Selected magnetostratigraphic studies in the main Karoo Basin (South Africa): implications for mass extinction events and the supercontinent of Pangea
- Authors: De Kock, Michiel Olivier
- Date: 2009-01-27T07:18:31Z
- Subjects: Stratigraphic geology , Paleomagnetism , Paleoclimatology , Pangaea (Geology) , Karoo Basin (South Africa)
- Type: Thesis
- Identifier: uj:14829 , http://hdl.handle.net/10210/1953
- Description: M.Sc. , The Late Carboniferous to early Jurassic Karoo Supergroup of South Africa witnessed two of the “big five” Phanerozoic mass extinction events, and the formation and subsequent break-up of the supercontinent Pangea. The closure of the Permian Period witnessed the greatest biotic crisis in the history of life. What is known about the Permian-Triassic boundary (hereafter referred to as the PTB) comes almost exclusively from marine successions in Europe and Asia. Although a major extinction event has been recognized in terrestrial successions, surprisingly little is known about its effects and timing. The exact placement of the PTB in the Karoo basin is not well constrained due to shortcomings of stratigraphic methods employed to date. This has made it extremely difficult to correlate the mass extinction events in the marine and non-marine environments; however, paleomagnetic studies could provide answers to both problems of absolute placement and correlation of the PTB in non-marine and marine successions. The PTB appears to lie within an interval of reversed polarity in many marine successions. A detailed magnetostratigraphic survey across the presumed PTB in the Karoo succession at localities in the north and south of the main Karoo Bain reveal two magnetic chrons, reversed followed by normal (with the boundary close to the reversal), which extends to slightly younger results from a previous study that identified an N/R pattern, thereby identifying a R/N/R pattern. The normal chron might correlate with the long basal Triassic normal polarity interval and the reversed polarity zones above and below it known from marine successions in the Alps, Russia, Pakistan and China. The PTB is thought to be situated coincident with the LAD of Dicynodon and the event bed of Ward et al. (2000), apparently above but not necessarily diachronous with a lithology change from predominantly green- to predominantly red mudstone. This placement falls within a normal polarity interval, but could conceivably have taken place at a time of reverse polarity due to delayed acquisition of magnetic remanence. The idea of an extraterrestrial impact as the cause of the end-Permian mass extinctions is strongly enhanced by a synchronous relationship between them. The configuration of the supercontinent Pangea during this time of earth history has been the matter of debate for the last three decades, with numerous alternative reconstructions to the classic Pangea A1 having been proposed for the time preceding the Jurassic. Paleomagnetic data from the Karoo allow for the definition of a new paleopole for West Gondwanaland, which prove a valuable tool for evaluating these various reconstructions. It is neither consistent with a Pangea B-type not C reconstruction for Pangea during this time interval, because of geological ambiguities. The most likely solution to the problem is that of a persistent non-dipole field contribution to the geomagnetic field during this time. Approximately 50 million years later Pangea was unambiguously in a classic Pangea A1 configuration, and life on earth suffered yet another set back. The end-Triassic mass extinction, which marks the sequence boundary between the Triassic and the Jurassic, has not received as much attention as the other four big Phanerozoic biotic disasters. In the Karoo a pronounced turnover in faunal assemblages from typical Triassic fauna to Jurassic Fauna (dinosaurs) is seen in the Elliot Formation. Magnetostratigraphic study of localities in the north and south of the Karoo Basin provided a magnetic zonation pattern for the Elliot Formation, a tool that has led to the constraining of the sequence boundary to the transition from the lower Elliot Formation to the middle Elliot and added to the hypothesis that the faunal turnover is globally synchronous. The determination of a paleolatitude for the Elliot Formation in combination with characteristically arid lithologies (eolian sandstones) provided the base for the evaluation of the paleoclimate that characterized Pangea during the Late Triassic to Early Jurassic. Key words: Karoo Basin, Magnetostratigraphy, Mass Extinction, Paleoclimate, Paleogeography, Paleomagnetism, Pangea, Permian-Triassic, Triassic-Jurassic
- Full Text:
- Authors: De Kock, Michiel Olivier
- Date: 2009-01-27T07:18:31Z
- Subjects: Stratigraphic geology , Paleomagnetism , Paleoclimatology , Pangaea (Geology) , Karoo Basin (South Africa)
- Type: Thesis
- Identifier: uj:14829 , http://hdl.handle.net/10210/1953
