Arrowie Basin Research Articles

Lower Cambrian volcanism in the Hawker Group and the Billy Creek Formation, Arrowie Basin, Flinders Ranges, South Australia

Widespread tuffs are known from the lower Cambrian succession of the Arrowie Basin, Flinders Ranges, mainly from the lower parts of both the Mernmerna Formation and the Billy Creek Formation. Up to 2.5 m of potassium-rich (K2O 6.32–9.60 wt%) rhyolite tuffs are known from the Mernmerna Formation, with the ‘Big Green Tuff’ from Bunyeroo Gorge yielding a TIMS age of 515.4 ± 0.2 Ma (i.e. unnamed Cambrian stage 3). The petrography of the Big Green Tuff, with numerous glass shards, suggests an explosive subaqueous pyroclastic deposit or ash-flow tuff. The presence of several layers of identical green tuff indicates that these were produced by a multi-phase volcanic event. There are up to thirty tuff horizons (5–50 cm thick) within the Warragee Member of the Billy Creek Formation. The tuffs within the Billy Creek Formation occur over a wide area, with an east–west extent of 250 km and a north–south extent of up to 80 km. It is suggested that they are in part ash-flow tuffs. A previous TIMS age for the Billy Creek Formation was 511.87 ± 0.14 Ma (i.e. unnamed Cambrian stage 4). The source of the tuffs, both from the Mernmerna Formation and the Billy Creek Formation is unknown. Detailed study of the whole-rock and trace-element geochemistry is required to fully document them.

Sedimentology and integrated chronostratigraphy of the lower Heatherdale Shale (Cambrian, stages 2–3), Stansbury Basin, South Australia

AbstractMajor progress has recently been made regarding the biostratigraphy, lithostratigraphy and isotope chemostratigraphy of the lower Cambrian successions in South Australia, in particular of the Arrowie Basin, which has facilitated robust global stratigraphic correlations. However, lack of faunal and sedimentological data from the lower Cambrian Normanville Group in the eastern Stansbury Basin, South Australia – particularly the transition from the Fork Tree Limestone to the Heatherdale Shale – has prevented resolution of the age range, lithofacies, depositional environments and regional correlation of this succession. Here we present detailed sedimentologic, biostratigraphic and chemostratigraphic data through this transition in the eastern Stansbury Basin. Three lithofacies are identified that indicate a deepening depositional environment ranging from inner-mid-shelf (Lithofacies A and B) to outer shelf (Lithofacies C). New δ13C chemostratigraphic data capture global positive excursion III within the lower Heatherdale Shale. Recovered bradoriid Sinskolutella cuspidata supports an upper Stage 2 (Micrina etheridgei Zone). The combined geochemistry and palaeontology data reveal that the lower Heatherdale Shale is older than previously appreciated. This integrated study improves regional chronostratigraphic resolution and interbasinal correlation, and better constrains the depositional setting of this important lower Cambrian package from the eastern Stansbury Basin, South Australia.

Mars Rover Techniques and Lower/Middle Cambrian Microbialites from South Australia: Construction, Biofacies, and Biogeochemistry.

The Perseverance rover (Mars 2020) is equipped with an instrumental and analytical payload capable of identifying a broad range of organic molecules in geological samples. To determine the efficacy of these analytical techniques in recognizing important ecological and environmental signals in the rock record, this study utilized analogous equipment, including gas chromatography/mass spectrometry, Raman spectroscopy, X-ray fluorescence (XRF), Fourier transform infrared spectroscopy, along with macroscopic and petrographic observations, to examine early-middle Cambrian microbialites from the Arrowie Basin, South Australia. Morphological and petrographic observations of these carbonate successions reveal evidence of hypersaline-restricted environments. Microbialites have undergone moderate diagenesis, as supported by XRF data that show mineral assemblages, including celestine and the illitization of smectite. Raman spectral data, carbon preference indices of ∼1, and the methylphenanthrene index place the samples in the prehnite/pumpellyite metamorphic facies. Pristane and phytane are the only biomarkers that were detected in the least thermally mature samples. This research demonstrates a multitechnique approach that can yield significant geological, depositional, paleobiological, and diagenetic information that has important implications for planning future astrobiological exploration.

