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Unravelling source‐to‐sink relationships of sediment in coastal regions can be particularly challenging due to a variety of transport directions and mixing within varying local environments in response to sea level fluctuations. Post‐glacial sea level rise in the Holocene has resulted in the flooding of former continental margins, locally leading to the separation of islands such as Rottnest in southwest Australia. Rottnest lies approximately 20 km offshore from the mouth of the Swan River, one of the largest permanent river systems across thousands of kilometres of west Australian coastline. In this contribution, we investigate the size, U–Pb age distribution and α‐dose values of detrital zircon grains within 13 sand samples collected from three upstream tributaries that drain the Archean Yilgarn Craton, the Swan River estuary, offshore waters surrounding Rottnest Island and modern beaches. We explore sediment derivation, storage and mixing on this passive margin. Carbonate–silicate sands of the region contain detrital zircon with Archean, Mesoproterozoic and Cambro‐Neoproterozoic age modes, reflecting regional crystalline basement. Eo‐ to Paleoarchean zircon grains, including a previously enigmatic >3500 Ma component, are traced from offshore into the estuary, and specifically the Avon River tributary. Detrital mixing models imply an overall fluvial contribution to the estuary and offshore systems of up to 50–65%. By contrast, modern beach samples are dominated by Swan Coastal Plain recycled sediment of up to 96%. The α‐dose values of the prominent 3300–3150 Ma age component suggest more efficient fluvial discharge in the Paleo‐Swan River than in more recent times. Modern estuary samples have lower average and progressively lower downstream zircon α‐dose values, consistent with prolonged chemical and physical reworking and loss of metamict grains with transport distance in the river. We conclude that fluvial drainage networks distribute a locally persistent catchment signal whilst coastal plains in tectonically quiescent settings appear characterized by sediment reprocessing and mixed provenance. [ABSTRACT FROM AUTHOR]

The importance of characterizing kerogen type in evaluating source rock and the nature of hydrocarbon yield is emphasized. However, traditional laboratory geochemical assessments can be time-intensive and costly. In this study, an innovative approach was taken to bridge this gap by utilizing machine learning techniques to ascertain key parameters—Organic Oxygen Index (OI), Hydrogen Index (HI), and kerogen type—from petrophysical logs of a well in the Perth Basin, Western Australia. This approach assembled geochemical data from 138 cutting samples of the Kockatea and Woodada formations and petrophysical log data. Subsequently, six machine learning algorithms were applied to predict the OI and HI parameters. The efficacy of these methods was assessed using statistical parameters, including Coefficient of Determination (R2), Average Percentage Relative Error, Average Absolute Percentage Relative Error, Root Mean Square Error, and Standard Deviation. The Support Vector Machines method emerged as the standout performer, with an R2 of 0.993 for the OI and 0.989 for the HI, establishing itself as an optimal tool for predicting these indices. Additionally, six classifiers were employed to determine kerogen types, with accuracy tested using precision, recall, F1-Score, and accuracy parameters.The study's findings highlight the superiority of the Gradient Boosting method in kerogen-type classification, achieving an impressive accuracy rate of 93.54%. It is concluded that when utilized with petrophysical logs, machine learning methodologies offer a powerful, efficient, and cost-effective alternative for determining OI, HI, and kerogen type. The novelty of this approach lies in its ability to accurately predict these crucial parameters using readily available well-log data, potentially revolutionizing traditional geochemical analysis practices. [ABSTRACT FROM AUTHOR]

Abstract The importance of characterizing kerogen type in evaluating source rock and the nature of hydrocarbon yield is emphasized. However, traditional laboratory geochemical assessments can be time-intensive and costly. In this study, an innovative approach was taken to bridge this gap by utilizing machine learning techniques to ascertain key parameters—Organic Oxygen Index (OI), Hydrogen Index (HI), and kerogen type—from petrophysical logs of a well in the Perth Basin, Western Australia. This approach assembled geochemical data from 138 cutting samples of the Kockatea and Woodada formations and petrophysical log data. Subsequently, six machine learning algorithms were applied to predict the OI and HI parameters. The efficacy of these methods was assessed using statistical parameters, including Coefficient of Determination (R2), Average Percentage Relative Error, Average Absolute Percentage Relative Error, Root Mean Square Error, and Standard Deviation. The Support Vector Machines method emerged as the standout performer, with an R2 of 0.993 for the OI and 0.989 for the HI, establishing itself as an optimal tool for predicting these indices. Additionally, six classifiers were employed to determine kerogen types, with accuracy tested using precision, recall, F1-Score, and accuracy parameters.The study's findings highlight the superiority of the Gradient Boosting method in kerogen-type classification, achieving an impressive accuracy rate of 93.54%. It is concluded that when utilized with petrophysical logs, machine learning methodologies offer a powerful, efficient, and cost-effective alternative for determining OI, HI, and kerogen type. The novelty of this approach lies in its ability to accurately predict these crucial parameters using readily available well-log data, potentially revolutionizing traditional geochemical analysis practices. Graphical abstract

Shale gas has become of interest of geoscientists globally because of its potentials to expand our energy supply. This research used well logs data and total organic carbon (TOC) data from Perth and Canning Basins, Australia. The objective of this research is to investigate source rock potential of the study area by examining the relationship between TOC content and seismic acoustic impedance (AI) derived from well log data, using regression analysis. The outcomes of this research show that for claystone/siltstone, the relationship between AI and TOC is nonlinear, while for shale the correlation is linear. However, there is no fixed equation that can be used as a standard for this linear/nonlinear relationship. Results show that for a certain type of lithology, the relationship between TOC and AI is different for different formations. This is interpreted to be caused by different depositional environment, diagenesis, mineralogical composition and different depth of burial. Findings of this study are expected to provide some new insights into the relationship between AI and TOC for various types of lithology and contribute to shale gas exploration studies. [ABSTRACT FROM AUTHOR]

The Pseudoreticulatispora confluens–P. pseudoreticulata spore-pollen zonal datum typically coincides with the end of widespread Permian glacial deposits in Western Australia. Although previously attributed to the mid-Sakmarian, chemical abrasion isotope dilution thermal ionisation mass spectrometry (TIMS) dating of zircons from volcanic tuffs in the Ditji Formation of the Bonaparte Basin and the Grant Group in the Canning Basin point to an Asselian age of about 295.25 Ma for this datum. All dated zircons from the Ditji Formation came from petroleum well cuttings but the accompanying palynology was mostly from sidewall cores; however, all Grant Group samples were from conventional core. TIMS dates from the Ditji Formation range in age from 295.2 to 292.7 Ma whereas the only productive tuff from the Grant Group yielded a 296.26 Ma date. By comparison, there are no zircon dates to constrain the onset of glacial deposition in Australia. The Bonaparte Basin ages overlap with those for the Edie Tuff (296.1–294.5 Ma) in Queensland's Galilee Basin, approximately 2000 km to the southeast, which also lies close to the base of the P. pseudoreticulata Zone. To date the only fossil group within the P. confluens Zone in Western Australia to provide independent age control, albeit loosely, are goniatites from the northern Perth Basin (Uraloceras irwinense and Juresanites jacksoni) that have consistently been attributed to the Sakmarian; these require a reassessment of their affinity with Russian faunas and therefore to global stratotypes. The position of the Carboniferous–Permian boundary is elusive in Australia and will remain so until additional volcanic tuffs containing young datable zircons are found; however, spore-pollen and zircon dates from Namibia place this boundary within the P. confluens Zone. [ABSTRACT FROM AUTHOR]

