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Abstract Carbonate sediments are often regarded as problematic in geotechnical engineering due to the high variability of their properties. Understanding and quantifying this variability will become increasingly critical in the years ahead, notably with respect to upcoming developments in offshore renewable energy, for which limited in-situ data are typically available to characterise large areas. Here, six intervals from the North West Shelf of Australia, each composed of similar carbonate grains but accumulated in different environments, are investigated to better understand how the post-depositional cementation, alteration and dissolution of sediments, known as diagenesis, impact their geotechnical properties. Intervals are primarily affected by mineralogy-driven meteoric diagenesis, comprising in-situ dissolution of metastable grains and subsequent precipitation of cement that occurred when the shelf was exposed during lower sea-levels, and by marine diagenesis. In both cases, increased diagenesis results in a higher cement-to-solid ratio and compressive strength. However, while marine diagenesis is associated with a reduction in void ratio, this is not initially observed with mineralogy-driven meteoric diagenesis. Additionally, for a similar cement-to-solid ratio, microcrystalline cement results in higher compressive strength than sparite cement. The data further reveal that the level of meteoric cementation and the compressive strength increase as a function of the duration of exposure and of the regional climate, along with a reduction of the specific gravity related to the replacement of aragonite by calcite. However, increased meteoric diagenesis also leads to the formation of macro-scale heterogeneities such as calcrete layers and karsts that can affect the holistic geotechnical behaviour of such deposits.

Carbonate sediments are often regarded as problematic in geotechnical engineering due to the high variability of their properties. Understanding and quantifying this variability will become increasingly critical in the years ahead, notably with respect to upcoming developments in offshore renewable energy, for which limited in-situ data are typically available to characterise large areas. Here, six intervals from the North West Shelf of Australia, each composed of similar carbonate grains but accumulated in different environments, are investigated to better understand how the post-depositional cementation, alteration and dissolution of sediments, known as diagenesis, impact their geotechnical properties. Intervals are primarily affected by mineralogy-driven meteoric diagenesis, comprising in-situ dissolution of metastable grains and subsequent precipitation of cement that occurred when the shelf was exposed during lower sea-levels, and by marine diagenesis. In both cases, increased diagenesis results in a higher cement-to-solid ratio and compressive strength. However, while marine diagenesis is associated with a reduction in void ratio, this is not initially observed with mineralogy-driven meteoric diagenesis. Additionally, for a similar cement-to-solid ratio, microcrystalline cement results in higher compressive strength than sparite cement. The data further reveal that the level of meteoric cementation and the compressive strength increase as a function of the duration of exposure and of the regional climate, along with a reduction of the specific gravity related to the replacement of aragonite by calcite. However, increased meteoric diagenesis also leads to the formation of macro-scale heterogeneities such as calcrete layers and karsts that can affect the holistic geotechnical behaviour of such deposits. [ABSTRACT FROM AUTHOR]

This document is a corrigendum for an article titled "A seasonal undercurrent along the northwest coast of Australia." The author acknowledges an error in the analytic solutions and figures presented in the original article. The corrected solutions and figures have been provided, and the author states that this error does not affect the scientific conclusions of the article. The corrigendum was published in the journal Frontiers in Marine Science. [Extracted from the article]

In the North West Shelf region of Australia is a surface current (Holloway Current), which flows southwestward along the shelf break. This paper describes a seasonal undercurrent below the Holloway Current. A 5-day climatology is constructed from the output of an eddy-resolving oceanic general circulation model (OGCM). A seasonal northeastward-flowing undercurrent is found on the upper continental slope during the climatological April-May. This undercurrent reverses during February-March. During its annual cycle, the phase of the undercurrent tends to propagate southwestward and upward. The annual frequency dominates, but the positive and negative phases of the undercurrent are not symmetric in the yearly cycle because of the contributions from the semi-annual and 1/3-annual components. We propose a hypothesis that this undercurrent is a beam of coastal trapped wave (CTW). As an initial attempt to assess the plausibility of this hypothesis, we construct an idealized linear coastal-trapped wave (CTW) solution driven by an idealized harmonic meridional winds at the annual frequency. The solution takes the form of a beam originating from the forcing region on the continental shelf and propagating offshore and southward. When it emerges on to the continental slope, it takes the form of an undercurrent. This idealized solution shares several properties with the undercurrent in the OGCM despite several discrepancies. [ABSTRACT FROM AUTHOR]

Nest temperature is the predominant driver of emergence success and primary sex ratios in sea turtles, with female offspring produced at higher temperatures due to temperature-dependent sex determination. However, emergence success and primary sex ratios are unfeasible to measure at scale, making methods to estimate these life-history traits from predicted sand temperatures highly desirable for long-term conservation planning in the context of climate change. To address this, we used a mechanistic microclimate model to predict hourly sand temperatures, over 32 nesting seasons since 1986, at 402 West Australian beaches supporting nesting by flatback turtles (Natator depressus). Predicted sand temperatures indicated that ∼70% of these beaches carried a 'very low' to 'intermediate' risk of subjecting embryos to thermal stress. By combining these temperature predictions with a physiological model, current and future emergence success and sex ratios were projected for ten different beaches spanning a range of thermal microclimates, under various climate change scenarios. Under recent climate conditions, emergence success averaged 76%, but declined to 63% and 37% with a 2°C and 4°C increase in air temperature, respectively. The sex ratios of hatchlings varied by location, but extremely skewed sex ratios were anticipated in a 4°C warming scenario. Our projections reveal that 'high risk' nesting beaches will regularly experience clutch failure as climate change progresses, while cooler beaches offer long-term nesting potential and require protection from additional anthropogenic impacts. These projections, covering an entire genetic stock, supply demographic data for assessing extinction risks and this method can be applied to sea turtle populations worldwide.

