Stratigraphy, sedimentary facies and diagenesis of the ECCA group, Karoo supergroup in the Eastern Cape, South Africa
- Authors: Nyathi, Nonhlanhla
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11528 , http://hdl.handle.net/10353/d1019776
- Description: This is a MSc research project, and is aimed at the new insight on the stratigraphy, sedimentary facies, diagenesis and depositional environments of the Ecca Group, Karoo Supergroup in the Eastern Cape Province. Methodologies used in this research include field investigation, stratigraphic logging, thin-section microscope study, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses. The stratigraphy of the Ecca Group is divided into five formations, namely the Prince Albert Formation, Whitehill Formation, Collingham Formation, Rippon Formation and the Fort Brown Formation from bottom upward. Based on the field investigation and laboratory correlation, the Prince Albert, Whitehill, Collingham, and Fort Brown Formations can each be subdivided into two new members, i.e. lower member and upper member; whereas three new members have been proposed for the Rippon Formation, i.e. lower, middle and upper members. The Ecca Group sediments were accumulated in various depositional environments, from bottom of deep marine environment, passed through the middle of deltaic environment, and ended in a lacustrine environment. The Prince Albert Formation, Whitehill Formation and the Collingham Formation were all deposited in a deep marine basin, whilst the Rippon Formation was laid down in a deltaic environment. As the climate gradually became warmer and drier, the top Fort Brown Formation was lastly deposited in a lacustrine environment. The stratigraphic succession of the Ecca Group constitutes a perfect regression sequence, indicating that the marine water gradually retreated and the sea-level gradually dropped. The rocks in the Ecca Group are mainly terrigenous sandstone and mudstone with some coarse grain-sized siliciclastic rock of conglomerate. The sandstones are dominated by feldspathic graywackes with minor quartz-wackes, and there are no arenites in the Ecca Group. Whereas the mudstones are dominated by grayish mudrocks and black shales, purer claystone was found in the turbidite facies of the Collingham Formation, which probably has economic significance for the future since the reserve is quite large. Optical microscope, XRD and SEM analyses demonstrated that the minerals in the Ecca Group include detrital minerals of quartz, orthoclase, microcline, plagioclase, biotite, muscovite; and clay minerals (smectite, kaolinite, illite and sericite). These minerals constitute the rock framework grains and cements whereas; the authigenic minerals of calcite and hematite were formed during diagenesis. Accessory minerals such as rutile and zircon are the heavy minerals present in the strata, and occur only in a small amount. Based on the lithologies, sedimentary structures and sequence stacking patterns, ten sedimentary facies have been recognised, namely 1) Grayish laminated and thin bedded shale facies, 2) Grayish laminated shale and intercalated chert facies, 3) Grayish rhythmite facies (all the three facies above were deposited in deep marine water); 4) Flat and lenticular bedded graywacke facies, 5) Grayish alternating mudstone and sandstone facies, 6) Dark organic rich mudstone facies, 7) Fossil bearing mudstone facies, 8) Laminated and thin bedded black mudstone with lenticular siltstone facies, 9) Interbedded grayish sandstone and mudstone facies (above Facies 4-9 were deposited in deltaic environment and appeared in the Rippon Formation); and 10) Varved rhythmic mudstone facies, which occurs only in the Fort Brown Formation and represents lacustrine sediments. Four types of cements have been identified in the rocks of the Ecca Group, including quartz, smectite, calcite and feldspar cements. The first three cement types are the major cement types, whilst the feldspar cement is minor and occurs only locally. Recrystallisation in Ecca sediments includes quartz, feldspar, clay mineral recrystallisation and conversion from smectite and kaolinite to illite and then to sericite. Replacement involves calcite replacing quartz, feldspar and clay matrix; accompanied by albitization, i.e. albite replacing other feldspar minerals in a deep burial