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Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology
The Vanrhynsdorp Group is a mainly fluvio-marine siliclastic succession that outcrops in the northwestern part of South Africa. The critical Precambrian-Cambrian boundary falls within the group, however the depositional environments across the boundary, its exact stratigraphic position and nature ar...
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| Format: | Thesis |
| Language: | English |
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Department of Geological Sciences
2019
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| _version_ | 1867613202966118400 |
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| access_status_str | Open Access |
| author | Harrison, Bianca |
| author2 | Bordy, Emese M |
| author_browse | Bordy, Emese M Harrison, Bianca |
| author_facet | Bordy, Emese M Harrison, Bianca |
| author_sort | Harrison, Bianca |
| collection | Thesis |
| description | The Vanrhynsdorp Group is a mainly fluvio-marine siliclastic succession that outcrops in the northwestern part of South Africa. The critical Precambrian-Cambrian boundary falls within the group, however the depositional environments across the boundary, its exact stratigraphic position and nature are unresolved. The group was deposited in the Vanrhynsdorp Basin, which has been shown to be the southernmost extension of the Nama Foreland Basin. Consequently, the Vanrhynsdorp Group has been correlated with the world-famous Nama Group, which features diverse Ediacaran-Cambrian fossils. To date, no body fossils have been discovered in the Vanrhynsdorp Group. Through U-Pb dating of detrital zircons using LA-ICP-MS, radiometric ages for the middle part of the Vanrhynsdorp Group (Besonderheid Formation) were obtained in a preliminary study of this project. The radiometric data, yielding a maximum depositional age of 524 to 528 Ma from the youngest zircon grain population, indicated that the Precambrian-Cambrian boundary is stratigraphically lower in the group than it was thought before. To further constrain the age of the lower Vanrhynsdorp Group, and by extension the position of the Precambrian-Cambrian boundary, several detrital zircon samples were processed for age determination from the succession in this study. In addition, using sedimentary facies analysis, the lateral and vertical facies variation in this lower part of the group were (re)documented in order to refine the palaeoenvironmental setting. The current results suggest a dominantly shallow marine, partly storm-dominated depositional environment for the lowermost units as opposed to the previous interpretations of dominantly alluvial settings. Because of the global importance of the Ediacaran-Cambrian transition for diversification of marine biota in the Cambrian, addressing these palaeoenvironmental inconsistencies is the vital outcome of this study. By integrating our sedimentological and geochronological results, the project presents an improved understanding of the depositional history of the Vanrhynsdorp Group during the critical Ediacaran-Cambrian transition. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/29450 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:24.523Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| publisher | Department of Geological Sciences |
| publisherStr | Department of Geological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/29450 Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology Harrison, Bianca Bordy, Emese M Taylor, Wendy L Geology The Vanrhynsdorp Group is a mainly fluvio-marine siliclastic succession that outcrops in the northwestern part of South Africa. The critical Precambrian-Cambrian boundary falls within the group, however the depositional environments across the boundary, its exact stratigraphic position and nature are unresolved. The group was deposited in the Vanrhynsdorp Basin, which has been shown to be the southernmost extension of the Nama Foreland Basin. Consequently, the Vanrhynsdorp Group has been correlated with the world-famous Nama Group, which features diverse Ediacaran-Cambrian fossils. To date, no body fossils have been discovered in the Vanrhynsdorp Group. Through U-Pb dating of detrital zircons using LA-ICP-MS, radiometric ages for the middle part of the Vanrhynsdorp Group (Besonderheid Formation) were obtained in a preliminary study of this project. The radiometric data, yielding a maximum depositional age of 524 to 528 Ma from the youngest zircon grain population, indicated that the Precambrian-Cambrian boundary is stratigraphically lower in the group than it was thought before. To further constrain the age of the lower Vanrhynsdorp Group, and by extension the position of the Precambrian-Cambrian boundary, several detrital zircon samples were processed for age determination from the succession in this study. In addition, using sedimentary facies analysis, the lateral and vertical facies variation in this lower part of the group were (re)documented in order to refine the palaeoenvironmental setting. The current results suggest a dominantly shallow marine, partly storm-dominated depositional environment for the lowermost units as opposed to the previous interpretations of dominantly alluvial settings. Because of the global importance of the Ediacaran-Cambrian transition for diversification of marine biota in the Cambrian, addressing these palaeoenvironmental inconsistencies is the vital outcome of this study. By integrating our sedimentological and geochronological results, the project presents an improved understanding of the depositional history of the Vanrhynsdorp Group during the critical Ediacaran-Cambrian transition. 2019-02-08T14:21:36Z 2019-02-08T14:21:36Z 2018 2019-02-07T07:04:51Z Master Thesis Masters MSc http://hdl.handle.net/11427/29450 eng application/pdf Department of Geological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Geology Harrison, Bianca Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| thesis_degree_str | Master's |
| title | Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| title_full | Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| title_fullStr | Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| title_full_unstemmed | Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| title_short | Palaeoenvironments and position of the Precambrian–Cambrian boundary within the lower Vanrhynsdorp Group of South Africa: sedimentary facies analysis, U-Pb series zircon geochronology and micropalaeontology |
| title_sort | palaeoenvironments and position of the precambrian cambrian boundary within the lower vanrhynsdorp group of south africa sedimentary facies analysis u pb series zircon geochronology and micropalaeontology |
| topic | Geology |
| url | http://hdl.handle.net/11427/29450 |
| work_keys_str_mv | AT harrisonbianca palaeoenvironmentsandpositionoftheprecambriancambrianboundarywithinthelowervanrhynsdorpgroupofsouthafricasedimentaryfaciesanalysisupbserieszircongeochronologyandmicropalaeontology |