M.Sc. / The sedimentary succession of the Paleoproterozoic Pretoria Group is very important for understanding Earth’s ancient history. It represents a time of extreme environmental changes on Earth, from global ice-ages to hot-houses. However, the genetic stratigraphy of the succession is poorly understood so that the stratigraphic relationships between the events remain uncertain. This dissertation provides a genetic stratigraphic model of the succession by utilising an integrated sedimentological and geochemical approach which culminates in a new sequence stratigraphic subdivision of the Pretoria Group. The study focuses on the Potchefstroom area in the western part of the Transvaal depository. The Pretoria Group commences with the Rooihoogte Formation which overlies the Chuniespoort Group with erosional contact. New stratigraphic data indicates that the Rooihoogte Formation is a correlative of the Duitschland Formation in the eastern Transvaal. The succession was deposited in a foreland basin. An important new finding is that a diamictite at the base of the formation contains striated and bull-nosed pebbles and is of glacial origin. The discordantly overlying Timeball Hill Formation is composed of a coarsening upward carbonaceous shale – hematite oolite-bearing quartzite unit overlain by a second carbonaceous shale, capped by a second glacial diamictite (the well known Rietfonteindam diamictite). The oolitic ironstones in the quartzites suggest that they formed in a warm oxidizing environment. The shales display mature chemical indices of alteration which supports this theory. ä13Corganic values increase from –35‰ to –24‰ from the bottom to the top of the Timeball Hill Formation indicating net carbon burial, which translate to a decrease in atmospheric CO2 and colder climates as deposition evolved. In turn this can be linked to the presence of the glacial Rietfonteindam diamictite in the upper part of the Timeball Hill Formation. The Rietfonteindam diamictite is overlain by conglomerate, quartzite and shale of the Boshoek Formation, which were deposited as an upwards fining transgressive sedimentary unit following on post-glacial eustatic sea-level rise. It is in turn overlain by the 2.22Ga. Hekpoort basalt. This basalt is metasomatically altered, but has remained virtually unaffected by regional metamorphism, as shown by detailed SEM petrographic analyses. Excellent examples of zeolite- filled amygdales are preserved in the lavas. The Hekpoort lavas are overlain by fluvial red beds of the Dwaalheuwel Formation. A lateritic paleosol (Hekpoort paleosol) is developed below the red bed succession. The red beds are overlain with sharp gradational contact by the carbonaceous shelf mudstone of the Strubenskop Formation which grades up into the shallow marine Daspoort quartzite. The Silverton Formation, mainly composed of carbonaceous shale, overlies the Daspoort Formation with sharp gradational contact and grades upwards into shallow marine Magaliesberg quartzite. ä13Corganic values decrease from –25‰ to –29‰, from middle to top of the Silverton Formation, most probably indicating carbon input into the atmosphere and therefore rising atmospheric temperature. The Machadodorp lava, which was previously thought to be restricted to the eastern part of the Transvaal basin, was found to be present in the Potchefstroom area as well. Five unconformity-bounded sequences are present in the succession. Estimates are that they were deposited in time intervals of 60m.y. each.

This thesis examines the geology of the Daspoort Formation (Pretoria Group, Transvaal Supergroup) of South Africa, with the accent on describing and interpreting its sedimentology. The Palaeoproterozoic Daspoort Formation (c. 2.1‐2.2 Ga) forms part of the Pretoria Group on the Kaapvaal craton. This sandstone‐ and quartzite‐dominated lithological formation covers an elliptical geographical area stretching from the Botswana border in the west to the Drakensberg escarpment in the east, with its northern limit in the Mokopane (Potgietersrus) area and Pretoria in the south; altered outliers are also found in the overturned units of the Vredefort dome in the Potchefstroom area. Deposition of the Daspoort Formation was in a postulated intracratonic basin which applies equally to the entire Transvaal Supergroup succession in the Transvaal depository. Various characteristics from the formation, such as sedimentary architectural elements (e.g., channel–fills etc.), maturity trends and distribution of lithofacies assemblages across the preserved basin give insight into the developing conditions during deposition and genesis of the Daspoort Formation. Subordinate evidence from basic geochemistry, ripple mark data and optical microscope petrology studies support the sedimentary setting inferred for this Palaeoproterozoic deposit. Fluvial and epeiric marine conditions prevailed during the deposition of the Daspoort clastic sediments into the intracratonic basin. This shallow epeiric sea was fed by fluvial influx, predominantly from the west when a transgressive regional systems tract led to the filling of the basin, evolving into the deeper marine Silverton Formation setting, laid down above the Daspoort. Transgression from the east (marine facies predominate) to the west (fluvial facies) is supported by cyclical trends, palaeoenvironmental and palaeogeographical interpretations. Accompanying poorly preserved microbial mat features contribute to the postulated shallow marine environment envisaged for the eastern part of the basin whereas ripple marks and grain size distribution support a fluvial setting for the west, with lithofacies assemblages accounting for both areas’ depositional interpretation. / Dissertation (MSc)--University of Pretoria, 2013. / tm2014 / Geology / Unrestricted