environment. Dissolution in the Ecca Group involved calcite and kaolinite dissolving and leaching, which created more pore-space and increased porosity. The sediments of the Ecca Group went through three stages of digenesis, namely the early stage, the late stage and the up lift stage which led the rocks being exposed on the Earth’s surface and being weathered. In each stage, some minerals became unstable, then replaced by a more stable mineral suitable for the new diagenetic environment. Precipitation of cements and formation of authigenic minerals mostly occurred in the early diagenetic stage, which led the soft sediments becoming a hard rock; whilst recrystallisation, replacement, and dissolution took place mostly in the later diageneti
- Full Text:
- Date Issued: 2014
- Authors: Nyathi, Nonhlanhla
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11528 , http://hdl.handle.net/10353/d1019776
- Description: This is a MSc research project, and is aimed at the new insight on the stratigraphy, sedimentary facies, diagenesis and depositional environments of the Ecca Group, Karoo Supergroup in the Eastern Cape Province. Methodologies used in this research include field investigation, stratigraphic logging, thin-section microscope study, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses. The stratigraphy of the Ecca Group is divided into five formations, namely the Prince Albert Formation, Whitehill Formation, Collingham Formation, Rippon Formation and the Fort Brown Formation from bottom upward. Based on the field investigation and laboratory correlation, the Prince Albert, Whitehill, Collingham, and Fort Brown Formations can each be subdivided into two new members, i.e. lower member and upper member; whereas three new members have been proposed for the Rippon Formation, i.e. lower, middle and upper members. The Ecca Group sediments were accumulated in various depositional environments, from bottom of deep marine environment, passed through the middle of deltaic environment, and ended in a lacustrine environment. The Prince Albert Formation, Whitehill Formation and the Collingham Formation were all deposited in a deep marine basin, whilst the Rippon Formation was laid down in a deltaic environment. As the climate gradually became warmer and drier, the top Fort Brown Formation was lastly deposited in a lacustrine environment. The stratigraphic succession of the Ecca Group constitutes a perfect regression sequence, indicating that the marine water gradually retreated and the sea-level gradually dropped. The rocks in the Ecca Group are mainly terrigenous sandstone and mudstone with some coarse grain-sized siliciclastic rock of conglomerate. The sandstones are dominated by feldspathic graywackes with minor quartz-wackes, and there are no arenites in the Ecca Group. Whereas the mudstones are dominated by grayish mudrocks and black shales, purer claystone was found in the turbidite facies of the Collingham Formation, which probably has economic significance for the future since the reserve is quite large. Optical microscope, XRD and SEM analyses demonstrated that the minerals in the Ecca Group include detrital minerals of quartz, orthoclase, microcline, plagioclase, biotite, muscovite; and clay minerals (smectite, kaolinite, illite and sericite). These minerals constitute the rock framework grains and cements whereas; the authigenic minerals of calcite and hematite were formed during diagenesis. Accessory minerals such as rutile and zircon are the heavy minerals present in the strata, and occur only in a small amount. Based on the lithologies, sedimentary structures and sequence stacking patterns, ten sedimentary facies have been recognised, namely 1) Grayish laminated and thin bedded shale facies, 2) Grayish laminated shale and intercalated chert facies, 3) Grayish rhythmite facies (all the three facies above were deposited in deep marine water); 4) Flat and lenticular bedded graywacke facies, 5) Grayish alternating mudstone and sandstone facies, 6) Dark organic rich mudstone facies, 7) Fossil bearing mudstone facies, 8) Laminated and thin bedded black mudstone with lenticular siltstone facies, 9) Interbedded grayish sandstone and mudstone facies (above Facies 4-9 were deposited in deltaic environment and appeared in the Rippon Formation); and 10) Varved rhythmic mudstone facies, which