Stratigraphic characterisation of the Collingham formation in the context of shale gas from a borehole (SFT 2) near Jansenville, Eastern Cape, South Africa
- Authors: Black, Dawn Ebony
- Date: 2015
- Subjects: Geology, Stratigraphic , Formations (Geology) -- South Africa , Collingham formation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10676 , http://hdl.handle.net/10948/d1021148
- Description: This study is an extensive lithological, petrographical, mineralogical and geochemical description of fresh Collingham Formation core samples collected from borehole SFT 2, located on the farm Slangfontein, south of Jansenville in the Eastern Cape, South Africa. The borehole, drilled to 295 m on the northerly limb of a shallow westerly plunging syncline, intersected the lower Ecca Group rocks of the Ripon, Collingham, Whitehill and Prince Albert Formations and terminated in the upper Dwyka Group. A comprehensive log and stratigraphic column were compiled for the Collingham Formation and fresh core samples were analysed using X-Ray Diffraction (“XRD”), X-Ray Fluorescence (“XRF”), mercury porosimetry, and Total Organic Carbon (“TOC”). Thin section microscopy and Scanning Electron Microscopy (“SEM”) analyses were carried out on selected samples of core from borehole SFT 2. The matrix supported, massive to laminated lithological units of the Collingham Formation are interpreted as detrital, terrigenous sediments. These sediments are composed of intercalated fine-grained, poorly sorted, non-fissile mudstone; fine- to very fine-grained, predominantly pyroclastic airfall tephra; and less common fine-grained sandstones. Sediments of the Collingham Formation are considered to be immature, composed primarily of clay and aluminosilicates. The predominance of a clay fraction and aluminosilicates in mudstone samples is indicated by elevated K2O/Al2O3 ratio values, and the relationship of Zr, Al2O3 and TiO2. The presence of glauconite within the Collingham Formation indicates deposition in a mildly alkaline, slightly reducing marine environment. Rb/K ratio values (1.9 – 2.3 x 10-3) indicate brackish to slightly marine conditions, while low Zr/Rb ratio values indicate a low hydro-energy environment, with stable bottom water conditions. Hf and Nb concentrations indicate that detrital input was greatest during the deposition of tuffaceous units; while stable mineral assemblages and a low Fe2O3/K2O ratio values indicate deposition close to the source. A variation in Si/Ca values indicate times when sediments were affected by turbidity, interspersed with times of relative quiescence. The predominance of K2O over Na2O indicates that the Collingham Formation is alkali-rich, while SiO2/Al2O3 ratio values and the relationship of Zr, Al2O3 and TiO2 indicate that sediments are immature. In the lower portion of the formation, non-sulphidic, anoxic conditions are indicated by Mn/Al, V/(V+Ni), V/Cr ratio values, the Fe-Mn- V content, and the correlation between V and TOC. The upper portion of the formation is considered dysoxic, due to the presence and distribution of pyrite framboids, which indicate a fluctuating O2 level, likely indicating deposition at the interface between anoxic and slightly more oxic conditions. V/Cr ratio values indicate that the O2 regime was lowest during the deposition of the mudstones. The Chemical Index of Alteration (“CIA”) indicates a consistent weathering regime throughout the deposition of the Collingham Formation, associated with a temperate climate on the interface between glacial and tropical conditions. Although an anoxic and low hydro-energy environment is generally favourable for hydrocarbon accumulation, the Collingham Formation contains low levels of Total Organic Carbon (well below 0.9 per cent) and low porosities (ranging from 0.35 per cent to a maximum of 2.22 per cent), both of which are characteristic of a poor source for gas accumulation. Due to the laminate nature, permeability and fracturability of the Collingham Formation, there is the potential that the formation may form a good sealing sequence to the potentially gas-rich Whitehill Formation below. The metamorphic impact related to the Cape Orogeny (± 250 Ma), and reflected in the textures of the minerals making up the sediments of the Collingham Formation, suggests the enhancement in the sealing efficiency of this formation.
