Australian Continental Margin Research Articles

Cretaceous-Paleogene rifting on the NW margin of the Australian continent, SE Banda Arc region

The Banda Terrane successions of Timor Island and correlative units in Sumba are widely considered allochthonous with respect to the Australian continental margin successions that form the main part of the Banda arc-continent collision complex. A new interpretation is proposed for the Banda Terrane, which suggests that these units originated on the outermost (northern) edge of the Australian continent. Volcanic successions in the Banda Terrane, which date to the Cretaceous and Paleogene (Aptian/Albian to Eocene), are interpreted as originating in a backarc/marginal basin setting behind a northward-facing arc that rifted away from the NW margin of Australia through this period. The Banda terrane successions are interpreted as representing the southern, continent-attached portion of the marginal basin, and occupied a position on the distal edge of Australia up to the onset of Banda arc-continent collision in the Miocene.Supporting evidence for an Australian margin origin of the Banda Terrane includes very similar age ranges for zircons dated to the Cretaceous in Sumba and Timor (Banda Terrane) and in sandstones of the Ungar Formation in Tanimbar, the latter forming an element of the Australian margin succession. In Timor there is also previously reported evidence for continental margin rifting during the Late Cretaceous, while contemporaneous Late Cretaceous-Paleogene volcanism is also recognised in the Bird’s Head-Misool region of eastern Indonesia, which forms part of the Australian continental margin. In addition, a number of stratigraphic links between the Banda Terrane and the Australian continental margin successions in Timor are summarised in this study.The effects of the Cretaceous-Paleogene rifting event are also apparent in subsidence curves derived from petroleum exploration wells drilled on the northern ‘passive’ continental margin of Australia from SW of Timor to the Bird’s Head-Misool region of eastern Indonesia. Inferred rift-related subsidence commenced in the Aptian-Albian on the Australian palaeo-margin immediately east of Timor and developed sporadically but in regionally consistent groupings throughout the Late Cretaceous and Paleogene.

Jurassic-Paleogene spreading history of the northern Indian Ocean as a constraint on the evolution of the north Australia continental margin

The spreading history of the northern Indian Ocean is re-examined with the aim of interpreting the late Mesozoic-Paleogene evolution of the northern Australian continental margin in eastern Indonesia and Timor-Leste. The earliest seafloor spreading (‘Argo phase’) developed between approximately 155-131Ma (Kimmeridgian, Late Jurassic to Valanginian, Early Cretaceous). A clockwise pole of rotation relative to Australia (‘Argo pole’) is interpreted at 7°09’S, 133°07’E, a present-day location near the Tanimbar islands in eastern Indonesia. A second ‘Gascoyne’ phase of spreading, between 131-100Ma (late Early Cretaceous), had an interpreted clockwise rotation pole at 3°40’N, 125°00’E, a present-day location between the islands of Mindanao (southern Philippines) and Sulawesi (eastern Indonesia). A third ‘Wharton’ phase of spreading, commencing at the beginning of the Late Cretaceous (~100Ma) had a more distant pole (clockwise pole at 5°S, 171°E: Jacob et al., 2014), although more local rotations are interpreted for the Greater Sula Spur continental terrane, about a pole estimated at 9°24’S, 134°40’E, close to the earlier Argo pole.The motions of two continental terranes are inferred from the spreading history. The Argoland Terrane, which is identified in this study as eastern Sundaland (Borneo and Java), would not have entirely detached from Australia before the mid Cretaceous due to the relatively proximal locations of the Argo and Gascoyne rotation poles. In this scenario Argoland could not have collided with Eurasia in the Cretaceous, as suggested by several previous studies. The Greater Sula Spur Terrane (several continental fragments in present-day eastern Indonesia), is repositioned in the initial reconstructions immediately north of Timor, and did not move northward to its late Paleogene (pre-Neogene collision) location until the Wharton phase of rifting that commenced in the Late Cretaceous. This northward motion of the Greater Sula Spur was accommodated by the development of a narrow oceanic basin (the Banda Embayment).The reconstructions suggest that the Argoland and Greater Sula Spur continental terranes formed a continuous crustal connection between SE Asia and northern Australia throughout the late Mesozoic and early Paleogene, and that the Indian Ocean developed entirely within the body of the disrupting Gondwanaland supercontinent, rather than linking eastwards into the Pacific Ocean.