Photic zone euxinia (PZE) has previously been identified in the Early Triassic Kockatea Shale of the northern Perth Basin, based on the presence of biomarkers such as isorenieratane, which is derived from isorenieratene produced by green sulfur bacteria. However, green and purple sulfur bacteria can also occur in microbial mats. In this study we present a basin-scale assessment of biomarkers associated with open water column PZE and/or microbialites. The lithofacies from the Early Triassic of the northern part of the northern Perth Basin consist of dark coloured mudstones (black to dark grey) with microbialites, which were deposited away from basin margins. These samples are found to contain okenane, chlorobactane and isorenieratane derived from carotenoid pigments of purple, green-green and green–brown sulfur bacteria, respectively. These biomarkers are not observed in the light coloured mudstones (medium grey) formed under oxic conditions in a tidal environment with higher clastic input close to the basin margins in the southern part of the basin where shallow marine sandstones were also deposited. Okenane and chlorobactane were abundant in facies containing microbialites which developed in a shallow water setting on intra-basinal structural highs. The development of oxic conditions near the basin margins in the Perth Basin provided refuges for organisms during the end Permian mass extinction event. Okenane was more abundant in the microbialite facies compared with the dark coloured mudstones deposited under PZE. C 33 n -alkylcyclohexane (n-C 33 ACH) has previously been described as a biomarker associated with ecosystem collapse during the lower Triassic, and its ratio relative to the C 34 n -alkane was elevated in facies that contain abundant microbialites. Mercury (Hg) to total reduced inorganic sulfur (TRIS) and Hg to total organic carbon (TOC) ratios are positively correlated, supporting the development of euxinia as sulfide sequesters Hg. The high Hg/TRIS values in microbialite facies support mat development with high Hg concentrations. The values of δ13C OM and δ34S were isotopically lighter in microbialite facies when compared with mudstones formed under PZE, although samples deposited under oxic conditions showed the isotopically lightest δ13C OM and isotopically heaviest δ34S. The variation in δ13C OM probably reflects the different carbon fixation pathway of various sulfur bacteria, while it appears that the difference of δ34S values between PZE and microbialites is a result of differences in the microbial community structure and the higher relative abundance of purple sulfur bacteria. In addition, fluctuations between PZE and oxic conditions were identified throughout the sampled intervals attributed to fluctuations in the depth of chemocline. Under the shallower chemocline, PZE developed widely in the basin, even in shallower waters. Under the deeper chemocline PZE was absent or limited to deeper water, and oxic conditions developed in shallower water. The fluctuations of PZE and oxic conditions in the northern Perth Basin suggest the development of multiple episodes of harsh environmental conditions after the end-Permian mass extinction, similar to those identified in other regions (e.g., Meishan in China and Peace River in Canada). [ABSTRACT FROM AUTHOR]

Throughout geological history, biodiversity trends have been punctuated by sharp declines coinciding with mass extinction events. Certain organisms—known as disaster forms—flourish during the extinction aftermath from a lack of ecological competition and predation. Microbialites (in particular, stromatolites) are known to increase in environmental diversity following these biotic crises. However, it remains important to identify whether individual microbialite occurrences are a result of globally driven competition reduction or favourable local conditions. Here, we reconsider stromatolites from the northern Perth Basin of Western Australia, previously reported as Smithian (late Olenekian) in age and part of a biotic rebound following the end-Permian mass extinction and re-evaluate their paleodepositional setting and age. Detailed mapping, macro-analysis and meso-analysis of the Perth Basin locality have identified a well-preserved and diverse morphological assemblage of stromatolites that are intimately associated with a coarse siliciclastic facies. The characteristics of, and relationships between the stromatolitic and coarse siliciclastic facies support a restricted aquatic paleodepositional environment with fluvial/alluvial influences. In the Perth Basin, such depositional environments occurred most commonly during the Permian (Guadalupian to Lopingian). The robustness of previous age constraints interpreted from overlying strata (Kockatea Shale) are questioned by the identification of a depositional hiatus and onlapping relationship of the Kockatea Shale on the stromatolitic sequence. Therefore, we suggest that the mid-Phanerozoic northern Perth Basin Stromatolitic Sequence cannot be unequivocally associated with the end-Permian mass extinction and may have instead thrived owing to a favourable paleodepositional setting. The mid-Phanerozoic northern Perth Basin stromatolites are not a unique case. A compilation of reported Permian and Triassic microbialite occurrences shows that stromatolites, although most common following the end-Permian mass extinction, also occur before and after the extinction event in a range of environmental settings. Ten microbialite forms were described and mapped out over 30 km in the northern Perth Basin. Perth Basin Stromatolitic Sequence formed in a restricted aquatic depositional setting with fluvial and/or alluvial influences. Stromatolites from the northern Perth Basin are unlikely to be associated with the end-Permian mass. [ABSTRACT FROM AUTHOR]

In this paper, we describe porosity variations in Miocene to Holocene carbonates off the west coast of Australia and assess their compaction trends. The porosity values were measured using discrete samples of Sites U1459–U1464 obtained by the International Ocean Discovery Program Expedition 356. The carbonate deposits have been influenced by a range of textures and diagenetic conditions throughout a nearly continuous sequence of geological ages from the Miocene to Holocene and at core depths from 0 to 1100 m below the seafloor. The collected samples were mostly grainstone, packstone, wackestone and mudstone textures. Dolostones and dolomitic carbonates were described at the Miocene intervals. Compaction trends were estimated exponentially and linearly based on cored sites, carbonate textures and dominant mineralogies (dolomite, calcite/aragonite). At all six sites, porosity distribution and reduction were generally depth-dependent. The porosity converged to about 30% between 750 and 1100 m, which suggests that the carbonates were close to the densest packing by mechanical compaction at a burial depth of ∼750 m. The porosity deviations are associated with textures and dominant mineralogies. Increasing mud content from grainstone to mudstone is a controlling factor for initial porosity and porosity reduction rate. Dolomitisation, dolomitic cementation, aragonite needle-rich mud and non-skeletal grains cause deviations from the depth-dependent compaction trends. Reflux-related cementation generally decreases porosity in Miocene dolomitic intervals. Higher porosity values of the Quaternary wackestone and mudstone at Site U1461 resulted from the presence of aragonite needle-rich mud hosting abundant micropores and from a high sedimentation rate. The occurrence of non-skeletal grains, such as ooids and peloids, as well as occasional meteoric exposure led to porosity inversion, occluding interparticle permeability and the creation of moldic pores. Porosity variations of Miocene–Holocene carbonates off the west Australian coast are primarily depth-dependent. Mechanical compaction affected porosity reduction down to a value of ∼30% at a burial depth of ∼750 m. Differences in texture-based compaction trends were affected by increasing mud content. Major porosity deviations are associated with dolomitisation, dolomitic cementation, aragonite needle-rich mud and non-skeletal grains. [ABSTRACT FROM AUTHOR]

