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1.
AbstractLongstanding debates on the tectonic setting and provenance of the Lower Cretaceous Lingshandao Formation have hindered basin analysis and tectonic studies of the collision of the Yangtze Craton and the North China Craton, and thus the evolution of the Sulu Orogen. Thin-section analysis, identification of rock particles, cathodoluminescence, heavy minerals and trace-element analysis have, in addition to field investigations, been applied to reconstruct the source area and transport pathways of the sediments that build the Lower Cretaceous Laiyang Group on the Lingshan Island, western Yellow Sea. These analyses indicate that the Laiyang Group consists mainly of material derived from a recycled orogen and from transitional continental sediments. The Laiyang Group on Lingshan Island has been sourced from igneous and metamorphic rocks. Comparing analyses of detrital minerals with rocks from surrounding areas leads to the conclusion that the main source area is the Sulu Orogen that supplied sediment to rift basin rather than a residual basin between the Yangtze Craton and the North China Craton. A recycled orogenic belt is the source area for the Laiyang Group on Linshan Island. Felsic metamorphic and igneous rocks form the most probable sources. The rift basin was filled by sediments supplied from the Sulu Orogen on both sides.
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2.
AbstractThe Charters Towers Province, of the northern Thomson Orogen, records conversion from a Neoproterozoic passive margin to a Cambrian active margin, as characteristic of the Tasmanides. The passive margin succession includes a thick metasedimentary unit derived from Mesoproterozoic rocks. The Cambrian active margin is represented by upper Cambrian–Lower Ordovician (500–460?Ma) basinal development (Seventy Mile Range Group), plutonism and metamorphism resulting from an enduring episode of arc–backarc crustal extension. Detrital zircon age spectra indicate that parts of the metamorphic basement of the Charters Towers Province (elements of the Argentine Metamorphics and Charters Towers Metamorphics) overlap in protolith age with the basal part of the Seventy Mile Range Group and thus were associated with extensional basin development. Detrital zircon age data from the extensional basin succession indicate it was derived from a far-field (Pacific-Gondwana) primary source. However, a young cluster (<510?Ma) is interpreted as reflecting a local igneous source related to active margin tectonism. Relict zircon in a tonalite phase of the Fat Hen Creek Complex suggests that active margin plutonism may have extended back to ca 530?Ma. Syntectonic plutonism in the western Charters Towers Province is dated at ca 485–480?Ma, close to timing of metamorphism (477–467?Ma) and plutonism more generally (508–455?Ma). The dominant structures in the metamorphic basement formed with gentle to subhorizontal dips and are inferred to have formed by extensional ductile deformation, while normal faulting developed at shallower depths, associated with heat advection by plutonism. Lower Silurian (Benambran) shortening, which affected metamorphic basement and extensional basin units, resulted in the dominant east–west-structural trends of the province. We consider that these trends reflect localised north–south shortening rather than rotation of the province as is consistent with the north–south paleogeographic alignment of extensional basin successions. - KEY POINTS
Northern Tasmanide transition from passive to active margin tectonic mode had occurred by ca 510?Ma, perhaps as early as ca 530?Ma. Cambro-Ordovician active margin tectonism of the Charters Towers Province (northern Thomson Orogen) was characterised by crustal extension. Crustal extension resulted in the development of coeval (500–460?Ma) basin fill, granitic plutonism and metamorphism with rock assemblages as exposed across the Charters Towers Province developed at a wide range of crustal levels and expressing heterogeneous exhumation. Protoliths of metasedimentary assemblages of the Charters Towers Province include both Proterozoic passive margin successions and those emplaced as Cambrian extensional basin fill.
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3.