Provenance of the Papuan Peninsula (Papua New Guinea): Zircon Inheritance from Miocene–Pliocene Volcanics and Volcaniclastics

Plate tectonic reconstructions of Papua New Guinea prior to the late Cenozoic are characterized by a lack of provenance data to constrain the relative origin of the allochthonous terranes. At present, plate tectonic reconstructions of this region infer that the accreted New Guinea terranes at the northern Australian continental margin are likely autochthonous or para-autochthonous in nature. This study presents the results of an investigation into zircons derived from Miocene–Pliocene volcanics and volcaniclastics of the Papuan Peninsula. Results from U-Pb zircon geochronology inform the recent geological history of the Papuan Peninsula, with magmatism active in the late Miocene and early Pliocene, between approximately 9 Ma and 4.5 Ma. More significantly, however, is the recognition of extensive inherited zircon grains within the volcanic and volcaniclastic sequences. These inherited zircon grains are most likely sourced from the Owen Stanley Metamorphics, which form the basement rocks of the Papuan Peninsula. Provenance of the inherited zircon grains imply that the Cretaceous volcaniclastic protolith of the Owen Stanley Metamorphics must have had input from continental detritus, but this cannot be derived from North Queensland, Australia as inferred by current reconstructions. Instead, zircon U-Pb age spectra correlate with probable source regions further to the south, adjacent to the Shoalwater Formation of the Central Queensland margin, and New Caledonia. These findings suggest that late Mesozoic and Cenozoic regional reconstructions of eastern Australia and the Southwest Pacific require major revision and that additional work is undertaken to inform the provenance of such allochthonous terranes.

The ephemeral history of Earth’s youngest supra-subduction zone type ophiolite from Timor

Ophiolites occur widely in orogenic belts, yet their origins remain controversial. Here we present a modern example with a geodynamic model from Timor, eastern Indonesia, where Earth’s youngest supra-subduction zone (SSZ)-type ophiolitic fragments are exposed. Zircon U-Pb ages and geochemical data indicate a short timespan (~10 to 8 Ma) for the magmatic sequence with boninitic and tholeiitic arc compositions. We interpret the Timor ophiolite as part of the infant Banda arc-forearc complex, which formed with the opening of the North Banda Sea and subsequent arc-continent collision along the irregular Australian continental margin. Our study connects the occurrence of small, short-lived ocean basins in the western Pacific with orogens around the globe where ephemeral SSZ-type ophiolites occur. These orogenic ophiolites do not represent preexisting oceanic crust, but result from upper-plate processes in early orogenesis and thus mark the onset of collision zone magmatism.

‘Banda Terrane’ basement and cover in the Noil Meto River section, southern West Timor (Timor Barat, Nusa Tenggara Timur, Indonesia)

A previously undocumented body of Mutis metamorphic complex is reported from the Noil Meto River, approximately 7km south of Soe town in southern West Timor. Cover sequences overlying the Mutis Complex include the Cretaceous Haulasi Formation (the upper element of the Palelo Group) which most likely has an unconformable relationship to the metamorphic complex; and (possibly) the Permian Maubisse Formation which may overlie the Mutis Complex with an unresolved stratigraphic or structural contact. This is the first substantial documentation of the Mutis Complex and the Palelo Group to the south of the Central Basin. These elements of the so-called Banda Terrane, widely considered allochthonous ‘Asiatic’ elements, are overthrust by Triassic-Jurassic cover sequences (Aitutu and Wai Luli Formations) of the Australian continental margin succession.

Broad distribution of spider-shaped lebensspuren along the Australian continental margin

During feeding and burrowing, many epibenthic and infaunal animals bioturbate sediments and form a range of traces called lebensspuren (German for ‘life traces’), defined as any type of sedimentary structure produced by a living organism. During a 2020 survey along western Australia in the Gascoyne Marine Park, a distinct trace was observed several times, identical to the ‘spider trace’ observed in a 2007 survey along eastern Australia, over 4000 km away. The purpose of this brief note is to document and describe the occurrence of this unique and distinctive type of lebensspuren and to discuss ways in which similar observations may be effectively shared to increase our understanding of deep-sea biology.