occurs only in the Fort Brown Formation and represents lacustrine sediments. Four types of cements have been identified in the rocks of the Ecca Group, including quartz, smectite, calcite and feldspar cements. The first three cement types are the major cement types, whilst the feldspar cement is minor and occurs only locally. Recrystallisation in Ecca sediments includes quartz, feldspar, clay mineral recrystallisation and conversion from smectite and kaolinite to illite and then to sericite. Replacement involves calcite replacing quartz, feldspar and clay matrix; accompanied by albitization, i.e. albite replacing other feldspar minerals in a deep burial environment. Dissolution in the Ecca Group involved calcite and kaolinite dissolving and leaching, which created more pore-space and increased porosity. The sediments of the Ecca Group went through three stages of digenesis, namely the early stage, the late stage and the up lift stage which led the rocks being exposed on the Earth’s surface and being weathered. In each stage, some minerals became unstable, then replaced by a more stable mineral suitable for the new diagenetic environment. Precipitation of cements and formation of authigenic minerals mostly occurred in the early diagenetic stage, which led the soft sediments becoming a hard rock; whilst recrystallisation, replacement, and dissolution took place mostly in the later diageneti
- Full Text:
- Date Issued: 2014
Nature of occurrence and economic potential of granitic pegmatites of Mzimba district in Northern Malawi
- Authors: Salima, Jalf William Joseph
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11527 , http://hdl.handle.net/10353/d1016192
- Description: A swarm of granitic pegmatites occurs in Mzimba district from northern Kasungu to Kafukure near the western international border with Zambia. The granitic pegmatites are hosted by a mobile belt, within the Mozambiquan orogenic belt (c. 900 - 1800 Ma). They have been dated as 485 Ma. They intruded metasediments of high to medium grade metamorphic rocks of a Precambrian Basement Complex. The dominant trend of the pegmatites is NW - SE, exhibiting a cross-cutting relationship with the country rocks and their contacts with the latter are usually sharp. The six pegmatites investigated in this study are inhomogeneous, composed of a massive quartz core, an intermediate zone composed of a blocky pink K-feldspar rich sub-zone and muscovite rich sub-zone and a wall zone composed of quartz - pink K-feldspar - muscovite mineral assemblage. The Mzimba pegmatites are classified as lithium-caesium-tantalum (LCT) family of rare element granitic pegmatites as described by Černý and Ercit (2005). They belong to the beryl-columbite subtype and beryl-columbite-phosphate subtype of the rare element pegmatites. It is suggested that the pegmatites are the product of magmatic differentiation and that they form roofs of granite plutons lying deep below the current level of erosion. The six pegmatites were sampled and minerals analysed using standard analytical methods such as petrographic microscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. Mineralogy of the granitic pegmatites indicates that they are predominantly composed of perthitic K-feldspar (perthite), Na-plagioclase (albite), quartz and muscovite as main mineral phases and accessory minerals including beryl, tantalite-columbite (ferrotantalite), iron-titanium oxides (ilmeno-rutile and ilmenite), tourmaline (schorl), garnet (almandine-spessartine) and triplite. Triplite is a very rare mineral found in a few pegmatites around the world, and this is the first reported account of this mineral in the Mzimba pegmatites and probably in Malawi. These minerals are being exploited by artisanal and small scale miners. Trace elements in K-feldspar and muscovite are significant indicators for the evaluation of economic potential of pegmatites as well as for the differentiation degree and origin of the magma. The K/Rb ratio for K-feldspars ranges between 12.72 and 109.38, while for muscovites it is between 16.66 and 82.36 indicating that the pegmatites are moderately evolved. The Ta versus Cs and the Ta versus K/Cs discrimination diagram indicates that all the investigated pegmatites plot above the 20 ppm threshold suggesting that the pegmatites have potential for Ta and Nb mineralization.