AbstractReview and analysis of 1332 gas chromatography (GC) n-alkane traces of oils from the Cooper and Eromanga basins indicate the shape of any GC trace profile is primarily controlled by the degree of organic maturity (early, peak or late) at which the oils were expelled from the parent source rock, rather than indicating the depositional environment, and hence organic composition, of that source rock. The depositional environment of a source rock may still be inferred, however, from the position of the n-alkane maximum on the GC traces of early expulsion oils in association with the pour point of the oil. Departures of GC trace profiles from the standard early, peak or late expulsion profiles can indicate mixing of oils of different maturities, while variations in the GC trace profiles of oils within adjacent reservoir units may indicate phase separation of the parent liquid, or possible seal breach by an accumulation that exceeds the capacity of its overlying seal. - KEY POINTS
GC trace profiles of 1332 oils from across the Cooper and Eromanga basins of central Australia have been reviewed. Organic maturity, rather than organic composition, of the parent source rock controls the shape of any GC trace profile. All early maturity oils display a consistent GC trace profile shape that is different from all peak maturity oils and different again from all late maturity oils. Depositional environment of the source rocks within a basin can be inferred from the relative pour points of the resultant oils.
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4.
AbstractAn interpreted CA–IDTIMS age of 1642.2?±?3.9?Ma for a volcanogenic tuffaceous siltstone from the previously undated Fraynes Formation of the Birrindudu Basin in the northwestern Northern Territory enables a rigorous chronostratigraphic correlation to be made with the economically important Barney Creek Formation of the southern McArthur Basin. This result supports previous interpretations that these geographically widely separated formations are probably linked in the subsurface. It also establishes the stratigraphic interval encompassing the Fraynes and Barney Creek formations as a potential target for greenfields base metals and petroleum exploration programs across the greater McArthur Basin. - KEY POINTS
A new interpreted CA–IDTIMS age provides a chronostratigraphic link between the Fraynes Formation of the Birrindudu Basin and the economically important Barney Creek Formation of the southern McArthur Basin. The Fraynes and Barney Creek formations are probably linked in the subsurface. This stratigraphic level is a potential target for greenfields base metals and petroleum exploration across the greater McArthur Basin.
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5.
AbstractSilicified fossil macrofloras of the Willalinchina Sandstone, at Stuart Creek in the Billa Kalina Basin of northern South Australia, are most likely early Miocene–early Pliocene with preference for the younger age, based on reinterpretation of published evidence including basin stratigraphy, paleogeography, isotopic and other dating. The macrofloras include Eucalyptus and occur in fluvial channel sandstones. The Willalinchina Sandstone is equated with the Danae Conglomerate Member of the Mirikata Formation, interpreted as older than the Watchie Sandstone, Millers Creek Dolomite Member and Billa Kalina Clay Member, and here regarded as of upper Neogene age. The Billa Kalina Basin lies between Lake Eyre, Torrens and Eucla basins, and has affinities with all three. The Kingoonya Paleochannel, peripheral to the Eucla Basin, joins the southern margin of the Billa Kalina Basin across the Stuart Range Divide, and contains the Garford Formation of mid-Miocene to Pliocene age (palynological dating), here partly equated with the Mirikata Formation. Interpretations of paleolake Billa Kalina and associated paleochannel environments are made, based on a new assessment of stratigraphic and paleogeographic relationships. - KEY POINTS
The Billa Kalina Basin sediments in northern South Australia are equated with the later Neogene ‘upper’ Garford Formation of the Kingoonya Paleochannel, which flowed into the Eucla Basin, and depositional processes are clarified. A variety of consistent age data from adjacent basins and the Kingoonya Paleochannel indicate the Stuart Creek ‘silcrete floras’, associated with the Willalinchina Sandstone channel deposits, are Neogene, probably early Pliocene, but the possibility remains that they may be incised into the Watchie Sandstone and therefore late Pliocene. The Billa Kalina Basin was linked to the Kingoonya Paleochannel through much of its history, with flow disrupted by the Stuart Range Divide, local tectonics, and regional tilting.
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6.