- Full Text:
- Date Issued: 2015
- Authors: Black, Dawn Ebony
- Date: 2015
- Subjects: Geology, Stratigraphic , Formations (Geology) -- South Africa , Collingham formation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10676 , http://hdl.handle.net/10948/d1021148
- Description: This study is an extensive lithological, petrographical, mineralogical and geochemical description of fresh Collingham Formation core samples collected from borehole SFT 2, located on the farm Slangfontein, south of Jansenville in the Eastern Cape, South Africa. The borehole, drilled to 295 m on the northerly limb of a shallow westerly plunging syncline, intersected the lower Ecca Group rocks of the Ripon, Collingham, Whitehill and Prince Albert Formations and terminated in the upper Dwyka Group. A comprehensive log and stratigraphic column were compiled for the Collingham Formation and fresh core samples were analysed using X-Ray Diffraction (“XRD”), X-Ray Fluorescence (“XRF”), mercury porosimetry, and Total Organic Carbon (“TOC”). Thin section microscopy and Scanning Electron Microscopy (“SEM”) analyses were carried out on selected samples of core from borehole SFT 2. The matrix supported, massive to laminated lithological units of the Collingham Formation are interpreted as detrital, terrigenous sediments. These sediments are composed of intercalated fine-grained, poorly sorted, non-fissile mudstone; fine- to very fine-grained, predominantly pyroclastic airfall tephra; and less common fine-grained sandstones. Sediments of the Collingham Formation are considered to be immature, composed primarily of clay and aluminosilicates. The predominance of a clay fraction and aluminosilicates in mudstone samples is indicated by elevated K2O/Al2O3 ratio values, and the relationship of Zr, Al2O3 and TiO2. The presence of glauconite within the Collingham Formation indicates deposition in a mildly alkaline, slightly reducing marine environment. Rb/K ratio values (1.9 – 2.3 x 10-3) indicate brackish to slightly marine conditions, while low Zr/Rb ratio values indicate a low hydro-energy environment, with stable bottom water conditions. Hf and Nb concentrations indicate that detrital input was greatest during the deposition of tuffaceous units; while stable mineral assemblages and a low Fe2O3/K2O ratio values indicate deposition close to the source. A variation in Si/Ca values indicate times when sediments were affected by turbidity, interspersed with times of relative quiescence. The predominance of K2O over Na2O indicates that the Collingham Formation is alkali-rich, while SiO2/Al2O3 ratio values and the relationship of Zr, Al2O3 and TiO2 indicate that sediments are immature. In the lower portion of the formation, non-sulphidic, anoxic conditions are indicated by Mn/Al, V/(V+Ni), V/Cr ratio values, the Fe-Mn- V content, and the correlation between V and TOC. The upper portion of the formation is considered dysoxic, due to the presence and distribution of pyrite framboids, which indicate a fluctuating O2 level, likely indicating deposition at the interface between anoxic and slightly more oxic conditions. V/Cr ratio values indicate that the O2 regime was lowest during the deposition of the mudstones. The Chemical Index of Alteration (“CIA”) indicates a consistent weathering regime throughout the deposition of the Collingham Formation, associated with a temperate climate on the interface between glacial and tropical conditions. Although an anoxic and low hydro-energy environment is generally favourable for hydrocarbon accumulation, the Collingham Formation contains low levels of Total Organic Carbon (well below 0.9 per cent) and low porosities (ranging from 0.35 per cent to a maximum of 2.22 per cent), both of which are characteristic of a poor source for gas accumulation. Due to the laminate nature, permeability and fracturability of the Collingham Formation, there is the potential that the formation may form a good sealing sequence to the potentially gas-rich Whitehill Formation below. The metamorphic impact related to the Cape Orogeny (± 250 Ma), and reflected in the textures of the minerals making up the sediments of the Collingham Formation, suggests the enhancement in the sealing efficiency of this formation.