- Full Text:
- Date Issued: 2014
- Authors: Salima, Jalf William Joseph
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11527 , http://hdl.handle.net/10353/d1016192
- Description: A swarm of granitic pegmatites occurs in Mzimba district from northern Kasungu to Kafukure near the western international border with Zambia. The granitic pegmatites are hosted by a mobile belt, within the Mozambiquan orogenic belt (c. 900 - 1800 Ma). They have been dated as 485 Ma. They intruded metasediments of high to medium grade metamorphic rocks of a Precambrian Basement Complex. The dominant trend of the pegmatites is NW - SE, exhibiting a cross-cutting relationship with the country rocks and their contacts with the latter are usually sharp. The six pegmatites investigated in this study are inhomogeneous, composed of a massive quartz core, an intermediate zone composed of a blocky pink K-feldspar rich sub-zone and muscovite rich sub-zone and a wall zone composed of quartz - pink K-feldspar - muscovite mineral assemblage. The Mzimba pegmatites are classified as lithium-caesium-tantalum (LCT) family of rare element granitic pegmatites as described by Černý and Ercit (2005). They belong to the beryl-columbite subtype and beryl-columbite-phosphate subtype of the rare element pegmatites. It is suggested that the pegmatites are the product of magmatic differentiation and that they form roofs of granite plutons lying deep below the current level of erosion. The six pegmatites were sampled and minerals analysed using standard analytical methods such as petrographic microscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. Mineralogy of the granitic pegmatites indicates that they are predominantly composed of perthitic K-feldspar (perthite), Na-plagioclase (albite), quartz and muscovite as main mineral phases and accessory minerals including beryl, tantalite-columbite (ferrotantalite), iron-titanium oxides (ilmeno-rutile and ilmenite), tourmaline (schorl), garnet (almandine-spessartine) and triplite. Triplite is a very rare mineral found in a few pegmatites around the world, and this is the first reported account of this mineral in the Mzimba pegmatites and probably in Malawi. These minerals are being exploited by artisanal and small scale miners. Trace elements in K-feldspar and muscovite are significant indicators for the evaluation of economic potential of pegmatites as well as for the differentiation degree and origin of the magma. The K/Rb ratio for K-feldspars ranges between 12.72 and 109.38, while for muscovites it is between 16.66 and 82.36 indicating that the pegmatites are moderately evolved. The Ta versus Cs and the Ta versus K/Cs discrimination diagram indicates that all the investigated pegmatites plot above the 20 ppm threshold suggesting that the pegmatites have potential for Ta and Nb mineralization.
- Full Text:
- Date Issued: 2014
Stratigraphy and sedimentology of the Mzamba formation in the Eastern Cape, South Africa
- Authors: Susela, Zamampondo
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11529 , http://hdl.handle.net/10353/d1019807
- Description: This research project is aimed at providing new information to the stratigraphy, sedimentology, palaeontology and diagenesis of the Mzamba Formation. The study area is located at the south of Port Edward, Eastern Cape. The methodologies employed in this study include field geological investigation and sampling, stratigraphic measurement and logging, thin-section microscope study, powder samples of XRD analysis, and SEM-EDX analysis of rock textures and mineral compositions. The stratigraphy of the Mzamba Formation can be divided into three newly established members, i.e. the Lower Conglomerate Member, Middle Silt/Mudstone-Shell Bed Member and Upper Mudstone-Shell Bed Member with a total thickness of 31.26m in an inland borehole and 30.05m in the field measurement. The Lower Conglomerate Member is 2.65m thick and consists of pebbly conglomerate with coarse sandstone, shell fragments and silicified wood trunks, representing shallow marine nearshore deposits. The Middle Silt/Mudstone and Shell Bed Member is 9.5 m thick and consists of black mudstone and fine-grained siltstone alternated