Brachiopods from the Byrd Group (Cambrian Series 2, Stage 4) Central Transantarctic Mountains, East Antarctica: biostratigraphy, phylogeny and systematics

AbstractBrachiopods from Cambrian Series 2, Stage 4 carbonate strata of the Byrd Group in the Central Transantarctic Mountains, East Antarctica, are described for the first time. These include six lingulate, one paterinate and one rhynchonelliform taxon, including the new lingulate brachiopod Plicarmus wildi gen. et sp. nov. The biostratigraphy correlates closely to the brachiopods recently reported from the Xinji Formation (Shuiyu section) in North China, as well as brachiopods recovered from the Dailyatia odyssei Zone across the Arrowie Basin of South Australia. These findings also support the previously identified close palaeobiogeography of these regions. The first unambiguous example of the acrotretid brachiopod Eohadrotreta zhenbaensis Li & Holmer outside South China is also identified in the context of its ontogenetic stages. Well‐preserved specimens of the acrotheloid Schizopholis yorkensis (Holmer & Ushatinskaya) facilitate a new reconstruction of its musculature and visceral region. These data are synthesized into a new cladistic analysis that resolves Acrotheloidea as a well‐supported monophyletic clade and supports previous hypotheses of a morphocline in acrotheloid evolution.

Significance of the middle Cambrian (Wuliuan) trilobite Pagetia from Yorke Peninsula, South Australia

The presence of a trilobite, assigned to Pagetia cf. edura, from the Coobowie Limestone in the Port Julia-1A drillhole on Yorke Peninsula indicates that sedimentation in the Stansbury Basin, and probably also in the Arrowie Basin, did not terminate until at least the Wuliuan (middle Cambrian, Templetonian). It further indicates that the folding of the Delamerian Orogeny did not commence until at least the Wuliuan (509–504.5 Ma).

Facies, phosphate, and fossil preservation potential across a Lower Cambrian carbonate shelf, Arrowie Basin, South Australia

The effects of sedimentological, depositional and taphonomic processes on preservation potential of Cambrian small shelly fossils (SSF) have important implications for their utility in biostratigraphy and high-resolution correlation. To investigate the effects of these processes on fossil occurrence, detailed microfacies analysis, biostratigraphic data, and multivariate analyses are integrated from an exemplar stratigraphic section intersecting a suite of lower Cambrian carbonate palaeoenvironments in the northern Flinders Ranges, South Australia. The succession deepens upsection, across a low-gradient shallow-marine shelf. Six depositional Facies Sequences are identified ranging from protected (FS1) and open (FS2) shelf/lagoonal systems, high-energy inner ramp shoal complex (FS3), mid-shelf (FS4), mid- to outer-shelf (FS5) and outer-shelf (FS6) environments. Non-metric multi-dimensional scaling ordination and two-way cluster analysis reveal an underlying bathymetric gradient as the main control on the distribution of SSFs. Unlike groups that produced primary organophosphatic biominerals, taxa that built calcareous skeletons are more taphonomically-controlled, which is further exacerbated by sampling and processing biases. A strong facies association with condensed and reworked horizons suggests the stratigraphic occurrence of calcareous groups reflects conditions conducive to preservation (phosphogenesis and phosphatization) rather than true stratigraphic ranges. Consequently, organophosphatic taxa should take precedence in the erection of biostratigraphic zones for subdivision of lower Cambrian successions.

Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia

Geological mapping in 1970 of lower Cambrian outcrop in the eastern Flinders Ranges of South Australia included the description and naming of the Moorowie Formation, representing the uppermost Hawker Group. The mapping is supported by 885 m of measured sections. An early Cambrian regressive-marine shelf-margin succession is described, from the massive Wilkawillina Limestone (base), the grey laminated limestones, syndepositional slump-induced intraformational folds and breccias, collapse talus, and graded sediment gravity flow deposits of the Mernmerna Formation, terrace-edge attrition megabreccias and reefs of the Moorowie Formation, passing up to the red beds of the Billy Creek Formation (top). Rapid changes in sedimentary facies are attributed to basement block movements and diapiric influence on sedimentation with abrupt vertical relief and paleoslope indicated by syndepositional slumping and platform margin collapse. Tuffs in the Mernmerna Formation record contemporaneous volcanism. Massive archaeocyathan limestones, ooid grainstones, peloid limestones, reef-sourced megabreccias and red shales define five members in the overlying Moorowie Formation, signalling shallow-marine regressive conditions and the development of a biologically diverse carbonate platform seaward of evaporitic lagoons and supratidal sabkhas. The megabreccias of the Moorowie Formation formed as thin semi-autochthonous debris aprons or shallow tidal-channel infills resulting from gradual and persistent wave attrition and repeated collapse of a carbonate terrace that was vigorously reworked by tidal currents. Shale interbeds within the Moorowie Formation represent lightly channelised shallow-marine ramp deposits, with adjacent mud flats, as easterly equivalents of the Oraparinna Shale, the earliest of which formed the substrate to the attrition megabreccias. Emergent evaporite diapirs near Mt John and Mt Frome are the probable sources of coarse siliciclastics within the carbonates. Some of the siliciclastics were likely transported onto the carbonate platform by sandstorms or migrating dunes. Late in the Cambro-Ordovician Delamerian Orogeny, earlier salt diapirs at depth were compressed and reactivated as highly mobile evaporite-rubble breccias and intruded as small plugs and dykes into fissures in a lithified and folded cover.The intrusive breccias include metasediment and metabasic xenoclasts attributable to the Callanna Group, while diapir-related faults also host minor copper, lead and barite mineralisation. Documentation of this unique record contributes to wider investigations of the Ediacaran-to-early-Cambrian succession of the Flinders Ranges sector of the Arrowie Basin, adding to its global heritage values, effective management and appreciation by the wider community.

Stromatolite Construction, Biofacies and Biomarkers in the Lower Cambrian Hawker Group, Arrowie Basin, South Australia

Stromatolites are laminated microbial deposits, normally composed of accretionary layers of cyanobacteria and other (often anoxic) bacteria which form on the sediment-water interface. Stromatolites represent one of the earliest records of life on Earth, dating back at least 3.7 billion years. Stromatolites became extremely diverse and very abundant throughout the Archean era 4-2.5 billion years ago, eventually causing increasing levels of atmospheric oxygen on Earth, as part of the Great Oxidation Event. The emergence and radiation of bilaterian animals and the development of new and more complex food webs during the early Cambrian coincided with a sharp decline in the abundance of stromatolites, yet they continued to exist in a range of Cambrian carbonate environments. The appearance, environment, and possibly the biogeochemistry, of Cambrian stromatolites appears to have been altered after the evolutionary development of epifaunal grazing bilaterians. Stromatolites were sampled from a wide spectrum of carbonate facies in the lower Cambrian Hawker Group in the Flinders Ranges, South Australia. The appearance, construction, distribution, and biogeochemistry of stromatolites from different depositional environments, including phosphatic hardgrounds, intertidal shoals and shelf/ramp settings is being described as part of an investigation into their morphological variation and ecological association, aiding the clarification of specific stromatolitic biofacies, and taxonomic associations. There has been little previous research on the morphology, architecture, growth, and biogeochemistry of Cambrian stromatolites in the Arrowie Basin. This study is designed to provide novel data about stromatolite evolution and ecology during a period dominated by the radiation of complex animals.