- Description: M.Sc. , The Late Carboniferous to early Jurassic Karoo Supergroup of South Africa witnessed two of the “big five” Phanerozoic mass extinction events, and the formation and subsequent break-up of the supercontinent Pangea. The closure of the Permian Period witnessed the greatest biotic crisis in the history of life. What is known about the Permian-Triassic boundary (hereafter referred to as the PTB) comes almost exclusively from marine successions in Europe and Asia. Although a major extinction event has been recognized in terrestrial successions, surprisingly little is known about its effects and timing. The exact placement of the PTB in the Karoo basin is not well constrained due to shortcomings of stratigraphic methods employed to date. This has made it extremely difficult to correlate the mass extinction events in the marine and non-marine environments; however, paleomagnetic studies could provide answers to both problems of absolute placement and correlation of the PTB in non-marine and marine successions. The PTB appears to lie within an interval of reversed polarity in many marine successions. A detailed magnetostratigraphic survey across the presumed PTB in the Karoo succession at localities in the north and south of the main Karoo Bain reveal two magnetic chrons, reversed followed by normal (with the boundary close to the reversal), which extends to slightly younger results from a previous study that identified an N/R pattern, thereby identifying a R/N/R pattern. The normal chron might correlate with the long basal Triassic normal polarity interval and the reversed polarity zones above and below it known from marine successions in the Alps, Russia, Pakistan and China. The PTB is thought to be situated coincident with the LAD of Dicynodon and the event bed of Ward et al. (2000), apparently above but not necessarily diachronous with a lithology change from predominantly green- to predominantly red mudstone. This placement falls within a normal polarity interval, but could conceivably have taken place at a time of reverse polarity due to delayed acquisition of magnetic remanence. The idea of an extraterrestrial impact as the cause of the end-Permian mass extinctions is strongly enhanced by a synchronous relationship between them. The configuration of the supercontinent Pangea during this time of earth history has been the matter of debate for the last three decades, with numerous alternative reconstructions to the classic Pangea A1 having been proposed for the time preceding the Jurassic. Paleomagnetic data from the Karoo allow for the definition of a new paleopole for West Gondwanaland, which prove a valuable tool for evaluating these various reconstructions. It is neither consistent with a Pangea B-type not C reconstruction for Pangea during this time interval, because of geological ambiguities. The most likely solution to the problem is that of a persistent non-dipole field contribution to the geomagnetic field during this time. Approximately 50 million years later Pangea was unambiguously in a classic Pangea A1 configuration, and life on earth suffered yet another set back. The end-Triassic mass extinction, which marks the sequence boundary between the Triassic and the Jurassic, has not received as much attention as the other four big Phanerozoic biotic disasters. In the Karoo a pronounced turnover in faunal assemblages from typical Triassic fauna to Jurassic Fauna (dinosaurs) is seen in the Elliot Formation. Magnetostratigraphic study of localities in the north and south of the Karoo Basin provided a magnetic zonation pattern for the Elliot Formation, a tool that has led to the constraining of the sequence boundary to the transition from the lower Elliot Formation to the middle Elliot and added to the hypothesis that the faunal turnover is globally synchronous. The determination of a paleolatitude for the Elliot Formation in combination with characteristically arid lithologies (eolian sandstones) provided the base for the evaluation of the paleoclimate that characterized Pangea during the Late Triassic to Early Jurassic. Key words: Karoo Basin, Magnetostratigraphy, Mass Extinction, Paleoclimate, Paleogeography, Paleomagnetism, Pangea, Permian-Triassic, Triassic-Jurassic
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Thermal impact of dolerite sills on the shale gas potential of Ecca Group mudstone in a drill core from the Central Main Karoo Basin
- Authors: Adeniyi, Elijah Olusola
- Date: 2016
- Subjects: Karoo Basin (South Africa) , Sills (Geology) - South Africa - Karoo Basin , Diabase - South Africa - Karoo Basin , Shale gas reservoirs - South Africa - Karoo Basin , Mudstone - South Africa - Karoo Basin , Ecca Group
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235720 , uj:24111