- Full Text:
- Date Issued: 2015
The evolution of the Brosterlea Volcanic Complex, Eastern Cape, South Africa
- Authors: Surtees, Grant Bradley
- Date: 2000
- Subjects: Volcanism , Geology -- South Africa -- Eastern Cape -- Brosterlea Volcanic Complex , Geology -- South Africa -- Eastern Cape , Flood basalts , Geology, Structural -- South Africa , Formations (Geology) -- South Africa , Geology, Structural -- Maps , Geological mapping
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4944 , http://hdl.handle.net/10962/d1005556 , Volcanism , Geology -- South Africa -- Eastern Cape -- Brosterlea Volcanic Complex , Geology -- South Africa -- Eastern Cape , Flood basalts , Geology, Structural -- South Africa , Formations (Geology) -- South Africa , Geology, Structural -- Maps , Geological mapping
- Description: Detailed field mapping (Map, Appendix B) has been conducted in and around the boundaries of a 14x18km, volcanic complex 35km northeast of Molteno in the Eastern Cape Province, South Africa. The structure is interpreted as a subsidence structure, and is filled with two volcaniclastic breccias, numerous lava flows, a number of sedimentary facies, and lies on a base of Clarens Formation overlying Elliot Formation rocks. This is an important study because 'widespread, voluminous fields of basaltic breccias are very rare (see Hanson and Elliot, 1996) and this is the first time that this type of volcanic complex and its deposits have been described. Detailed analyses of the two volcaniclastic breccias revealed changes in colour, clast types, clast sizes, and degree of alteration over relatively short distances both vertically and laterally within a single breccia unit. The variation in clast sizes implies a lack of sorting of the breccias. The lower of the two volcaniclastic breccias fills the subsidence structure, and outcrops between the Stormberg sedimentary sequence and the overlying Drakensberg basalts and was produced from phreatomagmatic eruptions signalling the start of the break-up of Gondwanaland in the mid-Jurassic. The upper volcaniclastic breccia is interbedded with the flood basalts and is separated from the lower breccia by up to 100m of lava flows in places, it is finer-grained than the lower volcaniclastic breccia, and it extends over 10km south, and over 100km north from the volcanic complex. The upper breccia is inferred to have been transported from outside the study area, from a source presumably similar to the subsidence structure in the volcanic complex. The pyroclastic material forming the upper breccia was transported to the subsidence structure as a laharic debris flow, based on its poorly sorted, unwelded and matrix-supported appearance. However, both breccias are unlikely to have been derived from epiclastic reworking of lava flows as they contain glass shards which are atypical of those derived from the autoclastic component of lava flows. The breccias are therefore not "secondary" lahars. There is also no evidence of any palaeotopographic highs from which the breccias could have been derived as gravity-driven flows. Based on the occurrence of three, 1m thick lacustrine deposits, localised peperite, fluvial reworking of sandstone and breccia in an outcrop to the south of the subsidence structure, and channel-lags encountered only in the upper units of the Clarens Formation and only within the subsidence structure, the palaeoenvironment inferred for the subsidence structure is one of wet sediment, possibly a shallow lake, in a topographic depression fed by small streams. Magmatic intrusions below the subsidence structure heated the water-laden, partly consolidated Clarens Formation sandstones, causing the circulation of pore fluid which resulted in the precipitation of minerals forming pisoliths in the sandstones. Intruding magma mixed, nonexplosively, with the wet, unconsolidated sediments near the base of the Clarens Formation (at approximately 100m below the surface), forming fluidal peperite by a process of sediment fluidisation where magma replaces wet sediment and cools slowly enough to prevent the magma fracturing brittly. Formation of fluidal peperite may have been a precursor to the development of FCIs (Fuel Coolant Interactions) (Busby-Spera and White, 1987). The breccias may represent the products of FCIs and may be the erupted equivalents of the peperites, suggesting a possible genetic link between the two. The peperites may have given way to FCI eruptions due to a number of factors including the drying out of the sediments