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Type: Thesis
Title: Characterisation of late Palaeozoic glacigene sedimentary rocks of the Troubridge and Arckaringa basins and implications for palaeogeographic reconstructions of late Palaeozoic South Australia
Author: Normington, Verity Jayne
Issue Date: 2017
School/Discipline: School of Physical Sciences : Earth Science
Abstract: The majority of southern Australia was covered in ice during the Gondwanan Permo-Carboniferous glaciation. Glacigene sequences associated with this event are preserved within basins including the Late Palaeozoic sediments of the Arckaringa and Troubridge basins in South Australia. In this study, detailed sedimentology, geochronology and geochemistry of these sediments is used to inform an improved palaeogeographic reconstruction of South Australia during the late Palaeozoic and to understand background geochemistry relevant to their use as geochemical exploration media. Diamictite units with rounded to angular, locally-derived clasts are observed throughout the Troubridge Basin and the south Arckaringa Basin. These are consistent with deposition by ice tongues and icesheets. Diamictite units with subrounded to rounded clasts with both locally- and distally-derived clasts are observed in the eastern margin Arckaringa Basin. These are consistent with sedimentary rocks deposited by valley glaciers. Alternating clay and sandstone beds with lesser diamictite beds are observed in discrete exposures in the Troubridge Basin. These are consistent with a glacial environment where meltwater streams have alternating energy and sediment load. This is due to the periodic melting of the ice mass which fed into glacial lakes. The increasing frequency of diamictite beds up-sequence is indicative of the rapid retreat and melting of the ice mass. Massive to bedded, green glaciomarine clays observed in the Troubridge Basin are consistent with sedimentary rocks deposited in a transitional glacial to marine to deepening glaciomarine setting. Sedimentary rocks deposited during the marine regression are interbedded with increasingly fluvial sedimentary rocks suggesting that freshwater streams were active during the waning stages of the regression. The resulting terrestrial environment consisted of alternating fluvial and lacustrine environment with intermittent formation of coal swamps. Alternating clay and sandstone beds with minor carbonaceous beds are observed in the upper succession of the Arckaringa Basin. These are consistent with sedimentary rocks deposited in an environment where post-glacial isostatic rebound causes alternating fluvial and lacustrine conditions. Zircon provenance spectra of the glacigene sedimentary rocks of the Troubridge Basin are dominated by ages between ca 500 to 600 Ma. These ages correlate with proximal rock packages of the Kanmantoo Group (Adelaide Rift Complex) and the Transantarctic Mountains of Antarctica. These sources are likely from sources adjacent to and from the south which is consistent with deposition via an icesheet and ice tongue. The zircon provenance spectra for the glacigene sedimentary rocks of the Arckaringa Basin are dominated by ages of ca 900 to 1200 Ma and ca 1700 to 1900 Ma. These ages are typical of rocks from the nearby Adelaide Rift Complex and the Gawler Craton as well as the distal Kanmantoo Group, Transantarctic Mountains, Musgrave Province and Arunta Region. These sources are likely from adjacent highlands and consistent with being deposited via valley glaciers formed in nearby alpine glacial systems. Major and trace element geochemistry of the minimally weathered clay and silt packages interbedded with diamictite in the Troubridge and Arckaringa basins are similar to PAAS and likely sourced from of the Kanmantoo Group. The depositional setting of the glacigene sediment is shown in SiO2:Al2O3 ratios. High silica end members represent sand-rich lithologies and high Al end members represent clay-rich lithologies. The Al-rich end members include clay matrix diamictites that are most likely the result of glacial deposition (rock flour + clasts). The Si-rich end members represent lithologies where fluvial processes removed the fine-grained clay-rich component. The complexity of the observed geochemical trends and the influence of weathering on the concentration of potential mineral exploration pathfinder (trace) elements highlights the necessity of understanding depositional and post-depositional influences on geochemistry. Weathering processes largely control the major and trace element geochemistry of weathered and indurated glacigene sedimentary rocks. These weathering processes include terraneous weathering (carbonate, sulphate and dolomite), ferruginous weathering and kaolinitic weathering. The sedimentology, geochronology and geochemistry of the late Palaeozoic glacigene sedimentary rocks of the Troubridge and Arckaringa basins are used to interpret a three-stage model of evolution of the late Palaeozoic glaciation. Stage 1: Glacial advance (late Palaeozoic). During the Permo-Carboniferous glaciation, the South Australian landscape was dominated by both continental and alpine glaciation. The continental ice sheet spread rapidly north from Antarctica into central South Australia, extending to southern margin of the Arckaringa Basin at the glacial maximum at the Asselian. Ice tongues at the front of the ice sheet scoured, eroded and polished the exposed landscape, forming U-shaped valleys and polished, glaciated pavements. At paleolatitudes north of the continental icesheet alpine glaciers occupied the highlands and valley glaciers transported debris into lowlying depocentres adjacent to the highlands. Stage 2: Glacial retreat and marine transgression (Sakmarian). The ice sheet rapidly melted and retreated from northern South Australia shedding debris into the Troubridge Basin. Melting slowed as it retreated further south. The retreat of the ice mass from northern South Australia opened a seaway into which marine waters entered from the west initiating a marine transgression in northern South Australia. When the marine transgression was at its maximum most of South Australia was inundated with only the eastern Gawler Craton Highlands remaining above seawater. Stage 3: Post-glacial isostatic rebound (late Sakmarian to early Artinskian). During this time the seaway contracted toward the south (Troubridge Basin) and there was a transition to fluviolacustrine conditions in the north (Arckaringa Basin).
Advisor: Giles, David
Tiddy, Caroline
Hill, Steven
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2018
Keywords: Glacigene sedimentary rocks
late Palaeozoic
Troubridge basin
Arckaringa basin
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