Australian Continental Margin Research Articles

Jurassic uplift and erosion of the northeast Queensland continental margin: evidence from (U–Th)/He thermochronology combined with U–Pb detrital zircon age spectra

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.KEY POINTSU–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.(U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.

The sedimentology and tsunamigenic potential of the Byron submarine landslide off New South Wales, Australia

Abstract Extensive evidence for submarine landslide failure is found along the east Australian continental margin. This paper assesses the sedimentological properties and models the failure event that created the Byron landslide scar, located on the SE Australian continental margin, c. 34 km off the coast of Byron Bay, New South Wales. Sedimentological analyses and dating (radiocarbon and biostratigraphic) were conducted on three gravity cores collected from within the Byron landslide scar. A paraconformity, identified in one of the three cores by a distinct colour change, was found to represent a distinct radiocarbon age gap of at least 25 ka and probably represents the detachment surface of the slide plane. The core-derived sediment properties for the Byron landslide scar were used to inform hydrodynamic modelling using the freely available numerical modelling software, Basilisk. Model results highlight the important role of sediment rheology on the tsunamigenic potential of the slide and on the resulting inundation along the east Australian coastline, therefore providing a greater understanding of the modern hazard posed by comparable future submarine landslide events for the east Australian coastline.

The prospectivity of the Late Triassic intervals in the outboard Exmouth Plateau, Western Australia

The Exmouth Plateau is a deep-water plateau on the Australian continental margin underlain by 10–15 km of flat-lying, tilted and block-faulted Paleozoic–Mesozoic sedimentary rocks, which were deposited predominantly during periods of extension before continental break-up commenced in the middle Jurassic. The recent acquisition of the Mawson MC3D broadband seismic survey provides a modern, high-quality dataset located ~230 km to the north-west of Dampier, in the outboard Exmouth Plateau, in a relatively under-explored portion of the Northern Carnarvon Basin. The Late Triassic Mungaroo Formation is the primary reservoir target for the majority of the exploration in the Exmouth Plateau to date. A detailed investigation into the reservoir potential and prospectivity of the Mungaroo Formation is possible by utilising this modern dataset. The high-quality data presents a high-resolution view of the Rhaetian carbonate reef platforms and pinnacle reef complexes that are present within the Mawson survey footprint, revealing an under-explored play type within the region. The development of a detailed stratigraphic framework through the Late Triassic–Jurassic, combined with the use of attribute analyses and amplitude versus offset products can help de-risk identified prospects and highlight further prospectivity during the exploration process.

Sedimentology, structure, and age of the Wide Bay Canyon submarine landslide on the southeast Australian continental slope

Sedimentological analysis and radiocarbon dating of three marine sediment cores collected from the upper continental slope offshore from Fraser Island, Queensland, Australia, indicate the region is dynamic and provide strong evidence for mass movement processes occurring during the Late Pleistocene and Holocene. Two cores were collected within the Wide Bay Canyon submarine landslide scar with a third collected on the adjacent open slope. All three cores present intraformational, mud-clast conglomerates, interpreted to be debris flow deposits comprised of sub-angular to rounded, pebbled and cobble-sized clasts of the hemipelagic muds that typically accumulate in this area. One within-slide core and the open slope core also present coarse-grained, poorly sorted, unconsolidated sand layers that are interpreted to be grain flow deposits derived from continental shelf sands that were driven over the continental shelf edge by the East Australia Current during the Last Glacial Maximum. Radiocarbon dating of unconformities identified in the Wide Bay Canyon slide scar cores indicates that abrasion and sediment removal during the emplacement of debris flows occurred during several separate events prior to ~35.1 cal. yr. BP. The sand layers interpreted to be grain flow deposits contain Late Pleistocene age material that was probably re-deposited during the sea level low-stand associated with the Last Glacial Maximum. Consideration of the debris flow ages in the context of ages reported for similar materials and other landslide deposits recorded on the South-eastern Australian Continental Margin supports the previously advanced hypothesis that rare, moderate to large, intraplate earthquakes are a likely triggering mechanism for submarine landslides and/or mass failure events on the South-eastern Australian Continental Margin.