and/or an increase in the volume of intruded magma below the subsidence structure which may have resulted in a more explosive interaction between sediment and magma. Phreatic activity fragmented and erupted the Clarens Formation sandstone, and stream flows reworked the angular sandstone fragments, pisoliths and sand grains into channelised deposits. With an increase in magmatic activity below the subsidence structure, phreatic activity became phreatomagmatic. The wet, partly consolidated Clarens Formation, and underlying, fully consolidated Elliot Formation sediments were erupted and fragmented. Clasts and individual grains of these sediments were redeposited with juvenile and non-juvenile basaltic material probably by a combination of back fall, where clasts erupted into the air fell directly back into the structure, and backflow where material was erupted out of the structure, but immediately flowed back in as lahars. This material formed the lower volcaniclastic breccia. A fault plane is identified along the southwestern margin of the subsidence structure, and is believed to continue up the western margin to the northwestern corner. A large dolerite body has intruded along the inferred fault plane on the western margin of the structure, and may be related to the formation of the lower volcaniclastic breccia, either directly through fluidisation of wet sediment during its intrusion, or as a dyke extending upwards from a network of sill-like intrusions below the subsidence structure. Geochemical analysis of the Drakensberg basalt lava flows by Mitchell (1980) and Masokwane (1997) revealed four distinct basalt types; the Moshesh's Ford, the Tafelkop, the Roodehoek, and the Vaalkop basalts. Basalt clasts sampled from the lower volcaniclastic breccia were shown to belong to the Moshesh's Ford basalt type which does not outcrop in situ within the subsidence structure. This implies that the Moshesh's Ford basalts were emplaced prior to the formation of the lower volcaniclastic breccia, and may have acted as a "cap-rock" over the system, allowing pressure from the vaporised fluids, heated by intruding basalt, to build up. The Moshesh's Ford basalt type was erupted prior to the resultant phreatomagmatic events forming the lower volcaniclastic breccia.
- Full Text:
- Date Issued: 2000
- Authors: Surtees, Grant Bradley
- Date: 2000
- Subjects: Volcanism , Geology -- South Africa -- Eastern Cape -- Brosterlea Volcanic Complex , Geology -- South Africa -- Eastern Cape , Flood basalts , Geology, Structural -- South Africa , Formations (Geology) -- South Africa , Geology, Structural -- Maps , Geological mapping
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4944 , http://hdl.handle.net/10962/d1005556 , Volcanism , Geology -- South Africa -- Eastern Cape -- Brosterlea Volcanic Complex , Geology -- South Africa -- Eastern Cape , Flood basalts , Geology, Structural -- South Africa , Formations (Geology) -- South Africa , Geology, Structural -- Maps , Geological mapping
- Description: Detailed field mapping (Map, Appendix B) has been conducted in and around the boundaries of a 14x18km, volcanic complex 35km northeast of Molteno in the Eastern Cape Province, South Africa. The structure is interpreted as a subsidence structure, and is filled with two volcaniclastic breccias, numerous lava flows, a number of sedimentary facies, and lies on a base of Clarens Formation overlying Elliot Formation rocks. This is an important study because 'widespread, voluminous fields of basaltic breccias are very rare (see Hanson and Elliot, 1996) and this is the first time that this type of volcanic complex and its deposits have been described. Detailed analyses of the two volcaniclastic breccias revealed changes in colour, clast types, clast sizes, and degree of alteration over relatively short distances both vertically and laterally within a single breccia unit. The variation in clast sizes implies a lack of sorting of the breccias. The lower of the two volcaniclastic breccias fills the subsidence structure, and outcrops between the Stormberg sedimentary sequence and the overlying Drakensberg basalts and was produced from phreatomagmatic eruptions signalling the start of the break-up of Gondwanaland in the mid-Jurassic. The upper volcaniclastic breccia is interbedded with the flood basalts and is separated from the lower breccia by up to 100m of lava flows in places, it is finer-grained than the lower volcaniclastic breccia, and it extends over 10km south, and over 100km north from the volcanic