The Canning Basin is a prospective hydrocarbon frontier basin and is unusual for having limited offshore seismic and well data in comparison with its onshore extent. In this study, seismic mapping was conducted to better resolve the continuity of 13 key stratigraphic units from onshore to offshore to delineate prospective offshore hydrocarbon-bearing units, and better understand the distribution of mafic igneous units that can compartmentalise migration pathways and influence heat flow. The offshore Canning Basin strata are poorly constrained in six wells with limited seismic coverage; hence data availability was bolstered by integrating data from the onshore portion of the basin and adjacent basins into a single 3D seismic stratigraphic model. This model integrates over 10 000 km of historical 2D seismic data and 23 exploration wells to allow mapping of key stratal surfaces. Mapped seismic horizons were used to construct isochores and regional cross-sections. Seven of the 13 units were mapped offshore for the first time, revealing that the onshore and offshore stratigraphy are similar, albeit with some minor differences, and mafic igneous units are more interconnected than previously documented whereby they may constitute a mafic magmatic province. These basin-scale maps provide a framework for future research and resource exploration in the Canning Basin. To better understand the basin's geological evolution, tectonic history and petroleum prospectivity, additional well data are needed in the offshore Canning Basin where Ordovician strata have yet to be sampled. Coastlines act as barriers that can prevent parity of stratigraphic interpretations and geoscience data acquisition for adjacent onshore, offshore areas. This study features seismic stratigraphic mapping of 13 key units in the Canning Basin coastal area, including seven units mapped continuously from onshore to offshore for the first time. This research delivers a framework for future exploration and a better understanding of the Canning Basin's geological history. [ABSTRACT FROM AUTHOR]

Our understanding of the biology and ecology of many Australian marine snakes is inadequate to inform the conservation and management of their populations. Czeblukov's true sea snake Hydrophis czeblukovi (Elapidae:Hydrophiinae) is an example of this, with an IUCN classification of "Data Deficient". It is a wholly marine, ovoviviparous snake that is distinguishable by its dark colouration and unique pale banding forming dark pentagons on its dorsal surface and flanks. A recent biological survey in Exmouth Gulf, Western Australia found a recently dead H. czeblukovi specimen. This extends the species geographical range by approximately 300 kilometres southwest (minimum seaward distance). The stranding likely arose from the persistent onshore winds observed prior to the discovery or from self-stranding due to illness. This discovery brings the total number of marine snake species recorded from Exmouth Gulf to 11 out of ~24 known to occur in WA waters, which highlights the importance of this location for marine snake conservation. Here we compile the scarce knowledge for this data deficient species. We discuss the conservation implications of our findings in context of the dense industrial activity across the range of H. czeblukovi. We indicate the need for further research to inform conservation and management actions. [ABSTRACT FROM AUTHOR]

Offshore oil and gas (O&G) structures exist in nearshore and offshore marine environments globally, yet our understanding of their ecological implications is poorly understood, especially when it comes to decommissioning these structures at the end of life. Specifically, the influence of these structures on dispersal-based connectivity and population persistence of associated species has yet to be quantified. In this study, we provide insights into the ecological implications of O&G structures on the North West Shelf (NWS) of Western Australia. Specifically, we examine their impact on local and regional population connectivity patterns and metapopulation dynamics for two fish species and a coral. By integrating biophysical modeling, network analysis and metapopulation models, we estimate the contribution and impact of both O&G structures and natural reef systems in this complex seascape. Our findings indicate that collectively the reefs in this system contribute as the main sources of larval export and O&G structures contribute as destinations, with a higher import of larvae. These structures could also act as local stepping-stones, enhancing the ecological connectivity among reef subpopulations. Overall, O&G platforms and wells, as included in the model, do not have a significant impact on regional metapopulation dynamics for the reef species explored in this study. Knowledge gained from this research will inform regional spatial planning for decommissioning offshore infrastructure., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Over 1400 km of oil and gas pipeline infrastructure exists within the boundaries of the Pilbara Trap Managed Fishery (PTMF) operating on the North West Shelf of Australia. Some of this infrastructure has reached the end of its operational life and requires decommissioning. Location and speed data collected from 2008 to 2018 using vessel monitoring systems onboard all trap fishing vessels (n = 3) operating in the PTMF were used to understand how fishing activity near pipelines has changed through time, and to identify the best predictive variables to explain hours spent fishing km−2 week−1. The proportion of fishing activity within 200 m of a pipeline increased over the survey decade and averaged 4.2% across all years. Hours spent fishing km−2 within 200 m of any pipeline was found to be 8.0 h km−2, ~ 11.4 times more than that recorded, on average, for the remaining area of the PTMF (0.7 h km−2), and ~ 4.6 times more than the western portion of the PTMP (1.7 h km−2) where all pipeline infrastructure exists. Fishing activity within 1 km of pipelines increased after their installation, and hence time since installation was the best predictor of fishing. This study demonstrated that trap fishers in the PTMF allocate a small proportion of their time targeting pipeline infrastructure, with the area close to a pipeline experiencing a relatively greater magnitude of fishing than that elsewhere in the PTMF. As such, the results of this study provide decision makers with an understanding of the intrinsic value of this infrastructure to trap fishers. [ABSTRACT FROM AUTHOR]