Shallow water masses and their connectivity along the southern Australian continental margin

Four water masses are identified and described using hydrographic, nutrient and stable isotope data for the top 1000 m water depth of the southern Australian continental margin, from Cape Leeuwin to Tasmania. Three are identified from previous literature on the southeast Indian Ocean: Subtropical Surface Water (STSW), Tasmanian Subantarctic Mode Water (TSAMW) and Tasmanian Intermediate Water (TIW), and one is newly identified and named: South Australian Basin Central Water (SABCW). STSW (0–250 m) is transported east by the Leeuwin Current System and is modified by heating and evaporation along the subtropical continental shelf. SABCW (250–400 m) and TSAMW (400–650 m) form southwest of Tasmania from deep winter mixing in the region: SABCW at the Subtropical Front and TSAMW north of the Subantarctic Front. TIW (>650 m) forms southwest of Tasmania from mixing of warm, saline Antarctic Intermediate Water from the Tasman Sea and cool, fresh Antarctic Intermediate Water from the Antarctic Circumpolar Current. SABCW, TSAMW and TIW are transported west along the slope by the Flinders Current System, here defined as the western slope-trapped Flinders Current, Tasman Outflow and equatorward Sverdrup transport. Water mass distributions on the slope identify the interface between subantarctic water from the Southern Ocean and subtropical water transported by the Leeuwin Current System. This interface is ~300 m during winter and ~250 m during summer, but can be 150 m during summer in upwelling regions and off western Tasmania. Furthermore, stable isotope data of the water masses south and west of Australia show connectivity between the Subantarctic Zone, the southern Australian margin and the western Australian margin.

Surface geological investigation as the initial stage of hydrocarbon exploration in Kei Besar Island, Southern Maluku

Kei Islands are known to have hydrocarbon potentials in shallow rock layers, trapped by folds and faults. This potential is characterized by the amount of gas seepage found in Kei Kecil, Kei Besar and Tayandu Island. The study was conducted in central and southern part of Kei Besar Island through outcrop observations and stratigraphic measurements aim to recognize the physical characteristics of rock. Kei Besar Island located in the easternmost part of Australian continental passive margin separated by the extension of Aru Through. Digital Elevation Model of Kei Besar Island shows that the northern part of research area has a steeper morphology than the southern. The stratigraphic characteristic in the central part of research area dominated by clastic limestone showing a shallowing-up stacking pattern. While in the southern part, the lithology dominated by coralline limestone contains many fragments of coral and large foraminifera. Stratigraphic analysis shows that lithology in the study area was formed in carbonate submarine fan which formed Elat Formation. This formation underlained by shallow carbonate rock which contain large foraminifera from Tamangil Formation. Tamangil Formation interfingered with lower part of Weduar Formation. Based on the analysis of surface data above, concluded that subsurface exploration is necessary to reconstruct the petroleum system in research area.

Facies Structure and Quantitative Parameters of Pleistocene Sediments from the East Australian Continental Margin

Abstract—Lithological and facies zonality of Neopleistocene and Eopleistocene sediments of the Australian seas is described for the first time. Processing of these maps and isopach schemes by A.B. Ronov volumetric method gave us an opportunity to calculate the quantitative parameters of sedimentation for different types of the Pleistocene sediments. It was revealed that carbonate sediments predominate over other sediment groups. The Neopleistocene was characterized by more intense accumulation of carbonate planktic sediments and lithogenic sediments than Eopleistocene.

