Re-estimation of erosion levels in Group I and II kimberlites between Lesotho, Kimberley and Victoria West, South Africa
- Hanson, E Kelsey, Moore, John M, Robey, Julian van Aardt, Bordy, Emese M, Marsh, Julian S
- Authors: Hanson, E Kelsey , Moore, John M , Robey, Julian van Aardt , Bordy, Emese M , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , long abstracts
- Identifier: http://hdl.handle.net/10962/132144 , vital:36804
- Description: The estimation of post-emplacement kimberlite erosion in South Africa through the study of upper-crustal xenoliths is relatively unexplored; however the presence of these xenoliths has been recognized for well over a 100 years. Previously postemplacement erosion levels of a small number of kimberlite pipes have been inferred through the study of the degree of country-rock diagenesis, the depth of sill formation and the depth of the initiation of diatreme facies kimberlite.
- Full Text:
- Date Issued: 2006
- Authors: Hanson, E Kelsey , Moore, John M , Robey, Julian van Aardt , Bordy, Emese M , Marsh, Julian S
- Date: 2006
- Language: English
- Type: text , long abstracts
- Identifier: http://hdl.handle.net/10962/132144 , vital:36804
- Description: The estimation of post-emplacement kimberlite erosion in South Africa through the study of upper-crustal xenoliths is relatively unexplored; however the presence of these xenoliths has been recognized for well over a 100 years. Previously postemplacement erosion levels of a small number of kimberlite pipes have been inferred through the study of the degree of country-rock diagenesis, the depth of sill formation and the depth of the initiation of diatreme facies kimberlite.
- Full Text:
- Date Issued: 2006
The geology and geochemistry of the Palaeoproterozoic Makganyene diamictite
- Polteau, S, Moore, John M, Tsikos, Harilaos
- Authors: Polteau, S , Moore, John M , Tsikos, Harilaos
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6740 , http://hdl.handle.net/10962/d1007556
- Description: The Palaeoproterozoic Earth experienced a global glacial event at 2400 Ma that occurred during the transitional period from anoxic to aerobic conditions in the atmosphere and oceans. The Transvaal Supergroup in the Griqualand West Basin, South Africa, hosts glacial deposits and associated major iron and manganese deposits that are apparently related to these global changes. The focus of this study is to assess the stratigraphy and geochemistry of the glaciogenic Makganyene Formation, in order to constrain its palaeoenvironmental settings. The Makganyene Formation forms the base of the Postmasburg Group and has been regarded as resting on an erosive regional unconformity throughout the Northern Cape Province. Systematic regional field observations and regional mapping carried out during this study demonstrate that this stratigraphic relationship is not universal. The Makganyene Formation is, in fact, conformable with underlying formations of the Koegas Subgroup in the deep southern Prieska basin and rests on an unconformity only on the shallow Ghaap platform to the north-east. The Makganyene Formation displays lateral facies changes that reflect the palaeogeography of the study area, and the advance and retreat of ice sheets/shelves. Geochemical investigations of glacial strata of the Makganyene Formation demonstrate that underlying banded iron formations of the Transvaal Supergroup acted as the main clastic source for the diamictite detritus. Geographic variations in bulk composition of the diamictites correlate well with field observations, and show that sorting processes were controlled largely by the morphology of the palaeobasin. Carbon isotope results emphasize the transitional nature of the Makganyene Formation in terms of the environmental conditions that resulted in widespread global glaciation in the Palaeoproterozoic. On the basis of the above geological evidence, it is proposed that the Transvaal Supergroup in the Northern Cape Province represents a continuous depositional event that lasted approximately 250 Ma and hence provides a unique opportunity for assessing the transitional changes experienced by the Palaeoproterozoic Earth.
- Full Text:
- Date Issued: 2006
- Authors: Polteau, S , Moore, John M , Tsikos, Harilaos
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6740 , http://hdl.handle.net/10962/d1007556
- Description: The Palaeoproterozoic Earth experienced a global glacial event at 2400 Ma that occurred during the transitional period from anoxic to aerobic conditions in the atmosphere and oceans. The Transvaal Supergroup in the Griqualand West Basin, South Africa, hosts glacial deposits and associated major iron and manganese deposits that are apparently related to these global changes. The focus of this study is to assess the stratigraphy and geochemistry of the glaciogenic Makganyene Formation, in order to constrain its palaeoenvironmental settings. The Makganyene Formation forms the base of the Postmasburg Group and has been regarded as resting on an erosive regional unconformity throughout the Northern Cape Province. Systematic regional field observations and regional mapping carried out during this study demonstrate that this stratigraphic relationship is not universal. The Makganyene Formation is, in fact, conformable with underlying formations of the Koegas Subgroup in the deep southern Prieska basin and rests on an unconformity only on the shallow Ghaap platform to the north-east. The Makganyene Formation displays lateral facies changes that reflect the palaeogeography of the study area, and the advance and retreat of ice sheets/shelves. Geochemical investigations of glacial strata of the Makganyene Formation demonstrate that underlying banded iron formations of the Transvaal Supergroup acted as the main clastic source for the diamictite detritus. Geographic variations in bulk composition of the diamictites correlate well with field observations, and show that sorting processes were controlled largely by the morphology of the palaeobasin. Carbon isotope results emphasize the transitional nature of the Makganyene Formation in terms of the environmental conditions that resulted in widespread global glaciation in the Palaeoproterozoic. On the basis of the above geological evidence, it is proposed that the Transvaal Supergroup in the Northern Cape Province represents a continuous depositional event that lasted approximately 250 Ma and hence provides a unique opportunity for assessing the transitional changes experienced by the Palaeoproterozoic Earth.
- Full Text:
- Date Issued: 2006
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