Butterflies of the Cambrian benthos? Shield position in bradoriid arthropods

Mode of preservation and method of recovery strongly influences our understanding of the life habits of extinct organisms. Bradoriid arthropods were abundant, and diverse members of early Cambrian ecosystems and most life reconstructions display these animals with the two shields of the carapace open in a ‘butterfly’ configuration. This favoured reconstruction is largely based on the abundance of ‘crack-out’ specimens preserved in this position (e.g. Kunmingella from the early Cambrian of China). In contrast, large collections of acid processed bradoriids from the Arrowie Basin of South Australia (Cambrian Stage 3) are preserved with a narrow gape at the ventral margin or completely closed with the carapace folded along the dorsal midline. The relative abundance of conjoined, closed (or partially closed) specimens from the lower Cambrian Hawker Group succession suggests that at least some bradoriid taxa were capable of withdrawing appendages and tightly closing the shields, challenging the common view that the majority of bradoriids usually held their carapaces open in a ‘butterfly’ configuration during life. New data show that layers of the bradoriid carapace are continuous through the dorsal fold with no evidence for complex articulating structures as in ostracod hinges. The relatively pliable, sclerotized or lightly mineralized calcium phosphate composition of the carapace and the simple, flexible dorsal fold facilitated opening and closing of the shields. Despite not being closely related, ostracods share close biomechanical and ecological similarities with bradoriids. The evolution of more complex articulating hinge structures – together with well-developed musculature – in ostracods during the Early Ordovician, may have provided more efficient means for shield articulation and movement, thus promoting the ecological success of ostracods throughout the Phanerozoic.

Archaeocyaths of the White Point Conglomerate, Kangaroo Island, South Australia

The White Point Conglomerate at Cape d’Estaing, Kangaroo Island, South Australia contains a polymict suite of transported clasts up to boulder size, including archaeocyath-bearing limestone clasts. Reef boundstone and bioclast floatstone and rudstone textures are evident among the limestones. The formation is a constituent of the Kangaroo Island Group, exposed along the central northern coast of the island. A total of 32 species of archaeocyaths, one radiocyath and one acanthinocyathide are described from sampled clasts. New taxa are the ethmocyathid Ussuricyathellus bellidoi sp. nov. and the sajanocyathid Emucyathus elinorae gen. et sp. nov. The assemblage correlates with the post–Flinders Unconformity interval elswhere in the Stansbury Basin and in the Arrowie Basin to the north, and indicates a late Botoman age in terms of the Siberian Cambrian stage scale. A substantial proportion of species in common between the Cape d’Estaing assemblage and the Koolywurtie Limestone Member fauna on Yorke Peninsula confirm that the latter unit is the likely source for the archaeocyath-bearing limestone clasts in the White Point Conglomerate. In contrast, there are no species in common between the Cape d’Estaing assemblage and that of the upper Sellick Hill Formation and lower Fork Tree Limestone on Fleurieu Peninsula.http://zoobank.org/urn:lsid:zoobank.org:pub:FC416BB7-F7CF-403E-8343-D98214726CE9

Discussion on ‘Implications of cross-bedding data from the upper part of the Cambrian succession, Arrowie Basin, South Australia’ by J. B. Jago, C. G. Gatehouse, C. McA Powell and T. Casey

Discussion on ‘Implications of cross-bedding data from the upper part of the Cambrian succession, Arrowie Basin, South Australia’ by J. B. Jago, C. G. Gatehouse, C. McA Powell and T. Casey

Implications of cross-bedding data from the upper part of the Cambrian succession, Arrowie Basin, South Australia

The Cambrian succession in the Arrowie Basin, Flinders Ranges, South Australia comprises the carbonate-dominated Hawker Group overlain by the sandstones and siltstones of the Billy Creek Formation, Wirrealpa Limestone and the clastic-dominated Lake Frome Group. Cross-bedding and other current data indicate a change in provenance for the clastic sediments at about the level of the Wirrealpa Limestone. It is suggested that the clastics of the Hawker Group and the Billy Creek Formation were derived from the Curnamona Craton to the east and southeast whereas those of the Lake Frome Group were derived from the Gawler Craton. This change occurred at approximately the same time as a change in provenance within the upper Backstairs Passage Formation of the Kanmantoo Group on Fleurieu Peninsula and may indicate that the top part of the Backstairs Passage Formation would correlate approximately with the Billy Creek Formation. The provenance change suggests that the Delamerian Orogeny caused uplift of the Curnamona Craton prior to that of the Gawler Craton.

