DOCSLIB.ORG

Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin - South Africa

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin - South Africa Graduate Theses, Dissertations, and Problem Reports 2016 Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin - South Africa Clyde Pitt Findlay III Follow this and additional works at: https://researchrepository.wvu.edu/etd Recommended Citation Findlay III, Clyde Pitt, "Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin - South Africa" (2016). Graduate Theses, Dissertations, and Problem Reports. 5597. https://researchrepository.wvu.edu/etd/5597 This Thesis is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin – South Africa Clyde Pitt Findlay III Thesis submitted to the Eberly College of Arts and Sciences at West Virginia University In partial fulfillment of the requirements for the degree of Masters of Science In Geology Amy Weislogel, Ph.D., Chair Tim Carr, Ph.D. Jaime Toro, Ph.D. Department of Geology and Geography Morgantown, West Virginia 2016 Keywords: Karoo Basin, Gondwana, Permian, Triassic, Shale, Mudstone, Provenance, Geochemistry, Major Elements, Trace Elements, Rare Earth Elements, Sm-Nd, Subsidence Model, Foreland Basin Copyright 2016 Clyde Pitt Findlay III ABSTRACT Influence of the Gondwanide Magmatic Arc and Cape Fold Belt on the Karoo Basin – South Africa Clyde Pitt Findlay III The Permian Ecca Group in South Africa preserves a thick succession of clastic basin fill, including mud-rich turbidite sequences and hemipelagic mudstone units. Provenance of mud influx into the basin is an important constraint for understanding the tectonic processes influencing regional basin development and distribution of organic-rich Lower Ecca Group mudstone and subsequent depositional style of the Upper Ecca Group turbidite systems. In this study, we interpret the Ecca Group mudstones were sourced by the Cape Fold Belt and Gondwanide Magmatic Arc based on geochemistry and mineralogy of 38 mudstone samples. Muscovite and high quartz content (average 32.9%) indicate metamorphic and recycled sedimentary sources. Chemical index of alteration (CIA) values are greatest (CIA = 76 – 82) and Index of Compositional Variability (ICV) is depressed (ICV = 0.5 – 0.8) at the base of the Ecca Group, and indicate less weathering upsection. Rare earth element abundances display LREE enrichment and a negative Eu anomaly, and various trace element plots are consistent with mixing of sediment derived from Old Upper Continental Crust (OUC) and Young Differentiated Arc (YDA) terranes, such as the Cape Fold Belt and Gondwanide Magmatic Arc, respectively. Epsilon Nd and chondritic model ages are consistent with mixing of OUC and YDA sources. These results indicate that the southern Gondwanide Magmatic Arc and the Cape Fold Belt affected subsidence and sedimentation during early development of the Karoo Basin, and that the basin is a retroarc foreland basin. Acknowledgments First and foremost I thank my wife, Jenny, for helping me through my master’s degree. She not only kept me on track to finish writing this thesis, but supported me financially as well. I would also like to thank my advisor, Amy Weislogel, for introducing me to the Karoo project and guiding me through my research. I also thank my graduate committee, Tim Carr and Jaime Toro, for their support. This project would not have been possible without the help of my fellow classmates Matt McKay and Ben Johnson. Finally I would like to thank Harold Stowell and Liz Bollen at the University of Alabama, the GeoAnalytical lab at Washington State University, Actlabs, and the Shared Resource Facilities at West Virginia University for the use of their analytical facilities. iii Table of Contents ABSTRACT ................................................................................................................................................. ii Acknowledgments ...................................................................................................................................... iii List of Tables ............................................................................................................................................ viii Chapter 1: Introduction ............................................................................................................................. 1 1.1 Research Problem ............................................................................................................................. 1 1.2 Geologic Background ........................................................................................................................ 3 1.2.1 Tectonic setting ........................................................................................................................ 3 1.2.2 Karoo Basin Stratigraphy ........................................................................................................ 4 1.2.2.1 Laingsburg Subbasin ............................................................................................................. 6 1.2.2.2 Ripon Subbasin ...................................................................................................................... 6 1.2.3 Previous Provenance Studies .................................................................................................. 6 1.3. Provenance Terranes ....................................................................................................................... 7 1.3.1 Kalahari Craton and Namaqua-Natal Metamorphic Province ............................................. 8 1.3.2 Pan-African Orogenic belts ..................................................................................................... 8 1.3.3 North Patagonian and Deseado Massifs ................................................................................ 8 1.3.4 Cape Fold Belt ......................................................................................................................... 8 2.1 Sampling .......................................................................................................................................... 10 2.2 Petrography ..................................................................................................................................... 13 2.3 X-ray Diffraction Analysis ............................................................................................................. 