Supplying lava eruptions in the Karoo Province, South Africa: a geochemical comparison of the volcanic sequence with intrusions in the main Karoo basin
- Marsh, Julian S, Mitha, Vindina R
- Authors: Marsh, Julian S , Mitha, Vindina R
- Date: 2006
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132873 , vital:36901
- Description: Magma supply for lava eruptions remains a poorly understood facet of continental flood volcanism. In the Karoo Province a vast complex of dolerite sheets and dykes is exposed in the main Karoo sedimentary basin underlying the flood basalt remnant of Lesotho (Drakensberg Group) suggesting that lavas were erupted locally from a widely distributed network of fissures.
- Full Text:
- Date Issued: 2006
- Authors: Marsh, Julian S , Mitha, Vindina R
- Date: 2006
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132873 , vital:36901
- Description: Magma supply for lava eruptions remains a poorly understood facet of continental flood volcanism. In the Karoo Province a vast complex of dolerite sheets and dykes is exposed in the main Karoo sedimentary basin underlying the flood basalt remnant of Lesotho (Drakensberg Group) suggesting that lavas were erupted locally from a widely distributed network of fissures.
- Full Text:
- Date Issued: 2006
The kaolinitic clay deposits on Beaconsfield, north of Grahamstown
- Jacob, Roger E, Mitha, Vindina R, MacPherson, D
- Authors: Jacob, Roger E , Mitha, Vindina R , MacPherson, D
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6734 , http://hdl.handle.net/10962/d1007544
- Description: The Grahamstown clay deposits occur below the Grahamstown Formation silcrete, which forms a remnant of an extensive peneplain that developed on the African erosion surface during the Cretaceous–Tertiary period. This paper provides new data on the distribution of the kaolinitic clay deposits in the Beaconsfield area north of Grahamstown. These data include 23 borehole profiles through the deposits, and the chemistry and mineralogy of the clays. Relatively little information is available on this part of the peneplain. It was found that the thickness of the kaolin horizon varies considerably, but reaches 35m in places. It generally occurs under a silcrete cover, which attains a thickness of 8 m in places. Lithological logs enable direct comparison across the Beaconsfield area. The clays are developed in both the Witteberg Group shale and Dwyka Group tillite. The contact between the clay and underlying bedrock is gradational and relatively uneven. Major-element X-ray fluorescence analyses revealed that there is chemical variation, both vertically and laterally. Al2O3 content is generally near 20%, but may reach 29%. SiO2 content varies between 55 and 70+%. SiO2 contents are highest in the silcretes occurring just below soil level. Fe2O3 is high locally in the top part of the profile. K2O and Na2O are generally low, but increase towards the unweathered bedrock as the primary feldspar content increases. These compositional variations are compatible with residual concentrations of kaolinitic clays through deep weathering below the former African erosion surface.
- Full Text:
- Date Issued: 2004
- Authors: Jacob, Roger E , Mitha, Vindina R , MacPherson, D
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6734 , http://hdl.handle.net/10962/d1007544
- Description: The Grahamstown clay deposits occur below the Grahamstown Formation silcrete, which forms a remnant of an extensive peneplain that developed on the African erosion surface during the Cretaceous–Tertiary period. This paper provides new data on the distribution of the kaolinitic clay deposits in the Beaconsfield area north of Grahamstown. These data include 23 borehole profiles through the deposits, and the chemistry and mineralogy of the clays. Relatively little information is available on this part of the peneplain. It was found that the thickness of the kaolin horizon varies considerably, but reaches 35m in places. It generally occurs under a silcrete cover, which attains a thickness of 8 m in places. Lithological logs enable direct comparison across the Beaconsfield area. The clays are developed in both the Witteberg Group shale and Dwyka Group tillite. The contact between the clay and underlying bedrock is gradational and relatively uneven. Major-element X-ray fluorescence analyses revealed that there is chemical variation, both vertically and laterally. Al2O3 content is generally near 20%, but may reach 29%. SiO2 content varies between 55 and 70+%. SiO2 contents are highest in the silcretes occurring just below soil level. Fe2O3 is high locally in the top part of the profile. K2O and Na2O are generally low, but increase towards the unweathered bedrock as the primary feldspar content increases. These compositional variations are compatible with residual concentrations of kaolinitic clays through deep weathering below the former African erosion surface.
- Full Text:
- Date Issued: 2004
- «
- ‹
- 1
- ›
- »