complex. The upper breccia is inferred to have been transported from outside the study area, from a source presumably similar to the subsidence structure in the volcanic complex. The pyroclastic material forming the upper breccia was transported to the subsidence structure as a laharic debris flow, based on its poorly sorted, unwelded and matrix-supported appearance. However, both breccias are unlikely to have been derived from epiclastic reworking of lava flows as they contain glass shards which are atypical of those derived from the autoclastic component of lava flows. The breccias are therefore not "secondary" lahars. There is also no evidence of any palaeotopographic highs from which the breccias could have been derived as gravity-driven flows. Based on the occurrence of three, 1m thick lacustrine deposits, localised peperite, fluvial reworking of sandstone and breccia in an outcrop to the south of the subsidence structure, and channel-lags encountered only in the upper units of the Clarens Formation and only within the subsidence structure, the palaeoenvironment inferred for the subsidence structure is one of wet sediment, possibly a shallow lake, in a topographic depression fed by small streams. Magmatic intrusions below the subsidence structure heated the water-laden, partly consolidated Clarens Formation sandstones, causing the circulation of pore fluid which resulted in the precipitation of minerals forming pisoliths in the sandstones. Intruding magma mixed, nonexplosively, with the wet, unconsolidated sediments near the base of the Clarens Formation (at approximately 100m below the surface), forming fluidal peperite by a process of sediment fluidisation where magma replaces wet sediment and cools slowly enough to prevent the magma fracturing brittly. Formation of fluidal peperite may have been a precursor to the development of FCIs (Fuel Coolant Interactions) (Busby-Spera and White, 1987). The breccias may represent the products of FCIs and may be the erupted equivalents of the peperites, suggesting a possible genetic link between the two. The peperites may have given way to FCI eruptions due to a number of factors including the drying out of the sediments and/or an increase in the volume of intruded magma below the subsidence structure which may have resulted in a more explosive interaction between sediment and magma. Phreatic activity fragmented and erupted the Clarens Formation sandstone, and stream flows reworked the angular sandstone fragments, pisoliths and sand grains into channelised deposits. With an increase in magmatic activity below the subsidence structure, phreatic activity became phreatomagmatic. The wet, partly consolidated Clarens Formation, and underlying, fully consolidated Elliot Formation sediments were erupted and fragmented. Clasts and individual grains of these sediments were redeposited with juvenile and non-juvenile basaltic material probably by a combination of back fall, where clasts erupted into the air fell directly back into the structure, and backflow where material was erupted out of the structure, but immediately flowed back in as lahars. This material formed the lower volcaniclastic breccia. A fault plane is identified along the southwestern margin of the subsidence structure, and is believed to continue up the western margin to the northwestern corner. A large dolerite body has intruded along the inferred fault plane on the western margin of the structure, and may be related to the formation of the lower volcaniclastic breccia, either directly through fluidisation of wet sediment during its intrusion, or as a dyke extending upwards from a network of sill-like intrusions below the subsidence structure. Geochemical analysis of the Drakensberg basalt lava flows by Mitchell (1980) and Masokwane (1997) revealed four distinct basalt types; the Moshesh's Ford, the Tafelkop, the Roodehoek, and the Vaalkop basalts. Basalt clasts sampled from the lower volcaniclastic breccia were shown to belong to the Moshesh's Ford basalt type which does not outcrop in situ within the subsidence structure. This implies that the Moshesh's Ford basalts were emplaced prior to the formation of the lower volcaniclastic breccia, and may have acted as a "cap-rock" over the system, allowing pressure from the vaporised fluids, heated by intruding basalt, to build up. The Moshesh's Ford basalt type was erupted prior to the resultant phreatomagmatic events forming the lower volcaniclastic breccia.
- Full Text:
- Date Issued: 2000
- «
- ‹
- 1
- ›
- »