In the North West Shelf region of Australia is a surface current (Holloway Current), which flows southwestward along the shelf break. This paper describes a seasonal undercurrent below the Holloway Current. A 5-day climatology is constructed from the output of an eddy-resolving oceanic general circulation model (OGCM). A seasonal northeastward-flowing undercurrent is found on the upper continental slope during the climatological April–May. This undercurrent reverses during February–March. During its annual cycle, the phase of the undercurrent tends to propagate southwestward and upward. The annual frequency dominates, but the positive and negative phases of the undercurrent are not symmetric in the yearly cycle because of the contributions from the semi-annual and 1/3-annual components. We propose a hypothesis that this undercurrent is a beam of coastal trapped wave (CTW). As an initial attempt to assess the plausibility of this hypothesis, we construct an idealized linear coastal-trapped wave (CTW) solution driven by an idealized harmonic meridional winds at the annual frequency. The solution takes the form of a beam originating from the forcing region on the continental shelf and propagating offshore and southward. When it emerges on to the continental slope, it takes the form of an undercurrent. This idealized solution shares several properties with the undercurrent in the OGCM despite several discrepancies.

Subsea infrastructure of the oil and gas industry attracts commercial fish species as well as megafauna including sea lions, turtles, sharks and whales. Potential impacts of this attraction, whether positive or negative, are unknown. As part of a pilot study, we deployed acoustic telemetry equipment around offshore infrastructure to assess its effectiveness in detecting tagged marine animals and to gain insights into patterns of megafauna occurrence around these structures. Acoustic receivers were placed around four oil and gas platforms and on two remotely operated vehicles (ROVs) on Australia’s North West Shelf. Two whale sharks (Rhincodon typus) tagged in the World Heritage Ningaloo Reef Marine Park were detected at two platforms, North Rankin A and Pluto, located up to 340 km to the northeast. The shark at North Rankin A was detected infrequently and only 15 times over ∼6 weeks. The shark at Pluto was detected each day of the 24-day deployment, in total 4,894 times. Detections at Pluto platform were highest during the day, with peaks at dusk and dawn. Our study indicates that acoustic telemetry around platforms may be an effective method for understanding how marine megafauna utilise these structures. We recommend collaborating with industry to undertake receiver detection range testing to understand the effectiveness of the method. Furthermore, future studies should co-occur with tagging programs at sites like Ningaloo Reef and around the structures themselves to maximise the probability of detecting animals at these sites, thereby improving our understanding of how marine megafauna interact with these structures.

The Barrow Group was deposited in the Northern Carnarvon Basin from the latest Tithonian to the Late Valanginian. This moderately deep-water shelf-margin is composed of ~ 100–500 m high clinoforms that prograded during a syn-rift to post-rift transition. Integration of well data with extensive 2D and 3D seismic data was used to constrain the stratigraphic evolution of the Barrow Group in seven 3 rd order seismic sequences (calibrated to dinocyst zones) across four main depocentres. Five shelf-margin categories were recognized based on stratal stacking patterns, the trajectory styles and angles ( T se ), and the progradation/aggradation ratios ( P se / A se ) that were interpreted in terms of rates of accommodation creation and sediment supply ( A / S ratio). Following the uplift of the Southern Carnarvon Basin (sediment source), the stratigraphic evolution of the Barrow Group developed in three stages. During the first stage (late syn-rift I; 148–143.5 Ma), the shelf-margin prograded in a period of tectonic quiescence with relatively limited subsidence. During the second stage (late syn-rift II; 143.5–138.2 Ma), the shelf-margin was affected by increasing rates of accommodation and high sediment supply, which reflects an active period of rifting triggering both tectonic subsidence in the basin, and active uplift in the hinterland. During the third stage (early post-rift I; 138.2–135.4 Ma), the uplift of the continental shelf, following continental break-up, provided a new local source of sediment supply to the Barrow Group that then developed as a passive margin. The Lower Barrow Group (late syn-rift I and II) mainly developed under supply-dominated conditions. However, lateral variations in subsidence regime and shifts in sediment supply led to significant variations in shelf-margin architecture along-strike, directly impacting sediment partitioning between the shelf and the deep-water areas. Flat shelf-edge trajectories were associated with sediment bypass and increase in bottomset thicknesses, whereas rising shelf-edge trajectories were linked with sediment storage on the shelf. In contrast, the Upper Barrow Group (early post-rift I) developed in low-supply conditions with slow thermal subsidence, reflecting the passive context of the margin at this time. The Barrow Group provides a unique example of how rift tectonics can control the stratigraphic architecture of a regressive margin and reciprocally, how studying shelf-margin architecture can help constraining the dynamics and timing of rifting around the break-up stage. [ABSTRACT FROM AUTHOR]