Abstract Hydrothermal convection in porous geothermal reservoir systems can be seen as a double-edged sword. On the one hand, regions of upflow in convective systems can increase the geothermal energy potential of the reservoir; on the other hand, convection introduces uncertainty, because it can be difficult to locate these regions of upflow. Several predictive criteria, such as the Rayleigh number, exist to estimate whether convection might occur under certain conditions. As such, it is of interest which factors influence locations of upwelling regions and how these factors can be determined. We use the thermodynamic measure entropy production to describe the influence of spatially heterogeneous permeability on a hydrothermal convection pattern in a 2D model of a hot sedimentary aquifer system in the Perth Basin, Western Australia. To this end, we set up a Monte Carlo study with multiple ensembles. Each ensemble contains several hundred realizations of spatially heterogeneous permeability. The ensembles only differ in the horizontal spatial continuity (i.e., correlation length) of permeability. The entropy production of the simulated ensembles shows that the convection patterns in our models drastically change with the introduction and increase of a finite, lateral correlation length in permeability. An initial decrease of the average entropy production number with increasing lateral correlation length shows that fewer ensemble members show convection. When neglecting the purely conductive ensembles in our analysis, no significant change in the number of convection cells is seen for lateral correlation lengths larger than 2000 m. The result suggests that the strength of convective heat transfer is not sensitive to changes in lateral correlation length beyond a specific factor. It does, however, change strongly compared to simulations with a homogeneous permeability field. As such, while the uncertainty in spatial continuity of permeability may not strongly influence the convective heat transfer, our findings show that it is important to consider spatial heterogeneity and continuity of permeability when simulating convective heat transfer in an aquifer.

Reduction spheroids are small‐scale, biogenic, redox‐controlled, metal enrichments that occur within red beds globally. This study provides the first analysis of the compositionally unique reduction spheroids of the Tumblagooda Sandstone. The work aims to account for their composition and consequently improve existing models for reduction spheroids generally, which presently fail to account for the mineralogy of the Tumblagooda Sandstone reduction spheroids. Interstitial areas between detrital grains contained in the cores of these reduction spheroids are dominated by microplaty haematite, in addition to minor amounts of svanbergite, gorceixite, anatase, uraninite, monazite and illite. The haematite‐rich composition, along with an absence of base metal phases and the vanadiferous mica roscoelite, makes these reduction spheroids notable in comparison to other global reduction spheroid occurrences. Analyses of illite crystallinity provide values for samples of the Tumblagooda Sandstone host rock corresponding to heating temperatures of ca 200°C. Consequently, while Tumblagooda Sandstone reduction spheroids formed via the typical metabolic processes of dissimilatory metal‐reducing bacteria, the combination of a unique mineralogy and illite crystallinity analysis provides evidence of more complex late‐stage heating and reoxidation. This has not previously been recognised in other reduction spheroids and therefore expands the existing model for reduction spheroid genesis by also considering the potential for late‐stage alteration. As such, future reduction spheroid studies should consider the potential impact of post‐formation modification, particularly where they are to be used as evidence of ancient microbial processes; such as in the search for early evidence of life in the geological record on Earth or other planets. Additionally, because of their potential for modification, reduction spheroids serve as a record of the redox history of red beds and their study could provide insights into the evolution of redox conditions within a given red bed during its diagenesis. Finally, this paper also provides insights into the relatively understudied diagenetic history of the Tumblagooda Sandstone; supplying the first reliable and narrow constraints on its thermal history. This has important implications for the thermal history of the Carnarvon Basin and its petroleum prospectivity more broadly. [ABSTRACT FROM AUTHOR]

Highlights • New 40Ar/39Ar age of 135.9 ± 1.2 Ma and Sr–Nd–Pb isotopes for previously undated flow of Bunbury Basalt. • >80% of Cretaceous WA magmatism synchronous with breakup of eastern Gondwana at 137–136 Ma. • Kerguelen mantle plume under Greater India at 137–136 Ma cannot be origin for Bunbury Basalt. • Breakup of eastern Gondwana not caused by a thermochemical plume. • Volatile enrichment during ca. 550–500 Ma Kuunga Orogeny instead facilitated breakup. Abstract The link between mantle plumes and continental breakup remain a topic of debate. Here, a new 40Ar/39Ar age of 135.9 ± 1.2 Ma (2 σ) and previous ages from the Bunbury Basalt – lava flows that are part of the Greater Kerguelen large igneous province (LIP) – reveal that >80% of magmatism in the southern Perth Basin was concomitant with the continental breakup of eastern Gondwana at ca. 137–136 Ma. New and existing isotope geochemical data show that only lithospheric and depleted asthenospheric sources were melted to form the Bunbury Basalt and most other early, ca. 147–124 Ma magmatic products part of the Greater Kerguelen LIP. All lines of evidence strongly point towards passive continental breakup of eastern Gondwana, including the restriction of 147–124 Ma magmatism to continental rifts, the lack of excess oceanic magmatism in this period and the >1000 km distance between the Kerguelen plume underneath Greater Indian lithosphere and the breakup nexus. It is not possible to reconcile the influence of a thermochemical plume with the observed geochemical, spatial and geochronological information. Instead, we posit that eastern Gondwana breakup occurred because it was proximal to the former suture zone associated with the ca. 550–500 Ma Kuunga Orogeny between Indo–Australia and Australo–Antarctica. Enrichment of the mantle with volatiles associated with subduction during the Kuunga Orogeny permitted partial melting when the continental crust was sufficiently attenuated in the Early Cretaceous. Repeated and protracted rifting of Greater India from Australo–Antarctic since the mid-Paleozoic eventually led to the rupture of the continental lithosphere and to mafic magmatism at ca. 137–136 Ma, approximately along the position of the former suture zone, without the influence of a mantle plume. [ABSTRACT FROM AUTHOR]

We study the impact of spatially heterogeneous permeability on the formation and shape of hydrothermal porous flow convection in the Yarragadee Aquifer by modelling three simulation scenarios, each with differing permeability distributions. In all scenarios, the southern part of the model is characterised by convection rolls, while the north is dominated by a stable region of decreased temperatures at depth due to hydraulic interaction with shallower aquifers. This suggests that reservoir structure is a first-order controlling factor for the formation of the free convective system. The convective system adjusts to the spatially heterogeneous permeability distribution, yielding locally different convection patterns. [ABSTRACT FROM AUTHOR]

