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Paleoenvironmental and Paleotectonic Significance of Neoproterozoic Diamictites in Actively Rifting Basins

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Paleoenvironmental and Paleotectonic Significance of Neoproterozoic Diamictites in Actively Rifting Basins Paleoenvironmental and Paleotectonic Significance of Neoproterozoic Diamictites in Actively Rifting Basins by Kirsten Kennedy A thesis submitted in conformity with the requirements for the degree of Doctorate of Philosophy Department of Earth Sciences University of Toronto © Copyright by Kirsten Kennedy 2017 Paleoenvironmental and Paleotectonic Significance of Neoproterozoic Diamictites in Actively Rifting Basins Kirsten Kennedy Doctorate of Philosophy Department of Earth Sciences University of Toronto 2017 Abstract Thick successions of poorly-sorted admixtures of clasts and matrix (diamictite) are widely regarded as evidence for synchronous ‘panglacials’ of global extent during the Cryogenian period (c. 720-635 Ma). In this thesis, diamictite facies are examined in detail using an impressive collection of newly available sub-surface data consisting of some 300 km of drill core through the Grand Conglomérat, Democratic Republic of Congo, and by field investigations of the exceptionally well-exposed Kingston Peak Formation in eastern California, USA. Diamictites are shown to be of mass flow origin (debrites) present within thick (<3 km) successions of genetically-related sediment gravity flow facies (olistostromes, slumps, and turbidites) deposited in deep-water within rapidly subsiding rift basins. Thick slope aprons likely formed at the base of fault scarps and tectonically oversteepened and unstable gravelly slopes that periodically underwent collapse, forming diamictite as a consequence of mixing between slumped material and basinal material during transport. The term ‘mixtite’ is a useful descriptive term. A primary tectonic control dictated the basin stratigraphy such that thick diamictite-bearing mass flow successions can be related to phases of accelerated subsidence (i.e. ‘rift climax’); the internal stratigraphy of diamictite successions identifies higher order episodic pulses of faulting. Diamictites can therefore be identified as ‘tectonofacies’ rather than ‘climatofacies,’ marking ii episodes of accelerated faulting and subsidence in rift basins during protracted rifting associated with the end Neoproterozoic breakup of Rodinia; evidence of a cool climate and distal glacial influence is limited to rare striated clasts and dropstones. A primary subglacial origin historically proposed for these diamictite facies (e.g., tillites) is inconsistent with the simple architecture of the basin fill and associated facies, and any ice present was restricted to basin margins and thus regional in extent and likely diachronous. Preservation is controlled over long time scales by the creation and availability of accommodation space that filters and degrades high frequency climate signals. iii Acknowledgments It is a pleasure here to thank those that supported this dissertation. Firstly, special thanks go to my supervisor, Nick Eyles, for his encouragement, and for providing many exciting opportunities throughout my doctorate. This research could not have been carried out without the generous support provided by Ivanhoe Mines and the many personnel at the Kamoa Copper Project that made our time there so productive and enjoyable. In particular, geologists David Edwards and David Broughton were both the source of much appreciated support, discussion and assistance over the years. I am also very grateful to the members of my examining committee, Drs. Andrew Miall, Ulrich Wortmann, Lindsay Schoenbohm, and Dan Le Heron for dedicating their time and expertise, and ultimately accepting this thesis. Finally, I would like to acknowledge the friends and family that helped in a wide variety of ways including scientific discussion, technical expertise and moral support. iv Table of Contents Acknowledgments.......................................................................................................................... iv Table of Contents .............................................................................................................................v List of Figures ................................................................................................................................ ix List of Tables .............................................................................................................................. xxii List of Appendices ..................................................................................................................... xxiii Chapter 1 Introduction .....................................................................................................................1 1.1 Introduction ..........................................................................................................................1 1.2 Neoproterozoic glaciation ....................................................................................................1 1.3 Approach ..............................................................................................................................4 1.4 Significance..........................................................................................................................5 1.5 Structure of thesis ................................................................................................................5 1.6 References ............................................................................................................................6 Chapter 2 The evolution of a mass-flow dominated rift basin; insights from new subsurface data from the Neoproterozoic Grand Conglomérat at Kamoa, Democratic Republic of Congo. .......................................................................................................................................10 Abstract .....................................................................................................................................10 2.1 Introduction ........................................................................................................................10 2.1.1 Purpose and structure of this paper ........................................................................11 2.1.2 Geologic setting of the Katanga Basin, Democratic Republic of Congo ..............12 2.1.3 Scope of investigation, data, and methods .............................................................14 2.2 Facies types within the Poudingue, Mwashya Sub-group and Grand Conglomérat..........15 2.2.1 Mudstones ..............................................................................................................16 2.2.2 Sandstones..............................................................................................................17 2.2.3 Conglomerates .......................................................................................................18 2.2.4 Breccias ..................................................................................................................19 2.2.5 Basaltic volcanic rocks ..........................................................................................20 v 2.2.6 Diamictites .............................................................................................................20 2.3 Facies associations of the Poudingue and Mwashya Sub-group .......................................23 2.3.1 FA1: Sandstone turbidite-dominated association ..................................................23 2.3.2 FA2: Conglomeratic debrite-dominated association .............................................24 2.3.3 FA3: Breccia-dominated association .....................................................................24 2.4 Facies associations of the Grand Conglomérat ..................................................................25 2.4.1 FA4: Diamictite debris flow-dominated association .............................................25 2.4.2 FA5: Siltstone turbidite-dominated heterolithic association..................................26 2.4.3 FA6: Sandstone and conglomerate turbidite-dominated association .....................27 2.4.4 FA7: Mafic volcanic rocks.....................................................................................28 2.5 Spatial distribution and relationships of facies associations within the Kamoa Sub- basin ...................................................................................................................................28 2.5.1 Regional stratigraphic relationships between facies associations of the Poudingue and Mwashya Sub-group .....................................................................28 2.5.2 Regional stratigraphic relationships between facies associations of the Grand Conglomérat ...........................................................................................................30 2.6 Summary of depositional environments ............................................................................34 2.6.1 Regional tectonic setting ........................................................................................36 2.7 Discussion ..........................................................................................................................38 2.8 Conclusions ........................................................................................................................42 2.9 References ..........................................................................................................................43 2.10 Tables .................................................................................................................................61
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