The Rowley Shelf, the southern half of the tropical, carbonate-dominated, North West Shelf of Australia, is covered with linear ridges that can be tracked parallel to the coast over 1100 km between the modern coast and the 140 m isobath. Here, we investigate the origin and nature of these ridges based on the integration of extensive borehole data, high-resolution geophysical data, age dating and compaction analysis. Our investigation reveals that each ridge consists of now-submerged relict coastal deposits that were formed over the last 200,000 years through wave, tidal, fluvial and aeolian processes. These features were dominantly preserved through early diagenesis and illustrate the longest continuous submerged palaeoshorelines reported to date. The distribution of relict coastal features, and therefore early diagenesis, controls the morphology of the continental shelf. First, relict coastal features tend to be stacked on top of each other, resulting in the formation of composite diachronous coastal deposits that form distinctive steps on the seabed, up to 10s m high. Second, relict coastal features form a hard substrate that controls the location of coral reefs along the shelf. Reefs, including a 20-m-thick MIS 3 drowned coral reef described here for the first time, as well as modern reefs of the Muiron Islands, Montebello Islands and Dampier Archipelago, are all developed on top of relict coastal features. The distribution, size and mineralogy of relict coastal features highlight climatic changes along the Rowley Shelf. High relative sea levels (RSL) are associated with low carbonate production and up to 50% of terrigenous grains, while low RSL deposits exhibit increased carbonate production and reduced terrigenous grain content. This asymmetry is interpreted to reflect the onset of the monsoon associated with increased fluvial runoffs during interglacial periods. Lastly, our work shows that compaction analyses are critical for palaeoenvironment and RSL reconstructions. Indeed, the accumulation of 50 m of sediment on a RSL indicator can result in an offset of the measurement by 12.7 m. • The NWS (Australia) is covered with linear ridges that can be tracked over 1100 km. • These ridges are interpreted as palaeoshorelines from borehole and geophysical data. • They are formed by coastal processes and preserved through early diagenesis. • Relict coastal features control the continental shelf morphologies and coral-reef distribution. [ABSTRACT FROM AUTHOR]

Viviparous sea snakes (Elapidae: Hydrophiinae) are fully marine reptiles distributed in the tropical and subtropical waters of the Indian and Pacific Oceans. Their known maximum diving depth ranges between 50 and 100 m and this is thought to limit their ecological ranges to shallow habitats. We report two observations, from industry‐owned remotely operated vehicles, of hydrophiine sea snakes swimming and foraging at depths of approximately 250 m in the Browse Basin on Australia's North West Shelf, in 2014 and 2017. These observations show that sea snakes are capable of diving to the dim‐lit, cold‐water mesopelagic zone, also known as the 'twilight' zone. These record‐setting dives raise new questions about the thermal tolerances, diving behaviour and ecological requirements of sea snakes. In addition to significantly extending previous diving records for sea snakes, these observations highlight the importance of university‐industry collaboration in surveying understudied deep‐sea habitats. [ABSTRACT FROM AUTHOR]

Knowledge of the in-situ stress field is essential in petroleum basins, as it exerts a prime control over seal integrity, fracture stimulation, wellbore stability, and fluid flow. Previous geomechanical analysis of Australia's Carnarvon Basin, the continent's premier hydrocarbon region, highlights a normal to strike-slip fault stress regime. However, neotectonic evidence and contemporary seismicity suggest the possibility of a strike-slip to reverse-fault stress regime. We attempt to reconcile these conflicting datasets through new analysis of the in-situ stresses; Principal stress magnitudes and orientations were defined with data from 76 previously unanalysed petroleum wells. Wellbore image logs yield a maximum horizontal stress orientation of 113°N, consistent with modelling of the stress-field throughout the Indo-Australian Plate. Vertical stress magnitudes are estimated to range from 20 MPa km − 1 to 22.4 MPa km − 1 . Leak-off tests (LOT) from 42 wells are analysed using two methodologies (one assuming tensile failure as traditionally accepted, the other assuming shear failure as outlined by Couzens-Schultz and Chan, 2010) and result in two different sets of horizontal stress magnitude estimates. Traditional interpretation of LOTs results in a minimum horizontal stress gradient of 16.8 MPa km − 1 and a maximum horizontal stress gradient of 21.8 MPa km − 1 . The new method for LOT interpretation results in a minimum horizontal stress gradient of 18.1 MPa km − 1 and a maximum horizontal stress gradient of 25.4 MPa km − 1 . Inclined natural fractures observed at LOT depths supports application of the new method of LOT interpretation. Traditional interpretation of stress magnitudes implies a normal to strike-slip fault stress regime, while the new method implies a strike-slip fault stress regime. This latter interpretation is favoured by the authors, as it allows for a reconciliation of the geological and geomechanical datasets. The assessment undertaken herein allows for reinterpretation of stress magnitudes in seismically-active basins hosting differing geomechanical and neotectonic regimes, potentially altering existing understanding of seal integrity, fracture stimulation, wellbore stability, and fluid flow. [ABSTRACT FROM AUTHOR]

