- Title
- A preliminary investigation and photographic atlas of nodules found in the Bokkelveld group (Gydo formation), Steytlerville district, South Africa
- Creator
- Browning, Claire
- Subject
- Gydo formation -- South Africa
- Subject
- Formations (Geology) -- South Africa -- Western Cape
- Subject
- Formations (Geology) -- South Africa -- Eastern Cape
- Subject
- Groups (Stratigraphy) -- South Africa -- Western Cape
- Subject
- Geology -- Stratigraphic
- Subject
- Bokkeveld group (South Africa)
- Date Issued
- 2009
- Date
- 2009
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- vital:10656
- Identifier
- http://hdl.handle.net/10948/927
- Identifier
- Gydo formation -- South Africa
- Identifier
- Formations (Geology) -- South Africa -- Western Cape
- Identifier
- Formations (Geology) -- South Africa -- Eastern Cape
- Identifier
- Groups (Stratigraphy) -- South Africa -- Western Cape
- Identifier
- Geology -- Stratigraphic
- Identifier
- Bokkeveld group (South Africa)
- Description
- Nodules within the lower Bokkeveld shales often contain well-preserved invertebrate fossil material. The aim of this study was to describe some characteristics seen at various scales (macro-, micro- and ultra -) within nodules that might contribute to an understanding of aspects of nodule formation and the reasons for the excellent preservation of the fossil material within these nodules. Detailed, high quality macro-photographs were taken of sliced and whole nodule surfaces and a catalogue was produced to tentatively identify fossils present and illustrate the variations seen within nodules. Selected nodules were then subjected to petrographic, ultra-structural (SEM) and some chemical (EDS, XRD & XRF) analysis to investigate the possible reasons for these variations. The chemical results have indicated that nodules are enriched with quartz compared to the surrounding shale. Quartz is also the dominant mineral replacing trilobite carapace material within nodules, while trilobite material within shales is replaced with equal proportions of hematite, biotite and quartz. It appears that the higher resistance of quartz to weathering is the dominant factor leading to the preservation of both nodules within the shales and trilobite material within the nodules examined. A comparison with some Western Cape nodules highlighted possible variations in overall nodule chemical composition along strike. Western Cape nodules are predominantly composed of apatite whereas the Cockscomb nodules are mainly composed of quartz. This quartz-apatite compositional variation in nodules occurring within a single formation has been reported from nodules found in the Armorican Massif of France which are very similar in a number of respects to the Bokkeveld nodules described in this study. Based on various features of the fossils present and the structure of nodules they were probably formed during early diagenesis within an epeiric marine deposit greatly affected by sea level fluctuations.
- Format
- xiv, 160 leaves
- Format
- Publisher
- Nelson Mandela Metropolitan University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela Metropolitan University
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