New constraints on regional brecciation in the Wernecke Mountains, Canada, from He, Ne, Ar, Kr, Xe, Cl, Br and I.

Origin of Proterozoic Wernecke Breccia and associated IOCG Mineralization

Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. These line dataset from the GA302 Capel and Faust Basins MSS survey were acquired in 2006 for Geoscience Australia. This survey acquired a range of pre-competitive geological and geophysical data that included seismic reflection, gravity, magnetic and swath bathymetry measurements, as well as seafloor dredge samples.

Deep-water demersal fishes are an important component of continental shelf and slope ecosystems and play an important role in the economies of many countries. Strong and predictable relationships of fishes with seabed habitats, in conjunction with rapid advances in acoustic seabed mapping capabilities, indicate there is great potential for using habitats as proxies or ‘surrogates’ to predict species distribution and abundance patterns at broad regional scales. However, few studies have evaluated this potential in complex seabed environments. In this study, we examined the spatial distributions, assemblage composition, and benthic habitat associations of deep-water demersal fish species over three spatial scales across Cordell Bank, a deep-water bank in central California. Demersal fishes were counted and habitats quantified from 60 strip-transects allocated over the extent of the bank using in situ observer and video-recorded data from the two-person Delta submersible. Both abundance and distribution of demersal fish species on Cordell Bank were strongly correlated with spatial location and habitat composition on the bank. Habitat structure was heterogeneous at several spatial scales. At broad scales, the rocky bank itself contained the highest diversity of both habitats and fishes. At intermediate scales, transition zones (10-100s of m wide) between the bank and continental slope and shelf sediments supported a diverse and characteristic suite of fish species. Habitats were also heterogeneous at finer-scales (1-10s of m) within these broad-scale zones, and fish responses to these habitat characteristics were taxon-specific, and often contingent on the spatial configuration of fine scale habitats within the broader-scale landscape. The results of this study indicate that for many species it is not sufficient to just know the fine-scale habitat association to predict fish assemblages.

Australia has some of the best documented Permian basins in Gondwana, but much of the succession is nonmarine. Calibration of the local palynostratigraphic scheme (Price, 1997) to the global timescale was indirect and very difficult, having traditionally relied on correlations from relatively sparse, high-latitude, marine strata, within which ammonoids and conodonts are rare, fusulinids are unknown, and much of the other fauna (brachiopods, bivalves) is endemic. Tie points are rare and often tenuous (Mantle et al., 2010): one example is the record of a single specimen of the ammonoid Cyclolobus persulcatus from the Cherrabun Member of the Hardman Formation, in the Canning Basin, Western Australia (Foster and Archbold, 2001), dated as ¿post-Guadalupian¿ by Glenister et al. (1990) and ¿Capitanian¿Dzhulfian¿ by Leonova (1998). In eastern Australia, the Permian succession is replete with felsic ash beds, many of which contain zircons. Ash beds are rare in Western Australia, but some have been found in the Canning Basin. Sampling of ash beds has been coupled with sampling of adjacent clastics for palynomorphs, mostly from drillcore and coalmines in the Sydney, Gunnedah, Bowen and Galilee basins in eastern Australia, and drillcore in the Canning Basin in Western Australia. The zircons have been subjected to the Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) technique for U-Pb dating (Mattinson, 2005). The resultant radioisotopic dates, with associated palynostratigraphic determinations, permit the direct calibration of the Price (1997) scheme to the numerical timescale. Some of the data has been cited previously (Smith & Mantle, 2013; Nicoll et al., 2015, 2016; Metcalfe et al., 2015; Phillips et al., 2016). A more detailed synthesis of the Guadalupian and Lopingian will be published soon (Laurie et al., in press) and a study of the Cisuralian is in progress. The results of Laurie et al. (in press) indicate that the palynozones in the Guadalupian and Lopingian of Australia are significantly younger than currently calibrated (Figure 1). The recalibrations indicate: 1. the top of the Praecolpatites sinuosus (APP3.2) Zone lies in the early Roadian; 2. the top of the Microbaculispora villosa (APP3.3) Zone lies in the middle Roadian; 3. the top of the Dulhuntyispora granulata (APP4.1) Zone lies in the Wordian; 4. the top of the Didecitriletes ericianus (APP4.2) Zone lies in the first half of the Wuchiapingian; 5. the entire Dulhuntyispora dulhuntyi (APP4.3) Zone lies within the Wuchiapingian; and 6. the top of the Dulhuntyispora parvithola (APP5) Zone lies at or near the Permian¿Triassic boundary. These new calibrations involve some major changes, the most significant being the base of the Dulhuntyispora parvithola (APP5) Zone, which is about 6 million years younger than previously calibrated. A preliminary assessment of the Cisuralian, in eastern Australia, suggests that the Pseudoreticulatispora pseudoreticulata (APP2.1) Zone and the Microbaculispora trisina (APP2.2) Zone (APP2.2) are both of greater duration than previously thought. Contrastingly, the Pseudoreticulatispora confluens (APP1.2.2) Zone is older and of shorter duration than previously suggested (Mantle et al., 2010). However, at this stage this interpretation is based on relatively few dated ash beds (Figure 1). Preliminary data indicates that similar miscorrelations are also a feature of the current Mesozoic palynomorph zonation, and future work will attempt to remedy this.