Australia's northwestern passive margin intersects the eastern termination of the Java trench segment of the Sunda arc subduction zone and the western termination of Timor trough along the Banda arc tectonic collision zone. Differential relative motion between the Sunda arc subduction zone and the Banda arc collision zone has reactivated the former rifted margin of northwestern Australia evidenced by Pliocene to Quaternary age deformation along a 1400 km long offshore fault system. The fault system has higher rates of seismicity than the adjacent nonextended crustal terranes, has produced the largest historical earthquake in Australia (1941 ML 7.3 Meeberrie event), and is dominated by focal mechanism solutions consistent with dextral motion along northeast trending fault planes. The faults crosscut late Miocene unconformities that are eroded across middle Miocene inversion structures suggesting multiple phases of Neogene and younger fault reactivation. Onset of deformation is consistent with the timing of the collision of the Scott Plateau part of the passive continental margin with the former Banda trench between 3.0 Ma and present. The range of estimated maximum horizontal slip rates across the zone is ~1.4 to 2.6 mm yr−1, at the threshold of geodetically detectable motion, yet significant with respect to an intraplate tectonic setting. The folding and faulting along this part of the continental margin provides an example of intraplate deformation resulting from kinematic transitions along a distant plate boundary and demonstrates the presence of a youthful evolving intraplate fault system within the Indo-Australian plate. [ABSTRACT FROM AUTHOR]

Satellite tracking was used to identify the foraging areas of post-nesting flatback turtles ( n = 66) from four rookeries (Barrow Island, Thevenard Island, Mundabullangana and Port Hedland) within the South East Indian Ocean Regional Management Unit. Foraging areas were in water shallower than 130 m and within 315 km of the shore, with many areas located in 50 m water depth and 66 km from shore. Thirty-one turtles departed their first foraging area prior to the tracking unit transmissions ceasing, with 15 identified as utilising more than one separate foraging area. The furthest foraging area was situated 2511 km from the original nesting site within the Gulf of Carpentaria in Queensland state waters. Identified overlaps of individual's foraging home range areas were used to delineate five important foraging areas, with each area utilised by flatback turtles tracked from more than one rookery. Four of these areas were situated within the Kimberley region and one area within the Pilbara region of Western Australia. There was a large overlap of foraging home range areas and foraging locations with existing protected areas in the region, with 48.5% of the combined overall home range area overlapping with a protected marine reserve. There was minimal interaction between foraging home range areas and the three identified regional fisheries, with the highest overlap occurring with the Northern Prawn Fishery (12.5% of combined overall home range area). There was a high overlap between petroleum title areas (areas that currently host, or have the potential to host, resource sector activities) with foraging areas (67.1% of combined overall home range area). Characteristics of their foraging behaviour were considered to reduce their susceptibility to potential anthropogenic and natural threats within the region i.e. they foraged in areas that were broadly dispersed across the entire region, they utilised inter-connecting pathways between several foraging areas and the same foraging areas were used by multiple turtles. Foraging behaviour by some flatback turtles appeared flexible, with this strategy further reducing their susceptibility by facilitating a capability to adapt to anthropogenic or natural threats within the region. [ABSTRACT FROM AUTHOR]

Nicholas et al. (2016) restate the results and conclusions of their own past work and that of colleagues on the North West Shelf. Although they accept that fish may be involved in ‘pockmark’ maintenance, they do not accept that fish can initiate such features. The fluid flow theory with which they have been working therefore remains intact. However, the restatement also provides no new information and no cause to revise the conclusions of Mueller (2015). More field data is required. [ABSTRACT FROM AUTHOR]

The palynological assemblages of 134 legacy and 212 new palynological preparations from the Callovian–Kimmeridgian of the North West Shelf of Western Australia, were used to identify new species of dinoflagellate cysts with biostratigraphic utility. Samples were derived from cores and sidewall cores from nine wells; four from the Bonaparte Basin, and five from the Northern Carnarvon Basin. This work describes 11 new species of dinoflagellate cyst, one species of acritarch, and emends the descriptions of two genera and five species of dinoflagellate cyst. The new forms include: Batiacasphaera elongata , Cleistosphaeridium ? oxfordianum , Egmontodinium twiggii , Evansia ? rotundata , Jansonia thormalleus , Lanterna foveolata , Lanterna reticulata , Lanterna spongiosa , Orobodinium tantillum , Oligosphaeridium ? varifenestratum , and Sepispinula florida , and the acritarch Triovalium attenuatum. Emendations are proposed for the genera Lanterna and Tringadinium , and the species Broomea fusticula , Egmontodinium toryna , Pyxidiella pandora , Microdinium jurassicum , Jansonia jurassica , and Tringadinium bjaerkei. • New marine microplankton maker species from the Callovian–Oxfordian. • Eleven new species of Jurassic dinocysts from the North West Shelf, Australia. • One new genera and species of acritarch from the Oxfordian of the NWS, Australia. [ABSTRACT FROM AUTHOR]