First occurrence of a new Ocruranus-like helcionelloid mollusc from the lower Cambrian of East Gondwana

A new cap-shaped mollusc, Emargimantus angulatus gen. et sp. nov. is described from the Arrowie Basin of South Australia. The new species is closely comparable to mollusc species from South China and North-East Greenland previously described under the generic name Ocruranus Liu, a genus recently reinterpreted as a multiplated, possibly polyplacophoran mollusc. Emargimantus is interpreted as a univalved helcionelloid mollusc and differs from Ocruranus in both morphology and function. E. angulatus represents the first discovery of Ocruranus-like helcionelloids in the lower Cambrian of eastern Gondwana and demonstrates that these molluscs had a global distribution during the early Cambrian.

Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome.

The role of deep seismic reflection data in understanding the architecture and petroleum potential of Australia's onshore sedimentary basins

The onshore energy security program, funded by the Australian Government and conducted by Geoscience Australia, has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Detailed interpretation of deep seismic reflection profiles from four onshore basins, focussing on overall basin geometry and internal sequence stratigraphy, will be presented here, with the aim of assessing the petroleum potential of the basins. At the southern end of the exposed part of the Mt Isa Province, northwest Queensland, a deep seismic line (06GA–M6) crosses the Burke River structural zone of the Georgina Basin. The basin here is >50 km wide, with a half graben geometry, and bounded in the west by a rift border fault. Given the overall architecture, this basin will be of interest for petroleum exploration. The Millungera Basin in northwest Queensland is completely covered by the thin Eromanga Basin and was unknown prior to being detected on two seismic lines (06GA–M4 and 06GA–M5) acquired in 2006. Following this, seismic line 07GA–IG1 imaged a 65 km wide section of the basin. The geometry of internal stratigraphic sequences and a post-depositional thrust margin indicate that the original succession was much thicker than preserved today and may have potential for a petroleum system. The Yathong Trough, in the southeast part of the Darling Basin in NSW, has been imaged in seismic line 08GA–RS2 and interpreted in detail using sequence stratigraphic principles, with several sequences being mapped. Previous studies indicate that the upper part of this basin consists of Devonian sedimentary rocks, with potential source rocks at depth. In eastern South Australia, seismic line 08GA–A1 crossed the Cambrian Arrowie Basin, which is underlain by a Neoproterozoic succession of the Adelaide Rift System. Stratigraphic sequences have been mapped and can be tied to recent drilling for mineral and geothermal exploration. Shallow drill holes from past petroleum exploration have aided the assessment of the petroleum potential of the Cambrian Hawker Group, which contains bitumen in the core, indicating the presence of source rocks in the basin system.

The TommotiidCamenella reticulosafrom the Early Cambrian of South Australia: Morphology, Scleritome Reconstruction, and Phylogeny

The tommotiid Camenella reticulosa is redescribed based on new collections of well preserved sclerites from the Arrowie Basin (Flinders Ranges), South Australia, revealing new information concerning morphology and microstructure. The acutely pyramidal mitral sclerite is described for the first time and the sellate sclerite is shown to be coiled through up to 1.5 whorls. Based on Camenella, a model is proposed by which tommotiid sclerites are composed of alternating dense phosphatic, and presumably originally organic-rich, laminae. Camenella is morphologically most similar to Lapworthella, Kennardia, and Dailyatia, and these taxa are interpreted to represent a monophyletic clade, here termed the camenellans, within the Tommotiida. Potential reconstructions of the scleritome of Camenella are discussed and although a tubular scleritome construction was recently demonstrated for the tommotiids Eccentrotheca and Paterimitra, a bilaterally symmetrical scleritome model with the sclerites arranged symmetrically on the dorsal surface of a vagrant animal can not be ruled out.