Stratigraphic record of continental breakup, offshore NW Australia—Discussion

AbstractReeve et al. (2022) address the stratigraphic record of continental breakup by focusing on a set of stratigraphic unconformities from a proximal sector of the NW Australian continental margin, inboard from the Exmouth Plateau. They suggest that such unconformities can potentially document a well‐defined three‐stage process: end of the syn‐rift phase, formation of a wide continent‐ocean transition zone (COTZ) and generation of ‘true’ Penrose‐type oceanic crust. We counterargue that continental breakup is a protracted event that can only be understood via seismic‐ and chronostratigraphic correlations of strata, and their composing sequences, across and along rifted margins. Tying proximal stratigraphic unconformities to magnetic anomalies outboard from the study area in Reeve et al. (2022) is open to question. In parallel, we suggest that age resolutions of ca. 1 Ma are not achievable using the micropaleontological data presented in Reeve et al. (2022), with an important reworking of microfossil assemblages potentially occurring during the erosional process forming local and regional unconformities. Our discussion addresses these points in more detail.

Unveiling deep-sea habitats of the Southern Ocean-facing submarine canyons of southwestern Australia

Here we present the outcomes of the first deep-sea remotely operated vehicle study of previously unexplored submarine canyon systems along the southwest Australian continental margin. This was conducted around: (1) the Bremer Marine Park; (2) the Mount Gabi seamount and nearby slope-shelf margin at the interface of the Southern and Indian oceans; with new information from (3) the Perth Canyon Marine Park located in the SE Indian Ocean. These canyons differ from many explored around the world in having no connectivity to continental river systems, thus little detrital input, with the Bremer systems and Mount Gabi facing the Southern Ocean which plays a key role in the global ocean circulation and climate systems. Such studies in the vast deep waters around the Australian continent are rare given the lack of local ROV capability available for research, thus little is known about these environments.Using the resources of the Schmidt Ocean Institute, we characterised the submarine topography from high-resolution bathymetric mapping, geology, physical and chemical oceanography, and provide an overview of these environments including the fauna observed and collected. We show that these Southern Ocean-influenced environments incorporate South Indian Central Water, Subantarctic Mode Water, Antarctic Intermediate Water, and Upper and Lower Circumpolar Deep Water, with Antarctic Bottom Water present in deep water just south of the Bremer canyon systems. The richness in megabenthos, especially along the steep, rocky substrates of the canyon heads and walls around the Bremer canyon systems, contrasts to the comparatively depauperate fauna of the more northerly Perth Canyon. Various corals serve as important substrates for a range of other species and often exhibit particular faunal associations. Especially notable are distinct ecological zones including a bryozoan and sponge-dominated (animal) forest on the shelf edge, spectacular coral gardens along canyon margins, and the occurrence of solitary scleractinians well below the aragonite saturation horizon. Subfossil coral deposits were discovered across all three study areas, reflecting periodic waxing and waning of deep-water Scleractinia throughout this southwest region. Extensive pre-modern assemblages at Mount Gabi contrast markedly with the sparse populations of living species and suggest that it might have once been a major coral hotspot, or whether they reflect long-term coral aggregations is yet to be determined. Nevertheless, stark differences in both living and past coral distribution patterns across our study sites point to at least localised fluctuations in Southern Ocean-derived nutrient and/or oxygen supplies to these deep-sea communities.

Deformation and uplift at the transition from oceanic to continental subduction, Sumba Island, Indonesia

• The Australian margin boundary collision produces forearc dextral transpression . • Interplate transfer of shear stress and forearc block escape induce trench migration. • Northeastward folding has been propagating across Sumba Island since the Pliocene . • One-third of Sumba Island was inundated by flexure and gravitational collapse . The transition along the strike of the Sunda subduction zone, from oceanic subduction in the west to subduction of continental Australian lithosphere in the east is envisioned as one of the canonical examples of the structural changes that take place within an overriding plate when a continental lithosphere wedge enters a subduction zone. Yet, the along-strike offset of the trench toward the Australian margin represents a structural response opposite to the predictions of numerical models. To understand this paradox, we analyse the morphotectonic evolution of Sumba island located at the transition from oceanic to continental Indo-Australian lithosphere subduction. Drainage evolution allows us to constrain the topographic evolution of the island since the Pliocene. Flights of uplifted coral reef terraces document Quaternary deformation. Focal mechanisms of shallow crustal earthquakes constrain the current stress field. Together, these data reveal that the island is affected by dextral en-échelon folding. Offshore, west of the island, reverse and strike-slip focal mechanisms evidence an active dextral transpressional zone. The emergence of the island and dextral shearing of the accretionary prism were triggered by subduction of the western lateral boundary of the Australian continental margin. We contend that the Plio-Quaternary tectonic evolution of the region, with transpression and migration of the trench toward the Australian margin is primarily dictated by shear stress transfer from the lower plate to the overriding plate, favored by strong interplate coupling, and by southwestward escape of the Savu-Sumba block following the impingement of the Australian continental margin against Timor island.