The Raman Maturity Method (RaMM) is a non-graphical technique for thermal maturity determination based on the multi-linear regression analysis of parameters derived from carbon Raman spectra of humic macerals. It is calibrated against vitrinite reflectance with a suite of Australian mostly Permian coals. In a previous communication an equation to cover the range 0.4–1.2% equivalent vitrinite reflectance was derived. In this report we extend the range with a second equation for the range 1.0–2.5%, and validate its use by testing a series of Australian Permian and German Carboniferous coals. The special features of the technique are that it is equally applicable to vitrinite and inertinite, it corrects internally for the suppression of vitrinite reflectance effect, grains as small as 5 μm are suitable, and it does not require well depth information to be available. The technique has been applied to two wells, Cape Range-2 and Dampier-1, from the rift margin of the North West Shelf of Australia. Both wells intersect large thicknesses of fine-grained marine Jurassic and Cretaceous sediments including the major source rock formation of the Carnarvon Basin. There are no terrestrial sediments for control. There is good agreement between RaMM and VR results for VR > 1.2% for Cape Range-2. However within the oil window in both wells RaMM results indicate the vitrinites in many of the samples have reflectance suppression to such a degree that the VR results would be misleading or useless for maturity modeling. It is likely that this problem, which is well documented for marine influenced coals, to some degree affects organic matter in marine source rocks worldwide. [ABSTRACT FROM AUTHOR]

The generally accepted formation mechanism of pockmarks worldwide is the expulsion of fluid at the seafloor, but such a mechanism does not explain the close association between pockmarks and seabed infrastructure such as pipelines and wellheads within the Stag oil field on the North West Shelf of Australia. Furthermore, certain characteristics of the pockmarks, such as conical mounds of sediment positioned around their perimeters, are strongly suggestive of a biotic origin. Pockmarks in this case are typically 5 m in diameter and 1 m deep, excavated within a sandy seabed in 45 m water depth. Inspection of ROV footage acquired during oilfield operations within the Stag field supports but does not entirely confirm without doubt the proposition that the pockmarks are created by fish of the genus Epinephelus . Having determined the characteristic features of pockmarks within the Stag field which mark them as biotic excavations, data from commercial seabed surveys at 11 other sites on the North West Shelf, all of which reveal numerous pockmarks, was reviewed for evidence of similar pockmark characteristics. Based on the review, it appears likely that the majority of pockmarks on the shallow North West Shelf (between 40 m and 130 m water depth) are representative of biological rather than geological activity. The probability that pockmarks less than approximately 10 m in diameter throughout the remainder of the Australian continental shelf are also the result of purely biological activity is high, as demonstrated by the analysis of data from three further sites. Close inspection of seabed survey data from further afield could extend the findings of this paper throughout not only the tropical Indo-West Pacific (the range of the particular fish species implicated on the North West Shelf), but potentially worldwide if other species can be shown to display similar behaviour. [ABSTRACT FROM AUTHOR]

Studies of global sea-level changes, plate kinematics, marine inundation, and morphology of the continental shelves suggest that the Australian continent has been tilting north eastwards since the Late Cretaceous. Here we investigate the direct impact of this phenomenon and the preceding tectonic events on the evolution of the Northern Carnarvon Basin and discuss their implications for hydrocarbon resources. We use backstripping and decompaction techniques to develop subsidence, sedimentation, and porosity evolution models for the basin, which sits on the axis of the tilt. The goal is to highlight the spatial and temporal variation of subsidence and sedimentation rates and assess their impacts on the porosity of the Early Cretaceous reservoirs within the basin, then give insights into the factors that created accommodation space for sediments. The results reveal a north-eastward shift of subsidence and sedimentation rates within the region. Thus, we observe the highest subsidence rates (∼90 m/Ma) in the southwest (Exmouth and Barrow sub-basins) from Early Jurassic to Early Cretaceous. In the Middle Cretaceous, subsidence and sedimentation moved north-east towards the Dampier (∼40 m/Ma) and some parts of the Barrow sub-basin (∼35 m/Ma). In the Cenozoic era, the highest subsidence rates moved further north-east towards the Beagle sub-basin (∼40 m/Ma) and the North Rankin platform. The results show that the Palaeozoic-Mesozoic rifting events produced higher tectonic subsidence (∼3 km) and higher sediment supply in the southwestern Exmouth and Barrow sub-basins, which reduced towards the north-east in the Dampier and Beagle Sub-basins (∼1.5 km). Subsidence plots along a NE-SW transect and the porosity evolution model results also demonstrate the tilting occurring in these sub-basins. We propose that mantle-driven and subduction-driven tilting of the Australian continent caused the observed local tilting of these sub-basins. Additionally, porosity evolution results provide further information for the definition of periods of hydrocarbon migration in the area. [Display omitted] • Jurassic syn-rift subsidence propagated north-eastwards from the Exmouth Sub-basin towards the Dampier Sub-basin. • The onset of Australian plate tilting (∼75 Ma) coincides with a northeastward change of sedimentation patterns in the NCB. • We attribute the Cenozoic subsidence in Dampier and Beagle sub-basins to the mantle-driven northeastward continental tilt. • Porosity profiles in the NCB indicate Late Cretaceous regional uplift in the south and subsidence in the northeast. [ABSTRACT FROM AUTHOR]