Core material from an exploratory diamond drillhole (DDH CL5) in the Irwin Terrace, northern Perth Basin, Western Australia, contains a profuse and well-preserved palynofloral assemblage composed almost exclusively of trilete miospores. These comprise at least 32 species, distributed among 23 genera. Two species –Retusotriletes separatussp. nov. andApiculiretusispora tersasp. nov. – are new, andVelamisporites cortaderensis(Césari & Limarino, 1987) is proposed as a new binomial combination. The palynoflora essentially replicates compositionally theGrandispora maculosaAssemblage, first described in 1968 from New South Wales (Italia Road Formation of the Southern New England Orogen) with revised dating of late Visean. Particularly noteworthy in both local and regional biostratigraphical contexts is the combined presence ofG. maculosa,Reticulatisporites magnidictyus,Cordylosporites asperidictyus,Foveosporites pellucidus,Indotriradites kuttungensis,I. daemonii,Verrucosisporites aspratilis,V. gregatus,V. quasigobbettii,Raistrickia accinta,R. radiosa,Diatomozonotriletes daedalusandPsomospora detecta. Of these,V. quasigobbettiiandI. kuttungensisare predominant. Additionally, the assemblage contains some trilete species reported subsequently (in 1992) from a slightly younger (Pennsylvanian) succession of the Galilee Basin, southern Queensland; e.g.Cyclogranisporites firmus,Verrucosisporites basiliscutis,Dibolisporites disfacies,Diatomozonotriletes birkheadensis,Densoisporites truswelliae(syn. Densoisporitessp. of Jones & Truswell),Grandispora(Spelaeotriletes)queenslandensisandVelamisporites cortaderensis(syn.,inter alia,Reticulatisporites bifronsJones & Truswell). Significantly, however, the CL5 palynoflora is devoid of gymnospermous prepollen (indeed any pollen grains) that have been documented from the Galillee Basin deposits. Many components of theG. maculosasuite have been reported from elsewhere in Gondwana, particularly Brazil and Argentina, attesting to its stratigraphical significance across the supercontinent, and to the widespread dispersal of its pteridophytic parental flora in a relatively narrow time interval, bracketed within the late Visean through early Serpukhovian. The present assemblage, and indeed its representatives elsewhere in Gondwana, was likely deposited in non-marine, fluvial or lacustrine, interglacial environments that preceded the extensive icehouse conditions that prevailed during much of the Pennsylvanian. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the role of a mantle plume in the genesis of the Bunbury Basalt using high-precision 40 Ar/ 39 Ar geochronology and whole-rock geochemistry, and by using crustal basement thickness of the eastern Indian Ocean and the western Australian continent. The Bunbury Basalt is a series of lava flows and deep intrusive rocks in southwestern Australia thought to be the earliest igneous products from the proto-Kerguelen mantle plume. Nine new plateau ages indicate that the Bunbury Basalt erupted in three distinct phases, at 136.96 ± 0.43 Ma , 132.71 ± 0.43 Ma and 130.45 ± 0.82 Ma . All Bunbury Basalt samples are enriched tholeiitic basalts with varying contributions from the continental lithosphere that are similar to other Kerguelen plume-products. Based on plate reconstructions and the present geochronological constraints, the eruption of the oldest Bunbury Basalt preceded the emplacement of the Kerguelen large igneous province by at least 10–20 m.y. Such age differences between a precursor and the main magmatic event are not uncommon but do require additional explanation. Low crustal stretching factors beneath the Bunbury Basalt ( β ≈ 1.4 ) indicate that decompression melting could not have been generated from asthenospheric mantle with a normal chemistry and geotherm. An elevated geotherm from the mantle plume coupled with the geochemical similarity between the Bunbury Basalt and other Kerguelen plume-products suggests a shared origin exists. However, new age constraints of the oldest Bunbury Basalt are synchronous with the breakup of eastern Gondwana and the initial opening of the Indian Ocean at ca. 137–136 Ma, which may mean an alternative explanation is possible. The enriched geochemistry can equally be explained by a patch of shallow mantle beneath the southern Perth Basin. The patch may have been enriched during Gondwana suturing at ca. 550–500 Ma, during early rifting events by magmatic underplating or by intruded melts into the subcontinental lithospheric mantle. This enriched geochemical signature would then be sufficient to trigger decompression melting from passive rifting between Greater India and Australia with no contribution from the Kerguelen hotspot. We conclude that although the proto-Kerguelen hotspot is certainly a possible explanation for the genesis of the Bunbury Basalt, decompression melting of an enriched patch of subcontinental lithospheric mantle is an alternative theory. [ABSTRACT FROM AUTHOR]

Aquifers in the Perth Metropolitan Region of Western Australia have been explored and exploited for water supply since the late 19th century. Throughout the early 20th century, the availability of warm groundwater from the Yarragadee confined aquifer at relatively shallow depths was popular with laundries, public baths and for industrial applications but it was not until 1997 that the first direct-use geothermal project for bathing and swimming was implemented. By 2016, a dozen commercially successful geothermal schemes will use low enthalpy geothermal water supplies from the Yarragadee aquifer at depths ranging from 750 to 1150 m for heating leisure centres, building air and outdoor pools. With distributed heat estimated to more than 110 × 10 3 GJ per year and up to 180 × 10 3 GJ when considering projects currently at construction stage but not yet commissioned, Perth currently has the biggest concentration of operating geothermal direct-use projects in Australia. The development of geothermal projects in Perth was made possible by early achievements pioneered by designers from the groundwater industry. This paper presents the hydrogeological setting of the Yarragadee aquifer which is the main geothermal resource in Perth, the well and surface heat exchanger design criteria, the economic and environmental considerations, and the best practices and circumstances that led to the 100% success rate of direct-use geothermal projects in Perth. [ABSTRACT FROM AUTHOR]

The evolution of faults and paleodrainage patterns on the southwestern Australian passive margin during and after the breakup of Gondwana in the Early Cretaceous remains poorly understood. This contribution investigates the fault and paleodrainage evolution in the southern Perth Basin with the use of the ‘Bunbury Basalt’, the only lava flows known to be synchronous with continental breakup. New aeromagnetic data have been integrated with well intersections and outcrop constraints to establish the first 3D model of the Bunbury Basalt. The model reveals that flows are up to 100 m thick and are predominantly confined to two north–south-trending paleovalleys and their tributaries situated in the Bunbury Trough in the southern Perth Basin. The Donnybrook Paleovalley flow ponded in a paleovalley proximal to the Darling Fault and is truncated by the two later flows within the Bunbury Paleovalley, which is positioned centrally in the Bunbury Trough. Offsets of the Bunbury Basalt have been used to identify new northeast- and northwest-trending faults in the southern Perth Basin, and broad folding is interpreted as a consequence of drag into the Darling and Busselton faults. The model has been used to determine post-basalt net displacements for the Darling and Busselton faults of 370 and 210 m, respectively, and <175 m for the northeast and northwest-trending faults. The source vents for the Bunbury Basalt were probably located at extensional jogs at intersections between the Darling Fault and subordinate oblique faults. These results challenge the views on longstanding quiescence of the post-breakup western Australian passive margin. [ABSTRACT FROM PUBLISHER]

