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The Ilkurlka structure is an ~12 km diameter buried circular aeromagnetic anomaly within the Officer Basin in Western Australia. Prior studies postulated a range of origins, including meteorite impact. We report the presence of pervasive deformation in the first drill cores from the structure. Brecciated sandstone and siltstone contain arrays of quartz grains with concussion fractures and rare shocked quartz grains with planar deformation features (PDF). Universal stage measurements of two quartz grains reveal one grain with PDF parallel to (0001) orientation and three PDF sets parallel to 101¯3. A second grain contains three PDF sets parallel to 101¯3 and one set parallel to 101¯4. The shocked grains are interpreted to have formed in situ, rather than representing transported detrital shocked grains. These results suggest local shock compression of at least 10 GPa; however, preservation of primary porosity and overall paucity of shocked grains may indicate lower mean shock pressures. (U‐Th)/He dating of 58 apatite grains from four samples across both cores shows a dominant age population at ~265 Ma and a minor age population at ~135 Ma. These dates overlap with regional events and thus do not provide an unambiguous impact age. An upper Carboniferous to lower Permian maximum impact age is provisionally proposed based on inferred missing target rock stratigraphy. [ABSTRACT FROM AUTHOR]

Quality and morphology of outcrop exposure places fundamental constraints on what ichnological observations can be made and the veracity of these observations. Whilst the limits and potential biases are well known and reported for core studies, in the majority of field studies the equivalent biases are typically overlooked. In this paper we present a widely applicable method for recording outcrop characteristics based on their morphology, and how these characteristics may affect observations. We consider the impacts of structural orientation, superficial cover, and outcrop location on outcrop quality. Finally, we present two case studies, from the Tumblagooda Sandstone of Western Australia and the Armorican Sandstone Formation of northwestern France, to highlight the importance of recording outcrop characteristics. [ABSTRACT FROM AUTHOR]

Geological storage has been proposed as a new technology to temporarily store significant amounts of hydrogen (H 2) gas in depleted gas reservoirs, underground salt caverns, or saline aquifers. Often, such subsurface reservoirs naturally contain trace amounts of organic acids, and these compounds can considerably alter the wettability of reservoir rocks, causing them to become less water-wet. We carried out Molecular Dynamics (MD) simulations of contact angles in a quartz-brine-H 2 system to evaluate wettability in realistic subsurface situations. MD simulations suggest that Humic acid makes quartz more hydrophobic, which can affect the overall behaviour of the storage reservoir. For the first time, this effect was experimentally investigated for a natural sandstone reservoir from the South West Hub Project, i.e., the Lesueur Sandstone (LS) formation. Multi-stage core flooding experiments were conducted on the same LS plug to investigate the impact of wettability alteration on initial and residual hydrogen saturation/trapping at depth. First, consecutive brine-H 2 drainage-imbibition cycles were carried out on the natural sample; the result indicated that the rock-brine-H 2 system was essentially water-wet. Then, the sample was aged in Humic acid with a molarity of 10−2 M for 42 days at 5 °C and 0.1 MPa. The wettability of the storage system shifted toward a less water-wet state, i.e., more hydrophobic. As a result of Humic acid ageing, the initial hydrogen saturation reduced from 29% to 15%, and the residual hydrogen trapping reduced from 23% to 11%. This is attributed to a change induced in the capillary force (i.e., snap-off) controlled by wettability and pore size. In addition, the wettability change induced by Humic acid increased the hydrogen recovery rate from 20.7% to 26.7%. [Display omitted] • Utilise Nuclear Magnetic Resonance (NMR) coreflooding cell to access hydrogen-rock interaction. • Impact of rock wettability on storage and mobility of hydrogen in subsurface reservoirs. • Laboratory assessment of Southwest Hub site of Western Australia for hydrogen storage. • Humic acid can positively impact the residual hydrogen saturation. • Molecular dynamics could be a good tool to study the H 2 -brine-silica interface. [ABSTRACT FROM AUTHOR]