Stratigraphic architecture of the Cenozoic Dugong Supersequence: implications for the late post-breakup development of the Eucla Basin, southern Australian continental margin

ABSTRACTThis study presents an appraisal of the Middle Eocene–Quaternary Dugong Supersequence of the Eucla Basin, offshore southern Australia. It combines details of the rock record with seismic-stratigraphical information, and the resulting stratigraphic framework provides constraints on the nature of the late post-breakup development of the southern Australian continental margin. It is well established that the onshore-to-mid-shelf succession comprises a predominantly aggrading-to-prograding unconformity-bounded succession of carbonate platform deposits; however, our analysis of the outer shelf–upper slope section challenges the widely held view that this shelf-margin wedge represents a distally steepened prograding carbonate ramp primarily modulated by global eustasy. Instead, our results show that the Middle Eocene–Quaternary succession is punctuated by a series of unconformities that reflect a persistent tectonic instability and differential vertical movements throughout the late post-breakup period, the genesis of which is most closely related to tectonic events. Moreover, the upper slope clinoform succession was constructed and shaped predominantly by alongslope processes, and four different contourite drift types are recognised based on their seismic-stratigraphic expression: elongate mounded drift (Quaternary); infill drift (Pliocene); plastered drift (Oligocene); and separated drift (Middle–Upper Eocene). The Quaternary drift – herein termed the ‘Eyre Terrace Drift’ – is a spectacular basin-scale deposit, over 500 m thick and traced for up to 200 km along the upper slope Eyre Terrace. Upslope-migrating sediment waves are associated with this drift. Key sedimentary attributes consistent with a contourite origin include fine-grained sediment, multi-scale gradational bed contacts and pervasive bioturbation. There is also evidence of episodic downslope mass-movement processes ranging from the large-scale Late Neogene Slide, which extends downslope for 15–20 km, to sporadic slumped beds and turbidites recovered in boreholes. The interaction of alongslope and downslope processes indicates a more dynamic sedimentary setting than previously assumed along the outer margin of the Eucla Basin.

How do tectonics influence the initiation and evolution of submarine canyons? A case study from the Otway Basin, SE Australia

The architecture of canyon-fills can provide a valuable record of the link between tectonics, sedimentation and depositional processes in submarine settings. We investigated the role of plate tectonics in the initiation and evolution of submarine canyons. We demonstrate that events at the plate tectonic scale (i.e. continental break-up and shortening) have a first-order influence on the initiation and development of submarine canyons. The Late Cretaceous ( c. 65 Ma) separation of Australia and Antarctica initially resulted in extensional fault systems, which then formed a steep stair-shaped palaeoseabed. Subsequently, the Late Miocene ( c. 5 Ma) collision of Australia and Eurasia resulted in substantial uplift and exhumation on the SE Australian continental margin. These tectonic events led to elevated seismicity, which ultimately gave rise to gravity-driven processes (i.e. turbidity currents and mass wasting processes) and formed the base of the canyon. The inherited stair-shaped topography then facilitated further gravity-driven processes that established a mature sediment conduit extending from the shallow marine shelf to the abyssal plain. We suggest that the stratigraphic architecture of canyons can be used as an archive to record tectonic movements. Moreover, the factors that precondition and trigger gravity-driven processes can induce canyon initiation and facilitate canyon development. Supplementary material: A PDF file containing all the clean, uninterpreted seismic sections is available at https://doi.org/10.6084/m9.figshare.c.5937760

The Margin‐Oblique Kumawa Strike‐Slip Fault in the Banda Forearc, East Indonesia: Structural Deformation, Tectonic Origin and Geohazard Implication

AbstractThe northeast Banda margin is affected by the arc‐continent collision between the Australian continental margin and the Banda arc. Unlike margin‐parallel strike‐slip faults in other subduction zones, the margin‐oblique Seram‐Kumawa Shear Zone (SKSZ) has greatly deformed the Banda forearc with 80 km displacement along plate boundary. It trends ∼ WNW‐ESE comprising the Kawa shear zone (KSZ, >200 km) on the Seram island and the Kumawa fault (KF, >200 km) offshore SE Seram. Using multibeam bathymetry, marine seismic reflection and earthquake data, we studied the active tectonics and driving mechanism of the SKSZ with focus on its offshore part (KF). Our results show: (1) the KF is a young (∼2 Ma), linear crustal structure with three segments from NW to SE: pull‐apart basin (dextral), diffuse shear zone (sinistral) and distinct fault trace (sinistral); (2) It propagates southeastward and cross‐cuts the entire upper plate with prominent seafloor expression, but without seismicity along it, similar to the Banda detachment caused by forearc extension; (3) By incorporating the oblique collision and regional tectonics with our results, we proposed that the KF is formed primarily by the upper plate extension induced by subduction rollback during the last 2 Ma, with minor contribution from oblique arc‐continent collision; (4) The slip rate of the KF has reduced from 40 mm/yr over 2 Ma to <14 mm/yr at present. These observations combined with the clear seafloor faulting, 80‐km displacement and occurrence of a Mw 5.2 earthquake on its horsetail fault suggest it is currently locked awaiting a large earthquake.

