Heavy mineral characterization and provenance interpretation of the Ecca Group of geological formations in Eastern Cape Province, South Africa
- Authors: Sinuka, Sikhulule
- Date: 2016
- Subjects: Minerals -- South Africa -- Eastern Cape -- Classification Geology -- South Africa -- Eastern Cape Formations (Geology) -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/2911 , vital:28125
- Description: The aim of the research focuses on characterizing heavy mineral assemblages and interpretation of the provenance of the Ecca Group of in the Eastern Cape Province, South Africa. In South Africa, the Ecca Group outcrops extensively in the Main Karoo Basin. Mudstone, siltstone, sandstone, minor conglomerate and coal are the major constituent lithologies within the group. For descriptive purposes, the Ecca is categorized into three different geographical areas: the southern area, the western and northwestern area and the northeastern area. Six of the sixteen geological formations, namely the Prince Albert, Whitehill, Collingham, Ripon, Fort Brown, Waterford and Koonap Formations are present in the study area and are best exposed in road cuttings. For purposes of comparison, the underlying Witteberg Group, the Dwyka (which has Formation status here), and the overlying Koonap Formation of the Beaufort Group, are included in the study. This study is motivated by the relatively little information that is available on the heavy minerals of the Ecca Group, and that research of this nature had not been undertaken in the study area before. Another contributing motivation was to determine whether heavy mineral assemblages could be used to identify formations of the Ecca Group and for correlating between different localities in accordance with studies done elsewhere. Additionally, diagnostic heavy mineral assemblages could aid with stratigraphic selection of future boreholes in the Ecca Group. Heavy minerals are natural provenance tracers because of their stable nature and hydrodynamic behaviour. They are both non-opaque and opaque, with apatite, epidote, garnet, rutile, staurolite, tourmaline and zircon being good examples of non-opaque grains while ilmenite and magnetite are the most common opaques. Heavies are either derived from stable minor accessory minerals or from abundant but unstable mafic components of the host rock. They are very useful in interpreting the provenance due to the fact that some minerals are diagnostic of certain source rocks. However, sediments are exposed to several factors (conditions) such as weathering, erosion, breakage due to abrasion, mixing and recycling during transportation from the source to the depositional area. This implies that there are parameters other than the parent lithology that determine their final composition.
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Stratigraphic interrelationships, sedimentology and post Karoo intrusions in the Katberg and Burgersdorp formations around the town of Whittlesea, Eastern Cape province, South Africa
- Authors: Mzana, Siphokazi Kwamnandi
- Date: 2016
- Subjects: Formations (Geology) -- South Africa -- Eastern Cape Sedimentology -- South Africa -- Eastern Cape Geology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/15046 , vital:40157
- Description: 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.
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