In sedimentary basins, the determination of the absolute timing of deposition and diagenetic events is a challenging yet critical parameter necessary in the reconstruction of paleo-fluid evolution and burial histories. Here we demonstrate the practical application of in situ calcite U–Pb geochronology on core samples from the Olympic 1 well in the Canning Basin of Western Australia. Using quantitative mineralogy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analytical techniques, we obtained an authigenic calcite U–Pb age of 469.7 ± 4.3 Ma for limestone in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation. This precise depositional age can be independently verified using zircon thermal ionisation mass spectrometry U–Pb ages of 479.4 to 470.2 Ma determined on adjacent volcanic ash beds. Further geochronology studies on calcite cements from the Lower Ordovician Fly Flat Member sandstone from the Nambeet Formation returned a U–Pb age of 365.3 ± 5.8 Ma. This is the first study to place absolute age constraints on the diagenetic event that occluded the intergranular space in a sandstone reservoir. The calcite cementation age suggests that impairment of reservoir quality in the Fly Flat Member sandstone occurred in the Late Devonian, much earlier than major petroleum charge events in the Canning Basin. The calcite U–Pb geochronometer, when combined with complementary quantitative mineralogical analysis, can build direct temporal constraints on the depositional and diagenetic processes in both carbonate and clastic sedimentary rocks in basins worldwide. The integration of automated scanning electron microscopy/energy-dispersive X‐ray spectrometry quantitative mineralogical analysis with LA-ICP-MS analysis enables more reliable and efficient in situ calcite U–Pb dating. An accurate age of 469.7 ± 4.3 Ma is obtained for carbonate sedimentation in the Samphire Marsh Member of the Lower Ordovician Nambeet Formation in the Canning Basin. The calcite cementation age of 365.3 ± 5.8 Ma provides an absolute time constraint on pore-occluding lithification of the Fly Flat Member sandstone reservoir in the Canning Basin. In situ calcite U–Pb dating can place precise temporal constraints on sediment deposition and paragenetic sequence in sedimentary basins. [ABSTRACT FROM AUTHOR]

The nature of Earth's earliest crust and the processes by which it formed remain major issues in Precambrian geology. Due to the absence of a rock record older than ~4.02 Ga, the only direct record of the Hadean is from rare detrital zircon and that largely from a single area: the Jack Hills and Mount Narryer region of Western Australia. Here, we report on the geochemistry of Hadean detrital zircons as old as 4.15 Ga from the newly discovered Green Sandstone Bed in the Barberton greenstone belt, South Africa. We demonstrate that the U-Nb-Sc-Yb systematics of the majority of these Hadean zircons show a mantle affinity as seen in zircon from modern plume-type mantle environments and do not resemble zircon from modern continental or oceanic arcs. The zircon trace element compositions furthermore suggest magma compositions ranging from higher temperature, primitive to lower temperature, and more evolved tonalite-trondhjemitegranodiorite (TTG)-like magmas that experienced some reworking of hydrated crust. We propose that the Hadean parental magmas of the Green Sandstone Bed zircons formed from remelting of mafic, mantle-derived crust that experienced some hydrous input during melting but not from the processes seen in modern arc magmatism. [ABSTRACT FROM AUTHOR]

The establishment of permanent animal communities on land was a defining event in the history of evolution, and one for which the ichnofauna and facies of the Tumblagooda Sandstone of Western Australia have been considered an archetypal case study. However, terrestrialization can only be understood from the rock record with conclusive sedimentological evidence for non-marine deposition, and original fieldwork on the formation shows that a marine influence was pervasive throughout all trace fossil-bearing strata. Four distinct facies associations are described, deposited in fluvial, tidal and estuarine settings. Here we explain the controversies surrounding the age and depositional environment of the Tumblagooda Sandstone, many of which have arisen due to the challenges in distinguishing marine from non-marine depositional settings in lower Palaeozoic successions. We clarify the terminological inconsistency that has hindered such determination, and demonstrate how palaeoenvironmental explanations can be expanded out from unambiguously indicative sedimentary structures. The Tumblagooda Sandstone provides a unique insight into an early Palaeozoic ichnofauna that was strongly partitioned by patchy resource distribution in a littoral setting. The influence of outcrop style and quality is accounted for to contextualize this ichnofauna, revealing six distinct low-disparity groups of trace fossil associations, each related to a different sub-environment within the high-ichnodisparity broad depositional setting. The formation is compared with contemporaneous ichnofaunas to examine its continued significance to understanding the terrestrialization process. Despite not recording permanent non-marine communities, the Tumblagooda Sandstone provides a detailed picture of the realm left behind by the first invertebrate pioneers of terrestrialization. [ABSTRACT FROM AUTHOR]

