Large R.R.,University of Tasmania |
Halpin J.A.,University of Tasmania |
Danyushevsky L.V.,University of Tasmania |
Maslennikov V.V.,Russian Academy of Sciences |
And 8 more authors.
Earth and Planetary Science Letters | Year: 2014
Sedimentary pyrite formed in the water column, or during diagenesis in organic muds, provides an accessible proxy for seawater chemistry in the marine rock record. Except for Mo, U, Ni and Cr, surprisingly little is known about trace element trends in the deep time oceans, even though they are critical to developing better models for the evolution of the Earth's atmosphere and evolutionary pathways of life. Here we introduce a novel approach to simultaneously quantify a suite of trace elements in sedimentary pyrite from marine black shales. These trace element concentrations, at least in a first-order sense, track the primary elemental abundances in coeval seawater. In general, the trace element patterns show significant variation of several orders of magnitude in the Archaean and Phanerozoic, but less variation on longer wavelengths in the Proterozoic. Certain trace elements (e.g., Ni, Co, As, Cr) have generally decreased in the oceans through the Precambrian, other elements (e.g., Mo, Zn, Mn) have generally increased, and a further group initially increased and then decreased (e.g., Se and U). These changes appear to be controlled by many factors, in particular: 1) oxygenation cycles of the Earth's ocean-atmosphere system, 2) the composition of exposed crustal rocks, 3) long term rates of continental erosion, and 4) cycles of ocean anoxia. We show that Ni and Co content of seawater is affected by global Large Igneous Province events, whereas redox sensitive trace elements such as Se and Mo are affected by atmosphere oxygenation. Positive jumps in Mo and Se concentrations prior to the Great Oxidation Event (GOE1, c. 2500 Ma) suggest pulses of oxygenation may have occurred as early as 2950 Ma. A flat to declining pattern of many biologically important nutrient elements through the mid to late Proterozoic may relate to declining atmosphere O2, and supports previous models of nutrient deficiency inhibiting marine evolution during this period. These trace elements (Mo, Se, U, Cu and Ni) reach a minimum in the mid Cryogenian and rise abruptly toward the end of the Cryogenian marking the position of a second Great Oxidation Event (GOE2). © 2013 Elsevier B.V.
Calver C.R.,Mineral Resources Tasmania |
Grey K.,Geological Survey of Western Australia |
Laan M.,PO Box 428
Precambrian Research | Year: 2010
Horodyskia has been found at a single Tasmanian locality, in the Cassiterite Creek Quartzite (ca. 1300-800 Ma), part of a thick Proterozoic, mildly deformed, low greenschist facies, marine shelfal siliciclastic succession known as the Rocky Cape Group. The rock hosting the fossils is thinly interbedded and interlaminated dark grey slaty shale and quartzose siltstone. The sharp-based, graded siltstone layers are interpreted as distal storm surge deposits on an outer marine shelf. The 'strings of beads' are mostly preserved at the base of the siltstone layers, in concave hyporelief (external moulds) on the soles of the event beds, and as convex epirelief (casts) on the tops of the underlying shale beds. The casts comprise shale identical to the underlying bed. The beads average 1.7 mm in diameter, and the gap between the borders of adjacent beads tends to be approximately equal to the bead diameter. Occasionally, the fossils are preserved within shale, as wholly flattened beads delineated by a subtle darkened halo. The Tasmanian 'strings of beads' have most of the morphological attributes of previously described Horodyskia, including regularity of size and spacing of beads in any one string, lack of branching, and in some instances, 'haloes' and casts with apical depressions. The strings on at least one bedding plane have a strong N-S preferred orientation of unknown origin. Tectonic deformation has resulted in 30% shortening in a SW-NE direction. The morphologic similarity, but differing mode of preservation of the Tasmanian Horodyskia to the two previously described Mesoproterozoic species is strong evidence for a biologic origin for the string of beads phenomenon. After morphological and morphometric comparisons with other species of Horodyskia, the Tasmanian specimens are assigned to Horodyskia williamsii. Crown Copyright © 2010.
