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Rosny Park, Australia

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.

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.

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.

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.

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.

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