The United States Geological Survey (USGS) Three-part Undiscovered Mineral Resource Assessment provides a framework for estimating undiscovered mineral endowment. Previous studies that applied the Three-part Assessment to estimate the undiscovered orogenic gold endowment of the Sandstone Greenstone Belt, Western Australia, have relied upon dated or expert-derived grade-tonnage models. Here, several assessments are conducted using local grade-tonnage models, comprising known orogenic gold deposits within the entire Yilgarn Block and several individual terranes with contrasting lithosphere- to terrane-scale characteristics. These models are generated through comprehensive review of historical exploration, resource and production data. Based on these models, the Sandstone Greenstone Belt is estimated to contain significant undiscovered gold mineralisation, with a median total endowment of between 166 and 298 t gold, and mean of 167–319 t gold. Although these updated grade-tonnage models provide an approximately 80 per cent variation in predicted gold endowment, it is still evident that the belt remains an under-explored region within the Yilgarn Block, Western Australia. [ABSTRACT FROM AUTHOR]

In rock physics one of the important purposes of the determination of P- and S-wave velocities is to obtain the elastic constants and anisotropy parameters. This method is standardised in American Society for Testing and Materials (ASTM) by a standard D2845-95. The most challenging yet important part of these experiments is picking the first arrivals correctly and consistently. A sharp, clean first arrival of a wave is not always possible, especially when testing dry, porous sandstones at low pressures. The signal transmitted through such samples is weak due to a high damping effect, and picking the first break introduces uncertainties. Harvey sandstone is a sample type with high porosity and, therefore, some degree of anisotropy is expected. In order to study the anisotropy parameters of the Harvey 3 sandstone which belongs to Lesuer- Wonnerup Member of the Yalgorup Member, three core plugs in directions of horizontal, vertical and diagonal, were experimentally investigated. The laboratory measurements on three different samples which are cut at three different directions with regards to the base deposition system enabled us to calculate the anisotropy parameters using a standard acoustic equipment while applying stress. We concluded that Harvey 3 poses a more complex symmetry axis of anisotropy, and no sign of low-grade anisotropy was observed through the experimental data. To study the anisotropy degree of the Harvey 3 sandstone, a pressure cell, pore fluid injection pump, and ultrasonic system (consisting of P- and S-wave transducers, oscilloscope and pulser/receiver) were used to record the elastic waves passing through the samples. The specimens were fully saturated inside the pressure cell using vacuum injection for the best possible comparison of dry and saturated status. The results confirmed that the sample is far from weak anisotropy and possesses more axes of symmetries than simple layering anisotropy due to the pore orientation and distribution in the matrix of the background rock. The study also confirms that the anisotropy degree decreases under full compaction and full saturation, and the Harvey 3 anisotropy becomes elliptical when it's fully saturated. Large, stress-dependent changes in the ultrasonic velocities for porous media were observed in this experimental study, which confirms the usefulness of such studies in examining the inner structure change process. [ABSTRACT FROM AUTHOR]

Regional-scale ground selection presents a significant risk in mineral exploration targeting. As any exploration search space contains a finite and fixed number of ore bodies, selection of barren or depleted search spaces incurs wasted exploration expenditure. By defining regions of estimated high mineral endowment, via generation of quantitative information as to the value of potential discoveries, mineral exploration effectiveness, project acquisition, and exploration portfolio management can be improved. The Three-Part Mineral Resource Assessment, developed by the United States Geological Survey (USGS), is a methodology designed to assist in this process. Here, two separate assessments are applied to estimate the orogenic gold endowment of the Sandstone Greenstone Belt in the Yilgarn Craton, Western Australia. First, the results of a global regression assessment (median endowment of 33 t/1.16 Moz Au, mean of 130 t/4.59 Moz Au), based on an available, but outdated, global grade-tonnage model for low-sulfide gold-quartz vein deposits, suggest that most outcropping and shallow orebodies in the Sandstone Greenstone Belt have been discovered and fully delineated. In contrast, an expert assessment (median endowment of 210 t/7.41 Moz Au, mean of 220 t/7.76 Moz Au), using expert-derived grade and tonnage distributions specific to the Sandstone Greenstone Belt, predicts that significant gold mineralization remains to be discovered, largely beneath cover. The contrasting assessments imply a step change in exploration focus, from surficial deposits at the time of the USGS global grade-tonnage model to those buried under cover at the present time. The expert assessment, in contrast to the global regression assessment, implies the potential for deeper exploration targets within the Sandstone Greenstone Belt. Based on the predicted total number of deposits, much of the undiscovered mineral endowment is likely to be distal to known ore bodies, beneath cover, and at greater depths within the belt. [ABSTRACT FROM AUTHOR]