New Perspective of Mesozoic Hydrocarbon Prospectivity Within West Timor

Compared to the success of Mesozoic play in Westralian Superbasin (WASB), the lack of hydrocarbon discovery in West Timor within Timor Trough and North West Shelf Australia is still an enigma. The West Timor is still frontier petroleum province with problems in uncertainties of working petroleum system play as well as the hydrocarbon prospectivity. This paper tries to approach this issue by integrating of fieldwork data with published well data and offshore seismic data from recent publication to re-evaluating potential hydrocarbon prospectivity in this area. Using the dataset, this study identifies structural framework across West Timor Island and offshore area, as well as potential petroleum system plays including source rock, reservoir presence and trap configuration. The results of this study identify two potential petroleum province region including Timor deformation front and Australian passive continental margin. Within these areas, three main plays based on structural configuration were identified which are fold related fault, sub-thrust, and tilted fault block. Reservoir targets for these main plays are Jurassic sequences including sandstone of the Early-Middle Jurassic of Plover equivalent and Late Triassic Malita equivalent with seal rock including Early-Middle Jurassic shale of Wai Lui Formation and Early Cretaceous shale interval. These plays are expected to be charged from source rock interval of Triassic Formation. The novelty of hydrocarbon prospectivity in this study will guide exploration screening of petroleum system analysis in West Timor area where current play analysis has not been tested yet.

Modelling and visualising distributed crustal deformation of Australia and Zealandia using GPlates 2.0

The recently released GPlates 2.0 software (www.gplates.org) provides a framework for building plate motion models including distributed extension and compression, driven by the motions of the surrounding rigid plate interiors, with constraints assimilated from well and seismic data. Here we present a regional deforming plate model for Australia and Zealandia. It captures the progressive extension of all Australian continental margins, starting with the Jurassic extension of the northwest shelf, and the Cretaceous extension of the southern and eastern Australian margins. The model also includes the extension of the Lord Howe Rise and southern Zealandia in the mid- to Late Cretaceous and the subsequent complex compressional deformation of New Zealand since the early Miocene. The model enables the time-dependent computation of crustal stretching factors for passive margins, as well as compression factors for orogenic regions. The thinning/thickening can be tracked by points distributed within a deforming mesh, either by starting with an assumed initial stretching factor or by applying an iterative approach in estimating initial crustal thicknesses to account for present-day constraints. The latter is suitable for basins, while the former is more applicable for orogens, where the present-day crustal thickness is not a reliable indicator of total crustal thickening due to the effects of erosion. Modelled crustal stretching factors can also be ground-truthed with independently derived stretching factors from strain rate inversion of stratigraphic sequences from well data or forward models of tectonic subsidence. The model can be combined with estimates of mantle-driven dynamic topography through time to generate basement subsidence or uplift models that include isostatic and dynamic components, serving as boundary conditions for basin and source-to-sink sediment transport models to provide improved constraints for resource exploration.

Geological aspects of Banda Sea ecosystems and how they shape the oceanographical profile

The Banda Sea is a collage of young oceanic basins and fragmented Australian continental crust located at the heart of the Australia–SE Asia collision zone where Australian and Asian biogeographic regions converge. The formation of the sea was governed by the southeastward rollback of the Banda Slab since c. 16 Ma, which in its wake opened new oceanic basins and extended and fragmented Australian crust. These Australian crustal fragments are today either stranded within the Banda Sea where they form the prominent submarine ‘Banda Ridges’, or now reside as thrust-sheets on the NW Australian shelf after being transported all the way to the southern Banda Arc. The deepest part of the Banda Sea, the 7.2 km Weber Deep, was formed by extreme lithospheric extension that occured in the latter stages of Banda Slab rollback. This extension was accommodated by the vast low-angle ‘Banda Detachment’, which operated above the subducted fringes of the Australian continental margin.