Progressive depletion of several Archaean volcanic sequences in siderophile (Fe, Ti, Mn, V), lithophile (Zr, Sr, P, Y), and chalcophile (Zn, Cu) elements with higher stratigraphic level are reported for the Barberton Mountain Land (Tjakastad Subgroup) in South Africa, and are also observed in the eastern Pilbara Block (Western Australia), a number of sequences in the Yilgarn Block (Western Australia) and the Superior Province of Canada. These trends are shown by both high-Mg basalts and tholeiitic basalts, and are not dependent on the Mg number of the rocks. Because these variations are contrasted to the Skaergaard-type iron enrichment trend, and as they are unlikely to have been produced by secondary alteration, it is suggested they reflect secular depletion of source mantle regions following repeated extraction of basic partial-melt fractions. High-Mg basalts and peridotitic komatiites of the Tjakastad Subgroup are separated by compositional gaps for MgO, AI2O3, CaO, Ni and Co, as well as on the Ol-Op-Cp-Qz diagram, which militate against their relation by continuous crystal fractionation. Archaean high-Mg basalts are typically Qz normative, as distinct from picrites. Using the FeO-MgO (mol%) diagram, liquidus temperatures are estimated for the high-Mg basalts and komatiitic peridotites. The degree of partial melting (F) is deduced by mass balance calculation of FeO + MgO. Assuming olivine-dominated residues of partial melting, and using temperature-dependent Kd^MgO and Kd^FeO coefficients after Roeder and Emslie (1970), the mantle Mg number can be estimated. For the Archaean data, source Mg numbers fall mainly in the range 80-90, suggesting a relatively ferroan mantle. Computations of mantle trace-element levels are attempted, assuming equilibrium batch melting, normative residual mineral assemblages, and apply cited mineral/melt partion coefficients (D). The possibility of an Archaean mantle rich in iron, and possibly other siderophile elements, is supported by comparisons between Archaean and modern oceanic tholeiites. The distribution of mantle-melting events in space and time must have resulted in significant major- and trace-element heterogeneities. Subsidence of dense refractory mantle residues into undepleted regions may have triggered mantle diapirism, probably constituting a major factor underlying Archaean tectonic activity.

This paper is presented in Corriveau, L. and Mumin, A.H., eds, Exploring for iron oxide copper-gold deposits: Canada and global analogues

This study presents a method for rapidly collecting, processing, and interrogating real-time abiotic and biotic seabed data to determine seabed habitat classifications. This is done from data collected over a large area of an acoustically derived seabed map, along multidirectional transects, using a towed small camera-sled. The seabed, within the newly designated Point Harris Marine Reserve on the northern coast of San Miguel Island, California, was acoustically imaged using sidescan sonar, then ground-truthed using a towed small camera-sled. Seabed characterizations were made from video observations, and were logged to a laptop computer (PC) in real time. To ground-truth the acoustic mosaic, and to characterize abiotic and biotic aspects of the seabed, a three-tiered characterization scheme was employed that described the substratum type, physical structure (i.e., bedform or vertical relief), and the occurrence of benthic macrofauna and flora. A crucial advantage of the method described here, is that preliminary seabed characterisations can be interrogated and mapped over the sidescan mosaic and other seabed information within hours of data collection. This ability to rapidly process seabed data is invaluable to scientists and managers, particularly in modifying concurrent or planning subsequent surveys.

High-precision radiometric dating using Chemical Abrasion-Isotope Dilution Thermal Ionisation Mass Spectrometry (CA-IDTIMS) has allowed the recalibration of the numerical ages of Permian and Triassic spore-pollen palynozones in Australia. These changes have been significant, with some zonal boundaries in the Permian shifting by as much as six million years, and some in the Triassic by more than twice that. Most of the samples analysed came from eastern Australian coal basins (Sydney, Gunnedah, Bowen, Galilee) where abundant volcanic ash beds occur within the coal-bearing successions. The recalibrations of these widely used palynozones have implications for the dating of geological events outside the basins from where samples were obtained. Our revised dates for the Permian palynozones can now be applied to all Permian basins across Australia, including the Perth, Carnarvon, Canning and Bonaparte basins (along the western and northern continental margins), the Cooper and Galilee basins (in central Australia), and the Bowen, Gunnedah and Sydney basins (in eastern Australia). Revised regional stratigraphic frameworks are presented here for some of these basins. The impact of an improved calibration of biostratigraphic zones to the numerical timescale is broad and far-reaching. For example, the more accurate stratigraphic ages are the more closely burial history modelling will reflect the basin history, thereby providing control on the timing of kerogen maturation, and hydrocarbon expulsion and migration. These improvements can in turn be expected to translate in to improved exploration outcomes. We have initially focused on the Permian and provide preliminary results for the Triassic, but intend to expand recalibrations to include Jurassic, Cretaceous and Paleozoic successions beyond the Permian. Preliminary data indicates that significant changes to these calibrations are also likely.