- Description: M.Sc. (Geology) , Abstract: The Main Karoo Basin of South Africa, especially the Whitehill Formation of the Ecca Group is estimated as possessing shale gas reserve potential of between 368bcm to 13734bcm on a wide land area of over 183 000 km2, thus placing South Africa as the 8th largest potential shale gas resource in the world. However, this reserve could be overestimated due to the poorly studied thermal impact of voluminous magmatic intrusions into the basin strata. Jurassic-aged Karoo Large Igneous Province (KLIP) emplaced a myriad network of dykes and sills that takes up 0.55 x 106 km2 of the basin and up to 30% of the total thickness. This could bring additional heat to the thermal evolution of the basin likely to create thermal over-maturation and/or disrupt the preservation of generated hydrocarbon of the Main Karoo Basin source rocks. Here organic-rich mudstones of the Ecca Group with mineralogical, mineral chemistry, organic geochemistry and Ar – Ar age dating proxies were analysed. Illite crystallinity and chlorite chemistry studies show thermal evolution controlled by diagenesis and regional metamorphism as well as local contact metamorphic overprints in the vicinity of dolerite sills. 13Corg and TOC vary in proximity to the dolerite intrusions. Rock-Eval pyrolysis data show that the organic matters are mainly Type III gas-prone kerogens of mature to post mature thermal maturity. The source rocks are mainly over-mature, having poor generation potential which could reflect the thermal overcooking/exhaustion, probably accompanied by gas migration, driven by the thermal impact of dolerite intrusions. The clay mineral ages also show full and partial recrystallized ages in the metamorphic aureoles of dolerite sills. Overall, the finding of this research reveals that the shale gas potential of the basin could be much lesser than originally estimated. Load metamorphism and dolerite intrusions influenced organic matter transformation in the basin. The impact on the thermal maturity and hydrocarbon generation of the basin’s organic matter is greater around multiple to closely spaced thermal aureoles of intrusions. These findings correlate with results from other boreholes studied in the Main Karoo Basin and provide a better understanding of the thermal evolution of the Ecca Group organic rich mudstones and its shale gas potential.
- Full Text:
- Authors: Adeniyi, Elijah Olusola
- Date: 2016
- Subjects: Karoo Basin (South Africa) , Sills (Geology) - South Africa - Karoo Basin , Diabase - South Africa - Karoo Basin , Shale gas reservoirs - South Africa - Karoo Basin , Mudstone - South Africa - Karoo Basin , Ecca Group
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/235720 , uj:24111
- Description: M.Sc. (Geology) , Abstract: The Main Karoo Basin of South Africa, especially the Whitehill Formation of the Ecca Group is estimated as possessing shale gas reserve potential of between 368bcm to 13734bcm on a wide land area of over 183 000 km2, thus placing South Africa as the 8th largest potential shale gas resource in the world. However, this reserve could be overestimated due to the poorly studied thermal impact of voluminous magmatic intrusions into the basin strata. Jurassic-aged Karoo Large Igneous Province (KLIP) emplaced a myriad network of dykes and sills that takes up 0.55 x 106 km2 of the basin and up to 30% of the total thickness. This could bring additional heat to the thermal evolution of the basin likely to create thermal over-maturation and/or disrupt the preservation of generated hydrocarbon of the Main Karoo Basin source rocks. Here organic-rich mudstones of the Ecca Group with mineralogical, mineral chemistry, organic geochemistry and Ar – Ar age dating proxies were analysed. Illite crystallinity and chlorite chemistry studies show thermal evolution controlled by diagenesis and regional metamorphism as well as local contact metamorphic overprints in the vicinity of dolerite sills. 13Corg and TOC vary in proximity to the dolerite intrusions. Rock-Eval pyrolysis data show that the organic matters are mainly Type III gas-prone kerogens of mature to post mature thermal maturity. The source rocks are mainly over-mature, having poor generation potential which could reflect the thermal overcooking/exhaustion, probably accompanied by gas migration, driven by the thermal impact of dolerite intrusions. The clay mineral ages also show full and partial recrystallized ages in the metamorphic aureoles of dolerite sills. Overall, the finding of this research reveals that the shale gas potential of the basin could be much lesser than originally estimated. Load metamorphism and dolerite intrusions influenced organic matter transformation in the basin. The impact on the thermal maturity and hydrocarbon generation of the basin’s organic matter is greater around multiple to closely spaced thermal aureoles of intrusions. These findings correlate with results from other boreholes studied in the Main Karoo Basin and provide a better understanding of the thermal evolution of the Ecca Group organic rich mudstones and its shale gas potential.
- Full Text:
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