The scleritome ofPaterimitra: an Early Cambrian stem group brachiopod from South Australia

Early Cambrian tommotiids are problematic fossil metazoans with external organophosphatic sclerites that have been considered to be basal members of the lophophorate stem group. Tommotiids are almost exclusively known from isolated or rarely fused individual sclerites, which made previous reconstructions of the actual organism highly conjectural. However, the recent discovery of the first articulated specimens of the tommotiid Eccentrotheca revealed a tubular sclerite arrangement (scleritome) that limited the possible life habit to sessile filter feeding and thus further supported a lophophorate affinity. Here, we report the first articulated specimens of a second tommotiid taxon, Paterimitra from the Early Cambrian of the Arrowie Basin, South Australia. Articulated specimens of Paterimitra are composed of two bilaterally symmetrical sclerite types and an unresolved number of small, asymmetrical and irregular crescent-shaped sclerites that attached to the anterior margin of the symmetrical sclerites. Together, the sclerites form an open cone in which the symmetrical sclerites are joined together and form a small posterior opening near the base of the scleritome, while the irregular crescent-shaped sclerites defined a broad anterior opening. The coniform scleritome of Paterimitra is interpreted to have attached to hard substrates via a pedicle that emerged through the small posterior opening (sometimes forming a tube) and was probably a sessile filter feeder. The scleritome of Paterimitra can be derived from the tubular scleritome of Eccentrotheca by modification of basal sclerites and reduction in tube height, and probably represents a more derived member of the brachiopod stem group with the paired symmetrical sclerites possibly homologous to brachiopod valves.

A review of the Cambrian biostratigraphy of South Australia

Cambrian rocks in South Australia occur in the Stansbury, Arrowie, eastern Officer and Warburton Basins. The succession in the Stansbury and Arrowie Basins can be divided into three sequence sets (supersequences), 1, 2 and 3. Sequence set 1 can be divided into five third-order sequences: 1.0, 1.1A, 1.1B, 1.2 and 1.3. Trilobites from the Stansbury and Arrowie Basins are restricted largely to the lower part of the succession. Four trilobite zones are recognized: Abadiella huoi (latest Atdabanian–earliest Botoman), Pararaia tatei, Pararaia bunyerooensis and Pararaia janeae Zones (all Botoman). Trilobites higher in the succession are known from only a few horizons and in part correlate with the upper Lower Cambrian Lungwangmiaoan Stage of China, equivalent to the top Toyonian. Pagetia sp. has been reported in the Coobowie Formation of the Stansbury Basin, thus suggesting an early Middle Cambrian age. The Cambrian faunas of the Warburton Basin range in age from early Middle Cambrian (Late Templetonian) to very Late Cambrian, although the richest faunal assemblages are late Middle Cambrian ( Ptychagnostus punctuosus to Goniagnostus nathorsti Zones). Conodonts, including Cordylodus proavus, occur in a Datsonian fauna. The Arrowie Basin contains the most complete and best studied archaeocyath succession in the Australia–Antarctica region. The Warriootacyathus wilkawillensis, Spirillicyathus tenuis and Jugalicyathus tardus Zones from the lower Wilkawillina Limestone (Arrowie Basin) and equivalents are correlated with the Atdabanian. Botoman archaeocyathids occur higher in the Wilkawillina Limestone. The youngest (Toyonian) archaeocyath fauna in Australia occurs in the Wirrealpa Limestone (Arrowie Basin). Brachiopods and molluscs of the Arrowie and Stansbury Basins can be divided into four biostratigraphic assemblages. Several informal Early Cambrian SSF biostratigraphic assemblages are recognized. Probable tabulate-like corals occur in the Botoman Moorowie Formation. Seven informal acritarch assemblages occur in the Early Cambrian of the Stansbury and Arrowie Basins. Trace fossils may mark the Precambrian–Cambrian boundary. Only two of several tuffaceous horizons from the Stansbury and Arrowie Basins have been dated (i) a date of 522.0 ± 2.1 Ma from the Heatherdale Shale of the Stansbury Basin, about 400 m above latest Atdabanian archaeocyathids and (ii) a date of 522.0 ± 1.8 Ma from the lower part of the Billy Creek Formation in the Arrowie Basin. Neither date is regarded as reliable.