13 2.4 X-ray Fluorescence analysis ........................................................................................................... 13 2.5 ICP-MS Analysis ............................................................................................................................. 14 2.7 Samarium and Neodymium Isotopes ............................................................................................ 15 Chapter 3: Results ..................................................................................................................................... 15 3.1 Petrography Results ........................................................................................................................ 15 3.2 Mineralogy Results ......................................................................................................................... 19 3.2.1 Laingsburg Subbasin ............................................................................................................. 19 3.2.2 Ripon Subbasin ...................................................................................................................... 20 3.3 Major Element Results ................................................................................................................... 21 3.3.1 Laingsburg Subbasin ............................................................................................................. 21 iv 3.3.2 Ripon Subbasin ...................................................................................................................... 23 3.3.3 Comparison of Major Element Composition ........................................................................ 25 3.4 Trace Element Results .................................................................................................................... 28 3.5 Rare Earth Element Results........................................................................................................... 30 Chapter 4: Discussion ............................................................................................................................... 37 4.1 Provenance of mudstone units in the Ecca and Beaufort groups ............................................... 37 4.1.1 Lithology and Composition of the source terranes ............................................................... 37 4.1.2 Weathering of the source terranes .......................................................................................
Load more

Recommended publications
  • JVP 26(3) September 2006—ABSTRACTS
    Neoceti Symposium, Saturday 8:45 acid-prepared osteolepiforms Medoevia and Gogonasus has offered strong support for BODY SIZE AND CRYPTIC TROPHIC SEPARATION OF GENERALIZED Jarvik’s interpretation, but Eusthenopteron itself has not been reexamined in detail. PIERCE-FEEDING CETACEANS: THE ROLE OF FEEDING DIVERSITY DUR- Uncertainty has persisted about the relationship between the large endoskeletal “fenestra ING THE RISE OF THE NEOCETI endochoanalis” and the apparently much smaller choana, and about the occlusion of upper ADAM, Peter, Univ. of California, Los Angeles, Los Angeles, CA; JETT, Kristin, Univ. of and lower jaw fangs relative to the choana. California, Davis, Davis, CA; OLSON, Joshua, Univ. of California, Los Angeles, Los A CT scan investigation of a large skull of Eusthenopteron, carried out in collaboration Angeles, CA with University of Texas and Parc de Miguasha, offers an opportunity to image and digital- Marine mammals with homodont dentition and relatively little specialization of the feeding ly “dissect” a complete three-dimensional snout region. We find that a choana is indeed apparatus are often categorized as generalist eaters of squid and fish. However, analyses of present, somewhat narrower but otherwise similar to that described by Jarvik. It does not many modern ecosystems reveal the importance of body size in determining trophic parti- receive the anterior coronoid fang, which bites mesial to the edge of the dermopalatine and tioning and diversity among predators. We established relationships between body sizes of is received by a pit in that bone. The fenestra endochoanalis is partly floored by the vomer extant cetaceans and their prey in order to infer prey size and potential trophic separation of and the dermopalatine, restricting the choana to the lateral part of the fenestra.
    [Show full text]
  • Exkursionen Excursions
    EXKURSIONEN EXCURSIONS 174 MITT.ÖSTERR.MINER.GES. 161 (2015) A GEOLOGICAL EXCURSION TO THE MINING AREAS OF SOUTH AFRICA by Aberra Mogessie, Christoph Hauzenberger, Sara Raic, Philip Schantl, Lukas Belohlavek, Antonio Ciriello, Donia Daghighi, Bernhard Fercher, Katja Goetschl, Hugo Graber, Magdalena Mandl, Veronika Preissegger, Gerald Raab, Felix Rauschenbusch, Theresa Sattler, Simon Schorn, Katica Simic, Michael Wedenig & Sebastian Wiesmair Institute of Earth Sciences, University of Graz, Universitaetsplatz 2, A-8010 Graz Frank Melcher, Walter Prochaska, Heinrich Mali, Heinz Binder, Marco Dietmayer-Kräutler, Franz Christian Friedman, Maximilian Mathias Haas, Ferdinand Jakob Hampl, Gustav Erwin Hanke, Wolfgang Hasenburger, Heidi Maria Kaltenböck, Peter Onuk, Andrea Roswitha Pamsl, Karin Pongratz, Thomas Schifko, Sebastian Emanuel Schilli, Sonja Schwabl, Cornelia Tauchner, Daniela Wallner & Juliane Hentschke Chair of Geology and Economic Geology, Mining University of Leoben, Peter-Tunner-Strasse 5, A-8700 Leoben Christoph Gauert Department of Geology, University of the Free State, South Africa 1. Preface Almost a year ago Aberra Mogessie planned to organize a field excursion for the students of the Institute of Earth Sciences, University of Graz. The choices were Argentina, Ethiopia (where we had organized past excursions) and South Africa. Having discussed the matter with Christoph Hauzenberger concerning geology, logistics etc. we decided to organize a field excursion to the geologically interesting mining areas of South Africa. We contacted Christoph Gauert from the University of Free State, South Africa to help us with the local organization especially to get permission from the different mining companies to visit their mining sites. We had a chance to discuss with him personally during his visit to our institute at the University of Graz in May 2014 and make the first plan.