Exploration in the Sandstone Greenstone Belt (SSGB), with its widespread complex regolith cover, is extremely difficult as targeted orogenic gold deposits have no consistent parameters that allow direct geophysical detection, and gold and ore-metal surface geochemistry reflects variations from in situ to highly transported responses. Based on aeromagnetic interpretations, the gold deposits of the SSGB can be viewed within broad litho-structural frameworks, and NNW-NW and NNE-NE–trending domains, with more favourable orientation with respect to the inferred principal maximum stress during the time of gold mineralisation, can be defined. Fault jogs and high-angle corridors of cross faults further constrain more-prospective zones. However, the aeromagnetic data cannot identify relatively small volumes of critical host rocks which can localize ore-fluid flux and fluid-rock reactions that control the deposition of gold mineralisation. In the SSGB, these critical host rocks include thin granodiorite intrusions within ultramafic schists or specific mafic bodies in mafic-ultramafic sequences. A reconnaissance study using the immobile trace elements, Ti and Zr, demonstrates that these critical rock types can be readily recognized at surface and in drill chips. In particular, Ti–Zr geochemistry identifies previously unknown 20-km-long differentiated dolerite units with granophyric zones that localize gold mineralisation. A combination of aeromagnetic interpretation of structures and major Domains, plus the location of critical host units using Ti–Zr geochemistry, allows production of an exploration targeting map for this district with definition of priority targets based on a mineral system approach. Thus, in the SSGB, for gold exploration under regolith cover that represents in situ weathering of those host rocks, rather than later cover sequences, immobile trace element geochemistry provides an effective, low-cost methodology, as an adjunct to conventional ore-metal geochemistry, and should be used in other orogenic gold provinces worldwide. [ABSTRACT FROM AUTHOR]

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]

The 920 km2 Archean Sandstone greenstone belt lies in the central-northern part of the Southern Cross Domain of the Youanmi Terrane, Western Australia. The belt, forming an arrow-head geometry, is bounded by the Youanmi and Edale shear zones on its eastern and western margins, respectively. The belt has a total gold endowment, including historic production, resources and reserves, of approximately 62 t (2.0 Moz). Most known deposits are situated within a central-southern ultramafic domain, although this is likely a function of exploration focus. The distribution of historical exploration efforts and domaining of deposit types, based on litho-structural controls on ore formation, highlight the potential for significant undiscovered deposits, hosted within arrays of shear zones parallel and adjacent to the lithosphere-scale Youanmi and Edale shear zones. [ABSTRACT FROM AUTHOR]

We present updated U–Pb ages and Hf isotopic compositions of detrital zircons and whole-rock geochemical data to investigate the provenance and tectonic setting of late Neoproterozoic and early Cambrian sandstones from the Cathaysia Block, in order to offer new constraints on its tectonic evolution and its palaeo-position within the supercontinent. The source rocks for the studied sandstones were dominated by felsic–intermediate materials with moderate weathering history. U–Pb dating results show major populations at c. 2500 Ma, 1000–900 Ma and 870–716 Ma with subordinate peaks at 655–532 Ma, consistent with the global Neoarchean continental crust growth, assembly and break-up of Rodinia, and Pan-African Event associated with the formation of Gondwana. Zircon U–Pb ages and Hf isotopic data suggest that most derived from exotic terranes once connected to the Cathaysia Block. Using whole-rock geochemical analysis, it was determined that the studied sedimentary rocks were deposited in a passive continental margin and the Cathaysia and Yangtze blocks were part of the same continent; no Cambrian ocean existed between them. Compiling a detrital zircon dataset from Qiangtang, northern India, the Lhasa Terrane and Western Australia, the Cathaysia Block seems to be more similar to the Qiangtang and western part of the northern India margin, instead of having a direct connection with the Lhasa Terrane and Western Australia in the Gondwana reconstruction during the late Neoproterozoic and Cambrian eons. [ABSTRACT FROM AUTHOR]