AbstractCoal measures located in marginal sea basins are important hydrocarbon source rocks. For the purpose of effectively guiding future oil and gas exploration, the characteristics and distribution patterns of coal seams in coal measures of a marginal sea basin are systematically outlined. Coal measures in marginal sea basins can have large thicknesses, but the individual coal seams can be very thin and lack lateral continuity. In the study area, the organic micro-components of the coal are dominated by vitrinite, with very low amounts of inertinite and liptinite. The amount of inorganic microscopic components is large, but with limited drilling results, few cores and thin coal seams, which are easily overlooked during logging activities, a comprehensive analysis of the logging data may improve efficiency in coal-seam identification and thickness determination. The development and distribution of coal seams in marginal sea basins are controlled by various factors, including (1) paleoclimatic and paleobotanic conditions, which could fundamentally limit coal formation, (2) coal-forming sedimentary environmental conditions that may limit the scope of coal-seam development from a macroscopic perspective, and (3) paleotectonic and paleotopographic conditions that define the coal-forming structures. Therefore, the descending and rising cycles of base-levels, along with changes in the growth rates of the accommodation spaces, can be used to determine the horizons that are potentially favourable for coal formation and can also indicate the migration trends of coal-forming environments on the structural plane. Seismic wave impedance inversion methods could be utilised for semi-quantitative assistance for prediction of coal seams. In summary, for models of coal-seam development in marginal sea basins, the grades should be divided according to reliability, and the different reliability levels should be predicted separately. The characteristics of coal seams developed in marginal sea basins are described. The macerals of coals developed in marginal sea basins have been ascertained. A development model and distribution prediction method for coal seams are assessed according to the control factors. A model for the prediction of coal-seam distribution is presented.
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7.
AbstractInformation, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations. - KEY POINTS
The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites. Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks. The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.
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8.
AbstractThe sedimentary facies of the Huagang Formation, the major petroleum exploration horizon in the Xihu Depression in the East China Sea Basin, have not been well constrained, owing to limited drilling and core recovery. Interpretations are vague and vary from beach bar, braided river and braided-river delta front sediments. In this paper, the paleosedimentary environments of the Huagang Formation are discussed based on detailed organic and inorganic geochemical analysis and proxies used to interpret the sedimentary facies. Kerogen, dominated by sapropelinite, is mainly of Type I and Type II, and n-Paraffins are dominated by short-chain and medium-chain, with no obvious odd-over-even advantages. The distribution of isoprenoid alkanes and steroids indicates that the organic matter in mudstones is mainly of lacustrine and mixed origins. Elemental ratios of Th/U (4–6), V/Cr (1–4), Ni/Co (3–11) and V/(V?+?Ni) (0.5–0.75) indicate that in the area studied, the Huagang Formation was deposited under anoxic to reduced conditions with some oxygen-enriched horizons. Both inorganic and organic geochemical signatures show that the Huagang Formation was mainly deposited in an aquatic environment but with some minor periods of subaerial exposure. The sequence of the Huagang Formation is characterised by interbedded grey-white thick sandstones and grey-black thin mudstones. Normally graded cycles are widely developed, with rare mudstone in the upper part and scoured surfaces at the base. The cumulative grainsize distribution curve is mainly a two-stage type. The sedimentary facies indicative markers are dominated by braided-river channel deposits and combined with the paleosedimentary environments it is inferred that the sedimentary system in the study area was typical of a braided-river delta front. The cores available were intensively analysed using a hand-held X-ray fluorescence spectrometer to probe the variations in the paleoclimate and show that the braided-river channels were controlled by paleoclimate. During arid climatic settings, the sediments within individual channels were thin, and grainsizes varied significantly; at the base of each channel, basal conglomerates were common. In contrast, under humid climatic settings, thin multi-stage channels were superimposed, and the bottom often developed erosion surface. - KEY POINTS
The paleosedimentary environments are discussed based on detailed organic and inorganic geochemical analysis. The Huagang Formation was deposited in a freshwater lacustrine basin under warm and humid climatic settings. The Huagang Formation is characterised by braided-river delta front facies. The development of braided-river channels was controlled by paleoclimate.