Seismic Imaging of the Subducted Australian Continental Margin Beneath Timor and the Banda Arc Collision Zone

AbstractDetailed crustal and uppermost mantle structure is imaged for the first time utilizing ∼4 years of broadband seismic data newly collected in the Timor‐Leste and Nusa Tenggara Timor region of Indonesia. We apply three techniques, ambient noise tomography, teleseismic P wave receiver function, and coda autocorrelation, to resolve a 3D Vs model and Moho structure. Our tomographic images show low‐velocity anomalies (<30 km) beneath Timor related to underthrusted Gondwana sequence from the Australian plate, which are vertically offset by the high‐velocity backstop of the Banda forearc terrane. The structure progressively changes along strike, reflecting different collisional stages developed as a result of the oblique convergence. At greater depth, we detect seismically fast lithospheric mantle (>30 km) and the arc‐ward dipping Moho beneath Timor, both interpreted to be from the Australian plate. Our findings provide direct structural evidence of the Australian continental margin at lithospheric depths beneath the Banda Arc collisional zone.

Evolution of the Southwest Australian Rifted Continental Margin During Breakup of East Gondwana: Results From International Ocean Discovery Program Expedition 369

AbstractInternational Ocean Discovery Program Expedition 369 drilled four sites on the southwestern Australian continental margin, in the deep water Mentelle Basin (MB) and on the neighboring Naturaliste Plateau (NP). The drillsites are located on continental crust that continued rifting after seafloor spreading began further north on the Perth Abyssal Plain (PAP) between magnetochrons M11r and M11n (133–132 Ma), ending when spreading began west of the NP between chrons M5n and M3n (126–124 Ma). Drilling recovered the first in situ samples of basalt flows overlying the breakup unconformity on the NP, establishing a magnetostratigraphically constrained eruption age of >131–133 Ma, and confirming a minimal late Valanginian age for the breakup unconformity (coeval with the onset of PAP seafloor spreading). Petrogenetic modeling indicates the basalts were generated by 25% melting at 1.5 GPa and a potential temperature of 1380°C–1410°C, consistent with proximity of the Kerguelen plume during breakup. Benthic foraminiferal fossils indicate that the NP remained at upper bathyal or shallower depths during the last 6 Myr of rifting and for 3–5 Myr after breakup between India and Australia. The limited subsidence is attributed to heat from the nearby Kerguelen plume and PAP spreading ridge. The margin subsided to middle bathyal depths by Albian time and to lower bathyal (NP) or greater (MB) depths by late Paleogene time. Periods of rapid sedimentation accompanied a westward jump of the PAP spreading ridge (108 Ma), rifting on the southern margin (100–84 Ma), and opening of the southern seaway between Australia and Antarctica (60–47 Ma).

Stratigraphic Model of East Biak Based on Magnetotelluric Data

Biak Island is thought to have originated from the Australian Continental passive margin in the Mesozoic. This passive margin underwent tectonic collision to form the bedrock of Biak Island during the Paleogene. East Biak is covered by limestone, which is an obstacle to knowing the deeper stratigraphy. This study’s aim was to identify the subsurface geology of the East Biak area based on rock resistivity values. Magnetotelluric (MT) surveying is a passive geophysical method that is able to interpret subsurface geology based on rock resistivity values at depths of up to 5 to 10 km. The MT measurements in East Biak used 25 measurement points. Cross-sectional variations in rock resistivity values generated from the MT measurements were used to identify rock types in the East Biak subsurface. Five rock units were identified. The East Biak stratigraphy model is dominated by carbonates, comprising two sequences, i.e. an Early Neogene sequence with a thickness of 1,000 to 3,000 m and a Late Neogene to Quaternary sequence with a thickness of 180 to 2,450 m. The unconformity between these two sequences is due to tectonic activity, which separated Supiori and Biak Island.

