- Title
- A sedimentological and structural study of the lower Ecca Group, with a focus on facies analysis of the Collingham Formation, north of Grahamstown, SE Karoo Basin, South Africa
- Creator
- Slamang, Shereen
- Subject
- Formations (Geology) -- South Africa -- Grahamstown Facies (Geology) -- South Africa -- Grahamstown
- Date Issued
- 2017
- Date
- 2017
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/21099
- Identifier
- vital:29439
- Description
- A study of the Collingham Formation was conducted in the area of the Ecca Pass and Committees Drift Road some 20km north of Grahamstown, Eastern Cape. The study incorporates outcrops of the lower Ecca Group, with a focus on the Collingham Formation. The structural and sedimentological characteristics have been documented, and a detailed description and facies outcrop characterization of the Collingham Formation has been undertaken. The combined thickness of the Prince Albert (~55m), Whitehill (~12m), and Collingham (~20m) Formations is approximately 85m. These formations are composed of fine grained parallel laminated mudrocks of mostly silt- and clay-size particles. A general north-easterly dip direction is recorded with three prominent joint directions striking NNE, NNW, and ESE. Intense small scale folding is evident in the Whitehill Formation, and is likely linked to local décollement structures; while north-verging duplex faults in the Prince Albert Formation is possibly linked to a sole thrust/detachment fault rooted in rocks of the Cape Supergroup. The foreland model has been proposed for these deformational structures. Six lithofacies have been recognised in the Collingham Formation, namely; claystone facies, mudstone facies, siltstone facies, chert facies, tuff facies, and shale facies. The Collingham Formation is comprised of an upward fining sequence of sediments; seen from the gradual change from siltstone facies in the lower layers, to mudstone facies, and claystone facies in the upper layers. This was created in a delta environment whereby clay particles were held in suspension in a hypopycnal mouth bar, and slowly settled to form claystone facies. An influx of sediment caused silt particles to settle further out to sea under the influence of gravity in a hyperpycnal mouth bar, thereby forming siltstone facies. Mudstone facies formed as the sediment supply gradually depleted, subsequently reducing the concentration of silt particles. The dominance of clay particles present suggests deposition to have occurred in tranquil waters, in a possible intracratonic basin setting, where the water depth is known to be a lot shallower. An upward decrease in organic content is seen by the colour change of mudrocks from dark grey near the base to dark green grey in the upper layers. Chlorite is commonly found in thin section, SEM, and XRD, and is an indication that the formation was later subject to low grade greenschist facies metamorphism.
- Format
- xii, 215 leaves
- Format
- Publisher
- Nelson Mandela Metropolitan University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela Metropolitan University
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