Abstract Correlations within and between Precambrian basins are heavily reliant on precise dating of volcanic units (i.e., tuff beds and lava flows) in the absence of biostratigraphy. However, felsic tuffs and lavas are rare or absent in many basins, and direct age determinations of Precambrian basaltic lavas have proven to be challenging. In this paper, we report the first successful application of 40 Ar/ 39 Ar dating to pyroxene from a Neoproterozoic basalt unit, the Keene Basalt in the Officer Basin of central Australia. 40 Ar/ 39 Ar analyses of igneous pyroxene crystals yielded an age of 752 ± 4 Ma (mean squared weighted deviation = 0.69, p = 72%), which is underpinned by 40 Ar/ 39 Ar plagioclase age (753.04 ± 0.84 Ma) from the basalt. This age is significant because the Keene Basalt is one of the very few extrusive igneous rocks identified within the Neoproterozoic successions of central Australia and is potentially an important time marker for correlating the Neoproterozoic stratigraphy within, and beyond, the central Australian basins. Our geochronological and geochemical data show that the Keene Basalt, which is characterized by enriched elemental and Nd‐Pb isotopic signatures, is strikingly similar to, and coeval with, the 755 ± 3 Ma Mundine Well Dolerite in northwestern Australia. Here we suggest that both are part of the same large igneous province (~6.5 × 10 5 km 2 ) related to breakup of the supercontinent Rodinia. This study demonstrates the potential of pyroxene 40 Ar/ 39 Ar geochronology to date ancient flood basalts and to provide pivotal time constraints for stratigraphic correlations of Precambrian basins.
Funded by Geoscience Australia’s Exploring for the Future initiative and operated by the Geological Survey of Western Australia, the Waukarlycarly 1 deep stratigraphic drillhole was designed to investigate the geology of the little-known Waukarlycarly Embayment and assess the petroleum, mineral, groundwater and CO2 storage potential of the area. Based on consultation with the Western Desert Lands Aboriginal Corporation on the cultural significance of the name, Waukarlycarly, it has been agreed to change the name of the well to Barnicarndy 1 and the tectonic subdivision to the Barnicarndy Graben. This and all future publications will now refer to the Barnicarndy 1 stratigraphic drillhole (previously Waukarlycarly 1) and the Barnicarndy Graben (previously Waukarlycarly Embayment). Drilling commenced on 1 September 2019 and reached a total depth (TD) of 2680.53m on 30 November 2019, recovering more than 2km of continuous core. The cored interval extended from 580m to TD in Neoproterozoic Yeneena Basin dolostone, which was unconformably overlain by a thick, lower Canning Basin Ordovician stratigraphy, including richly fossiliferous marine mudstones with common volcanic ash beds. A major unconformity is located at the top of the Ordovician section where it is overlain by sandstones and muddy diamictites of the Carboniferous–Permian Grant Group, followed by a Cenozoic succession near surface. Ditch cuttings were collected from surface to 580m at 3m intervals. The pre-Grant Group Paleozoic succession is unique within the Canning Basin, indicating that the Barnicarndy Graben’s depositional history is markedly different when compared with adjacent structural subdivisions, such as the Munro Arch and Kidson Sub-basin. Detrital zircon geochronology, biostratigraphy and borehole imaging interpretation assisted in the definition of two new geological units within the Ordovician stratigraphy of Barnicarndy 1: the Yapukarninjarra and Barnicarndy formations. Preliminary routine core analysis data indicates the potential for CO2 storage within the Barnicarndy Formation beneath a Grant Group seal. The well also provides new insights into the structural interpretation of the Barnicarndy Graben.
A review of available geochronology and biostratigraphy leads to the conclusion that a considerable thickness of Cambrian sedimentary rocks exposed in the Arrowie and Stansbury Basins, South Australia, was probably deposited in a foreland setting during early phases of the Delamerian Orogeny. In contrast to most previous stratigraphic correlation schemes, we consider that the pre‐tectonic Kanmantoo Group was deposited synchronously with the locally thick upper Hawker Group in essentially en echelon basins during a final phase of extensional sedimentation within the Adelaide 'Geosyncline'. The base of the locally overlying 'redbed package' (base of the Billy Creek and Minlaton Formations) is interpreted as the sedimentological signature of the onset of convergent deformation and associated uplift within the Delamerian Orogen at about 522 Ma. This early ('Kangarooian') phase of the Delamerian Orogeny is interpreted as the progressive development of a coherent sigmoidal fold‐thrust belt within the combined Fleurieu‐Nackara Arcs, with locally developed high‐temperature‐low‐pressure metamorphism and granitoid intrusions dating from about 516 Ma. The 'redbed package' is absent from the Fleurieu‐Nackara Arc region and displays isopach, palaeocurrent and facies trends consistent with derivation from this uplifted area or from the associated flexural bulge to the west. From seismic evidence we conclude that thick foreland basin deposits are present beneath Gulf St Vincent. Late phases of the Delamerian Orogeny led to local and relatively mild deformation of the early foreland deposits.