    [Show full text]
  • South Africa's Coalfields — a 2014 Perspective
    International Journal of Coal Geology 132 (2014) 170–254 Contents lists available at ScienceDirect International Journal of Coal Geology journal homepage: www.elsevier.com/locate/ijcoalgeo South Africa's coalfields — A 2014 perspective P. John Hancox a,⁎,AnnetteE.Götzb,c a University of the Witwatersrand, School of Geosciences and Evolutionary Studies Institute, Private Bag 3, 2050 Wits, South Africa b University of Pretoria, Department of Geology, Private Bag X20, Hatfield, 0028 Pretoria, South Africa c Kazan Federal University, 18 Kremlyovskaya St., Kazan 420008, Republic of Tatarstan, Russian Federation article info abstract Article history: For well over a century and a half coal has played a vital role in South Africa's economy and currently bituminous Received 7 April 2014 coal is the primary energy source for domestic electricity generation, as well as being the feedstock for the Received in revised form 22 June 2014 production of a substantial percentage of the country's liquid fuels. It furthermore provides a considerable source Accepted 22 June 2014 of foreign revenue from exports. Available online 28 June 2014 Based on geographic considerations, and variations in the sedimentation, origin, formation, distribution and quality of the coals, 19 coalfields are generally recognised in South Africa. This paper provides an updated review Keywords: Gondwana coal of their exploration and exploitation histories, general geology, coal seam nomenclature and coal qualities. With- Permian in the various coalfields autocyclic variability is the norm rather than the exception, whereas allocyclic variability Triassic is much less so, and allows for the correlation of genetically related sequences. During the mid-Jurassic break up Coalfield of Gondwana most of the coal-bearing successions were intruded by dolerite.
    [Show full text]
  • Footprint of a Late Carboniferous Ice Sheet D.P
    https://doi.org/10.1130/G46590.1 Manuscript received 3 June 2019 Revised manuscript received 31 July 2019 Manuscript accepted 7 August 2019 © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 23 September 2019 Scratching the surface: Footprint of a late Carboniferous ice sheet D.P. Le Heron1, P. Dietrich2,3, M.E. Busfield4, C. Kettler1, S. Bermanschläger1 and B. Grasemann1 1 Department für Geodynamik und Sedimentologie, Althanstraße 14, Universität Wien, 1190 Vienna, Austria 2 Department of Geology, University of Johannesburg, Auckland Park Kingsway Campus, Johannesburg 2092, South Africa 3 Géosciences Rennes, UMR6118, Université de Rennes 1, 263 Avenue du Général Leclerc, Bâtiment 15, Campus de Beaulieu, 35042 Rennes Cedex, France 4 Department of Geography and Earth Sciences, Aberystwyth University, Llandinam Building, Aberystwyth SY23 3DB, UK ABSTRACT records deglaciation punctuated by short-term Field observations in conjunction with aerial images from an unmanned aerial vehicle stillstands and minor readvances (Dietrich and were used to create the first map of a glacial unconformity underlying the late Carboniferous Hofmann, 2019). Such basin-margin locali- Dwyka Group of South Africa. Crosscutting relationships reveal that the glacial unconformity ties record glacially striated pavements of two at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, types: (1) hard-bedrock pavements, recording formed in a three-phased process charting a periodic shift in the locus of subglacial erosion. the direct abrasion of LPIA ice sheets onto The unconformity formed by a periodically decoupled ice sheet in a probable tidewater set- hard bedrock material (Du Toit, 1954; Visser ting.