Existing knowledge of the tracks left by sauropod dinosaurs (loosely 'brontosaurs') is essentially two-dimensional, derived mainly from footprints exposed on bedding planes, but examples in the Broome Sandstone (Early Cretaceous) of Western Australia provide a complementary three-dimensional picture showing the extent to which walking sauropods could deform the ground beneath their feet. The patterns of deformation created by sauropods traversing thinly-stratified lagoonal deposits of the Broome Sandstone are unprecedented in their extent and structural complexity. The stacks of transmitted reliefs (underprints or ghost prints) beneath individual footfalls are nested into a hierarchy of deeper and more inclusive basins and troughs which eventually attain the size of minor tectonic features. Ultimately the sauropod trackmakers deformed the substrate to such an extent that they remodelled the topography of the landscape they inhabited. Such patterns of substrate deformation are revealed by investigating fragmentary and eroded footprints, not by the conventional search for pristine footprints on intact bedding planes. For that reason it is not known whether similar patterns of substrate deformation might occur at sauropod track-sites elsewhere in the world. [ABSTRACT FROM AUTHOR]

New xenotime ages are obtained from the Paleoproterozoic King Leopold Sandstone of the Kimberley Group, NW Australia. The concordant age of 1679 ± 13 Ma can be equated with the ca 1.7 Ga xenotime age within errors obtained from the Warton and Pentecost Sandstones of the same group. These ages are much younger than the robust SHRIMP ages (1790 ± 4 Ma) obtained from zircons from the dolerite dyke intrusions, and thus indicate that the xenotime growths recorded in the Kimberley Group are unlikely to be diagenetic in origin but may have resulted from the post-depositional hydrothermal event. The overgrowth of xenotime recorded from these three units of the Kimberley Group was probably caused by the same hydrothermal event that took place ca 1.7 Ga ago in Kimberley. Radiogenic Pb loss occurred at ca 325 Ma, which could have been caused by the 400–300 Ma Alice Springs Orogeny. This Pb loss event was responsible for the discordant U–Pb ages from 1.6 to 1.1 Ga. [ABSTRACT FROM AUTHOR]

Abstract: A new species of abundant macrofossil, previously described informally as a ‘string of beads’, is here assigned to the genus Horodyskia Yochelson and Fedonkin, 2000, and formally named Horodyskia williamsii. It is known from Mesoproterozoic siliciclastic rocks that are older than 1070Ma and younger than 1465Ma; the Backdoor Formation of the Collier Group, and the poorly time-constrained, but probably correlative, Stag Arrow Formation of the Manganese Group, both part of the Bangemall Supergroup of the Ashburton region of Western Australia. The fossils are most commonly found as impressions on the sole of thin, frequently ripple-marked, sandstones. Very rarely, they are present as traces on the tops of sandstone beds. At some localities, there are thin, silty partings separating the sandstone beds. Some strings are current oriented, but commonly most strings crosscut current directions. Much of the observed variation appears to be taphonomic. [Copyright &y& Elsevier]

