Ice margin influence on glaciomarine sedimentation in the Permo—Carboniferous Dwyka Formation from the southwestern Karoo, South Africa

Abstract

A persistent sedimentary unit, interbedded in massive diamictite over a distance of almost 400 km near the top of the PermwCarboniferous Dwyka Formation in the southwestern Karoo, consists of stratified diamictite, rhythmite, lonestone argillite and black shale. The stratified diamictite facies association is interpreted as ice-marginal debris-flow, the diamictite-lonestone argillite facies association as proximal to intermediate debris-flow, debris rain and suspension settling, and the shale-diamictite facies association as distal debris-flow and suspension settling deposits. An analysis of the mudrock and diamictite facies relationships suggests deposition from a rapidly calving oscillating ice margin in the east and at a consistently retreating grounded ice margin with few icebergs in the west. Sediment sources, volume of ice rafting, resedimentation processes, ice marginal recession and advance, and configuration of the ice margin influenced the distribution of debris-flow deposits and bergstone mud in the east and resulted in a nearrandom facies arrangement. Due to a lack of icebergs in the west, debris-flow deposits and bergstone mud were poorly developed which reduced the number of facies transitions and variation, resulting in a more systematic upward-fining sequence.

Depositional environments of the lower Permian Dwyka diamictite and Prince Albert shale inferred from the geochemistry of early diagenetic concretions, southwest Karoo Basin, South Africa

“…locally modified by sediment gravity flows (Visser and Loock, 1987;Visser, 1989Visser, , 1994a. The DS4 diamictites have higher carbonate contents than the older Dwyka diamictites and include a number of carbonate concretions.…”

“…1. Map showing the extent of the Dwyka Group in the southwest Karoo Basin, South Africa, and the location of the study area in the vicinity of Matjiesfontein after Visser and Loock (1987).…”

Arenitos Lapa-Vila Velha: Um Modelo De Trato De Sistemas Subaquosos Canal-Lobos Sob Influência Glacial, Grupo Itararé (C-P), Bacia Do Paraná

“…Estudos recentes mostram que as plataformas continentais bordejando terrenos glaciais são os mais importantes repositórios de sedimentos glacigênicos (Anderson 1983, Eyles et al 1985, Eyles 1988). Os sedimentos de plataformas rasas têm excelente potencial de preservação e, provavelmente, formam a maior parte das fácies glacigênicas preservadas no registro geológico (Visser & Loock, 1987;Eyles, 1988;Visser, 1991;e Eyles, 1993).…”

Modes of Sedimentation and Glaciological Aspects of the Permo-Carboniferous Dwyka Group in the Elandsvlei - Elandsdrif Area, South Africa

“…Stratten, 1968), was shown to be westwards. Visser and co-workers, subsequently, published on aspects of the Dwyka glacials including the Elandsvlei and Elandsdrif (Die Mond) areas (inter alia: Loock (1982 and1987), Hall (1984 and1985)). Later publications by Visser and co-workers ((Visser (1994), Visser et al (1997), Visser 1997) stress the idea that the full Dwyka Group, including the massive diamictites, is the product of deglaciation.…”