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9.
AbstractAccurate soil-moisture monitoring is essential for water-resource management and agricultural applications, and is now widely undertaken using satellite remote sensing or terrestrial hydrological models’ products. While both methods have limitations, e.g. the limited soil depth resolution of space-borne data and data deficiencies in models, data-assimilation techniques can provide an alternative approach. Here, we use the recently developed data-driven Kalman–Takens approach to integrate satellite soil-moisture products with those of the Australian Water Resources Assessment system Landscape (AWRA-L) model. This is done to constrain the model’s soil-moisture simulations over Australia with those observed from the Advanced Microwave Scanning Radiometer-Earth Observing System and Soil-Moisture and Ocean Salinity between 2002 and 2017. The main objective is to investigate the ability of the integration framework to improve AWRA-L simulations of soil moisture. The improved estimates are then used to investigate spatiotemporal soil-moisture variations. The results show that the proposed model-satellite data integration approach improves the continental soil-moisture estimates by increasing their correlation to independent in situ measurements (～10% relative to the non-assimilation estimates). HighlightsSatellite soil-moisture measurements are used to improve model simulation. A data-driven approach based on Kalman–Takens is applied. The applied data-integration approach improves soil-moisture estimates.
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10.
AbstractSmall- and medium-sized basins are widely distributed, and some contain commercial gas reservoirs demonstrating their gas-generation potential. The Xuanhua Basin, which is a small-sized coal-bearing basin in north China, includes a promising target for shale-gas exploration in the Xiahuayuan Formation. In this study, we used this basin as a case study to assess the critical geochemical features for small or medium-sized basins to form commercial gas reservoirs. Total organic carbon (TOC) analysis, Rock-Eval pyrolysis, microscopic observation of macerals, vitrinite reflectance measurement and kerogen stable carbon isotope analysis were performed to characterise the organic geochemistry of the Xiahuayuan shales. The original total organic carbon (TOC o) content and hydrocarbon-generative potential ( S2o) were reconstructed to further evaluate the gas-generation potential of these shales. In addition, geochemical data of shales from other similar-sized basins with gas discoveries were compared. The results showed that the kerogen from the Xiahuayuan Formation is Type III (gas-prone), and macerals are dominated by vitrinite. TOC values showed a strong heterogeneity in the vertical profiles, with most higher than 1.5?wt%. The measured Ro values ranged from 1.4 to 2.0%. However, thermal maturity was not correlated with the present-day burial depth with higher maturity in the wells closest to the diabase intrusion centre. The remaining generation potential ( S2) averaged 0.91?mg HC/g rock, equal to 1.4?cm 3 CH 4/g rock, and the average amount of hydrocarbon generated was 4.33?cm 3 CH 4/g rock. In small and medium-sized basins, the TOC content of commercially developed gas shales ranged from 0.5 to 2.5?wt%, organic matter was mainly humic (gas-prone), and the burial depth was generally shallow. Biogenic gas reservoirs for commercial exploitation tend to have larger shale thicknesses (120–800?m) than thermogenic gas reservoirs (60–90?m). The Xiahuayuan Formation is a good gas-source rock with gas-prone kerogen type, relatively high TOC values and moderate thermal maturity. The average amount of hydrocarbon generated from the Xiahuayuan shales is about 4.33?cm3 CH4/g rock, indicating a potential to form a shale gas reservoir. Owing to the influence of diabase intrusions, the Xiahuayuan shales have entered the dry gas window at relatively shallow-buried depths. Small- and medium-sized basins have the potential to generate commercial gas reservoirs with the generated volume mainly a product of the thickness and maturity of black shales.
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11.
