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Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup
Dissertation (MSc (Geology))--University of Pretoria, 1995.
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2024
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| access_status_str | Open Access |
| author2 | Snyman, Johanna Elizabeth Wilhelmina |
| author_browse | Snyman, Johanna Elizabeth Wilhelmina |
| author_facet | Snyman, Johanna Elizabeth Wilhelmina |
| collection | Thesis |
| dc_rights_str_mv | © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Dissertation (MSc (Geology))--University of Pretoria, 1995. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/99481 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:39:39.216Z |
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| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2024 |
| publishDateRange | 2024 |
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| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/99481 Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup Snyman, Johanna Elizabeth Wilhelmina Mass extinction Permian-Triassic Geological Karoo supergroup UCTD Dissertation (MSc (Geology))--University of Pretoria, 1995. This work comprises a study of the sedimentary rocks and petrified wood found across the Permian-Triassic boundary. The study area is situated in the northeastern Orange Free State, near the towns Harrismith and Senekal, South Africa. The aim of the study is to determine a possible reason for the mass extinction at the Permian-Triassic boundary by investigating the relevant lithostratigraphic units. The lithostratigraphy across the Permian-Triassic boundary consists of the Beaufort Group, which forms part of the Karoo Supergroup. The Permian-Triassic boundary occurs at the contact between the Harrismith Member (at the top) and the Schoondraai Member (at the base) of the Normandien Formation. Two reptile biozones, which form part of the biostratigraphy of the Beaufort Group, can be related to the Harrismith and Schoondraai Members. The Schoondraai Member is equivalent to the Dicynodon - Theriognathus Assemblage Zone and the Harrismith Member to the Lystrosaurus - Procolophon Assemblage Zone. Six lithofacies are recognised from the Schoondraai Member and five lithofacies from the Harrismith Member. Mudstones provide evidence of suspension settling of fine material in a low energy system. This fine material was probably deposited on a floodplain. Fine sandstone interbedded with the mudrock points to a fluctuation in energy levels, most probably due to pronounced seasonality. Moderate to well sorted sandstones were more effectively transported and it is proposed that they were fluvial channel deposits, which tend to be upward-fining. A trend of declining energy levels upwards in the succession can be observed from the Schoondraai Member to the Harrismith Member. The palaeoenvironment appears to have become more arid with time. Petrographic studies of the sandstones show a red pigment (hematite) that covers the sand grains. This can indicate a warm climate, for brown limonite alters to red hematite relatively rapidly in warm and dry conditions. No shattered mineral grains, shock lamellae in quartz nor small shatter cones on the clasts, which could be indicative of impact metamorphism, could be observed. The source area of the sandstones was probably granitic. The sandstones are classified as feldspathic arenites. The mineralogy of the clay fraction shows the presence of quartz, plagioclase, smectite, illite and chlorite. No glass shards, cristobalite and/or laumontite, which would indicate a probable volcanic source of the clay minerals, and no potassium feldspar, were observed. The sediments were therefore not related to volcanic ash layers, but were rather detrital, terrestrial sediments. The diagenetic environment was most likely alkaline. The geochemistry of the mudrocks shows a slight enrichment of SiO 2 , Al 2O3 , TiO 2 , Cao, K2O and Na 2O, and a slight depletion of MgO and Fe 2O3 , across the PermianTriassic boundary. The TiOi Al 2O3 ratios, as well as the CIA-values of the mud rocks point to ordinary or 11 typical shales 11 rather than altered volcanic ash layers. Cr /Zr ratios suggest a granitic source area with few or no contributions from ultramafic rocks. Palaeosalinity indicators such as the Rb/K ratio may indicate a brackish water to marine transition, but due to a limited number of samples and no evidence of tidal activity from the sedimentological data, care should be taken when interpreting these results. Analyses for platinum-group elements indicate values below the respective detection limits. The petrified wood was studied macroscopically as well as microscopically. The woods all belong to the class Gymnospermae. No angiosperm woods were found. The trunks were found in fine-grained sandstone or in situ in weathered soil. Only some in situ petrified logs have roots embedded in a clay layer. The presence of prominent growth rings indicates a seasonal control. Analysis of these growth rings shows that the trees grew under limited to favourable climatic conditions. The width of the rings from both assemblage zones indicates that the growth rates of the trees were fast. The petrifying mineral in all the specimens is silica (quartz), but high concentrations of zinc and iron also occur. The concentrations of zinc and iron increases upwards in the succession across the Permian-Triassic boundary. This iron enrichment can probably be linked to oxidation of the iron due to a palaeoenvironment that became more arid. The results from this study point to a gradual change of climatic conditions across the Permian-Triassic boundary, rather than an abrupt change due to volcanic activity or an asteroid impact. Geology MSc (Geology) 2024-11-27T09:15:57Z 2024-11-27T09:15:57Z 21/10/27 1995 Dissertation http://hdl.handle.net/2263/99481 en © 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | Mass extinction Permian-Triassic Geological Karoo supergroup UCTD Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title | Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title_full | Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title_fullStr | Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title_full_unstemmed | Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title_short | Mass extinction on the Permian - Triassic boundary : geological evidence from the Karoo Supergroup |
| title_sort | mass extinction on the permian triassic boundary geological evidence from the karoo supergroup |
| topic | Mass extinction Permian-Triassic Geological Karoo supergroup UCTD |
| url | http://hdl.handle.net/2263/99481 |