Cracknell M.J.,University of Tasmania |
Reading A.M.,University of Tasmania |
McNeill A.W.,Mineral Resources Tasmania
Australian Journal of Earth Sciences | Year: 2014
The Hellyer-Mt Charter region of western Tasmania includes three known and economically significant volcanic-hosted massive sulfide (VHMS) deposits. Thick vegetation and poor outcrop present a considerable challenge to ongoing detailed geological field mapping in this area. Numerous geophysical and soil geochemical datasets covering the Hellyer-Mt Charter region have been collected in recent years. These data provide a rich source of geological information that can assist in defining the spatial distribution of lithologies. The integration and analysis of many layers of data in order to derive meaningful geological interpretations is a non-trivial task; however, machine learning algorithms such as Random Forests and Self-Organising Maps offer geologists methods for indentifying patterns in high-dimensional (many layered) data. In this study, we validate an interpreted geological map of the Hellyer-Mt Charter region by employing Random Forests™ to classify geophysical and geochemical data into 21 discrete lithological units. Our comparison of Random Forests supervised classification predictions to the interpreted geological map highlights the efficacy of this algorithm to map complex geological terranes. Furthermore, Random Forests identifies new geological details regarding the spatial distributions of key lithologies within the economically important Que-Hellyer Volcanics (QHV). We then infer distinct but spatially contiguous sub-classes within footwall and hangingwall, basalts and andesites of the QHV using Self-Organising Maps, an unsupervised clustering algorithm. Insight into compositional variability within volcanic units is gained by visualising the spatial distributions of sub-classes and associated statistical distributions of key geochemical data. Compositional differences in volcanic units are interpreted to reflect contrasting primary composition and VHMS alteration styles. We conclude that combining supervised and unsupervised machine-learning algorithms provides a widely applicable, robust means, of analysing complex and disparate data for machine-assisted geological mapping in challenging terranes. © 2013 © 2013 Geological Society of Australia.
Cracknell M.J.,University of Tasmania |
Roach M.,University of Tasmania |
Green D.,Mineral Resources Tasmania |
Lucieer A.,University of Tasmania
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013
A high-resolution digital elevation model (DEM), generated from airborne light detection and ranging (LiDAR) remote sensing data, is used here to estimate the 3-D orientation of bedding planes. Methods for enhancement, manual identification and extraction of lineaments, and estimation of best fit planes representing bedding are presented and evaluated for a study area in foldedmetasedimentary rocks in northeast Tasmania, Australia. Estimated bedding plane dip directions are shown to be accurate and reliable when compared with field-based observations. The same cannot be said for dip angle estimates. It is likely that small errors in the location of a manually digitized lineament will affect dip estimation more than dip direction estimation, particularly for steeply dipping structures. Fold axis orientations calculated from the stereographic analysis of estimated bedding closely correspond to orientations determined from field data. The mean absolute differences ± standard error for 12 of the 14 regularly spaced domains located within the study area were 8.7° ± 1.2° for the fold plunge and 4.9° ± 0.9° for the fold trend. The techniques described here for the extraction of bedding plane orientations from high-resolution DEMs complement field-based geological mapping and can assist structural interpretations. © 2012 IEEE.
Calver C.R.,Mineral Resources Tasmania |
Crowley J.L.,Boise State University |
Wingate M.T.D.,Geological Survey of Western Australia |
Wingate M.T.D.,University of Western Australia |
And 3 more authors.
Geology | Year: 2013
U-Pb zircon data from the uppermost Cottons Breccia, representing the Marinoan glacialpostglacial transition on King Island, Tasmania, provide the first direct age constraint on the Cryogenian-Ediacaran boundary in Australia. Zircons in four samples from the topmost meter of the Cottons Breccia, dated by sensitive high-resolution ion microprobe, exhibit two modes ca. 660 Ma and ca. 635 Ma. The younger component predominates in the uppermost sample, a possibly volcanolithic dolomitic sandstone, apparently lacking glacially transported debris, in the transition to cap carbonate. Chemical abrasion-thermal ionization mass spectrometry (CA-TIMS) U-Pb dating of euhedral zircons from that sample yields a weighted-mean age of 636.41 ± 0.45 Ma. Equivalence to published TIMS ash bed dates from Cryogenian-Ediacaran transitional strata in Namibia (635.51 ± 0.82 Ma, within glacial deposit) and China (635.23 ± 0.84 Ma, 2 m above glacial deposit) supports correlation of those strata to the Australian type sections and globally synchronous deglaciation at the end of the Cryogenian Period. © 2013 Geological Society of America.