Abstract Seismic reflection surveys suggest that the Gulf St Vincent area of the Stansbury Basin, South Australia is filled with four pre‐Permian sedimentary packages. The upper three packages (S0‐S2) are interpreted as Early Palaeozoic rocks that are considered to be underlain by a Neoproterozoic package. The Early Palaeozoic packages are up to 6000 m thick in the east but less than 500 m thick in the west. In particular, the middle package (S1) tapers distinctly westward and northwestward. The Early Palaeozoic successions show little internal deformation but are separated by faults from the highly deformed Delamerian Orogen to the east and are also faulted against Early to Middle Cambrian strata that crop out on Yorke Peninsula to the west. Early Palaeozoic reverse movement along faults that may have originated as growth faults during deposition of S0 outlasted deposition of package S1. Internal onlap relationships suggest a westward migration of the depocentre of the middle package S1 through time. Package S2 is not affected by Delamerian deformation and only shows imprints of Cenozoic deformation, which also affects the overlying Permian and Cenozoic sedimentary rocks. We interpret the lowest Palaeozoic package as an equivalent to the Early Cambrian Normanville Group. The middle and upper packages are interpreted as deposits of a hitherto unrecognised foreland basin to the Delamerian Orogen and are interpreted to be of Cambrian to Ordovician age. Key words: foreland basinPalaeozoicseismic reflection surveysseismic stratigraphyStansbury Basin
The Early Cambrian Kanmantoo Group of southeastern South Australia is a thick marine succession of immature and predominantly turbiditic sandstone and mudstone, and metamorphic equivalents, that was deposited within a continental-margin delta and submarine-fan complex. Deposition was very rapid and occurred just prior to the onset of deformation and metamorphism by the Delamerian Orogeny. The Kanmantoo Group contrasts with older units of the Adelaide Rift Complex (Adelaide Geosyncline) in terms of sedimentary facies, rapidity of deposition, composition and provenance. Importantly, the Kanmantoo Group represents the earliest appearance in Australia of a sedimentary sequence characterised by the 'Pan-Gondwanaland' detrital-zircon signature. Here we present geochemical and Nd–Sr isotope data for sandstone–mudstone pairs collected throughout the Kanmantoo Group. Interestingly, sandstone–mudstone pairs do not have a consistent polarity in terms of their εNd values. This argues against simple mixing/unmixing between two distinct sediment components and suggests a more complex and incompletely mixed multicomponent provenance. There appears to be an abrupt change in isotopic character within the Backstairs Passage Formation in the mid-Kanmantoo Group. Although the origin of this change remains problematic, an overall shift to more negative εNd(t) numbers up-section may reflect progressive exhumation of the provenance region(s) and accessing of increasingly ancient materials. Based on detrital-zircon signature the Kanmantoo Group must be sourced from an area containing abundant 0.7–0.5 Ga magmatism, with other components supplying 'Grenvillian' (1.2–0.9 Ga) and older zircons back to about 3.5 Ga. Large latest Neoproterozoic to Early Paleozoic orogenic and magmatic belts include the Ross Orogen in Antarctica and the Prydz–Leeuwin Belt on the inferred former suture between East Antarctica, India and Western Australia. The former is closer, but lacks known magmatism older than 0.55 Ga. The latter appears to be a more suitable provenance based on the zircon signature, and our Nd data show significant overlap with some existing datasets from along this belt. Recent suggestions that equivalent rocks may extend beneath the central East Antarctic ice sheet (including the Gamburtsev Subglacial Mountains) may provide a more geographically suitable location, particularly from the perspective of paleocurrent data, but are not testable with our present dataset.
Late Devonian time was a period of rapid upheaval in the Earth system, including climate change, sea level changes, widespread ocean anoxia, and the Frasnian-Famennian mass extinction; the cause(s) of these changes remain(s) uncertain. The Lennard Shelf of the Canning Basin in Western Australia contains carbonate reef sections spanning much of the Late Devonian Epoch and has been sampled for paleomagnetic analysis with studies by Hansma and colleagues in 2015 and Playton and colleagues in 2016. However, previous paleomagnetic directions were scattered and their use for magnetostratigraphy has been questioned. Here, rock magnetic data and magnetostratigraphy for a late Devonian drill-core from the Lennard Shelf were analyzed. Three magnetostratigraphic interpretations were made using different paleopoles that showed good correlation with each other and the earlier interpretations by Playton and colleagues in 2016. Additionally, the rock magnetic data revealed the samples contain various mixtures of detrital and diagenetic minerals, the former of which should be viable recorders of primary magnetic signatures. Even in samples with these detrital phases, paleomagnetic data were often noisy and produced ambiguous polarity assignments, likely due to the anomalously weak Devonian field. Because of this ambiguity and the absence of a robust paleopole, broader correlations for this critical time-period will be difficult without additional paleomagnetic data from the late Devonian Period. Expanded data for this interval could eventually shed light on the timing, causes, and rates of the Frasnian-Famennian mass extinction and other environmental shifts in the late Devonian Epoch.
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