Abstract: Marine and terrestrial palynomorphs from the Middle Jurassic Wanaea verrucosa dinoflagellate cyst zone are documented from subsurface sections of the North West Shelf of Australia. Selected intervals in the Perseus-3A, Sunrise-2 and Sunset West-1 wells were studied in detail and record evidence of brackish to shallow marine successions in the Northern Carnarvon and Bonaparte basins. The palynological data derived from these three wells constitute the basis for the formal definition of this important dinoflagellate cyst biozone and its three constituent subzones. The base of the Lower W. verrucosa Subzone is defined by the first appearance of the index species and is a relatively sparse, low diversity microphytoplankton assemblage; species richness increases up-section. The base of the succeeding Middle W. verrucosa Subzone is defined by the range base of Valvaeodinium spinosum, and the Upper W. verrucosa Subzone is defined by the incoming of the large and distinctive species Endoscrinium kempiae. Two new species, Meiourogonyaulax straussii sp. nov. and Valvaeodinium cookii sp. nov. are described and Jansonia scarffei is reattributed as Fostericysta scarffei (Tykoezinski et al. 2001) comb. nov. Taxa with epicystal and multiplate precingular archaeopyles are prominent, particularly in the Lower W. verrucosa Subzone; this represents the coeval evolutionary explosion of the gonyaulacacean dinoflagellate cysts observed in the latest Early to Late Bajocian of Europe. Further cosmopolitan dinoflagellate cyst occurrences are compared with European ranges to assign a Late Bajocian to Early Bathonian age to the W. verrucosa Zone. The associated spore–pollen assemblages are transitional from the upper Dictyotosporites complex to the lower Contignisporites cooksoniae zones. The latter zone is defined by the first appearance of the index species, but considerable care is required to separate this species from the many intermediate forms of Striatella–Contignisporites that occur through this interval. The palynofloras are dominated by araucariacean monosaccates (particularly Callialasporites spp.), corystosperm bisaccates (mostly Alisporites spp.) and moderately diverse bryophyte–lycophyte–pteridophyte spore assemblages. [Copyright &y& Elsevier]

Abstract: The chronostratigraphical ages of the 20 dinoflagellate cyst zones and one dinoflagellate cyst assemblage for the Middle Triassic (Ladinian) to the Jurassic–Cretaceous transition of the North West Shelf of Australia are comprehensively reviewed. Evidence from macro- and micropalaeontology, palynology and strontium isotopes made available after the establishment of these biozones in the 1980s has been used to reassess the ages of this important zonal scheme and to calibrate it to the international stratigraphical stages. The Shublikodinium Superzone is renamed herein as the Rhaetogonyaulax Superzone, and based on conodont evidence is determined to span the Ladinian to Early Sinemurian. This is significantly shorter in duration than was originally envisaged (Late Anisian to Late Pliensbachian). The Luehndea Assemblage is a low diversity dinoflagellate cyst association which marks a eustatic rise; it is subdivided into two subzones. It is of latest Pliensbachian to Early Toarcian age, based largely on palynological evidence. The Bajocian to earliest Oxfordian Pareodinia ceratophora Superzone represents the inception of a continuous Mesozoic–Cenozoic dinoflagellate cyst record in Australia. It comprises seven zones, which are considered to be slightly older than originally interpreted. The overlying Pyxidiella Superzone is characterised by diverse dinoflagellate cyst associations. It is Early Oxfordian to Kimmeridgian in age, and comprises three zones. The bases of the Wanaea spectabilis and Wanaea clathrata zones are reinterpreted as being slightly older than originally proposed. The superjacent Fromea cylindrica Superzone is Tithonian to earliest Valanginian and modified ages are indicated for four of the nine zones. This unit is dominated by endemic dinoflagellate cysts, reflecting a global trend towards provincialism at this time due to a regressive eustatic regime. [ABSTRACT FROM AUTHOR]

Bedforms are key components of Earth surfaces and yet their evaluation typically relies on manual measurements that are challenging to reproduce. Several methods exist to automate their identification and calculate their metrics, but they often exhibit limitations where applied at large scales. This paper presents an innovative workflow for identifying and measuring individual depositional bedforms. The workflow relies on the identification of local minima and maxima that are grouped by neighbourhood analysis and calibrated using curvature. The method was trialed using a synthetic digital elevation model and two bathymetry surveys from Australia's northwest marine region, resulting in the identification of nearly 2000 bedforms. The comparison of the metrics calculated for each individual feature with manual measurements show differences of less than 10%, indicating the robustness of the workflow. The cross-comparison of the metrics resulted in the definition of several sub-types of bedforms, including sandwaves and palaeoshorelines, that were then correlated with oceanic conditions, further corroborating the validity of the workflow. Results from this study support the idea that the use of automated methods to characterise bedforms should be further developed and that the integration of automated measurements at large scales will support the development of new classification charts that currently rely solely on manual measurements. [ABSTRACT FROM AUTHOR]