Grey K.,Geological Survey of Western Australia |
Hill A.C.,CSIC - National Institute of Aerospace Technology |
Calver C.,Mineral Resources Tasmania
Geological Society Memoir | Year: 2011
Cryogenian correlation in Australia is based on an extensive data set from the Centralian Superbasin and Adelaide Rift Complex and integrates biostratigraphy and isotope chemostratigraphy to provide a three-dimensional interpretation based on outcrop and drill holes. Studies are ongoing, but newer data are consistent with the distributions discussed here. From the chemostratigraphic and biostratigraphic viewpoint, the first appearance of the acritarch Cerebrosphaera buickii, coupled with a large negative isotope excursion at c. 800 Ma, supported by the first appearance of the stromatolite Baicalia burra, seems to have potential for boundary placement. It is widely recognized across Australia and seems to have potential globally. © The Geological Society of London 2011.
Nasir S.J.,Sultan Qaboos University |
Everard J.L.,Mineral Resources Tasmania |
McClenaghan M.P.,Mineral Resources Tasmania |
Bombardieri D.,Mineral Resources Tasmania |
Worthing M.A.,Mineral Resources Tasmania
Lithos | Year: 2010
Abundant mantle xenoliths are found in widespread undersaturated Cenozoic basaltic rocks in Northeastern Tasmania and comprise lavas, dykes, plugs and diatremes. The basanites and nephelinites, include primitive magmas (11-14. wt.% MgO) with OIB-like geochemical features. Trace element and Pb- and Sr-Nd isotope data suggest that they were generated by mixing of melts derived from low degree (< 5%) melting of both garnet- (~. 90%) and spinel lherzolite (~. 10%) facies mantle sources with HIMU and EMII characteristics. The associated xenolith suite consists mainly of spinel lherzolite and rare spinel pyroxenite with predominantly granoblastic textures. Calculated oxygen fugacities indicate equilibration of the xenoliths at 0.81 to 2.65. log units below the fayalite-magnetite-quartz (FMQ) buffer. Mantle xenolith equilibration temperatures range from 890-1050 ± 50 °C at weakly constrained pressures between 0.8 and 11.5. GPa. A hot xenolith's geotherm is indicated and attributed to tectonothermal events associated with the break-up of Gondwanaland and/or the opening of the Tasman Sea. © 2010 Elsevier B.V.
Calver C.R.,Mineral Resources Tasmania
Geological Society Memoir | Year: 2011
In Tasmania, Neoproterozoic glaciogenic deposits were laid down in one or more epicratonic basins, probably situated at the eastern margin of the Australian-Antarctic craton. Rifting and volcanism took place in the late Cryogenian to early Ediacaran. On King Island, north of Tasmania, the Cottons Breccia consists of 50-200 m of diamictite, conglomerate and sandstone. Limestone and dolostone clasts are abundant in the diamictite, although carbonate is unknown in the underlying successions. The Cottons Breccia is overlain by 10 m of laminated dolostone and limestone with a negative, upward-decreasing δ 13C profile. Rift volcanics and shallow intrusives higher in the sequence are dated at c. 575 Ma. In NW Tasmania, two diamictite units are found in the Togari Group. The Julius River Member, 200 m thick, contains dominantly dolostone clasts and overlies a shallow-marine dolostone unit with vase-shaped microfossils and C-isotopes consistent with a mid-Cryogenian age. Some clasts in the Julius River Member contain a stromatolite (Baicalia cf. B. burra) very similar to a form that is abundant in the middle part of the Burra Group, Adelaide rift basin. The Julius River Member is immediately overlain by black shale and impure carbonate dated by Re-Os at 641±5 Ma. The younger diamictite in the Togari Group is the Croles Hill Diamictite, 70 m thick, with predominantly volcanic clasts, underlain by a shale and mafic-volcaniclastic succession and overlain by thin mudstone followed by thick rift tholeiites. At one locality this diamictite is underlain by a rhyodacite flow dated at 582±4 Ma. In southern Tasmania, diamictites are found in the Wedge River Beds and in the Cotcase Creek Formation (Fm.) (Weld River Group). Laminated siltstone with dropstones is associated with the diamictites in the Cotcase Creek Fm. The southern Tasmanian deposits are poorly constrained in age. © The Geological Society of London 2011.