An Australian provenance for the eastern Otago Schist protolith, South Island, New Zealand: evidence from detrital zircon age patterns and implications for the origin of its gold

ABSTRACTUranium–lead age patterns of detrital zircons in Otago Schist meta-sandstones from eastern Otago, including areas of orogenic gold mineralisation, are mostly consistent with a Rakaia Terrane (Torlesse Composite Terrane) accretionary wedge protolith. Southwest of the Hyde-Macraes and Rise & Shine shear zones the depositional age is regarded as Middle–Late Triassic. At the south and west margins, there are two areas in the Late Triassic Waipapa Terrane protolith. Northeast of the Hyde-Macraes Shear Zone, the schist protolith has Middle to Late Triassic and middle to late Permian depositional ages of Rakaia Terrane affinity. At the northeastern margin of the Hyde-Macraes Shear Zone, there is a narrow strip with a mid-Carboniferous protolith, which may be a counterpart of the Carboniferous accretionary wedge in the New England Orogen, eastern Australia. Ordovician–Silurian zircons are a minor but distinctive feature in many of the protolith age patterns and form significant age components at hard-rock gold locations. These constrain the provenance of Rakaia Terrane protolith sediments to Late Triassic time and within the Permian–Triassic magmatic arcs at the northeastern Australian continental margin and partly within the Ordovician–Silurian granitoids of the Charters Towers Province hinterland and environs. The latter have extensive gold mineralisation and thus upon exhumation might be the origin of Otago gold.

Organic matter sources, transport, degradation and preservation on a narrow rifted continental margin: Shoalhaven, southeast Australia

The continental delivery of fine grained siliciclastic sediment, together with the composition of exported terrigenous organic matter (OM), has a strong impact on the content and composition of sedimentary OM accumulating on contemporary oxic continental shelf sediments. The composition of terrigenous OM appears to be, in turn, largely related to the geodynamic setting of the drained margin.This study provides results from a comprehensive source-to-sink investigation along the Shoalhaven River (New South Wales) and its associated non-deltaic deposits on the SE Australian continental margin, a margin whose dimensions and morphology differ from those of standard passive margins.The OM content of 23 surface sediment samples collected along the river course, estuary and adjacent continental shelf was investigated by integrating bulk OM measurements, such as total organic carbon content (TOC), TOC/total N (C/N), carbon stable isotope (δ13CTOC) and radiocarbon content of TOC (Δ14CTOC), with lipid biomarker analysis. Geochemical data were coupled with sediment particle size analysis. The TOC content correlated strongly with the clay+silt content in all the environments, confirming the importance of fine grained particles – OM association as an influential preservation factor.A three-component mixing model was used to show that OM in continental shelf sediments consisted of 15–20% terrigenous biospheric OM (mostly modern plants), 15–25% fossil C, and marine OM. While such bimodal terrigenous input (modern plants and fossil C) is typical of active margins, this study reinforces the paradigm that OM residence times within major bioactive reservoirs during transfer (in turn related to geomorphic characteristics) strongly influence the composition of exported OM.

Formation of Australian continental margin highlands driven by plate–mantle interaction

Passive margin highlands occur on most continents on Earth and play a critical role in the cycle of weathering, erosion, and atmospheric circulation. Yet, in contrast to the well-developed understanding of collisional mountain belts, such as the Alps and Himalayas, the origin of less elevated (1–2 km) passive margin highlands is still unknown. The eastern Australian highlands are a prime example of these plateaus, but compared to others they have a well-documented episodic uplift history spanning 120 million years. We use a series of mantle convection models to show that the time-dependent interaction of plate motion with mantle downwellings and upwellings accounts for the broad pattern of margin uplift phases. Initial dynamic uplift of 400–600 m from 120–80 Ma was driven by the eastward motion of eastern Australia's margin away from the sinking eastern Gondwana slab, followed by tectonic quiescence to about 60 Ma in the south (Snowy Mountains). Renewed uplift of ∼700 m in the Snowy Mountains is propelled by the gradual motion of the margin over the edge of the large Pacific mantle upwelling. In contrast the northernmost portion of the highlands records continuous uplift from 120 Ma to present-day totalling about 800 m. The northern highlands experienced a continuous history of dynamic uplift, first due to the end of subduction to the east of Australia, then due to moving over a large passive mantle upwelling. In contrast, the southern highlands started interacting with the edge of the large Pacific mantle upwelling ∼40–50 million years later, resulting in a two-phase uplift history. Our results are in agreement with published uplift models derived from river profiles and the Cretaceous sediment influx into the Ceduna sub-basin offshore southeast Australia, reflecting the fundamental link between dynamic uplift, fluvial erosion and depositional pulses in basins distal to passive margin highlands.

