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Rademan Radiometric 2018.Pdf (11.89Mb) Radiometric dating and stratigraphic reassessment of the Elliot and Clarens formations; near Maphutseng and Moyeni, Kingdom of Lesotho, southern Africa Ms. Zandri Rademan, 16964063 Thesis presented in partial fulfilment of the requirements for the degree of Masters of Science at University of Stellenbosch Supervisor: Dr. R. T. Tucker (University of Stellenbosch) Co-advisor: Dr. E. M. Bordy (University of Cape Town) Department of Earth Sciences Faculty of Science RSA December 2018 Stellenbosch University https://scholar.sun.ac.za DECLARATION By submitting this dissertation electronically, I declare that the entirety of the work contained herein is my own, original work, that I am the sole author thereof (except where explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third-party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: December 2018 Copyright © 2018 Stellenbosch University All rights reserved Stellenbosch University https://scholar.sun.ac.za ACKNOWLEDGEMENTS Firstly, I would like to thank my supervisor, Dr. R. T. Tucker (University of Stellenbosch), for his guidance throughout this project. Thank you for allowing this paper to be my own work; yet, steering me in the right direction whenever I hit a speed-bump and careened off the path. Thank you for your patience through all the blood, sweat and tears, it’s been quite the journey. My utmost gratitude goes to Dr. E. M. Bordy (University of Cape Town) for taking me under her wing and granting me the opportunity to tackle this project, as well as graciously offering advice and aid from her great well of expertise. Thank you for going beyond limits to ensure my project was a success. I would also like to thank everyone at CAF labs (Stellenbosch University) for the hours spent offering me the necessary training and support throughout the analytical phase of this project. Thanks also goes to George Olivier and Tannie Loxie Conradie for logistical support during this project. A proverbial tip of the hat goes to my fellow post-grad partner in crime, Louis Jonk, for the hours spent contemplating our fates over coffee and his invaluable assistance with the analytical stages. I am ever grateful to the friendly and helpful trackway museum supervisors and curators at Masitise (Ntate K. Phakisi and Ntate. L. N. Phakisi) and Moyeni (Ntate Leonesa) for taking time to escort me safely to each trackway and often joining in as impromptu field assistants. Thank you to Growing Nations and the ladies at Hillsview Lodge for their hospitality during my field work stays. My research would not have been possible without the necessary financial support from the following institutions: • National Research Foundation (NRF): MSc project student bursary • The Palaeontological Scientific Trust (PAST): Post-graduate degree support grant • International Association of Sedimentology (IAS): Student Travel Grant Stellenbosch University https://scholar.sun.ac.za I am profoundly grateful to my family and friends for supporting me every step of the way. A very special thank you goes to my parents, who offered me financial, logistical and emotional support without which this project would not have been a success. Thank you to my mother for believing in me and supporting me through numerous emotional breakdowns. Thank you to my father for offering up his valuable time to become my field assistant, aiding with vital solutions to problems I was too blind to see and lending a critical eye when needed. Thank you to my brother who kept a sense of humour when I had lost mine. Ek is verskriklik lief vir julle. A heartfelt thank you goes to my horses, who kept me grounded and sane throughout this entire experience. Lastly, but most importantly, may all of the glory go to the Lord our God. Stellenbosch University https://scholar.sun.ac.za ABSTRACT The Elliot and Clarens formations (Stormberg Group) of the Karoo Supergroup famously preserve not only a dynamic suite of depositional environments spanning the Late Triassic to Early Jurassic, but also boast a diverse assemblage of trace and body fossils. Due to the nature of these assemblages spanning the globally correlative Triassic-Jurassic Boundary (TJB) and end-Triassic Extinction Event (ETE), the accuracy of temporal placement and correlation via the stratigraphic framework is paramount. Yet, a distinct lack of robust temporal framework and inconsistencies between the bio-, magneto- and lithostratigraphic records persist. This project sought to provide localized context for three key fossil-bearing localities (southwestern Lesotho), which could thereafter be applied both at a regional and global scale. In-depth facies, palaeocurrent and architectural element analyses illustrated an overall increase in palaeoclimatic aridity, as evidenced by the change in depositional system from the meandering fluvial dominated lower Elliot Formation to the aeolian Clarens Formation. Detrital zircon geochronology ascertained a temporal framework ranging from the Norian to Pliensbachian (216.7-190.5 Ma) Elliot Formation to the Sinemurian to Pliensbachian (190.5-186.7 Ma) Clarens Formation. These temporal constraints also support the presence of a regional paraconformity at the lower and upper Elliot contact. The geochronology additionally indicated a shared source provenance of recycled grains from the Cape Supergroup and older Karoo strata, interspersed with direct source inputs from proximal magmatic/metamorphic provinces. Ultimately, the greater temporal and palaeoecological resolution provided by this study promotes the better understanding of the early Mesozoic history of southern Gondwana and lays the foundations for future geochronological investigations. Stellenbosch University https://scholar.sun.ac.za Table of Contents DECLARATION ......................................................................................................................................... II ACKNOWLEDGEMENTS .......................................................................................................................... III ABSTRACT ................................................................................................................................................ V 1 INTRODUCTION ............................................................................................................................... 1 2 GEOLOGICAL BACKGROUND ........................................................................................................... 5 2.1 Basin Setting ............................................................................................................................ 5 2.2 Stormberg Group .................................................................................................................. 10 2.2.1 Elliot Formation ............................................................................................................. 11 2.2.2 Clarens Formation ......................................................................................................... 16 2.2.3 Biostratigraphy of the Stormberg Group ...................................................................... 17 2.3 Temporal Setting ................................................................................................................... 22 2.3.1 Elliot and Clarens age constraints ................................................................................. 22 2.3.2 End-Triassic Extinction Event and Triassic-Jurassic Boundary ...................................... 25 3 METHODOLOGY ............................................................................................................................ 30 3.1 Sedimentological Analysis ..................................................................................................... 30 3.2 Sampling ................................................................................................................................ 31 3.3 Zircon separation and data processing ................................................................................. 34 4 RESULTS......................................................................................................................................... 39 4.1 Facies Analysis ....................................................................................................................... 39 4.1.1 Facies Assemblage I (Mudstone dominated): ............................................................... 42 4.1.2 Facies Assemblage 2 (Thick sandstone units): .............................................................. 46 4.1.3 Facies Assemblage 3 (Lenticular sandstones and siltstones): ....................................... 52 4.1.4 Facies Assemblage 4 (Thick cross-bedded sandstone): ................................................ 55 4.1.5 Facies Assemblage 5 (Intercalated sandstones, siltstones and mudstones): ............... 58 4.1.6 Facies Assemblage 6 (Conglomerate): .......................................................................... 62 4.2 Stratigraphy ........................................................................................................................... 65 4.2.1 lower Elliot Formation .................................................................................................. 67 4.2.2 upper Elliot Formation .................................................................................................
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