Modelling the architecture of distal sand-rich lobe deposits : an example from Fan 2, Skoorsteenberg Formation, Tanqua Karoo, South Africa

[摘要] Fan 2, one of five submarine fan systems of the Tanqua fan complex in thesouth-western Karoo Basin, South Africa, is subdivided into Lower, Middleand Upper units. Here, detailed analysis of the internal architecture anddistribution of lithofacies associations of Middle Fan 2 facilitated the 3-Dvisualisation of the sedimentological and stratigraphical changes towards thepinch-out.Middle Fan 2 is interpreted to be a lower-fan, sand-rich terminal lobe,comprising three sandstone-lobe elements, separated by two siltstone interlobeelements. It is fed by a distributary channel that is hypotheticallypositioned to the west-southwest of the study area. The sandstone-lobeelements pinch out downdip to the north-east and updip to the southsouthwestin the study area. The consecutive pinch out of lobe elements tothe north-east indicates a progradational stacking pattern similar to the entirelobe complex.Palaeocurrent analysis and the interpretation of isopach maps indicate thatthe transport direction of Middle Fan 2 was in a north-easterly direction. Thefringes of the lobe and the distribution of internal elements (channels,amalgamated sheets and sheets) show a finger-like geometry in plan-view, incontrast to simple radial-lobe bodies that are commonly envisaged.

[发布机构] Stellenbosch University