A LATE CARBONIFEROUS SUBAQUEOUS GLACIAL VALLEY FILL COMPLEX - FLUCTUATIONS IN MELTWATER OUTPUT AND SEDIMENT FLUX

An exhumed glacial valley northeast of Nieuwoudtville contains three t hinly stacked sequences, attaining a combined thickness of about 40 m, at the base of the glacigene Dwyka Group. Sequence 1, which overlies the basement unconformably, consists of stacked, massive debris-flow d iamictites, sequence 2 comprises a mudrock-stratified diamictite facie s with large dropstones, and sequence 3 consists of a conglomerate and sandstone facies up-valley and a diamictite-sandstone and sandstone f acies down-valley, with an erosional basal contact. Sequence 3 is conf ormably overlain by about 200 m of massive diamictite overlapping onto bedrock highs. These sequences, together with the massive diamictite, constitute four depositional phases in a subaqueous setting, beginnin g with valley floor resedimentation of debris cones at the ice margin (phase A), overlain by blanket-like deposits of suspension mud (phase B), and prograding to the formation of a steeply sloped outwash delta subjected to gravitational failure of the delta front beds during phas e C. Phases A to C represent a progressive change to a warmer climate, an increase in meltwater output and sediment flux, and accelerated ic e margin retreat. A subsequent change to colder conditions is shown by the readvance of the ice margin and diamicton deposition during phase D. As sedimentation involved mainly the infilling of a shallow glacia lly-incised valley, the principal controlling factor was the variation in meltwater flux.