 28-30th April 2003 University of Liverpool
R.C. King, S.S. Flint and G.J. Potts  Tectonic control on slope evolution, Karoo basin, Western Cape, South Africa.
Current work on the Cape Fold Belt (CFB) is investigating the interaction of the CFB oroclinal bend and associated Hexriverberge syntaxis with the evolution and formation of the Tanqua & Laingsburg sub-basin margins. A tectonic model is being developed to evaluate how the CFB and/or Hexriverberge syntaxis controls the sediment supply routes and sediment bypass to the sub-basins.
	The CFB is divided into two branches forming the oroclinal bend. The north-south striking Cederberge range forms the western margin of the Tanqua sub-basin while the east-west trending Swartberge forms the southern margin of the Laingsburg sub-basin. The two branches are structurally and geometrically different, the Cederberge contains south plunging folds with open, low-amplitude, parallel profiles and it exhibits a frontal monocline geometry. The Swartberge displays east plunging folds with box and chevron profiles that terminate northwards as a collection of kilometre scale folds. However, the two ranges are thought to be spatially and temporally synchronous. By modelling the variable end-member tectonic styles of the Cederberge (see figure, C), Swartberge and basin floor (see figure part A) it may be possible to develop an understanding of the topographical changes of shelf to basin floor slopes through time. Sequential restoration of present-day cross-sections will be used to understand the palaeotopography of the slope systems using palaeogradient to develop a further understanding the sedimentology of the slope successions. References Vann, I.R., Graham, R.H. and Hayward, A.B., (1986). The structure of mountain fronts. J. Struct. Geol., 8, pp 215-227.
R.J. Wild, S.S. Flint and D.M. Hodgson  Facies variation and stratigraphic evolution of a Permian siliciclastic submarine slope system, Tanqua sub-basin, Karoo, South Africa.
Ancient submarine slope systems commonly contain significant sandstone deposits within 'slope channels' and 'slope fans' and exhibit a range of erosional and depositional processes. The precise stratigraphic evolution of slope systems, which connect basin-floor fans to shelf feeder systems, is, however, poorly understood because modern continental margins provide a single snapshot in time and most ancient slope successions are incompletely exposed or tectonically deformed. The Karoo basin of South Africa provides extensive, largely undeformed exposures of a slope system and has allowed the investigation of facies variations in space and time, and how intraslope ponded accommodation alternated with periods of sediment bypass to the deeper basin. Fieldwork indicates that the nature of the 'slope' changed through time. The sand-rich Hangklip succession (stratigraphically older) exhibits abrupt vertical and lateral facies variations and architectural changes. Facies associations include thick-bedded, sharp-based sandstones (with common large-scale dewatering features) laterally associated with thin-bedded turbidites and channelised sandstones interbedded with mudstones. Locally, bed tops are re-worked and show increased bioturbation and soft-sediment deformation indicating abrupt palaeoenvironmental changes. The younger Koedoesberg succession displays pronounced high frequency cyclicity. Cycles (80m average) thicken and coarsen upwards through the >250m succession and comprise turbiditic claystone and siltstone interbeds overlain by medium to thick bedded sandstones with HCS and slumped horizons. The abrupt vertical changes in facies are more consistent with a ramp-apron margin geometry, in which moderately small changes in relative sea level produced significant shifts in depositional setting. Ongoing work is addressing the classification and characterisation of slope type and identification of the controlling factors on slope accretion and/or bypass and to develop a sequence stratigraphic model for evolution of the shelf-slope-basin profile.
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