    [Show full text]
  • A. the Cape Province Fold Belt
    SECTION II-A BRIEF SURVEY OF THE GEOLOGY OF THE CAPE SYSTEM A. THE CAPE PROVINCE FOLD BELT 1. Distribution and Folding The main occurrence of the Cape System in South Africa is confined to the Cape Province where a threefold division is recognised, namely the Table Mountain Series, or T.M.S., the Bokkeveld Series and, at the top, the Witte­ berg Series. The rocks occur along the western and southern margins of the sub-continent (see map on p. 10) where they lie with marked unconformity on older formations with granite intrusives. In the south and southwest, the Cape System dips beneath and is overlain conformably by the tillite of the Dwyka Series which forms the base of the Karroo System, but along the 'western margin the tillite when followed northwards, gradually overlaps the variolls series of the Cape System and finally lies directly on pre-Cape rocks. The whole system has been folded with a general N-S strik on the West and more intensely with a general E-W strike in the south with especially complex crumpling in the SW in the vicinity of Ceres and the Hex River Mountains, where the two fold axes Ineet. The folds in the south are frequently overturned, and are sometimes isoclinal. Usually lateral folds display a fairly teep pitch with the result that they ar hortened, outcrops occur en echelon and a particular horizon may reappear a nwnber of times in a traverse acros the ),stem. Pressure .has resulted in the alteration of organic matter to graphite in many cases and the cOlnplete de truction of micro flora.
    [Show full text]
  • The Origin and Early Evolution of Dinosaurs
    Biol. Rev. (2010), 85, pp. 55–110. 55 doi:10.1111/j.1469-185X.2009.00094.x The origin and early evolution of dinosaurs Max C. Langer1∗,MartinD.Ezcurra2, Jonathas S. Bittencourt1 and Fernando E. Novas2,3 1Departamento de Biologia, FFCLRP, Universidade de S˜ao Paulo; Av. Bandeirantes 3900, Ribeir˜ao Preto-SP, Brazil 2Laboratorio de Anatomia Comparada y Evoluci´on de los Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Avda. Angel Gallardo 470, Cdad. de Buenos Aires, Argentina 3CONICET (Consejo Nacional de Investigaciones Cient´ıficas y T´ecnicas); Avda. Rivadavia 1917 - Cdad. de Buenos Aires, Argentina (Received 28 November 2008; revised 09 July 2009; accepted 14 July 2009) ABSTRACT The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks (approximately 230 Ma) accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis,andPanphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister-group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid-Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node-based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as ‘‘all descendants of the most recent common ancestor of birds and Triceratops’’.
    [Show full text]
  • The Sauropodomorph Biostratigraphy of the Elliot Formation of Southern Africa: Tracking the Evolution of Sauropodomorpha Across the Triassic–Jurassic Boundary
    Editors' choice The sauropodomorph biostratigraphy of the Elliot Formation of southern Africa: Tracking the evolution of Sauropodomorpha across the Triassic–Jurassic boundary BLAIR W. MCPHEE, EMESE M. BORDY, LARA SCISCIO, and JONAH N. CHOINIERE McPhee, B.W., Bordy, E.M., Sciscio, L., and Choiniere, J.N. 2017. The sauropodomorph biostratigraphy of the Elliot Formation of southern Africa: Tracking the evolution of Sauropodomorpha across the Triassic–Jurassic boundary. Acta Palaeontologica Polonica 62 (3): 441–465. The latest Triassic is notable for coinciding with the dramatic decline of many previously dominant groups, followed by the rapid radiation of Dinosauria in the Early Jurassic. Among the most common terrestrial vertebrates from this time, sauropodomorph dinosaurs provide an important insight into the changing dynamics of the biota across the Triassic–Jurassic boundary. The Elliot Formation of South Africa and Lesotho preserves the richest assemblage of sauropodomorphs known from this age, and is a key index assemblage for biostratigraphic correlations with other simi- larly-aged global terrestrial deposits. Past assessments of Elliot Formation biostratigraphy were hampered by an overly simplistic biozonation scheme which divided it into a lower “Euskelosaurus” Range Zone and an upper Massospondylus Range Zone. Here we revise the zonation of the Elliot Formation by: (i) synthesizing the last three decades’ worth of fossil discoveries, taxonomic revision, and lithostratigraphic investigation; and (ii) systematically reappraising the strati- graphic provenance of important fossil locations. We then use our revised stratigraphic information in conjunction with phylogenetic character data to assess morphological disparity between Late Triassic and Early Jurassic sauropodomorph taxa. Our results demonstrate that the Early Jurassic upper Elliot Formation is considerably more taxonomically and morphologically diverse than previously thought.