The Argo and Gascoyne Abyssal plains in the easternmost Indian Ocean document the last stages of eastern Tethys evolution before the breakup of eastern Gondwana. Thus they provide crucial information not only for modelling the evolution of the eastern Tethys and Proto-Indian Ocean, but also to understand the complex geodynamic history of the North West Shelf. We have revisited the marine magnetic anomaly record of the Argo and Gascoyne Abyssal Plains in combination with other geological and geophysical data from the North West Shelf and southeast Asia. Based on the combined data, we have created a revised plate-tectonic model and a set of palaeogeographic reconstructions for the evolution of the North West Shelf for the early stages after the breakup. The main difference between this model and previously published models is that we have interpreted a complete section of anomalies, M25A – M22A, in the Gascoyne Abyssal Plain, northwest of the Exmouth Plateau. The magnetic anomalies have the same trend as in the Argo Abyssal Plain. Our new plate-tectonic reconstructions show that continental breakup in the Argo and northern Gascoyne Abyssal Plains, east and northwest of the Exmouth Plateau, respectively, started simultaneously in the Oxfordian with M25A identified as the oldest anomaly. In the Gascoyne Abyssal Plain, the oldest anomaly sequence, M25A – M22A (154.5 – 150.4 Ma) indicates that the ‘Argo’ spreading ridge continued around the northern margin of Greater India, and was probably linked with the Somali Basin. Sea-floor spreading continued until M14, separating the West Burma Block and possibly other smaller continental fragments like the Sikuleh Terrane of Western Sumatra from the northern Australian margin. A southward-directed ridge jump at M13 (134 Ma) transferred segments of Australian Plate oceanic crust to the West Burma Plate. Contemporaneously, an anticlockwise change in spreading direction fixed the West Burma Block relative to Greater India until its collision with the southern Eurasian margin. [ABSTRACT FROM AUTHOR]

The Western Australian margin is a unique coral reef province, with modern coral reef development occurring at latitudes as far south as 29°S. The genesis of this coral reef province may go back to the Oligo-Miocene, since geological features ~30 million-year-old and younger interpreted as coral reefs are known from offshore seismic surveys. The nature of these seismic reefs is, however, uncertain, as they are only sparsely sampled, and as time-equivalent outcrops are only present in a few remote and understudied locations. This study investigates middle Miocene shallow-water limestones with tropical fauna formed along the North West Shelf (NWS) between ~13 Ma and ~15 Ma, when the southward extension of the seismic reefs was at its maximum. The outcrops and cores investigated are dominantly composed of peloidal packstones and micritic floatstones containing larger benthic foraminifera, Halimeda sp. and scleractinian corals, including reef-building genera, that accumulated in a protected and oligotrophic, warm-water lagoonal environment. Climate was therefore warm during the middle Miocene acme of seismic reefs development, despite the NWS being located ~7° further south than its present position at that time. Results of this investigation also support the existence of a strong southward flowing Leeuwin-current-style oceanic circulation during the middle Miocene, which could have transported fauna from south-east Asia along the Western Australian margin. Development of the lagoon and seismic reefs may have also been promoted by middle Miocene aridification of the coast bordering the NWS, and by repeated eustatic-driven exposures of the NWS. [Display omitted] • Lagoon 15–13 Ma with taxa characteristic of tropical oligotrophic reef environments • Facies with micrite, scleractinian corals, Halimeda and larger benthic foraminifera • Outcrops time-equivalent to offshore Middle Miocene Western "Great Barrier Reef" • Time-equivalent to Miocene Climatic Transition, post-date Miocene Climatic Optimum • Climatic, paleoceanographic (proto-Leeuwin current), eustatic or tectonic controls [ABSTRACT FROM AUTHOR]

Hydrocarbon fluid correlation studies often rely on compounds that are source-specific, but only represent a minor fraction of the bulk fluid (e.g. steranes). The correlation in the present study utilises compounds that represent a significant proportion of the bulk fluid, namely semi-volatile aromatics (SVA), and diamondoids. Comprehensive two dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) was used to analyse diamondoids and SVA in whole oil/condensate samples from the Browse Basin, North West Shelf, Australia. Together with aromatic maturity ratios and the stable carbon isotopic composition for selected diamondoids and alkylbenzenes, these analyses demonstrate that numerous accumulations within the Browse Basin contain hydrocarbons from mixed sources. The diamondoid and SVA data provides further information on the current hydrocarbon fluid discrimination, which is primarily based on saturated biomarker compositions. Results of this study reveal a complex fill history by identifying the presence of a high maturity fluid(s) in the biodegraded accumulations on the Yampi Shelf, i.e. in the greater Cornea field and at Gwydion-1. This high maturity fluid is most likely derived from the Lower–Middle Jurassic Plover Formation (J10–J20 supersequences) in the greater Cornea area and, in the case of Gwydion-1, additional hydrocarbons may also be derived from the Upper Jurassic Vulcan Formation (J30–K10 supersequences). Other accumulations that comprise mixtures include Mimia-1 and Concerto-1 ST1 Deep, located to the north of the Ichthys field, and could represent charge from several Jurassic source rocks. The most mature fluids analysed in this basin are family II Plover-sourced and reservoired condensates from Kronos-1, Dinichthys North-1 and Gorgonichthys-1, as demonstrated by their elevated concentrations of the methyladamantanes and methyldiamantanes. The Dinichthys North-1 and Gorgonichthys-1 condensates also show a significant enrichment in the δ13C compound-specific values of the di-, tri- and tetra-methylbenzenes, whereas the Kronos-1 condensate does not, suggesting derivation from different source kitchens. • Hydrocarbon fluid correlation in the Browse Basin, North West Shelf, Australia. • Diamondoids and aromatics complement and expand on biomarker assessments. • Condensates lacking biomarkers can be successfully typed with diamondoids and aromatics. • δ13C of methylbenzenes provide further information on fill history. [ABSTRACT FROM AUTHOR]