AbstractThe shape and structural development of the box-like Parrabel Dome (PD) within the Hastings Block is poorly understood because it has only been weakly cleaved, complexly folded and extensively faulted in comparison to the adjoining blocks. Better characterising this block will provide important controls on the tectonics of the southern New England Orogen. The structural development of the PD and southern Hastings Block (SHB) provides evidence of the degree of rotation, translation and deformation of the Hastings Block, a key terrane within the southern New England Orogen. A major decollement under the Hastings Block–Nambucca Block was suggested to facilitate south-directed deformation caused by the developing Coffs Harbour Orocline. The orientation of bedding and the stratigraphic facing of some fault blocks within the northern Hastings Block (NHB) are consistent with development of the PD, while other fault blocks indicate significant disruption of the NHB prior to, during and after dome development. A deep-seated fault is suggested by the gravity worm analysis consistent with the boundary zone between the PD, NHB-Yarrowitch Block and the east-dipping and younging sequences in the SHB. The eastern limb of the PD underwent clockwise rotation after formation. Fault blocks have been rotated and translated within a restraining bend as the NHB moved post-PD formation northwest along the interface between the NHB and SHB. - KEY POINTS
The Hastings Block was translated and rotated into its current position from the southeastern end of the Tamworth Belt. Gravity worm data indicate a boundary between northern and southern Hastings Block. The Hastings and Nambucca blocks have been detached from the basement Gondwana rocks. Fault block analysis within the Parrabel Dome, northern Hastings Block indicates relocation of some blocks by faulting.
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12.
AbstractIn Australian stratigraphic nomenclature, the concept of granitic rock suites has been in formal use for over a decade. The basis for this suite classification of granitic rocks is inconsistent and, in eastern Australian usage, unsound on several levels. We also note that the approach used in Western Australia is different. Granitic intrusions are probably not truly amenable to any strict, comprehensive, lithostratigraphic classification. If these rocks are integrated into such a scheme, group- and supergroup-level units ( i.e. formal suites and supersuites) should not be incorporated. For the present, mappable units should be recognised at the levels of formation and member. The use of granite suites and supersuites in formal stratigraphic hierarchies is not recommended. Instead, granitic bodies could be grouped into individual plutons, which may or may not form parts of larger batholiths. - KEY POINTS
The suite-based classification of granitic bodies, as currently used in the Australian Stratigraphic Units Database, is based on unsound principles, and is not employed in a consistent manner. Granitic intrusive rocks probably cannot be grouped using lithostratigraphic principles that are consistent with either the local or international codes. Granitic bodies can be grouped into batholiths, plutons and members, but the names of these units should, for the moment, remain informal.
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13.
AbstractQuaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160?±?15?ka; MIS 6), an unnamed alluvial succession (42?±?3.2?ka; MIS 3), a late last glacial colluvial succession within bedrock depressions ( ca 15?ka; MIS 2) and a late last glacial alluvium ( ca 15?ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5?±?0.3?ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9?±?7?ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118?ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments. - KEY POINTS
Luminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present. Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating. Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.
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14.
AbstractThis paper summarises current knowledge on metamorphism within the entire New England Orogen (NEO) of eastern Australia. Rocks recording metamorphic assemblages characteristic of each of the three metamorphic facies series (high, medium and low P/T) have been identified within the orogen. These include high P/T blueschists and eclogites, mid P/T orogenic metamorphism and low P/T contact aureoles and sub-regional high-temperature–low-pressure (HTLP) metamorphism (regional aureoles). Metamorphism is described as it relates to six tectonic phases of development of the NEO that together comprise two major cycles of compression–extension. Medium–high-grade contact metamorphism spans all six tectonic phases while low-grade burial and/or orogenic metamorphism has been identified for four of the six phases. In contrast, exposure of high P/T eclogites and blueschists, and generation of sub-regional low P/T metamorphism is restricted to extensional phases of the orogen. Hallmarks of the orogen are two newly identified zones of HTLP metamorphism, the older of which extends for almost the entire length of the orogen. - KEY POINTS
The orogen is dominated by low-temperature rocks while high-temperature amphibolite to granulite facies rocks are restricted to small exposures in HTLP complexes and contact aureoles. Blueschist metamorphism falls into two categories; that associated with subduction during the Currabubula-Connors continental arc phase occurring at depths of ～13–30?km; and the other of Cambrian–Ordovician age, exposed within a serpentinite melange and associated with blocks of eclogite. The eclogite, initially from depths of ～75–90?km, appears to have been entrained in the deep crust for an extended period of geological time. A comprehensive review of contact metamorphism in the orogen is lacking and as studies on low-grade metamorphism are more extensive in the southern part of the orogen than the north, this highlights a second research gap.
