High-constructive lobate deltas in the Lower Permian Vryheid Formation, Rietspruit, South Africa.

Sediments deposited by a high-constructive lobate delta are well exposed at Rietspruit coal mine in the southern Witbank Coalfield north of the Smithfield Ridge, Transvaal. Upward-coarsening cycles typify the interval between the No. 4 and 5 coal seams. Basal carbonaceous siltstone grades upward into interlaminated siltstone and sandstone, medium- to coarse-grained sandstone and, finally, coal which caps the sequence. A lower upward-coarsening cycle is overlain by two clastic wedges composed of asymptotically based, low-angled, giant foresets. The lower giant foresets erosively overlie strata below, while upper foresets are not erosively based but are tangentially interbedded with siltstone below. Coarse-grained to gravelly trough cross-bedded and flat-bedded sandstone terminates the sequence with basal scour surfaces eroding the underlying sandstone wedges. Prodelta siltstones grade vertically into distal bar deposits of interlaminated siltstone and sandstone which display steep depositional slopes. Sand dominated distributary mouth bar sediments overlie these distal bar deposits, and erosively based, coarse-grained, distributary channel sandstone and gravel end the sequence.-from Authors