Assessment and successful exploration for, and exploitation of, aquifers in the Perth Basin require knowledge of their petrophysical and sedimentological characteristics and geometries. This study provides a sedimentological and lithofacies analysis of core from the Mesozoic Yarragadee Formation, Cadda Formation, Cattamarra Coal Measures, Eneabba Formation and Lesueur Sandstone of Western Australia recovered from Pinjarra-1, Cockburn-1, Gingin-1 and Gingin-2 wells provide insights into changes in depositional environment over time and space in the central Perth Basin. In studied sections, nine different fluvial-dominated lithofacies have been identified in the Yarragadee Formation, Cadda Formation and Cattamarra Coal Measures that occur in similar proportions, whereas the Lesueur Sandstone is dominated by coarse-grained deposits of high energy fluvial systems. Vertical variation in lithofacies on the order of 10 cm to approximately 2 m vertical scale is observed in all formations and wells. Changes in the lithofacies, linked to local depositional environments, are probably associated with fluvial-alluvial to fluvio-deltaic systems that have complex 3D architecture, including braided and to probably meandering systems, and are affected by channel avulsion. Point counting and automated mineral analysis of thin sections of core showed detrital mineralogy dominated by monocrystalline quartz, with rare polycrystalline quartz, a moderate amount of alkali feldspar and very minor amounts of garnet, organic fragments, muscovite and biotite. These data show a lithofacies-dependence of the proportion of minerals, with little variation between equivalent lithofacies from different depths, formations or wells. Grain size and sorting, that have a first order control on porosity, are strongly lithofacies dependent. Individual lithofacies types show a trend of decreasing porosity with depth due to the increasing effects of compaction, quartz overgrowth cementation and authigenic clay mineral development. Lithofacies and depth are the main controls on permeability, and so lithofacies distribution exerts a key control on hydraulic behaviour. [ABSTRACT FROM AUTHOR]

A new terrestrial–marine assemblage from the lower beds of a thin outcrop section of the Kockatea Shale in the northern Perth Basin, Western Australia, contains a range of fossil groups, most of which are rare or poorly known from the Lower Triassic of the region. To date, the collection includes spinose acritarchs, organic-cemented agglutinated foraminifera, lingulids, minute bivalves and gastropods, ammonoids, spinicaudatans, insects, austriocaridid crustaceans, actinopterygians, a temnospondyl-like mandible, plant remains, and spores and pollen. Of these groups, the insects, crustaceans and macroplant remains are recorded for the first time from this unit. Palynomorphs permit correlation to nearby sections where conodonts indicate an early Olenekian (Smithian) age. The locality likely represents the margin of an Early Triassic shallow interior sea with variable estuarine-like water conditions, at the southwestern end of an elongate embayment within the East Gondwana interior rift–sag system preserved along the Western Australian margin. Monospecific spinose acritarch assemblages intertwined with amorphous organic matter may represent phytoplankton blooms that accumulated as mats, and suggest potentially eutrophic surface waters. The assemblage represents a mixure of marine and terrestrial taxa, suggesting variations in water conditions or that fresh/brackish-water and terrestrial organisms were transported from adjacent biotopes. Some of the lower dark shaly beds are dominated by spinicaudatans, likely indicating periods when the depositional water body was ephemeral, isolated, or subjected to other difficult environmental conditions. The biota of the Kockatea Shale is insufficiently known to estimate biotic diversity and relationships of individual taxa to their Permian progenitors and Triassic successors, but provides a glimpse into a coastal-zone from the interior of eastern Gondwana. Specialist collecting is needed to clarify the taxonomy of many groups, and comparisons to other Lower Triassic sites are required to provide insights into the pattern of biotic decline and recovery at the end-Permian crisis. [ABSTRACT FROM AUTHOR]

Laboratory measurements of porosity, P-wave velocity and thermal conductivity from samples from two geothermal reservoirs in France and Australia are compared to the predictions from different models involving mineralogical considerations, and effective medium theory models yields <10% error in dry and saturated conditions in the Australian aquifer, and <30% deviation under saturated conditions in the French reservoir. Thermal conductivity derived from models involving detailed mineralogy is in good agreement with laboratory-measured data. Possible explanations for minor discrepancies using SEM/XRD include the effects of secondary minerals (i.e. ±undetected carbonates and fine particles) and the hydration of clays. [ABSTRACT FROM AUTHOR]

Numerical modeling of geothermal systems requires the best possible knowledge of porosity and permeability within the geothermal reservoir. The deep Jurassic Yarragadee Aquifer in the Perth Basin consists of various different lithofacies but is characterized by a high average permeability and the likely occurrence of free convection, making this Aquifer to a promising low-medium enthalpy geothermal reservoir unit. We define a log(permeability) - porosity model based on a combination of the Kozeny-Carman equation and fractal theory and calibrate it by nonlinear regression using a least-squares approach to the Yarragadee Aquifer in the Perth Basin. For the calibration, we use over 100 measurement pairs of porosity and permeability from three boreholes in the vicinity of our model domain. The calibrated model reasonably covers the control of lithofacies on permeability. [ABSTRACT FROM AUTHOR]

The calibration of large-scale geothermal models for entire sedimentary basins is challenging as direct measurements of rock properties and subsurface temperatures are commonly scarce and the basal boundary conditions poorly constrained. Instead of the often-applied trial-and-error manual model calibration, we examine here the use of an automatic model calibration method, implemented in iTOUGH2, for a large-scale conductive geothermal simulation of the Perth Basin, Australia. The application shows that we obtain valuable insights into parameter sensitivities and correlations. In addition, outlier analysis, parameter bounds and the spatial variation of temperature residuals provide indication for convective heat transport in the basin. These interesting results will be addressed with future work. [ABSTRACT FROM AUTHOR]

Accurate porosity and permeability evaluation of rock formations is critical to estimate the quality and resource potential of a reservoir. In addition to directly measure the porosity and pore size distribution, low field Nuclear Magnetic Resonance (NMR) is able to measure the effective porosity and estimate the in-situ formation permeability, though its robustness is arguable and requires calibrations on cores with specific lithologies. The Mesozoic formations of the central Perth Basin (Western Australia) host hot sedimentary aquifers and recently became key targets for geothermal heat extraction. A collection of cores was retrieved from three wells intersecting these units. The characterisation of their flow properties complements the current evaluation of the Perth Basin by adding new data on effective porosity, pore size distribution, pore geometry and calibration of predictive models for the permeability according to a comprehensive facies classification scheme. This study highlights the consistency of the NMR approach when compared to conventional helium injection method. Most favourable lithologies for well production correspond to very coarse to fine sandstones of fluvial channel fill with porosities >15% and permeabilities >>1 mD. Similarly, these facies exhibit (i) the highest effective porosities, (ii) the highest pore space to pore throat ratio, and (iii) the lowest contribution of clay bound water. These aspects confirm the importance of clay occurrence in the assessment of the flow efficiency of a formation. The Yarragadee Formation presents the best reservoir quality regarding its porosity and permeability, even though high discrepancies occur locally owing to the great variability of lithofacies encountered. The scattered values observed for the Lesueur Sandstone are likely to be due to the basin architecture and fault system which generate different mechanical compaction and secondary cementation. Given an adequate facies analysis, the NMR method represents a powerful tool to estimate the flow efficiency of a reservoir. [ABSTRACT FROM AUTHOR]