with medium grained pecten beds, which was deposited in a storm influenced deeper marine environment. The Upper Mudstone-Shell Bed Member is 17.9m thick and is made up of fine-mudstones with articulated pecten layers which were deposited in a deep and quiet marine environment. Petrology studies showed that the Mzamba Formation consists of mixed sediments of carbonate and siliciclastic rocks. Siliciclastic rocks include pebbly conglomerates, medium to coarse sandstones and fine-grained mudstones, whereas carbonate rocks include packstone, wackstone and grainstone (pecten beds). The formation shows cyclical pattern of a series fining-upward cyclicities, changing from bottom conglomerate to sandstone, then upward repeated series of cyclotherms from pecten bed to mudstone. Mineralogy of the Mzamba Formation consists of terrigenous minerals of quartz, orthoclase, plagioclase, muscovite and various igneous and metamorphic rock-lithics, clay minerals of smectite, illite and sericite, and carbonate minerals of calcite and dolomite; with minor diagenetic minerals of pyrite, glauconite, hematite, gypsum, albite and organic maceral of vitrinite. Heavy minerals of garnet, zircon and rutile are minor minerals in the strata, which were detrital in origin. Mzamba Formation is a fossiliferous sequence, and contains both fauna and flora fossils in the strata. The pecten beds host well-preserved bivalve, gastropod, brachiopoda, ammonite, and echinoderm; whereas trace fossils of coprolites, burrows and tracks, as well as plant fossils of silicified wood trunks were also found in the formation. Some new fossil species were collected and studied, which include Bivalve: Pteriaceae, Pinnacea and Ostreacea; Gastropod: Cerithiacea and Mesogastopoda; Echinoderm: Echinocystoidea and Crinoidea. The benthonic species predominate in the lower part in the succession, whilst the planktonic species are abundant in the upper part of the sequence, which points to increase in water depths of the depositional environment. Based on lithology, sedimentary structures, and stratum architecture, seven different facies have been distinguished. Facies A (Flat bedded pebbly conglomerate), Facie B (Cross-bedded coarse calcareous sandstone facies), Facies C (Burrowed sandstone facies), Facies D (Shell-fragmental fine-grained calcareous sandstone facies), Facies E (Horizontal bedded calcareous mudstone facies), Facies F (Calcareous patch reef), Facies G (Wash out reef facies). Wash out reef facies is rich in algae, bivalve shells, broken oysters, coral fragments and small pebbles. Four types of cements were found in the Mzamba Formation, including calcite, smectite, illite and quartz. Calcite cement can be further classified into two types, micrite calcite cement and sparite calcite cement. The clay cement consists of smectite and illite and mainly occurs as matrix. The isopachous rim calcite and bright isopachous rim of silica cements indicate diagenesis in a marine phreatic zone. Authigenic minerals which formed in early diagenetic stage include quartz, plagioclase, glauconite and organic maceral of vitrinite. Three stages of diagenesis have been recognised in the sequence, i.e. syndiagenesis, early and late diagenesis. Glauconite pellets and worm faecal pellets were formed in syndiagenetic stage; cementation and authigenic minerals were formed in early diagenetic stage; whereas clay mineral conversion of smectite to illite, quartz overgrowth, bioclast recrystallization and calcite replacement took place during late diagenetic stage. The pebbly conglomerate at the bottom of the Mzamba Formation represents high energy deposits in a shallow marine environment; the grain-size gradually becomes finer in the middle succession and finest mudstone facies at the top of the succession, which represents deep marine deposits. Meanwhile, benthonic fossils are dominant in the bottom succession while plankton fossils are more abundant in the top succession. These features indicate that the Mzamba Formation constitutes a perfect transgression sequence, and the depositional environments started from shallow marine near shore environment, and gradually shifted to a deep marine quiet water environment.