Clark K.,Institute of Geological & Nuclear Sciences |
Cochran U.,Institute of Geological & Nuclear Sciences |
Mazengarb C.,Mineral Resources Tasmania
Holocene | Year: 2011
Stratigraphic investigations of three coastal waterbodies in southeastern Tasmania reveal major paleoenvironmental phases related to sea level change and anomalous deposits consistent with tsunami inundation. Twenty-two short sediment cores were examined for their sedimentology and fossil diatom, foraminifera and macrofossil assemblages; nine radiocarbon ages were obtained. Despite diverse Holocene histories at each site, four common phases of Holocene paleoenvironmental evolution can be distinguished. In Phase I (pre-8000 yr BP) terrestrial environments existed. During Phase II (8000-6500 yr BP) ponded freshwater environments formed behind transgressive coastal barriers. In Phase III (6500-2000 yr BP) the sites were subject to varying degrees of marine influence, resulting in environments ranging from current-swept tidal inlets to sheltered brackish-marine lagoons. In Phase IV (2000 yr BP to present) there was a decrease in marine influence, one site changed to a freshwater wetland environment while the other two changed to ephemeral salt pans. This study suggests that postglacial sea level rise culminated after c. 7300 cal. yr BP in southeastern Tasmania and that there was probably a late-Holocene fall in sea level. These paleoenvironmental histories provide a framework within which to identify anomalous deposits and assess them for likely causes. Five anomalous deposits are identified, three of which are considered likely to have been deposited by tsunami occurring at c. 4000 cal. yr BP, c. 2000 cal. yr BP and <2000 cal. yr BP, although deposition by large storms cannot be ruled out. © The Author(s) 2011.
Green G.R.,Mineral Resources Tasmania
Episodes | Year: 2012
Tasmania contains a broad variety of economic mineral deposits, which includes several that have been known for over a century and are still operating today or were worked in the recent past. The Arthur Lineament, a belt of allochthonous amphibolite, carbonate rocks, psammite and pelite in northwest Tasmania hosts the Savage River magnetite deposit, which is now considered to be a Proterozoic carbonate replacement deposit with affinities to Kiruna-style iron-oxide Cu-Au deposits. The allochthon was formed during an early Cambrian collisional event between an east-facing passive margin sequence and an intraoceanic island arc. Post collisional, proximal submarine volcanism at c. 500 Ma in the Mount Read Volcanics followed and associated mineralisation includes world-class deposits. High grade Zn-Pb-Au-Ag- Cu massive sulfide deposits (e.g., Rosebery and Hellyer) were formed from seawater-dominated hydrothermal fluids. Disseminated Cu-Au-Ag deposits of the Mount Lyell field are associated with broad alteration zones that include phyllosilicate assemblages indicative of a component of oxidised magmatic fluid, as does the Henty Au deposit in the north. Orogenic Au is an important deposit style in northeast Tasmania and includes the Tasmania deposit, Australia's largest single Au reef. Largely post-orogenic granitic magmatism (Lower Devonian-Tournaisian) includes an important Sn-Wbase metal±magnetite mineralising event associated with reduced, fractionated granite in northeast and western Tasmania. World class Sn±Cu sulfide skarn and vein deposits are the product of interpreted magmatic fluids exsolved from these granitic magmas. The highly unusual disseminated Avebury Ni deposit is associated with granite of this type. World class scheelite skarn deposits on King Island lie in the contact aureole of moderately oxidised, unfractionated Tournaisian granodiorite on King Island.