Sixteen species of molluscs are described from the Late Eocene Merlinleigh Sandstone, Carnarvon Basin, Western Australia. The assemblage, a random thanatocoenose, is dominated by bivalves (11 species) and a cephalopod, with a few gastropod specimens. All primary shell carbonate -- calcite or aragonite -- is replaced by silica. The assemblage is distinctive in composition, resembling no other known from the Australian Eocene. Terrestrial plant material, all silicifi ed, is associated with the marine fossils, consistent with a depositional environment of the energised sandy littoral, subject to river fl ood discharge. At a height of +280 to 300 m AHD, the formation compares closely with others of similar age in southwestern Australia, which also consist of a combination of marine and terrestrial fossil material. Faunal affi nities with the southern Australian Eocene were weak; an apparent Tethyan- Indo-Southwest Pacifi c infl uence is present, possibly with a weak endemic element. The taxonomy of the nautiloid Aturia clarkei is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The 1.8Ga King Leopold glaciation in northwestern Australia is recorded in the Kimberley Basin by subglacial erosional forms cut in an unconformity surface at the top of the Speewah Group and buried by glaciofluvial deposits at the base of the King Leopold Sandstone, the lowest formation of the Kimberley Group. The glaciofluvial deposits are conformably overlain by texturally mature, locally glauconitic quartzarenite of shallow-marine origin, implying that glaciation occurred near sea level. Palaeomagnetic data for five sites (29 specimens) in the hematite-bearing Elgee Siltstone of the upper Kimberley Group in the northeastern Kimberley Basin gave a dip-corrected mean direction of declination D =95.4°, inclination I =13.8° (α 95 =9.7°), indicating a palaeolatitude λ =7.0 +5.3/−5.0°. Results for red beds from five sites (28 specimens) in the conformably overlying Pentecost Sandstone gave a dip-corrected mean direction of D =94.1°, I =13.0° (α 95 =11.7°), λ =6.6 +6.4/−5.9°. Combining our data for the Elgee Siltstone and Pentecost Sandstone with results for the Elgee Siltstone in the southeastern Kimberley Basin [Li, Z.X., 2000. Palaeomagnetic evidence for unification of the North and West Australian cratons by ca. 1.7Ga: new results from the Kimberley Basin of northwestern Australia. Geophysical Journal International 142, 173–180.] yielded a dip-corrected mean direction for 17 sites of D =93.5°, I =15.1° (α 95 =4.4°), palaeolatitude λ =7.7±2.3°, and an overall pole position at latitude λ p =5.4°S, longitude φ p =211.8°E, with confidence semi-axes d p =2.3° and d m =4.5°. A positive fold test at 99% confidence was obtained for the combined data for the 17 sites. The basinwide concordance of results for the Elgee Siltstone and the positive fold test argue for an early magnetisation acquired prior to late Palaeoproterozoic initial folding of the Kimberley Group and close to the time of deposition. Our results imply a low palaeolatitude for the Kimberley Group and the King Leopold glaciation. Palaeomagnetic data for the 1.822Ga Plum Tree Creek Volcanics in the Pine Creek Orogen to the east of the Kimberley Basin are consistent with northwestern Australia being in low palaeolatitudes during the late Palaeoproterozoic. Hence the enigma of glaciation near sea level in low palaeolatitudes, which marks the Neoproterozoic and early Palaeoproterozoic, applies also to the late Palaeoproterozoic. Red beds from the Lansdowne Arkose of the Speewah Group also were studied, but only directions ascribable to Tertiary regolith weathering processes were found. Similar findings for the late Palaeoproterozoic McArthur Basin in northern Australia suggest some units in that basin also record Tertiary regolith processes. [Copyright &y& Elsevier]

The centre of the 13  ×  11 km Spider impact structure, Western Australia, displays an unusual system of eroded folds and imbricated thrusts surrounding a sandstone dome. As inferred from GIS-integrated remote sensing, geological and digital elevation data, the structural setting of the original crater was influenced by, and hence post-dates, the formation of the Mt Barnett Syncline, the east  –  west-oriented axis of which runs through the Spider structure. The syncline formed during the regional Yampi Orogeny ( ca 900 Ma), thus constraining the maximum age of the impact event. The sandstone dome in the centre of Spider formed prior to the imbrication, as interpreted from the present setting that indicates a deflection of the southward moving material during the crater collapse. Two modes of formation are discussed in order to explain the south-directed shortening in the Spider impact structure: (i) impact into the bottom of a syncline-controlled palaeovalley leading to uplift of the central crater floor followed by gravity-driven asymmetric sliding preferentially from the northern crater wall and valley slope, respectively; and (ii) moderately oblique (∼⃒10  –  30°) impact from the north onto the axis of the syncline, producing a central uplift under the influence of downrange residual momentum and, thus, asymmetric deformation inside the uplift and farther downrange. Neither model alone explains all the observations, and only a combination of both may provide a satisfactory solution. [ABSTRACT FROM AUTHOR]