- Full Text:
- Date Issued: 2014
- Authors: Susela, Zamampondo
- Date: 2014
- Language: English
- Type: Thesis , Masters , MSc (Geology)
- Identifier: vital:11529 , http://hdl.handle.net/10353/d1019807
- Description: This research project is aimed at providing new information to the stratigraphy, sedimentology, palaeontology and diagenesis of the Mzamba Formation. The study area is located at the south of Port Edward, Eastern Cape. The methodologies employed in this study include field geological investigation and sampling, stratigraphic measurement and logging, thin-section microscope study, powder samples of XRD analysis, and SEM-EDX analysis of rock textures and mineral compositions. The stratigraphy of the Mzamba Formation can be divided into three newly established members, i.e. the Lower Conglomerate Member, Middle Silt/Mudstone-Shell Bed Member and Upper Mudstone-Shell Bed Member with a total thickness of 31.26m in an inland borehole and 30.05m in the field measurement. The Lower Conglomerate Member is 2.65m thick and consists of pebbly conglomerate with coarse sandstone, shell fragments and silicified wood trunks, representing shallow marine nearshore deposits. The Middle Silt/Mudstone and Shell Bed Member is 9.5 m thick and consists of black mudstone and fine-grained siltstone alternated with medium grained pecten beds, which was deposited in a storm influenced deeper marine environment. The Upper Mudstone-Shell Bed Member is 17.9m thick and is made up of fine-mudstones with articulated pecten layers which were deposited in a deep and quiet marine environment. Petrology studies showed that the Mzamba Formation consists of mixed sediments of carbonate and siliciclastic rocks. Siliciclastic rocks include pebbly conglomerates, medium to coarse sandstones and fine-grained mudstones, whereas carbonate rocks include packstone, wackstone and grainstone (pecten beds). The formation shows cyclical pattern of a series fining-upward cyclicities, changing from bottom conglomerate to sandstone, then upward repeated series of cyclotherms from pecten bed to mudstone. Mineralogy of the Mzamba Formation consists of terrigenous minerals of quartz, orthoclase, plagioclase, muscovite and various igneous and metamorphic rock-lithics, clay minerals of smectite, illite and sericite, and carbonate minerals of calcite and dolomite; with minor diagenetic minerals of pyrite, glauconite, hematite, gypsum, albite and organic maceral of vitrinite. Heavy minerals of garnet, zircon and rutile are minor minerals in the strata, which were detrital in origin. Mzamba Formation is a fossiliferous sequence, and contains both fauna and flora fossils in the strata. The pecten beds host well-preserved bivalve, gastropod, brachiopoda, ammonite, and echinoderm; whereas trace fossils of coprolites, burrows and tracks, as well as plant fossils of silicified wood trunks were also found in the formation. Some new fossil species were collected and studied, which include Bivalve: Pteriaceae, Pinnacea and Ostreacea; Gastropod: Cerithiacea and Mesogastopoda; Echinoderm: Echinocystoidea and Crinoidea. The benthonic species predominate in the lower part in the succession, whilst the planktonic species are abundant in the upper part of the sequence, which points to increase in water depths of the depositional environment. Based on lithology, sedimentary structures, and stratum architecture, seven different facies have been distinguished. Facies A (Flat bedded pebbly conglomerate), Facie B (Cross-bedded coarse calcareous sandstone facies), Facies C (Burrowed sandstone facies), Facies D (Shell-fragmental fine-grained calcareous sandstone facies), Facies E (Horizontal bedded calcareous mudstone facies), Facies F (Calcareous patch reef), Facies G (Wash out reef facies). Wash out reef facies is rich in algae, bivalve shells, broken oysters, coral fragments and small pebbles. Four types of cements were found in the Mzamba Formation, including calcite, smectite, illite and quartz. Calcite cement can be further classified into two types, micrite calcite cement and sparite calcite cement. The clay cement consists of smectite and illite and mainly occurs as matrix. The isopachous rim calcite and bright isopachous rim of silica cements indicate diagenesis in a marine phreatic zone. Authigenic minerals which formed in early diagenetic stage include quartz, plagioclase, glauconite and organic maceral of vitrinite. Three stages of diagenesis have been recognised in the sequence, i.e. syndiagenesis, early and late diagenesis. Glauconite pellets and worm faecal pellets were formed in syndiagenetic stage; cementation and authigenic minerals were formed in early diagenetic stage; whereas clay mineral conversion of smectite to illite, quartz overgrowth, bioclast recrystallization and calcite replacement took place during late diagenetic stage. The pebbly conglomerate at the bottom of the Mzamba Formation represents high energy deposits in a shallow marine environment; the grain-size gradually becomes finer in the middle succession and finest mudstone facies at the top of the succession, which represents deep marine deposits. Meanwhile, benthonic fossils are dominant in the bottom succession while plankton fossils are more abundant in the top succession. These features indicate that the Mzamba Formation constitutes a perfect transgression sequence, and the depositional environments started from shallow marine near shore environment, and gradually shifted to a deep marine quiet water environment.
- Full Text:
- Date Issued: 2014
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