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15.
AbstractTwo north–south-trending belts of high-temperature–low-pressure (HTLP) sub-regional metamorphism have been identified in the New England Orogen of eastern Australia. Metamorphic complexes in the ～1300?km long Early-Permian Inland belt have ages ca 300–290?Ma, and those of the ～400?km long Mid-Permian Coastal belt ca 275–270?Ma. These periods correspond to the beginning and end of an extended (early–mid Permian) phase of subduction rollback and crustal thinning in eastern Australia. This paper describes and incorporates recent work on the Wongwibinda Metamorphic Complex in the southern New England Orogen as a basis for comparison with thirteen other HTLP sub-regional occurrences within the orogen. These are described in as much detail as is currently available. Some outcrops of HTLP rocks in difficult terrain have been subject to limited study and only conditional comparisons can be made. However, a significant number of characteristics shared between the complexes including: their location at the higher-temperature end of broad areas of very low-grade to greenschist facies metamorphic rocks, indicative of tilted crustal blocks; their association with major shear zones; the presence of migmatite at the high-temperature end of a steep metamorphic field gradient; the presence of two-mica granite formed by the melting of the local sedimentary pile; and temporal association with S-type granites; imply a common extension-related mechanism of formation for these HTLP belts. The connection with major faults and shear zones suggests the belts trace major crustal-scale extensional structures that migrated eastwards from ca 300 to 270?Ma. - KEY POINTS
Two previously undocumented belts of HTLP subregional metamorphism are identified within the NEO. Available dating indicates that metamorphism occurred along the belts at the beginning and end of a major early–mid Permian extensional phase in eastern Gondwana/Australia. The characteristics of the HTLP complexes including their association with shear zones indicates they may delineate major loci of extension.
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16.
AbstractFor the past 200?years, there have been numerous investigations and much speculation concerning the formation of the dramatic valleys of the Blue Mountains of NSW. In this paper, further evidence for the uplift and erosional history of the Blue Mountains is obtained from longitudinal river profiles, detailed mapping of the Rickabys Creek Gravel on the Lapstone Structural Complex and consideration of the topographical position of Miocene basalts. Knickpoints on the main rivers flowing east from the Great Dividing Range are identified and interpreted to be due to uplift events linked to the northward movement of the Australian continent over mantle inhomogeneities. At the Lapstone Structural Complex on the eastern range front, the occurrence of the Rickabys Creek Gravel and the nature of the over-steepened reaches on the rivers and streams crossing the Complex, suggest a more recent ongoing phase of uplift and antecedent river erosion. The Miocene basalts provide evidence of this landscape 20–15?Ma. Their locations with respect to the current rivers and ridges are interpreted to show additional evidence for recent uplift that has resulted in the formation of the Lapstone Structural Complex. It is suggested that this uplift commenced 10–5?Ma when the contemporary compressive stress field was established. - KEY POINTS
Longitudinal profiles for major rivers in the Blue Mountains are consistent with a model of initial Cretaceous uplift followed by further Cenozoic uplift associated with dynamic topography. Mapping of Rickabys Creek Gravel within the Lapstone Structural Complex suggests the presence of antecedent rivers. Within the Lapstone Structural Complex, stream profiles, gravels and nearby outcrops of Miocene basalts are interpreted to indicate a third phase of uplift, possibly since 10?Ma.
