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ItemStratigraphy and sedimentology of Cryogenian carbonates, Flinders Ranges, South AustraliaFromhold, Thomas Alexander ( 2011)The Adelaide Geosyncline of South Australia contains a Neoproterozoic-aged sedimentary succession consisting of a complex accumulation of sedimentary formations and units recording a diverse and unique depositional record. A detailed stratigraphic and sedimentological investigation of the interglacial period within the Cryogenian-aged Umberatana Group of the Northern and Central Flinders Ranges reveals a complex array of sedimentary successions lying between the Sturtian and Marinoan glacial deposits. In the Northern Flinders Ranges a major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a sub-aerial erosion surface with terrestrial and marginal marine sediments directly above the Angepena and Balcanoona formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with the previously defined Sturtian-Marinoan time series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta Reef Complex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. In the Northern Flinders Ranges the Angepena Formation occurs as a marginal marine red-bed succession consisting of supratidal mudstones which are interbedded with subtidal and intertidal carbonates. The Angepena Formation is interpreted as a coastal mudflat succession that formed as a shoreward, laterally equivalent facies of the extensive carbonate platforms (reefs) of the Balcanoona Formation. Sedimentological and geochemical investigation of the Angepena Formation reveal that the unit contains a diverse accumulation of shallow marine carbonates including ooidal sands, tepee buckled algal mats, intraformational breccia (palaeo-caliche) and fenestral-bearing microbial deposits. The stratigraphic and sedimentological relationship within the interglacial successions of the Umberatana Group of the Northern Flinders Ranges are found to extend well over a hundred kilometres southwards into regions of the Central Flinders Ranges. The post-glacial Sturtian-aged Tapley Hill Formation records a near-identical depositional record to the Tapley Hill Formation of the Northern Flinders Ranges. In the Central regions, the Tapley Hill Formation is overlain by deep-marine carbonates and calcareous shales of the Wockerawirra Dolomite and Sunderland Formations respectively. The base of the Wockerawirra Dolomite is defined by an erosional surface, which is directly correlated to the unconformity found overlying the Tapley Hill Formation in the Northern Flinders Ranges (Sturtian-Marinoan series boundary). This stratigraphic relationship indicates the Wockerawirra Dolomite and Sunderland Formations of the Central Flinders Ranges are direct correlatives of the Yankaninna Formation of the Northern Flinders Ranges. The regionally widespread carbonate platform complexes of the Balcanoona Formation in the Northern Flinders Ranges preserve a unique history of the depositional record within the middle Umberatana Group of the Adelaide Geosyncline. Cessation of reef development coincides with a major regression event situated immediately below the Sturtian-Marinoan boundary. The regional consistency of the stratigraphic features found at the Sturtian-Marinoan boundary (i.e. unconformities) suggests that regional scale mechanisms, such as glacio-eustasy, were probably active during this otherwise ‘interglacial’ succession of the Cryogenian-aged Umberatana Group.
ItemLate Neogene stratigraphy and sedimentation across the Murray Basin, southeastern AustraliaMiranda, J. A. ( 2007)The Late Neogene sedimentary sequence of the Murray Basin provides an excellent opportunity to examine paleoenvironmental change across southeastern Australia. A detailed stratigraphic analysis of sediments deposited within the basin in the last 10 Ma was undertaken to assess the influence of tectonic and eustatic processes on deposition. Stratigraphic observations and radiogenic isotope analysis reveals the onset of deposition by 7.2 Ma with a transgressive episode that deposited the marine marls of the Bookpurnong Beds. Deposition was restricted to the central and eastern parts of the basin due to the Hamley Fault. In the west, subsurface elevation contours indicate the presence of incised paleodrainage channels above Miocene limestones, which facilitated the formation of a large estuary system at 5.3 Ma. The sediments of the Norwest Bend Formation were deposited within this western region, while further east, the Loxton-Parilla Sands strandplain deposited over 214 coastal ridges. The basal parts of this unit occur as lateral equivalents to the sediments of the Lower Norwest Bend Formation (in the west). Topographic and magnetic data reveal that tectonism was active during this period and resulted in the erosion and truncation of strandlines. Tectonic evidence and an estimated minimum 28,037 year cyclicity between strandline sets, suggests that the Loxton-Parilla Sands strandlines do not represent an unbroken record of glacioeustatic change. The subaerial exposure of these sediments at approximately 3.0 Ma caused the formation of a calcareous karst above the Norwest Bend Formation and a ferruginous and/or silicious cap (the Karoonda Surface) above the Loxton-Parilla Sands. The stratigraphic position of these surfaces are indicative of a regional widespread unconformity. The Douglas-Blackburn paleodrainage system in western Victoria was dammed during the Mid-Late Pliocene by uplift associated with the Padthaway High, which caused the formation of a 400,000 km2 lacustrine system, known as Lake Bungunnia. Topographic analysis indicates that Lake Bungunnia comprised at least four distinct sub-basins with water depths of up to 30 metres, with lake shorelines indicating that active tectonism occurred during this period. The resulting lack of sediment input to the coast caused the formation of the Kanawinka Escarpment, a large erosional scarp along the southern margin of the Padthaway High. The geomorphology of the modern Murray Basin can be directly attributed to the demise of the Lake Bungunnia system. Movement along the Morgan Fault in the west at approximately 700 Ka, resulted in the draining and progressive drying of Lake Bungunnia as a breach was created along the Padthaway High. The Murray River gorge as observed today was incised following this episode. The modern Murray River (and playa lakes such as Lake Tyrell) occupy the lowest elevations along the former sub-basins of Lake Bungunnia. The Late Neogene sedimentary sequence across the Murray Basin illustrates a complex interaction of eustatic and tectonic processes on deposition. Sedimentation within strandline, estuarine and lacustrine systems, particularly in the western Murray Basin, display evidence of significant tectonic control. This highlights the important role that neotectonic processes have played in shaping southeastern Australia.