Goat Paddock in northern Western Australia is a ∼⃒5 km-diameter impact crater of Eocene age excavated in gently dipping Proterozoic sandstones. Roughly radial gorges formed by post-impact erosion provide cross-sectional views of the wall and rim zone. The predominant structural theme is one of synclinal rim folding with broad zones in which bedrock strata were deformed by impact to steep, vertical and overturned attitudes. Impact breccia is found craterward of deformed bedrock, on top of it, and downdropped into fault troughs roughly concentric to the crater. The bedrock  –  breccia contact is sharp in some places and gradational in others. In at least one section, the entire mass of upturned bedrock and breccia was displaced radially over essentially undisturbed bedrock, as indicated by slickensides on the horizontal contact. Talus deposits are similar to breccia, but show rough size sorting and clast orientation that dips steeply craterward, indicating that the talus formed as slides down the oversteepened crater wall immediately after crater formation. Shatter cones in some clasts indicate that allogenic material is incorporated in these deposits. Suevite, characterised by ropy flow textures, and by microclasts of quartz with planar deformation features, planar fractures, and of vesiculated silica glass, was found overlying deformed bedrock at a point where the surface of the bedrock forms a nearly horizontal bench midway up the crater wall. The crater was at least partially filled by later sediments, represented by bedded conglomerate close to the crater wall grading inward to sand, silt and mudstone recovered by drillholes on the crater floor. Some of the talus and conglomerate occupy re-entrants in the crater walls, suggesting an original scalloped outline to the crater. Two drillholes, one central and one halfway to the wall, both reached brecciated sandstone after penetrating 210 m of lake sediments. Goat Paddock has a flat floor with no indication of a central uplift and a depth/diameter ratio of ∼⃒0.073. This crater form, coupled with the modification of the crater walls by slumping and the scalloped outline of the crater rim suggests that Goat Paddock bridges the two traditional classes of impact crater: simple and complex. [ABSTRACT FROM AUTHOR]

Following the Frasnian–Famennian mass extinction, which eliminated most skeletal reef-building fauna, the early Famennian reefs of the Canning Basin were constructed primarily by reef-framework microbial communities. In the Napier and Oscar Ranges, the Famennian reef complexes had high-energy, reef-flat depositional environments on a reef-rimmed platform that transitioned into low-energy, deep-water reefs growing in excess of 50 m below sea level. High-energy, reef-flat depositional environments contain doming fenestral stromatolites that grade into porous thrombolites and are associated with coarse-grained sandstones and grainstones. The reef-margin subfacies contains mounds of microdigitate thrombolites, which are more delicate than the reef-flat thrombolites and locally contain abundant red algae, Girvanella, renalcids and sediment-filled tubes. Within the thrombolites, the red algae are in upright growth positions, suggesting that the thrombolites are largely composed of carbonate that precipitated in situ. Reefal-slope environments are dominated by Wetheredella and Rothpletzella with locally abundant Girvanella, renalcids and Uralinella. In reefal-slope strata, delicate fans and microdigitate stromatolites of Wetheredella and Rothpletzella are often oriented horizontal or diagonal to bedding and are interpreted as syndepositionally toppled over. Most mesoscale microbial community structures contain several species of microbial fossils, and no single microbial species appears to have controlled the morphology of the community structure. Therefore, the depositional environment must have determined the distribution and morphology of the stromatolites, thrombolites and other microbial community structures. The adaptability of microbial communities to various reef environments allowed them to fill ecological niches opportunistically after the Frasnian–Famennian mass extinction. [ABSTRACT FROM AUTHOR]

Intense post-deposited alteration has profoundly affected sandstones in the volcanic portions of Early Archaean (3.5-3.3 Ga) greenstone belts. The mineralogy and bulk compositions of most grains have been completely destroyed by pervasive metasomatism, but grain textures are commonly well preserved. Consequently, microtextural information coupled with present alteration compositions as determined petrographically can be used to estimate original framework modes. Silicified Early Archaean volcaniclastic sandstones assigned to the Panorama Formation and Duffer Formation, Warrawoona Group, eastern Pilbara Block, Western Australia, were originally composed of volcanic (VRF) and sedimentary (SRF) rock fragments, volcanic quartz, feldspar, traces of ferromagnesian minerals and pumice. Only volcanic megaquartz remained stable during alteration. All other primary components were replaced by granular microcrystalline quartz (GMC) and sericite. In most areas, the sandstones were composed of dacitic to rhyolitic VRFs, now totally replaced by sericite-poor GMC and recognized by preserved microporphyritic textures. In a few areas, quartz-poor dacitic to andesitic(?) VRFs dominated the detrital assemblage. Minor SRFs and mafic VRFs, now replaced by GMC, are recognized on the basis of colour, internal structures, and internal textures, including skeletal, possible spinifex textures. Detrital feldspar is represented by blocky, sericite-rich grain pseudomorphs. A semi-quantitative point-count scheme, developed for the analysis of heavily altered sandstones, indicates the following primary detrital-mode ranges for Panorama arenites: quartz, 0-28%; feldspar, 0-28%. VRFs, 58-86%, and SRFs 0-25%. In about half the point-counted samples, feldspar could not be distinguished from rock fragments. In such cases, both were counted as one grain type Lv', which makes up from 84 to 100% of the framework modes of these rocks. These sands were derived from a terrane composed largely of fresh... [ABSTRACT FROM AUTHOR]