Two new deep-water species of Ampharetidae (Annelida: Polychaeta) from the eastern Australian continental margin

Two new deep-water species of Ampharetidae (Annelida: Polychaeta) from the eastern Australian continental margin

Coastal and offshore provinces of Timor-Leste — Geophysics exploration and drilling

Regional geophysics research provides for prospect assessment of Timor-Leste, part of the Southeast Asia Archipelago in a region embracing the Banda Arc, Timor Island, and the northwest Australia Gondwana continental margin edge. Timor Island is a microcontinent with several distinct tectonic provinces that developed initially by rifting and drifting away from the Australian Plate. A compressive convergence began in the Miocene whereby the continental edge of the large craton collided with the microcontinent, forming a subduction zone under the island. The bulk of Timor Island consists of a complex mélange of Tertiary, Cretaceous, Jurassic, Triassic, Permian, and volcanic features over a basal Gondwana craton. Toward the north, the offshore consists of a Tertiary minibasin facing the Banda Arc Archipelago, with volcanics interspersed onshore with the basal Gondwana pre-Permian. A prominent central overthrust nappe of Jurassic and younger layers makes up the mountains of Timor-Leste, terminating south against an accretionary wedge formed by this ongoing collision of Timor and Australia. The northern coast of the island is part of the Indonesian back arc, whereas the southern littoral onshore plus shallow waters are part of the accretionary prism. Deepwater provinces embrace the Timor Trough and the slope of the Australian continental margin being the most prospective region of Timor-Leste. Overall crust and mantle tectonic structuring of Timor-Leste is interpreted from seismic and potential field data, focusing mostly on its southern offshore geology where hydrocarbon prospectivity has been established with interpretation of regional seismic data and analyses of gravity, magnetic, and earthquake data. Well data tied to seismic provides focal points for stratigraphic correlation. Although all the known producing hydrocarbon reservoirs of the offshore are Jurassic sands, interpretation of Permian and Triassic stratigraphy provides knowledge for future prospect drilling risk assessment, both onshore and offshore.

Exploring Sea Country through high-resolution 3D seismic imaging of Australia’s NW shelf: Resolving early coastal landscapes and preservation of underwater cultural heritage

Almost 2 million square km of Australia’s continental shelf was flooded following the termination of the last glacial maximum, and with it the cultural heritage of the first arrival and coastal occupation of Australia beginning some 65,000 years ago. In order to prospect for this missing cultural record, we must first identify submerged coastal landscapes and landforms that likely provided favourable environments for occupation and resource use. However, this task is challenged by the sheer size of the Australian continental margin. To help address this, we use industry 3D seismic datasets, that cover vast areas of Australia’s continental shelf, to map seafloor bathymetry at high resolution (10–25 m). Our study focuses an area of 6500 square km on the mid/outer shelf regions proximal to Barrow Island. The 3D seismic bathymetry revealed a highly complex and geomorphically mature coastal landscape preserved at depths of 70–75 m below sea level, including coastal barrier dunes, lagoonal systems, tidal flats and estuarine channels. Based on the depth of the submerged shorelines and reconstructed sea level curves, the age range of these coastal landforms is constrained to Marine Isotope Stage 3 (57–29 ka), which overlaps with the known onset of occupation at Barrow Island and the wider Carnarvon bioregion and the adjacent Pilbara. Such feature preservation has significant geoheritage value, but also allows for human behavioural ecology modelling and provides targets for future dating and site survey.

Deep-sea temperate-tropical faunal transition across uniform environmental gradients

The biogeography of the deep-sea benthic fauna is uncertain due to the vast size and incomplete exploration of these environments. While shallow water assemblages are differentiated into tropical, temperate and polar faunas, it is unknown whether these units extend to lower depths. Here we use model-based and multivariate statistics to analyse megafaunal benthic samples along a 2300 km transect off the eastern Australian continental margin. We show that a temperate-tropical transition between 33-30°S occurs at both lower bathyal (~2500 m) and abyssal (~4000 m) depths. This transition occurs despite almost uniform temperature, salinity and dissolved oxygen concentrations occurring across latitudes at these depths. Conversely, the patterns are consistent with the flux of organic matter to the seafloor, which varies from being relatively high in the productive temperate off SE Australia to low levels in more-oligotrophic tropical waters. Biodiversity is not uniform across the deep-sea and regional-scale heterogeneity needs to be incorporated into marine park designs.

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.