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17.
AbstractTwo spectacular cliff lines occur along Australia’s south and west coasts: the Great Southern Scarp (new name) and the Zuytdorp Cliffs. Detailed measurements of their length show that they are exceptionally long and unusually continuous. The Great Southern Scarp is the southern edge of the Nullarbor Plain’s Bunda Plateau; it is cut into shallow marine sediments and extends for 820?km. Once a continuous sea-cliff, local uplift has isolated two sections from the ocean, so it now comprises the Bunda Cliffs (210?km of coastal cliff, 180?km of which is uninterrupted cliff line), Hampton Range (inland; 300?km), Baxter Cliffs (160?km of coastal cliff) and Wylie Scarp (inland; 160?km). The Zuytdorp Cliffs are coastal cliffs cut into eolianite, and extend for 210?km with an uninterrupted section of 120?km. The length of the Great Southern Scarp and the Zuytdorp Cliffs results from an unusual combination of circumstances. They are both composed of poorly jointed, relatively homogenous biogenic calcarenites, presented to high-energy ocean waves by regional uplift. The carbonates are sufficiently well cemented to maintain a steep vertical cliff face, but susceptible to disintegration under direct wave attack. Cliff retreat has been fairly uniform because of the broad spatial scale of both lithology and erosion. The arid climate, absence of nearby non-karstic catchments and karstic nature of the cliffs’ hinterlands has discouraged integrated drainage development, so no significant fluvial systems dissect the cliffs; this is a key factor in cliff edge preservation. In the case of the Great Southern Scarp, these processes have formed the longest continuous cliff line in Australia and probably the world. Referenced against criteria from Australia’s National Heritage List, the cliffs have potentially international/national levels of significance for the rarity of their scale, their demonstration of landscape evolution, and their spectacular beauty. - KEY POINTS
Australia’s longest coastal cliffs, the Bunda (SA) and Zuytdorp (WA) cliffs, are equal in length (210?km, within defined confidence levels). The Bunda Cliffs are part of the Great Southern Scarp (new name), an 820 km-long feature of the Nullarbor Plain that also includes the coastal Baxter Cliffs (160?km in length) and two paleocoastal scarps. The unusual continuity of the cliff lines results from a landscape history specific to the Australian continent, and the Great Southern Scarp is likely to be unusual on a global scale. The Great Southern Scarp and the Zuytdorp Cliffs have potentially national and/or international levels significance for geoheritage values in the criteria of events and processes, rarity and aesthetics.
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18.
AbstractFour economic porphyry Cu–Au deposits and several prospects have been investigated in the Northparkes district, part of the Ordovician to early Silurian Junee–Narromine Belt of the Macquarie Arc, New whole-rock geochemical data from the Northparkes porphyry Cu–Au district, NSW, indicate that the mineralising intrusive complexes exhibit distinct arc signatures that are transitional from high-K calc-alkaline to silica-saturated alkalic. Based on ratios of Sr/Y vs Y ( e.g. Sr/Y > ～20 and Y < ～17?ppm) the mineralising intrusions are interpreted to have crystallised from fractionated hydrous melts indicating the suppression of plagioclase crystallisation in favour of hydrous mineral phases. This interpretation is supported by listric-shaped rare earth element curves and the presence of primary hornblende phenocrysts indicating elevated magmatic water contents. There is an association of mineralising intrusions with a low Zr trend both in the mineralised Northparkes district intrusive rocks and in mineralised porphyry-related intrusive rocks globally. A newly developed fertility indicator ratio Zr/Y ～10% is more accurate at identifying the mineralised rocks at Northparkes than the conventional Sr/Y vs Y fertility indicator diagram, successfully identifying 92% of the mineralising intrusions, mainly owing to the fact that it is less affected by hydrothermal alteration. The insensitivity of Zr–Y to alteration makes this indicator a useful new tool that may lead to enhanced probabilities for future discoveries in the Northparkes district, broader Macquarie Arc and altered rocks globally. - KEY POINTS
Mineralising intrusions in the Northparkes district have distinct Zr vs Y concentrations. The Zr vs Y indicator of magmatic fertility is less sensitive to alteration than Sr-based indicators. The Zr vs Y magmatic fertility indicator identified at Northparkes is not unique and identifies mineralising intrusions in other porphyry fields.
