Sedimentology of the southern Karoo ripon formation and the southwestern Karoo Vischkuil/Laingsburg formations of the Ecca Group: implications for basin and palaeoenvironmental reconstruction

Walters, Schalk Willem (2017-12)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Between the towns of Prince Albert (Western Cape) and Willowmore (Eastern Cape) the well-known Laingsburg depocenter and less-known Ripon depocenter of the southern Main Karoo Basin (South Africa) meet and exhibit an interfingering relationship involving the Laingsburg and Vischkuil formations (Laingsburg depocenter) on the one side and the Ripon Formation (Ripon depocenter) on the other. Studies regarding the link between these two submarine fan-dominated depocenters have been avoided to date due to the complex sedimentology and stratigraphic relationships involved. New sedimentologic and stratigraphic analysis presented in this thesis suggests that the Ripon depocenter is much more widespread than initially suggested. Channelized sandstones in the Pluto’s Vale Member, as well as in the upper Wonderfontein Member, also suggest that up-dip feeders for the Ripon depocenter are more widespread than previously thought. Through detailed facies and architectural analysis, this study provides a basin reconstruction model, suggesting that the lower Vischkuil Formation is the distal equivalent of the lower Pluto’s Vale Member submarine fan complex. Sedimentary petrology, including sandstone petrology and U-Pb detrital zircon geochronology, indicates that the two depocenters have slightly different source regions. Specifically, sandstones of the Laingsburg depocenter are characterized by feldspathic litharenites, whereas sandstones from the Ripon depocenter are characterized as ultralithofeldspathic. Zircon ages indicate that submarine fan development in the Laingsburg depocenter only initiated after deposition of the Pluto’s Vale Member in the Ripon depocenter. The zircon populations and U/Th ratios further indicate that zircon grains were derived from South American as well as a source in the southwestern part of Antarctica, known as the Dyer arc.

AFRIKAANSE OPSOMMING: Tussen die dorpe Prince Albert (Wes-Kaap) en Willowmore (Oos-Kaap) ontmoet die welbekende Laingsburg subkom en die minderbekende Ripon subkom van die suidelike Hoof Karookom (Suid-Afrika) mekaar en toon ‘n oorvleulende verhouding tussen die Laingsburg en Vischkuil formasies (Laingsburg subkom) aan die een kant en die Ripon Formasie (Ripon subkom) aan die ander kant. Navorsing oor die verband tussen hierdie twee diep-mariene waaiergedomineerde subkomme is tot dusver vermy weens die komplekse sedimentologie en stratigrafiese verhoudings wat daarby betrokke is. In hierdie tesis word ‘n nuwe sedimentologiese en stratigrafiese analise aangebied wat bewys dat die Ripon subkom meer wydverspreid as wat oorspronklik gesuggereer is. Kanaalsandstene in die Pluto’s Vale Lid, sowel as in die hoër Wonderfontein Lid, suggereer ook dat die aanvoer sisteme van die Ripon subkom meer wydverspreid is as wat aanvanklik vermoed is. Deur middel van gedetailleerde fasies en argitektoniese analise bied hierdie studie ‘n kom-herkonstruksiemodel wat suggereer dat die laer Vischkuil Formasie die distale ekwivalent van die laer Pluto’s Vale Lid diep-water waaierkompleks is. Sedimentêre petrologie, insluitend sandsteenpetrologie en U-Pb detritale sirkoon geochronologie, dui daarop dat die brongebied van die twee subkomme effens van mekaar verskil. Dit word spesifiek aangedui deurdat sandsteenlae van die Laingsburg subkom deur veldspaatryke litiese areniet gekenmerk word, terwyl sandstene van die Ripon subkom deur ultra-hoë litiese en veldspaat eienskappe gekenmerk word. Sirkoon-ouderdomme dui ook daarop dat diep-water waaierontwikkeling in die Laingsburg subkom eers ontstaan het ná afsetting van die Pluto’s Vale Lid in die Ripon subkom. Die sirkoon-populasies en U/Th-verhoudings toon verder aan dat die sirkoon-korrels van Suid-Amerika afkomstig is, sowel as van ‘n bron bekend as die Dyer eilandboog in die suidweste van Antarktika.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102681
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