The variation of crustal stretching and different modes of rifting along the Australian southern continental margin

ABSTRACTThe southern margin of Australia is a passive continental margin, formed during a Late Jurassic–Cretaceous rifting phase. The development of this passive margin is mainly associated with extensional processes that caused crustal thinning. In this work, we have measured the amount of extension and the stretching factor (β factor) across seven transect profiles approximately evenly distributed across the margin. The obtained results show that the amount of extension and the β factor along the margin vary from west to east. The lowest amount of extension, low–intermediate β factors and a very narrow margin are observed in the western part with 80 km of extension and is underlain mostly by the Archean Yilgarn Craton and the Albany–Fraser Orogen. The Gawler Craton in the centre of the south Australian margin is another region of low extension and low–intermediate β factor. The largest amount of extension (384 km) and the largest β factor (β = 1.88) are found in the eastern part of the passive margin in an area underlain by Phanerozoic Tasman Orogen units. Our results imply that there is a strong control of the age and thickness of the continental lithosphere on the style of rifting along the Australian passive margin. Rifting of old and cold lithosphere results in a narrow passive margin, with the formation of relatively few faults with relatively wide spacing, while rifting of younger, warmer lithosphere leads to wide rifting that is accommodated by a large number of faults with small spacing.

Provenance of Permian–Triassic Gondwana Sequence units accreted to the Banda Arc in the Timor region: Constraints from zircon U–Pb and Hf isotopes

Analysis of zircons from Australian affinity Permian–Triassic units of the Timor region yield age distributions with large age peaks at 230–400Ma and 1750–1900Ma, which are similar to zircon age spectra found in rocks from NE Australia and crustal fragments now found in Tibet and SE Asia. It is likely that these terranes, which are now widely separated, were once part of the northern edge of Gondwana near what is now the northern margin of Australia. The Cimmerian Block rifted from Gondwana in the Early Permian during the initial formation of the Neo-Tethys Ocean. The zircon age spectra of the Gondwana Sequence of NE Australia and in the Timor region are most similar to the terranes of northern Tibet and Malaysia, further substantiating a similar tectonic affinity. A large 1750–1900Ma zircon peak is also very common in other terranes in SE Asia.Hf analysis of zircon from the Aileu Complex in Timor and Kisar Islands shows a bimodal distribution (both radiogenically enriched and depleted) in the Gondwana Sequence at ~300Ma. The magmatic event from which these zircons were derived was likely bimodal (i.e. mafic and felsic). This is substantiated by the presence of Permian mafic and felsic rocks interlayered with the sandstone used in this study. Similar rock types and isotopic signatures are also found in Permian–Triassic igneous units throughout the Cimmerian continental block.The Permian–Triassic rocks of the Timor region fill syn-rift intra-cratonic basins that successfully rifted in the Jurassic to form the NW margin of Australia. This passive continental margin first entered the Sunda Trench in the Timor region at around 7–8Ma causing the Permo-Triassic rocks to accrete to the edge of the Asian Plate and emerge as a series of mountainous islands in the young Banda collision zone. Eventually, the Australian continental margin will collide with the southern edge of the Asian plate and these Gondwanan terranes will rejoin.