    [Show full text]
  • GAMMA-KAPPA 765Kv Transmission Line, Western Cape Province
    1 GAMMA-KAPPA 765kV Transmission Line, Western Cape Province SCOPING REPORT PALAEONTOLOGY Compiled by: Dr JF Durand (Sci.Nat.) For: MDT Environmental (Pty) Ltd 673 Glossoti Street, Garsfontein, Pretoria 0081, SOUTH AFRICA 25 July 2020 2 Table of Contents: 1. Executive Summary………………………………..…………………………....................3 2. Introduction……………………………………………………………………….................4 3. Terms of reference for the report………………………………………………................5 4. Details of study area and the type of assessment…………………………………….....8 5. Geological setting……………………………………………………………………………9 6. Palaeontology of the study area…………………………..……………………………...11 7. Conclusion and Recommendations………… …………………………………………20 8. Declaration of Independence……………………………………………………………..22 . List of Figures: Figure 1: Google Earth photo indicating the study area……...………………….……….. 8 Figure 2: Geological map of the study area with the proposed power grid for the Gamma-Kappa section (adapted from the 1: 1 000 000 Geology Map for South Africa, Lesotho and Swaziland, Geological Survey, 1970) ………………………10 Figure 3: Biostratigraphical map indicating the Karoo Supergroup strata including the biozonation of the Lower Beaufort Group in the study area (adapted from Rubidge, 1995)………………………………………………………………………...11 Figure 4: Mesosaurus fossil skeleton………………………………….…………………….12 Figure 5: Tapinocephalus skull……………………………………………………………… 14 Figure 6 : Bradysaurus skeleton …………………………………………………………… 15 Figure 7: Atherstonia………………………………………………………………………… 15 Figure 8: Rhinesuchus skull………………………………………………………………....16
    [Show full text]
  • Upper Mantle P and S Wave Velocity Structure of the Kalahari Craton And
    RESEARCH LETTER Upper Mantle P and S Wave Velocity Structure of the 10.1029/2019GL084053 Kalahari Craton and Surrounding Proterozoic Key Points: • Thick cratonic lithosphere extends Terranes, Southern Africa beneath the Rehoboth Province and Kameron Ortiz1, Andrew Nyblade1,5 , Mark van der Meijde2, Hanneke Paulssen3 , parts of the northern Okwa Terrane 4 4 5 2,6 and Magondi Belt Motsamai Kwadiba , Onkgopotse Ntibinyane , Raymond Durrheim , Islam Fadel , • The northern edge of the greater and Kyle Homman1 Kalahari Craton lithosphere lies along the northern boundary of the 1Department of Geosciences, Pennsylvania State University, University Park, PA, USA, 2Faculty for Geo‐information Rehoboth Province and Magondi Science and Earth Observation (ITC), University of Twente, Enschede, Netherlands, 3Department of Earth Sciences, Belt 4 • Cratonic mantle lithosphere Faculty of Geosciences, Utrecht University, Utrecht, Netherlands, Botswana Geoscience Institute, Lobatse, Botswana, 5 6 beneath the Okwa Terrane and School of Geosciences, The University of the Witwatersrand, Johannesburg, South Africa, Geology Department, Faculty Magondi Belt may have been of Science, Helwan University, Ain Helwan, Egypt chemically altered by Proterozoic magmatic events Abstract New broadband seismic data from Botswana and South Africa have been combined with Supporting Information: existing data from the region to develop improved P and S wave velocity models for investigating the • Supporting Information S1 upper mantle structure of southern Africa. Higher craton‐like velocities are imaged beneath the Rehoboth Province and parts of the northern Okwa Terrane and the Magondi Belt, indicating that the Correspondence to: northern edge of the greater Kalahari Craton lithosphere lies along the northern boundary of these A. Nyblade, terranes.