An Early Triassic stromatolite deposit in Gondwana is documented from the Smithian succession of the Lower Triassic Kockatea Shale Formation in the Northampton area, northern Geraldton, Western Australia. Abundant tube-like sheaths of filaments and tiny circular microspherule balls are well preserved in laminae of the Northampton stromatolites, which are characterized by finely laminated domes and digitate high-relief columns. These filament sheaths are superficially analogous to their counterparts of modern stromatolites, and thus are interpreted as putative fossilized filamentous cyanobacteria. Elemental mapping of EDS analysis shows very high contents of both Fe and Si elements as well as common presence of both S and Al elements along the laminae of the stromatolites, suggesting that the stromatolites may have been ferritized or silicified. Both ferritization and silicification may have played a crucial role in the exceptional preservation of the micro-structures in the Northampton stromatolites. The high content of Al along the laminae indicates that the stromatolites may have been influenced by terrigenous fine-grained clastics during their growth. The Northampton stromatolites show several growth modes, initiating on either pebbles/conglomerates or sandy seafloor and building laminar domes and digitate, high-relief columns during an initial transgression period. Steady increase in sea level facilitated the growth of stromatolites. The Early Triassic stromatolites ceased growth due to either rapid rise in sea level or increased clay influx probably sourced from increased weathering on land at that time, or both. The occurrence of the Northampton stromatolites in the siliciclastic succession, in comparison with published records of Early Triassic microbialites, reveals that post-extinction microbialites were widespread in the Smithian. Stromatolites show a broad geographic distribution from low-latitude to southern high-latitude regions of Gondwana and inhabited not only carbonate settings, but also siliciclastic nearshore settings. All features of these Early Triassic stromatolites indicate a microbial bloom in the aftermath of the P-Tr mass extinction. [ABSTRACT FROM AUTHOR]

Identifying reservoir electrofacies has an important role in determining hydrocarbon bearing intervals. In this study, electrofacies of the Kockatea Formation in the Perth Basin were determined via cluster analysis. In this method, distance data were initially calculated and then connected spatially by using a linkage function. The dendrogram function was used to extract the cluster tree for formations over the study area. Input logs were sonic log (DT), gamma ray log (GR), resistivity log (IND), and spontaneous potential (SP). A total of 30 reservoir electrofacies were identified within this formation. Integrated geochemical and petrophysics data showed that zones with electrofacies 3, 4, 9, and 10 have potential for shale gas production. In addition, the results showed that cluster analysis is a precise, rapid, and cost-effective method for zoning reservoirs and determining electrofacies in hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]

Abstract: Geoscience Australia (GA) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) conducted a marine survey including monitoring hydroacoustic flares in order to understand the natural leakage pathways in the offshore northern Perth Basin. 186 hydroacoustic contacts were encountered and classified and thirty two were interpreted as possible seeps or expulsion of gases from the subsurface. The contacts were typically distributed above areas of interpreted subsurface faulting. In the survey site Da (15 km2), nine probable seeps and sixteen other contacts were interpreted and are aligned with a fault segment (A2) interpreted on 2D seismic reflection data. The segment A2 is part of a major N–NNW trending fault system intersecting the sedimentary sequence from the near seabed to the Permian units, including the Kockatea Shale source rock located in the oil window. Evaluation of the stress state on the fault segment A2 suggests that it is not critically stressed and therefore not likely prone to reactivation and dilation and vertical leakage under the modelled stress field. We propose that fault segment A2 acts as a baffle delimiting a migration pathway in the wall rock and permitting hydrocarbons generated from the source rock to overcome capillary entry pressures of the overlying marginal seals. The interpreted seeps could therefore be associated with intraformational vertical migration in the wall rock focused by the faults. [Copyright &y& Elsevier]

Abstract: GSWA Harvey 1 was drilled as part of the South West CO2 Geosequestration Hub carbon capture and storage project (South West Hub) to evaluate storage volume, injectivity potential and carbon dioxide retention capacity in the south-western Perth Basin. Six cored intervals from the Triassic Lesueur Sandstone contain nine lithofacies consistent with fluvial depositional environments: the lower Wonnerup Member is dominated by fluvial lithofacies consisting of stacked beds of porous, permeable sandstone deposited as high-energy fill and barforms, with rare finer-grained swampy/overbank deposits. The overlying Yalgorup Member contains mainly floodplain palaeosols with low- to moderate-energy barforms. The high- to moderate-energy fluvial facies typically have a low gamma response and contain clean, medium to very coarse-grained quartz-dominated sandstones. Other clastic components include K-feldspar (8–25%) with trace muscovite, garnet and zircon, and interstitial diagenetic kaolinite (up to 15%) and Fe-rich chlorite (up to 13%). The low-energy facies contain variably interbedded mudstone and thin, moderate to well sorted fine-grained sandstone, typically with a high gamma response, and are consistent with deposition under swampy, overbank and palaeosol conditions. These facies have significantly higher proportions of mica and diagenetic clays, including smectite (up to 8%) and illite (up to 10%), and detrital plagioclase (up to 21%) and trace carbonate bioclasts. High porosity and permeability in the cored intervals of the Wonnerup Member indicate good reservoir characteristics in terms of storage capacity and injectivity at depths relevant to CO2 injection (>1500 m). High porosity and extremely variable permeability values in the Yalgorup Member were measured. The variation is due to permeable vertical sandstone features in low permeability sandy mudstone and indicate limited sealing potential, although the spatial connectivity of the vertical features cannot be resolved from the available core. A preliminary assessment of the area as a CCS site seems favourable; however, the project is only in the early stages of its characterization and far more regional and site-specific data are needed to evaluate how injected CO2 may behave in the subsurface. [Copyright &y& Elsevier]