Remotely sensed hyperspectral datasets were integrated with petrographic data to map the distribution of sedimentary rocks in order to infer grain size variations within the siliciclastic, Paleoproterozoic Bresnahan Group in Western Australia. Finer sandstones have greater compositional variation compared to coarser sandstones, with higher modal proportions of mudstone intraclasts, K-feldspar, and muscovite laths, and lower modal quartz. Partial Least Squares modelling indicates a link between visible to shortwave infrared spectral data collected on samples and their average grain size. Specific electronic absorptions are important for defining this relationship, particularly in the blue-green visible spectra, wavelengths related to water or hydroxyl bonds, along with certain wavelengths in the shortwave infrared (SWIR) spectra. The results from field samples were compared to airborne hyperspectral datasets which showed broad scale regional variations in composition could be discerned from processed white mica abundance maps and images that use spectral bands 2350 nm and 2200 nm. The remotely sensed compositional variations are relatable to changes in sandstone grain size. Diagenetic alteration and surface weathering may influence the absorption spectra, although the effect of the latter can be reduced by using processed white mica abundance maps. Overall, the results show that airborne hyperspectral datasets, particularly the SWIR part of the spectra, can be useful to remotely map spatial compositional variations associated with sandstone grain size. This shows the method can be used to remotely map siliciclastic successions in other sedimentary basins by aiding recognition of grain size trends and significant stratal surfaces associated with changes in composition. However, the important wavelengths may differ due to other controls on sandstone composition such as uplift history of the source region, changes in sediment dispersal, and transport mechanisms. • Sample spectral data detect compositional change linked to sandstone grain size. • Compositional change with grain size is detected in airborne spectral data. • Study indicates grain size of siliciclastic successions can be remotely inferred. [ABSTRACT FROM AUTHOR]

• Wettability is very sensitive to organic matter even for minute amount. • Organic matter (except kerogen) can be removed from the sample using organic solvents. • Sample cleaning is of particular importance in contact angle characterization. • Increase in CO 2 wettability may affect residual trapping capacities. CO 2 -rock wettability is a key factor which determines the fluid dynamics and CO 2 geo-storage capacity. However, the full understanding of real reservoir CO 2 -wettability is yet to be gained. We thus systematically analysed the wettability of CO 2 /brine/South West Hub sandstones at various pressures (0.1 MPa, 5 MPa, 10 MPa, 15 MPa, and 20 MPa) at 334 K. A new procedure based on organic carbon isotope tracking (δ 13C org) was proposed to eliminate the effect of artificial organic matter introduced by drilling mud penetration. The results indicate that the advancing (θ a) and receding (θ r) water contact angles for the CO 2 /brine/South West Hub sandstone system increase with increase in pressure (ranging from 71° to 118° and 66° to 111°). It can thus be suggested that the system is weakly water-wet to intermediate-wet. When the samples were treated with dichloromethane, a slight decline in organic content was observed leading to slight decrease in water contact angles (i.e. TOC decreased from 0.019% to 0.003% for core C, and the corresponding θ a and θ r decreased from 118° and 111° to 110° and 104°, respectively, at 20 MPa and 334 K). This wettability analysis demonstrates that (a) of the contact angle is very sensitive to the amount of organic matter and therefore care should be taken to remove artificial organic matter from the sample, and that (b) this condition prevails in a real proposed CO 2 -storage site. This analysis thus has important implications for assessing the feasibility of long-term CO 2 storage and enabling large-scale industrial carbon geological storage projects. [ABSTRACT FROM AUTHOR]