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Brisbane, Australia

De Jersey N.J.,77 Michelle Drive | McKellar J.L.,Geological Survey of Queensland

New evidence is presented on the Triassic-Jurassic boundary in eastern Australia, based on miospore assemblages from three continuously cored drillholes which penetrated the Raceview Formation to Ripley Road succession in the eastern Clarence-Moreton Basin of southeastern Queensland. Evidence for the age of this continental succession is provided by correlation based on the first appearances of five distinctive species. These taxa first appear at or close to the Rhaetian-Hettangian boundary in the marine, ammonite-dated succession of New Zealand and in the lower Ripley Road Sandstone of Queensland. The more gradual introduction of these species in the Queensland succession, as opposed to their near-synchronous appearance in New Zealand, is probably due to their gradual migration into an inland environment in contrast to their origin from a nearshore region in New Zealand. At higher levels the first appearance of intrastriate Classopollis, closely followed by its marked increase in abundance, is regarded as evidence for correlating assemblages from the upper Ripley Road Sandstone in the eastern Clarence-Moreton Basin with the earliest Sinemurian of New Zealand. The views of some previous workers that the Hettangian of eastern Australia is characterised by the appearance of abundant Classopollis must now be modified. From the aspect of biotic change, associated with climate change at the Triassic-Jurassic boundary, this study indicates a rapid local change in New Zealand. A new type of biozone, the Association Zone, is proposed as a type of interval zone. The need for a distinctive biozone to characterise palynofloral assemblages is indicated to allow for the frequent recycling of palynomorphs and also to better define the body of an interval zone. New Early Jurassic miospore zones are proposed for southeastern Queensland. Granamegamonocolpites campbellii sp. nov. is described and one new combination, Anapiculatisporities helidonensis (de Jersey) comb. nov., is proposed. Morphological and stratigraphical evidence is provided for gradualism in the lineage development of intrastructure in Classopollis, from massive (unstructured), to intrapunctate, to intrastriate specimens. © 2013 Copyright Taylor and Francis Group, LLC. Source

Fe-rich tholeiites intruded the lower Etheridge Group of the Georgetown Inlier, north Queensland during the late-Paleoproterozoic (ca. 1685-1640 Ma). Emplacement of the tholeiites occurred during a prolonged period of rift-related sedimentation associated with extension. The tholeiites comprise two lithologically distinct units: the extrusive Dead Horse Metabasalt (DHM), a conformable 1000 m-thick series of fine- to coarse-grained basalts and pillow lavas, and the intrusive Cobbold Metadolerite (CMD), a multitude of sills and lesser dykes that range up to 500 m thick. The DHM and CMD are comagmatic, and have compositions typical of relatively evolved, low-K, Fe-rich continental (rift) tholeiites. Immobile major and trace element patterns suggest that the tholeiites were derived from a depleted upper mantle source (initial εNd values range between +2.6 and +5.3). The parental melts evolved along a trend of increasing Fe-enrichment (Fe2O3* 6.81-21.11 wt%) via closed-system fractionation, with little or no replenishment. Several samples show distinct REE patterns, consistent with limited crustal contamination. Trace element and isotopic data show that the crustal contaminants were derived from the host metasediments of the lower Etheridge Group. The age and geochemical characteristics of the Etheridge Group Fe-rich tholeiites show striking similarities to similar mafic sills in the southeastern Curnamona Province around Broken Hill in western New South Wales, and to basaltic lavas and dolerites of the Soldiers Gap Group in the eastern edge of the Mt Isa Block (some 400 km west of the Georgetown Inlier), suggesting a spatial link between these terranes during the Paleoproterozoic. They may have formed along a more than 2000 km segment of a ca. 1685-1640 Ma volcanic passive margin, tectonically and magmatically akin to the modern East Greenland margin. © 2009 Elsevier B.V. All rights reserved. Source

Withnall I.W.,Geological Survey of Queensland | Henderson R.A.,James Cook University

The northern extremity of the late Neoproterozoic- Paleozoic Tasman Orogenic zone exposed in north Queensland forms a narrow belt of tectonised rock assemblages abutting Paleoproterozoic-Mesoproterozoic rocks of the North Australian craton. The craton-orogen contact (Tasman Line) is extensively exposed, a unique circumstance for Australia. Sedimentary protoliths of the cratonic rocks were mainly deposited between 1700-1600 Ma and multiply deformed between 1600-1500 Ma. The Lynd Mylonite Zone, one expression of the Tasman Line, separates rocks of the late Neoproterozoic-Ordovician Thomson Orogen from those of the craton. The succeeding Silurian-Devonian Mossman Orogen is generally faulted against the Thomson Orogen, but in its northern extent it may directly abut the craton along the Palmerville Fault, also an expression of the Tasman Line. These two orogenic systems are dominantly of active margin association and E-stepping but deep seismic imaging indicates that they are extensively underlain by crust of Archean or Paleoproterozoic age. The Tasman Orogenic Zone in its southern part represents a broad tract of crust c. 1,000 km across, added to the cratonic core of Australia in a phase of rapid accretion. In contrast, for its north Queensland development a much smaller volume of new crust was generated, expressing slow accretion. For this region the orogenic system laps extensively onto cratonic crust, a geometry which at least in part reflects overthusting during episodes of Paleozoic contractional orogenesis. As a consequence of little orogenic accretionary outgrowth of the north Queensland continental margin, three large-scale, successive igneous assemblages of active margin association generated throughout the Paleozoic form largely co-located and overprinting belts with plutonic suites stitching the Tasman Line and extending into the craton. Source