The Perth Basin (PB) hosts important aquifers within the Yarragadee Formation and adjacent geological formations with potential for economic exploitation by both geothermal energy and carbon capture and sequestration. Published studies on the reservoir quality of the sedimentary units of the PB are very few. This study reports some petrophysical and lithological characteristics of the sedimentary units of interest for geothermal and geosequestration scenarios and help interpolation toward non-sampled intervals. A new fluvial-dominated lithofacies scheme was developed for the Mesozoic stratigraphy from four wells drilled in the central PB (Pinjarra-1, Cockburn-1, Gingin-1 and Gingin-2) based on grainsize, sorting, sedimentary structures and colour that relate to the environment of deposition. Systematic laboratory measurements of permeability, porosity, and thermal conductivity were conducted on core samples to investigate a variety of lithofacies and depths from these wells. Empirical correlations are established among the different physical properties, indicating encouraging relationships for full PB basin interpolation such as between porosity and permeability, when the samples are grouped into ‘hydraulic units’ defined by a ‘flow zone indicator’ parameter. The common principal controls on the PB thermal conductivity are the pore space arrangement and mineralogical content, which are strongly lithofacies-specific. Therefore, the lithofacies type could be a good first-order discriminator for describing spatial variations of thermal conductivity and then estimate their flow zone indicator. [ABSTRACT FROM PUBLISHER]

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Abstract: Much of the deep sea comprises soft-sediment habitats dominated by comparatively low abundances of species-rich macrofauna and meiofauna. Although often not observed, these animals bioturbate the sediment during feeding and burrowing, leaving signs of their activities called Lebensspuren (‘life traces’). In this study, we use still images to quantify Lebensspuren from the eastern (1921 images, 13 stations, 1300–2200m depth) and western (1008 images, 11 stations, 1500–4400m depth) Australian margins using a univariate measure of trace richness and a multivariate measure of Lebensspuren assemblages. A total of 46 Lebensspuren types were identified, including those matching named trace fossils and modern Lebensspuren found elsewhere in the world. Most traces could be associated with waste, crawling, dwellings, organism tests, feeding, or resting, but the origin of 15% of trace types remains unknown. Assemblages were significantly different between the two regions and depth profiles, with five Lebensspuren types accounting for over 95% of the differentiation (ovoid pinnate trace, crater row, spider trace, matchstick trace, mesh trace). Lebensspuren richness showed no strong relationships with depth, total organic carbon, or mud, although there was a positive correlation to chlorin index (i.e., organic freshness) in the eastern margin, with richness increasing with organic freshness. Lebensspuren richness was not related to epifauna either, indicating that epifauna may not be the primary source of Lebensspuren. Despite the abundance and distinctiveness of several traces both in the current and previous studies (e.g., ovoid pinnate, mesh, spider), their origin and distribution remains a mystery. We discuss this and several other considerations in the identification and quantification of Lebensspuren. This study represents the first comprehensive catalogue of deep-sea Lebensspuren in Australian waters and highlights the potential of Lebensspuren as valuable and often untapped deep-sea datasets that can be used for biogeographical, evolutionary, behavioural, and ecological studies. [Copyright &y& Elsevier]

Abstract: The Kockatea Shale Formation is one of few marine Early Triassic successions recorded in the Gondwana. This formation is exposed at the Northampton area of the northern Perth Basin, Western Australia and was deposited in the Gondwana interior sea during the Permian and Early Triassic. Trace fossils identified within the Kockatea Shale Formation are extremely abundant and contain 16 ichnogenera (including a problematic ichnogenus). The Gondwanan ichnoassemblage is constrained as late Smithian in age and is the most diverse among coeval ichnofaunas around the world. Several types of grazing traces are also reported for the first time in the Lower Triassic. Several proxies such as bioturbation level, ichnodiversity, burrow size, trace-fossil complexity, and tiring level suggest that tracemakers diversified in the Gondwana interior sea during the late Smithian. The Gondwanan ichnofauna-dominated ecosystem may have reached the ecologic recovery stage 3 of Twitchett''s model in late Smithian. The rebound of ichnoassemblages in the aftermath of the end-Permian mass extinction was not controlled by particular environmental settings, all of which however were characterized by oxygenated substrata. [Copyright &y& Elsevier]

Abstract: The deep (>10km) Permian to present day Perth Basin in southwest Western Australia is composed of sedimentary successions of continental to shallow marine origin. This study examines the compositional variation, weathering and provenance of the early Cretaceous Leederville Formation within the Perth Basin. Over 200 sediment samples were retrieved from two deep boreholes of ~350 to 530m in depth encompassing the Leederville Formation, and analysed for major and trace element geochemistry and mineralogy. The Leederville Formation is composed of subarkosic sands, predominantly composed of quartz (64%) and K-feldspars (27%); silts and clays composed of kaolinite (24–54%), K-feldspars (20–29%) and quartz (18–40%), with their compositional variation reflecting weathering, hydraulic sorting during transport, mostly subaqueous deposition and subsequent diagenesis. Most trace elements are associated with fine grained lithologies due to their occurrence within clays, sulphide or zircon. Major and trace element geochemistry suggests a typical passive margin origin with minimal intrabasinal sediment recycling. The regionally extensive Yilgarn Craton, appears to be the main sediment source for the Leederville Formation within the study area. [Copyright &y& Elsevier]

Deep-water mounds located in greater than 1500 m water offshore Perth Basin in Western Australia are imaged by several vintages of seismic-reflection lines. The majority of the mounds, concentrated south of the deeply-incised submarine Murchison Canyon, are sharply defined with a pinnacle-like morphology, suggesting little erosion and a recent origin. The morphology of these mounds is discussed and either a bioherm origin, a volcanic origin or a combination of the two is considered likely. Should these mounds be related to hydrocarbon seepage, their presence may indicate an active hydrocarbon system. Other mounds appear to be igneous plugs or diatremes: proof of such an origin may require a reappraisal of the tectonic and magmatic history of the offshore Perth Basin and the maturation history of petroleum source beds. [ABSTRACT FROM AUTHOR]

Detrital zircons from the Permian Collie Coal Measures and modern sands on the northern part of the Albany Province have been analysed for U–Pb ages by a laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) and for Hf-isotope compositions by a laser ablation microprobe multi-collector inductively coupled plasma mass spectrometer (LAM-MC-ICPMS). Trace elements were determined by analysis on the electron microprobe (EMP) and the ICPMS''s. This combination of techniques makes it possible to determine for each grain not only the age but the nature and source of the host magma, whether crustal or juvenile mantle, and a model age (TDM) based on a depleted-mantle source, which gives a minimum age for the source material of the magma from which the zircon crystallised. The integrated analysis, applied to suites of detrital zircon, gives a more distinctive, and more easily interpreted, picture of crustal evolution in the provenance area than age data alone. Zircons from Permian and Triassic sediments already analysed for U–Pb ages by a sensitive high-resolution ion microprobe (SHRIMP) were also analysed for Hf isotopes and trace elements.Zircons from Collie and Permian and Early Triassic rocks of the northern Perth Basin have an age spectrum with a peak at about 1200 Ma that can be traced to the Albany Province. Differences, however, in Hf-isotope composition indicate that the Collie Coal Measures and the northern Perth Basin sandstones were not derived from the northern part of the Albany Province or from the coastal strip of felsic granitoids. The Perth Basin samples have a second peak age of 600–500 Ma that can be traced to the Leeuwin Block. One of the modern sands has a major peak at 2616 Ma that can be traced to the Yilgarn Craton.Compiled with previously published U–Pb zircon age spectra, the analyses provide insights into the paleogeographical history. The Yilgarn Craton sloped from the north at 1700 Ma, from the southeast at 1350–1140 and 490 Ma, its eastern part to the east at 300 Ma, and the southern part to the northwest from the Albany Province at 300–255 Ma. Denudational data from apatite fission-track analysis and vitrinite-reflectance studies suggest that the Yilgarn Craton was covered by a ∼5-km-thick blanket of Permian and Mesozoic sedimentary rock that was almost entirely removed by the Cenozoic, possibly because the craton was situated between the shoulders of rift systems that grew into the eastern and southeastern Indian Ocean.Ordovician, Permian, Early Triassic, and Quaternary sediment of the Perth Basin came from Proterozoic orogens. Only the Late Permian sample contains significant populations of Archean (Yilgarn) zircons but whether they came direct from the craton or were recycled from the postulated sedimentary cover is not known. The increased influx of sediment during the Jurassic matched by a peak in the denudation rate would seem to require a primary supply from the craton. This question could be resolved by dating zircon from the rapidly accumulated Jurassic formations. [Copyright &y& Elsevier]