    [Show full text]
  • Mafic Dyke Swarm, Brazil: Implications for Archean Supercratons
    Michigan Technological University Digital Commons @ Michigan Tech Michigan Tech Publications 12-3-2018 Revisiting the paleomagnetism of the Neoarchean Uauá mafic dyke swarm, Brazil: Implications for Archean supercratons J. Salminen University of Helsinki E. P. Oliveira State University of Campinas, Brazil Elisa J. Piispa Michigan Technological University Aleksey Smirnov Michigan Technological University, [email protected] R. I. F. Trindade Universidade de Sao Paulo Follow this and additional works at: https://digitalcommons.mtu.edu/michigantech-p Part of the Geological Engineering Commons, and the Physics Commons Recommended Citation Salminen, J., Oliveira, E. P., Piispa, E. J., Smirnov, A., & Trindade, R. I. (2018). Revisiting the paleomagnetism of the Neoarchean Uauá mafic dyke swarm, Brazil: Implications for Archean supercratons. Precambrian Research, 329, 108-123. http://dx.doi.org/10.1016/j.precamres.2018.12.001 Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/443 Follow this and additional works at: https://digitalcommons.mtu.edu/michigantech-p Part of the Geological Engineering Commons, and the Physics Commons Precambrian Research 329 (2019) 108–123 Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres Revisiting the paleomagnetism of the Neoarchean Uauá mafic dyke swarm, T Brazil: Implications for Archean supercratons ⁎ J. Salminena,b, , E.P. Oliveirac, E.J. Piispad,e, A.V. Smirnovd,f, R.I.F. Trindadeg a Physics Department, University of Helsinki, P.O. Box
    [Show full text]
  • Variations in the Thickness of the Crust of the Kaapvaal Craton, and Mantle Structure Below Southern Africa
    Earth Planets Space, 56, 125–137, 2004 Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa C. Wright, M. T. O. Kwadiba∗,R.E.Simon†,E.M.Kgaswane‡, and T. K. Nguuri∗∗ Bernard Price Institute of Geophysical Research, School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa (Received September 17, 2003; Revised March 3, 2004; Accepted March 3, 2004) Estimates of crustal thicknesses using Pn times and receiver functions agree well for the southern part of the Kaapvaal craton, but not for the northern region. The average crustal thicknesses determined from Pn times for the northern and southern regions of the craton were 50.52 ± 0.88 km and 38.07 ± 0.85 km respectively, with corresponding estimates from receiver functions of 43.58 ± 0.57 km and 37.58 ± 0.70 km. The lower values of crustal thicknesses for receiver functions in the north are attributed to variations in composition and metamorphic grade in an underplated, mafic lower crust, resulting in a crust-mantle boundary that yields weak P-to-SV conversions. P and S wavespeeds in the uppermost mantle of the central regions of the Kaapvaal craton are high and uniform with average values of 8.35 and 4.81 km/s respectively, indicating the presence of depleted magnesium-rich peridotite. The presence of a low wavespeed zone for S waves in the upper mantle between depths of 210 and about 345 km that is not observed for P waves was inferred outside the Kaapvaal craton.
    [Show full text]
  • The Role of Fossils in Interpreting the Development of the Karoo Basin
    Palaeon!. afr., 33,41-54 (1997) THE ROLE OF FOSSILS IN INTERPRETING THE DEVELOPMENT OF THE KAROO BASIN by P. J. Hancox· & B. S. Rubidge2 IGeology Department, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa 2Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa ABSTRACT The Permo-Carboniferous to Jurassic aged rocks oft1:J.e main Karoo Basin ofSouth Africa are world renowned for the wealth of synapsid reptile and early dinosaur fossils, which have allowed a ten-fold biostratigraphic subdivision ofthe Karoo Supergroup to be erected. The role offossils in interpreting the development of the Karoo Basin is not, however, restricted to biostratigraphic studies. Recent integrated sedimentological and palaeontological studies have helped in more precisely defming a number of problematical formational contacts within the Karoo Supergroup, as well as enhancing palaeoenvironmental reconstructions, and basin development models. KEYWORDS: Karoo Basin, Biostratigraphy, Palaeoenvironment, Basin Development. INTRODUCTION Invertebrate remains are important as indicators of The main Karoo Basin of South Africa preserves a facies genesis, including water temperature and salinity, retro-arc foreland basin fill (Cole 1992) deposited in as age indicators, and for their biostratigraphic potential. front of the actively rising Cape Fold Belt (CFB) in Fossil fish are relatively rare in the Karoo Supergroup, southwestern Gondwana. It is the deepest and but where present are useful indicators of gross stratigraphically most complete of several depositories palaeoenvironments (e.g. Keyser 1966) and also have of Permo-Carboniferous to Jurassic age in southern biostratigraphic potential (Jubb 1973; Bender et al. Africa and reflects changing depositional environments 1991).
    [Show full text]