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19.
AbstractWhere tectonics is not a factor, the landscapes of granite batholiths show variations in average pluton elevation that follow each pluton’s composition very closely. The granitoids of the Kosciusko and Maragle batholiths in the Highlands of southeastern New South Wales have clearly been influenced by tectonics. Examination of the relation between composition and mean pluton elevation reveals that the plutons of these batholiths lie in two groups, a Highlands group between the Jindabyne-Barney’s Range Thrusts and the Tumut Ponds Fault Zone and a Western group west of the Tumut Ponds Fault Zone. Composition and mean pluton elevation are strongly correlated within each group, indicating they have been uplifted as two coherent blocks along those two fault systems. The plutons of the Berridale Batholith east of the Highlands form a contrasting low-relief group. Pluton mineralogy determines elevation across a granite batholith. Kosciusko Highlands were uplifted as one block along the Jindabyne Thrust and Tumut Pond Fault Zone.
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20.
AbstractThere is significant economic interest in the Murray Basin of southeastern Australia as it is proving to be a major heavy mineral sands (HMS) province that will be one of Australia’s major source for production of rutile, zircon and ilmenite. The distribution and provenance of HMS resources in the Murray Basin is poorly understood because of its huge size, limited exploration and the complex depositional, structural and weathering mechanisms in their development. In this paper, we focus on the Copi North and Magic deposits some 130–180?km south of Broken Hill, NSW. The heavy mineral assemblages of the Copi North and Magic deposits are very similar, with the main economic minerals being ilmenite, leucoxene, pseudorutile, rutile and zircon. Intensive fracturing and brecciation are identified in many samples and are inferred to have been initially caused by multi-stage deformational processes associated with metamorphism and then further developed through alluvial and eolian transportation. Both deposits are classified as ‘medium sands, symmetrical, mesokurtic and moderately well-sorted’. The majority of economic minerals are of low to medium sphericity and subrounded, along with abundant polished eolian quartz grains. The Copi North deposit has coarser and more poorly sorted sediments with higher HMS grades and magnetics content than the Magic deposit, reflecting a higher energy depositional environment. The main source for the HMS for the Copi North and Magic deposits is largely ascribed to the Broken Hill Block. Previous studies have shown that the Broken Hill orebody underwent substantial sub-aerial weathering over hundreds of millions of years. In addition, the complex metamorphic events experienced by the Broken Hill Block were capable of forming the broad series of minerals identified within the Copi North and Magic deposits. The HMS were believed to have been transported through paleovalleys near the Mulculca Fault in a southeast direction representing a feeder system into the NW Murray Basin. Both deposits feature a relatively linear geometry (roughly parallel to the strike of the paleoshoreline), with high HMS grades, modest tonnages, and coarser sediments when compared to WIM-style offshore deposits. Compared to other strandline HMS deposits of the Murray Basin, they are smaller in size although have similar high grades of 3.7–6.9% THM and similar proportions of the HMS assemblage of ilmenite, leucoxene, rutile and zircon. Deposits of similar size and grade are likely to occur throughout the northern part of the Murray Basin. - KEY POINTS
Both the Copi North and Magic deposits contain similar mineral assemblages with the provenance of the heavy minerals ascribed to the Broken Hill Block. A relatively high energy inshore environment is inferred for the Copi North deposit while a lower energy environment associated with either a foreshore or backshore environment is inferred for the Magic deposit. Deposits of similar mineralogy, grades and size are likely to occur elsewhere throughout the northern Murray Basin.
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