Henderson R.A.,James Cook University | Innes B.M.,Level Inc | Fergusson C.L.,University of Wollongong | Crawford A.J.,University of Tasmania | Withnall I.W.,Geological Survey of Queensland
Australian Journal of Earth Sciences

A distinctive Late Ordovician volcano-sedimentary terrane, embracing the Carriers Well Formation and Everetts Creek Volcanics and dismembered slivers now structurally intercalated in the adjoining Wairuna Formation, is located within the Broken River Province of the northern Tasmanides. It abuts a basement of mafic-ultramafic rocks (Gray Creek Complex) and overlying Early Ordovician deep marine sedimentary and volcanic strata (Judea Formation) which host tonalitic plutons. The terrane lies at the western, inboard-margin of the Camel Creek Subprovince, a broad tract of multiply deformed mid-Paleozoic turbidites with minor basalt and chert variously interpreted as the infill of a backarc basin or an accretionary wedge. U-Pb dates from detrital zircon indicate a maximum Late Silurian age for siliciclastic rocks from the previously undated Wairuna Formation. Geochemistry of volcanic rocks from the volcano-sedimentary terrane show them to be largely of mafic to intermediate compositions of calc-alkaline affinity, comparable with broadly coeval Macquarie Arc volcanic suites of the southern Tasmanides. Trace-element systematics identify a subduction relationship for the volcanic suite and V/Ti employed as a discrimination tool identifies the terrane as representing an oceanic island arc, consistent with its sedimentary facies which include volcaniclastic mass flow deposits, limestone, and radiolarian chert. Continent-derived sandstone in the sedimentary assemblage, confirmed by the ages of detrital zircon from a sandstone sample from the Carriers Well Formation, indicates that the oceanic island arc developed proximal to the Late Ordovician continental margin of East Gondwana. Its nature and location bear on the tectonic setting of the entire Camel Creek Subprovince, for which interpretation as an Early Silurian-Early Devonian accretionary wedge is favoured. Collision of the island arc with the continental margin, and associated deformation of part the intervening oceanic crustal tract, now represented by the Gray Creek Complex and its sedimentary cover (Judea Formation) registers the initiation of subduction accretion in late Early Silurian (Llandoverian) time. It marks earlystage orogenesis in the Broken River Province, accurately timed by stratigraphic relationships in the basinal succession developed in the Graveyard Creek Subprovince immediately to the west of the arc assemblage. Tectonism was regionally developed in north Queensland at this time, coeval with the Benambran Orogeny of the Lachlan Orogen in which the Macquarie Arc was likewise accreted to the East Gondwana margin. Benambran orogenesis marks a general phase of shortening, and removal by subduction, of oceanic crust and inversion of continent-derived overlying sedimentary cover along the East Gondwana margin. © 2011 Geological Society of Australia. Source

Von Gnielinski F.,Geological Survey of Queensland
Memoirs of the Queensland Museum: Cultural Heritage Series

The geology of the Mabuyag Island Group, Torres Strait, Queensland is described from field observations carried out in April 2009. Dominant rock units of Pennsylvanian to Cisuralian age (307 to 284 million years) comprise l-type granites belonging to the Badu Suite and the co-magmatic Torres Strait Volcanic Group. A comparison of stratigraphic units within the 'Torres Strait Region' using petrographic and geochemical methods gives context to the geological evolution of the Mabuyag Island Group. Mapping here identified two units within the Badu Suite: 1. The Badu Granite outcrops on Mabuyag, Aipus and some islets around Taleb, with variations on Pulu and Mipa. 2. A red porphyritic microgranite (originally unnamed Cup, now associated with the Horn Island Granite to the south). The central and southern parts of Mabuyag comprise rhyolitic ignimbrites, lavas, intermediate to mafic volcanic rocks and minor sediments; mapped as undifferentiated Torres Strait Volcanics. These rocks have been compared to the volcanic sequence on the southern Torres Strait islands which comprises the Eborac Ignimbrite, Endeavour Strait Ignimbrite, Goods Island Ignimbrite and the Muralug Ignimbrite. The volcanic rocks on Mabuyag are similar to the Endeavour Strait Ignimbrite and the lower part of the Goods Island Ignimbrite, but probably have come from a separate local source. Quaternary and Tertiary deposits in the Mabuyag Island Group are very limited in extent. Notes on anthropogenic materials from Pulu yielded descriptions of rocks foreign to the islet, some of which may have been sourced from Mabuyag, others possibly from outside of the Torres Strait region. No mineral resources are known from the Mabuyag Island Group, even though gold, lead, zinc, wolfram and tin are reported from other areas within Torres Strait. Source

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