Stratigraphic interrelationships, sedimentology and post Karoo intrusions in the Katberg and Burgersdorp formations around the town of Whittlesea, Eastern Cape province, South Africa

Concentrating on the Katberg and Burgersdorp Formations, this research examined the sedimentary environments inter alia by conducting heavy mineral analysis, interpreting provenance and determining stratigraphic interrelationships of the two formations in the Tarkastad Subgroup (Beaufort Group, Karoo Supergroup) around the town of Whittlesea in the Eastern Cape Province of South Africa. It has been observed that the strata of the Katberg Formation are dominated by sandstones of a braided river system. On the other hand, the Burgersdorp Formation comprises mainly dark greyish-red mudstone, red shale with subordinate siltstone and red sandstone deposited on floodplains and channels of meandering rivers. The Katberg Formation becomes progressively less arenaceous to the north of the study area until it is virtually indistinguishable from the overlying Burgersdorp Formation. Dolerite dykes and sills that intruded the Karoo Supergroup disturbed and baked the sedimentary strata of the Tarkastad Subgroup as well as other Karoo successions. The Katberg formation is mostly found in elevated areas, commonly metamorphosed and capped by dolerite sills while the Burgersdorp is found in low lying areas and is less metamorphosed or not metamorphosed at all. Lithologies of the two formations and the Karoo dolerites have been geologically mapped and the interfingering relationship between the Burgersdorp and Katberg Formation is also shown on the map. Horizontal laminae, planar bedding and planar and trough cross-bedding characterise lithofacies in the two formations. The fossil hunt done during the course of the study did not yield any positive results in both formations. Initially, the pebbles from outcrops of the Katberg Formation in the East London area were described in hand specimen by Mountain (1939). This study took it further with petrographic- and modal analysis as well as grain size analysis for the sedimentary pebbles. Microscopic studies done on the rock samples collected in the study area revealed quartz and feldspar as the dominant constituents. Most of the feldspar is hazy as a result of dissolution and alteration to clays. Sparse sedimentary rock fragments and quartz overgrowths in some of the rocks and grains respectively, indicate phases of recycling from older sedimentary sources. Furthermore, the samples have a wide range of grain sizes, sorting, grain shapes and classification categories. Textural attributes of sediments such as mean grain size, sorting, skewness and kurtosis were used to characterise the nature of the transport processes and to reconstruct the depositional environment of the sediments. The sandstones of both the Katberg and Burgersdorp Formations are medium-grained and moderately sorted to moderately well sorted but the pebbles are very coarse- to coarse-grained. Deducing sediment provenance from the final product of a basin fill is anything but straight-forward because rocks break down and unstable minerals change during transportation along the pathways from source to basin and afterwards during diagenesis. Heavy mineral studies coupled with geochemical sandstone analysis were used to unravel the sources of sediments. Among the heavies found were opaque and non-opaque minerals which are highly resistant to weathering with zircon being the most dominant. The heavy mineral grains vary in shape from subround to angular-subround in shape. The integrated results of petrography, XRD, XRF and SEM/EDX were used to identify the source rock character and to evaluate the relative role of tectonics and climate in determining the geochemical composition of the Katberg and Burgersdorp sandstones. Sandstone composition was used to decipher the provenance and tectonic setting of source areas by standard triangular QtFL and QmFLt diagrams, tectonic setting discrimination diagrams and source rock composition diagrams to characterise the source rocks