The Westonia Formation comprises clayey quartz sand commonly exposed in interfluve breakaways in the southwestern Yilgarn Craton, Western Australia. As is typical of Cenozoic sediments in the region, it is texturally immature, poorly stratified and unfossiliferous, making it difficult to distinguish from the underlying deeply weathered Archaean granite. In order to verify the difference in origin and elucidate provenance, the varietal properties and U–Pb ages of zircons from the Westonia Formation and underlying granitic saprolite were compared. Zircons from the Westonia Formation comprise 11 distinct morphological varieties, seven of which are not present within the granitic saprolite. SHRIMP U–Pb ages of zircons from the granitic saprolite range from 2657 ± 13 to 2554 ± 10 Ma, corresponding to published age determinations of zircons from the Darling Range Batholith. Angular zircons from the Westonia Formation range in age from 2898 ± 12 to 2631 ± 11 Ma, reflecting a mixed provenance including local granitic rocks, and possibly greenstones in adjacent parts of the Yilgarn Craton. Rounded zircons from the Westonia Formation range in age from 1144 ± 38 to 467 ± 16 Ma (Late Mesoproterozoic – Early Palaeozoic), similar to detrital zircons from the Jarrahdale bauxite deposit and various stratigraphic levels in the Perth Basin. The Late Mesoproterozoic – Early Palaeozoic zircons at East Yornaning and Jarrahdale most likely resulted from burial of the southwestern Yilgarn Craton by sediment sourced from the Proterozoic Albany–Fraser–Wilkes and Pinjarra Orogens during the Early Permian glaciation, or during an earlier episode of mountain building associated with the final stages of the Pinjarra Orogeny. Most of the sedimentary cover was then reworked into the evolving Perth Basin during the Late Permian – Early Cretaceous. Remaining pockets on the craton were repeatedly recycled, leaving only the most chemically and physically resistant components, such as rounded zircons, in the Westonia Formation. [ABSTRACT FROM AUTHOR]

Liknopetalon is an unusual fern-like taxon with fan-shaped pinnae that bear ovate sporangial bodies in a single series along the distal margin. Previously, Liknopetalon has been described from two Permian localities in South Africa, and a single pinna has been identified from the Perth Basin in Australia. The original material of the type species, Liknopetalon enigmata Smithies, lacks critical morphological characters and the species’ taxonomic affiliations have remained obscure. A re-evaluation of existing collections and additional information provided by material obtained from a third South African locality necessitated emendation of the generic diagnosis of Liknopetalon, and erection of an additional species, Liknopetalon gracilis Adendorff sp. nov. Detailed drawings and photographs of several important specimens are presented and these have contributed to the reconstruction of both species. Newly clarified features include the opposite arrangement of the pinnae on the rachis, the division of the distal margin of the lamina into a series of contiguous lobes that each bear a single sporangial body, and the absence of a longitudinal, medial cleft in the pinna. Without anatomical data, the nature of the marginal bodies could not be unequivocally elucidated, but based on gross morphology, they appear to represent synangia or particularly large sporangia. The new South African specimens extend the stratigraphic range of the plant from the Lower Permian into the Middle Permian. [Copyright &y& Elsevier]

The facies distribution of the Lower Triassic Kockatea Shale in the northern Perth Basin is an important factor for assessing the Lower Triassic source rock potential in the basin. Seismic interpretation and well analyses demonstrate that Permian-aged faults are responsible for the morphology of the basin in the Early Triassic and created remnant topography that controls the deposition of Lower Triassic sediments. Cores from petroleum wells and their correlated wireline logs show the lithological variation and lateral distribution of facies across the base of the Kockatea Shale. Darker coloured mudstones were deposited under anoxic conditions in the deeper part of the basin, while lighter coloured mudstones and tidally influenced sediments with bioturbation were deposited under oxic conditions in a shallow marine setting. Microbial mats developed in shallower water depths on structural highs (Beagle Ridge and Turtle Dove Ridge) in the anoxic parts of the basin. The distribution of microbial mats is controlled by two factors during the period of ecological recovery from the end-Permian mass extinction: 1) the presence of topographic highs and, 2) distance from the edge of the basin. The source rock potential of both darker coloured mudstone and microbial mat facies is demonstrated by TOC values between 0.3 and 3.4% and HI values between 39 and 579 mg/gTOC. On the other hand, the lighter coloured mudstones, deposited under more aerobic tidal settings, have poor source rock quality and TOC values between 0.2 and 0.5% and HI values between 59 and 127 mg/gTOC. • Anoxic conditions were widely distributed in the northern Perth Basin around the Permo-Triassic boundary. • Distribution of anoxia is controlled by distance from the basin margin. • Distribution of microbial mats is controlled by the presence of shallow water on structural highs associated with anoxic facies. [ABSTRACT FROM AUTHOR]

Linked fault systems identified in the northern portion of the onshore Perth basin comprise north- striking normal faults, the dominant structures in the basin, and hard linkages—east-striking transfer faults. The former are either divided into segments of distinctive character by, or terminate at, the transfer faults. The fault systems were initiated by west-southwest–east-northeast extension in the Early Permian but were reactivated by subsequent rifting with approximately east–west extension in the Jurassic. They were also reactivated by the oblique extension of northwest–southeast orientation associated with Gondwana continental breakup in the Late Jurassic – earliest Cretaceous. In addition to reactivation, older structures of the linked fault families controlled the development of younger fractures and folds. During the oblique extension, the linked fault systems define releasing bends, characterised by a rollover anticline in the hangingwall of the Mountain Bridge Fault, and restraining bends where contractional folds are sites of major commercial hydrocarbon fields in the basin. [ABSTRACT FROM AUTHOR]