Modelling the architecture of distal sand-rich lobe deposits : an example from Fan 2, Skoorsteenberg Formation, Tanqua Karoo, South Africa
Thesis (MSc (Earth Sciences))—University of Stellenbosch, 2009.
Fan 2, one of five submarine fan systems of the Tanqua fan complex in the south-western Karoo Basin, South Africa, is subdivided into Lower, Middle and Upper units. Here, detailed analysis of the internal architecture and distribution of lithofacies associations of Middle Fan 2 facilitated the 3-D visualisation of the sedimentological and stratigraphical changes towards the pinch-out. Middle Fan 2 is interpreted to be a lower-fan, sand-rich terminal lobe, comprising three sandstone-lobe elements, separated by two siltstone interlobe elements. It is fed by a distributary channel that is hypothetically positioned to the west-southwest of the study area. The sandstone-lobe elements pinch out downdip to the north-east and updip to the southsouthwest in the study area. The consecutive pinch out of lobe elements to the north-east indicates a progradational stacking pattern similar to the entire lobe complex. Palaeocurrent analysis and the interpretation of isopach maps indicate that the transport direction of Middle Fan 2 was in a north-easterly direction. The fringes of the lobe and the distribution of internal elements (channels, amalgamated sheets and sheets) show a finger-like geometry in plan-view, in contrast to simple radial-lobe bodies that are commonly envisaged.