Australia going down under: Quantifying continental subduction during arc-continent accretion in Timor-Leste

Models of arc-continent accretion often assume that the period of subduction of continental lithosphere before plate boundary reorganization is fairly short lived, yet the timescale of this period is poorly constrained by observations in the geologic record. The island of Timor is the uplifted accretionary complex resulting from the active collision of the Banda volcanic arc with the Australian continental margin. The exposure of underplated and exhumed Australian strata on Timor allows for the characterization of the structural history of accretion of uppermost Australian crust and the quantification of subduction of its original continental lithospheric underpinnings. New structural mapping in East Timor (Timor-Leste) reveals that duplexing of a 2-km-thick package of Australian continental strata has built the majority of the structural elevation of the Timor orogen. Coupling new structural observations with previous thermochronology results reveals the sequence of deformation within the orogen, the presence of subsurface duplexing below the hinterland slate belt, and motion along a foreland subsurface thrust ramp. Construction of balanced cross sections allows for the quantification of the amount of shortening in the orogen, and from that, the length of the subducted Australian continental lithosphere. Two balanced cross sections in East Timor reveal 326–362 km of shortening and that 215–229 km of Australian continental lithosphere have been subducted below the Banda forearc. These results highlight the fact that considerable amounts of continental lithosphere can be subducted while accreting only a thin section of uppermost crust. Continental subduction may have been favorable at Timor because of fast subduction rates, old oceanic crust at the consumed Australian margin, and subduction of some length of transitional crust. These results provide quantitative constraints for future numerical modeling of the geodynamics of continental subduction and arc-continent collision.

Origin and intra-island diversification of Sulawesi endemic Adrianichthyidae

Although the family Adrianichthyidae is broadly distributed throughout East and Southeast Asia, 19 endemic species, over half of the family, are distributed in Sulawesi, which is an island in Wallacea. However, it remains unclear how this Adrianichthyidae biodiversity hotspot was shaped. In this study, we reconstructed molecular phylogenies for the Sulawesi adrianichthyids and estimated the divergence times of major lineages to infer the detailed history of their origin and subsequent intra-island diversification. The mitochondrial and nuclear phylogenies revealed that Sulawesi adrianichthyids are monophyletic, which indicates that they diverged from a single common ancestor. Species in the earliest branching lineages are currently distributed in the central and southeastern parts of the island, indicating that the common ancestor colonized Sula Spur, which is a large promontory that projects from the Australian continental margin, from Asia by oversea dispersal c.a. 20Mya. The first diversification event on Sulawesi, the split of the genus Adrianichthys, occurred c.a. 16Mya, and resulted in the nesting of Adrianichthys within Oryzias. Strong geographic structure was evident in the phylogeny; many species in the lineages branching off early are riverine and widely distributed in the southeastern and southwestern arms of Sulawesi, which suggests that oversea dispersal between tectonic subdivisions of this island during the late Miocene (7–5Mya) contributed to the distributions and diversification of the early branching lineages. In contrast, most species in the lineages branched off later are endemic to a single tectonic lake or lake system in the central Sulawesi, suggesting that habitat fragmentation due to the Pliocene collisions (c.a. 4Mya) among the tectonic subdivisions was the primary factor for diversification of the late branching, lacustrine lineages. Adrianichthys and some Oryzias in a certain late branching lineage are sympatric in Lake Poso, which indicates multiple colonizations of these distinct lineages into this tectonic lake. Thus, the diversification of Sulawesi adrianichthyids largely reflects the complex geological history of this island.

Present-day sedimentation rates on the southern and southeastern Australian continental margins

The Australian continental margin presents highly contrasted settings depending on (1) the presence or absence of a fluvial sediment supply, (2) the distance from the Australian mainland, and (3) the local hydrological setting. Despite the importance in surface area of the continental margin around the Australian mainland, so far only a few studies have dealt with sedimentation, most of them focusing on the northeastern Australian Shelf. This work presents the first large-scale investigation of modern sedimentation along the southern margin of Australia in the SE Indian Ocean, and the western margin of the Tasman Sea. Sedimentation intensity was assessed on a century timescale using a multi-tracer approach (234Th, 210Pb, 232Th) on interface cores around the 1000 m water depth contour. 234Th (half-life: 24.1 days) in excess was detected in all surface samples, testifying to the occurrence of freshly deposited particles. Sedimentation and mass accumulation rates based on sedimentary 210Pb excess profiles (CF:CS model) range between 0.027 and 0.280 cm y–1 and between 14 and 222 mg cm–2 y–1, respectively. Whereas sedimentation rates are low and associated with carbonates on the western margin, sediments are more influenced by the detrital fraction and organic carbon on the eastern side of the continent. In comparison with northern continental margins (e.g. Timor Sea, Gulf of Papua), the southern Australian margin receives little sediment today, as it is rarely linked to a river system that would otherwise deliver large amounts of sediment, and also because of the presence of the extended shelf south of Australia.