Sediment-hosted stratiform copper deposits in the Adelaide Geosyncline, South Australia: Geophysical responses of mineralisation and the mineralised environment

Numerous sediment-hosted stratiform copper deposits have been located in the Neoproterozoic and Cambrian sediments of the Adelaide Geosyncline and Arrowie Basin. The majority of the deposits were discovered in the 19th Century, and hence geophysics played no role in their discovery. However, a major phase of exploration in the late 1960s and 1970s made extensive use of IP/resistivity surveys, the poor conductivity of the mineralisation and the generally conductive near surface, precluding the use of EM methods. Gravity methods are ineffective for detecting mineralisation, because responses associated with weathering and stratigraphy dominate the data. Also, the mineralisation is nonmagnetic. The early IP/resistivity surveys proved capable of detecting sulphide mineralisation, but this was not necessarily copper-bearing. The practice of presenting data as metal factor (MF) was unfortunate, due to the conductive environment causing resistivity variations to be the dominate cause of MF anomalies. However, modelling of resistivity and PFE, using modern inverse techniques, has shown that useful information can be derived from these data. For example, at Kapunda there is an excellent correlation between modelled sub-surface chargeability and copper assays from drilling. Geological studies have shown that most of the copper deposits are structurally controlled at some scale. Analysis of modern regional airborne magnetic and radiometric datasets allows the structural and stratigraphic setting of the deposits to be determined, although weak overall levels of magnetisation mean that intensive filtering/enhancement of the aeromagnetic data is required. Most deposits are associated with the intersection of linear magnetic anomalies, which are interpreted as faults. Units within the host succession have distinctive radiometric responses, allowing the stratigraphy to be mapped confidence. The regional airborne geophysical data provide a cost-effective means of identifying further occurrences of the structural/stratigraphic scenarios of the known deposits.

Geology of the Beltana Willemite Deposit, Flinders Ranges, South Australia

Beltana is a high-grade hypogene willemite deposit hosted in Lower Cambrian carbonate rocks in the Arrowie basin, northern Flinders Ranges, South Australia. It is situated adjacent to a major growth fault on the basin margin. Ooid grainstone units of the Woodendinna Dolomite and units of Archaeocyathid -rich Wilkawillina Limestone are the main host lithologies. Lead minerals in subeconomic quantities are also present in karstic collapse breccias surrounding the willemite orebodies. Mineralization is structurally controlled and associated with brecciation and extensive hematite-rich hydrothermal zincian dolomitization. Ore minerals include willemite and coronadite with lesser mimetite, hedyphane, and smithsonite. Late-stage gangue minerals include manganocalcite, dolomite, and minor quartz. The texture of willemite is heterogeneous, resulting from various depositional mechanisms such as partial to massive replacement of the carbonate host rock, internal sedimentation, fracture fill, brecciation, and vein fill. On the periphery of the deposit, smithsonite formed by weathering of willemite. Beltana is centered on a karstic collapse breccia that extends at least 100 m vertically, formed in part through corrosion by acidic ore solutions. The geochemical signature of the orebody includes high levels of Zn, Pb, Cd, As, and Mn. Notably, silver is absent from the deposit and sulfur concentrations are low (<20 ppm). Fluid inclusion studies yield a low minimum temperature range of ore deposition between 50° and 170°C. K-Ar dating of coronadite associated with the willemite orebody indicates an age of formation of ~ 435 ± 5 Ma. Premining resources of willemite ore were 850,000 t at 36 percent Zn, and an associated body of subeconomic lead contained more than 800,000 t at 8.9 percent Pb, 3.9 percent Zn and 1 percent As. The deposit has some similarities with Mississippi Valley-type deposits but differs in ore and alteration mineral assemblages.