Cathodoluminescence guided zircon Hf isotope depth profiling: Mobilization of the Lu–Hf system during (U)HP rock exhumation in the Woodlark Rift, Papua New Guinea

Cathodoluminescence image guided Hf isotope depth profiling by laser ablation of zircons from two quartzofeldspathic host gneisses constrains the Lu–Hf system's behavior during rapid exhumation of (U)HP rocks in the Woodlark Rift, Papua New Guinea. Investigation of the depth profiling technique in individual and composite zircon standards demonstrates that it is possible to resolve ~8μm thick domains in which εHf(present) differs by as little as 4units. In a metasedimentary gneiss, 2.89±0.29Ma zircon overgrowths on Cretaceous aged inherited cores have radiogenic εHf(present) indicating growth in a medium that was originally in equilibrium with garnet undergoing recrystallization (the ‘garnet effect’ of Zheng et al., 2005). In a separate gneiss sample that originated as an exhumation related anatectic melt, 3.66±0.13Ma zircons lacking inheritance contain sub-domains that differ from each other by >15 εHf(present). Some of these sub-domains are radiogenic and can be explained by the ‘garnet effect’, whereas others also contain highly elevated Lu and Yb in addition to their radiogenic Hf compositions, thus necessitating a medium derived from the complete breakdown of garnet. Zircons in this sample also contain non-radiogenic sub-domains that grew in the presence of Hf mobilized from the surrounding rocks of the subducted and metamorphosed remnants of the Australian continental margin. The results confirm that rapid exhumation of (U)HP rocks can result in the following: 1) transmission of radiogenic Hf (and sometimes Lu and the other HREE) from garnet bearing mafic lithologies into the quartzofeldspathic gneisses, and 2) mobilization and transport of unradiogenic Hf present within the quartzofeldspathic remnants of subducted continental crust.

The deepwater demersal ichthyofauna of the western Coral Sea.

The highly diverse deepwater demersal ichthyofauna of the western Coral Sea was first systematically surveyed in two exploratory voyages in 1985 and 1986, and these fish assemblages have not been investigated at the same level since. Only recently have catch data and specimens, obtained from these first voyages almost 3 decades ago, been rigorously investigated and analysed. Some 393 species of fishes from 125 families were collected during the 1985 voyage which surveyed the northeastern Australian continental margin, and the Saumarez and Queensland Plateaus. A checklist of the species caught is provided. Levels of endemicity of deepwater fishes in the western Coral Sea are very high with about 50% of well-studied groups, such as sharks and rays, confined to this relatively small geographic region. A very high proportion of species caught during this voyage were either undescribed (78 species or 20%) or new Australian records (96 species or 24%) at the time of the survey. Another 68 species (17%) are the subject of further taxonomic investigation or are currently undergoing formal description. The fauna exhibits some intraregional differences in structure. Biogeographically informative fishes such as skates appear to be cryptically partitioned within the region, differing in composition to other Australian regions and those of French territories to the east. Strong depth-related partitioning of the fauna is also evident, and its structure follows zonation patterns observed across the wider Australian region. Given the high level of micro-endemicity and regional uniqueness of the fauna, there is a compelling argument for the existence of a faunal gyre in the Coral Sea. New gap-filling surveys are needed to better define the structure of this fauna and determine its distribution.