Sydney Basin Research Articles

Severe and Short Interval Fires Rearrange Dry Forest Fuel Arrays in South-Eastern Australia

Fire regimes have shaped extant vegetation communities, and subsequently fuel arrays, in fire-prone landscapes. Understanding how resilient fuel arrays are to fire regime attributes will be key for future fire management actions, given global fire regime shifts. We use a network of 63-field sites across the Sydney Basin Bioregion (Australia) to quantify how fire interval (short: last three fires <10 years apart, long: last two fires >10 years apart) and severity (low: understorey canopy scorched, high: understorey and overstorey canopy scorched), impacted fuel attribute values 2.5 years after Australia’s 2019–2020 Black Summer fires. Tree bark fuel hazard, herbaceous (near-surface fuels; grasses, sedges <50 cm height) fuel hazard, and ground litter (surface fuels) fuel cover and load were higher in areas burned by low- rather than high-severity fire. Conversely, midstorey (elevated fuels: shrubs, trees 50 cm–200 m in height) fuel cover and hazard were higher in areas burned by high- rather than low-severity fire. Elevated fuel cover, vertical connectivity, height and fuel hazard were also higher at long rather than short fire intervals. Our results provide strong evidence that fire regimes rearrange fuel arrays in the years following fire, which suggests that future fire regime shifts may alter fuel states, with important implications for fuel and fire management.

First Nations pre‐LGM ochre processing in Parramatta, NSW, Australia

ABSTRACTPrevious archaeological evidence and published analysis has suggested that ochre was first used in the Sydney Basin around 9000 years ago, and that the Parramatta region may not have been occupied by First Nations peoples before ∼14 ka. We present new evidence which firmly places both events before the Last Glacial Maximum (LGM). Multiple ochre fragments, two with microscopically visible evidence of anthropogenic grinding, were recovered from the George Street Gatehouse site within the Parramatta Sand Body (PSB) at Parramatta. The ground ochre was associated with a pit feature buried within the PSB and dated by optically stimulated luminescence (OSL) between ∼35 and 30 ka. This find is the earliest evidence for ochre processing in the Sydney Basin by some 25000 years. A previous model for the region had proposed that occupation prior to and during the LGM was focussed on the Hawkesbury‐Nepean River corridor as a refugium, with only equivocal evidence of occupation prior to ∼14 ka at Parramatta (Williams et al., 2021). We propose that the Parramatta River could also have acted as a refugium for people moving through and occupying the now‐drowned Pleistocene coastal zone; and that those people used ochre in their symbolic expressions.

Changes in Fe-redox and Fe-species across the end-Permian ‘Dead Zone’ in the Sydney Basin, Australia (252.10 ± 0.06 Ma): Evidence from X-ray absorption spectroscopy

The end-Permian mass extinction event is traceable across several non-marine basins in Australia. In the Sydney Basin, the lithological succession is characterized by a change from coal seams to mudstones and sandstones, recording a major environmental change following the disappearance of the Permian vegetation. A few millimeter-thick iron-rich ‘rusty’ layer occurs between the uppermost Permian coal seam and the mudstone, a layer that extends laterally across the basin and which has also been documented from coeval successions in Antarctica. This layer is overlain by the <1.5-m-thick Frazer Beach Member, whose basal 10-cm-thick microbreccia bed comprises 99% kaolinite and quartz, and is dated as 252.10 ± 0.06 Ma. The Frazer Beach Member corresponds to the so-called end-Permian ‘Dead Zone’ lacking fossil pollen and leaves. This distinctive member was deposited directly following the extinction of the Permian peat-forming forests.Here we identify, through X-ray absorption spectroscopy, a drastic redox shift across the extinction interval with increasing amount of reduced Fe-species followed by highly oxidized Fe-species, most resembling Fe(III) complexed with organic matter. Values subsequently normalise in younger samples through the ‘Dead Zone’, attaining only slightly higher redox-levels than before the event. The organically complexed Fe-species in the event bed is consistent with the standard Suwannee River fulvic acid, an acid Fe-complex with iron bound to organic matter, whereas the samples above and below the extinction layer yield spectra predominantly resembling magnetite (Fe3O4) mineral phase. We consider that the iron redox fluctuation marking the extinction interval is related to significant environmental changes with accumulation of organic matter following the mass extinction. The highly reduced iron in the extinction layer may relate to methane release from bacterial degradation, or emissions from clathrates. The presence of fulvic acid in the distinct iron-rich extinction layer indicates that an abrupt onset of the process of degradation of plant matter, lipids and calcium hydroxide (CaOH) took place, resulting in this ‘Death layer’. This was followed by millions of years of erosive conditions before new, complex vegetation could establish.

End-Permian marine ecosystem collapse was a direct consequence of deforestation: Evidence from the Kockatea Shale of the Perth Basin, Western Australia

The end-Permian mass extinction event resulted in devastated continental biomes, desolated land, and toxic waters. Anoxia led to widespread extinctions in marine ecosystems, affecting most oceanic clades. In this paper, the palynofacies of the marine Kockatea Shale, Western Australia, was studied in drill cores Hovea-3 and Redback-2, with the aim of linking changes in the marine and continental realms across the Permian–Triassic boundary interval in Australia. We show that the post-extinction ‘Dead Zone’ of the Frazer Beach Member of the Sydney Basin, eastern Australia, whose base is dated to 252.10 ± 0.06 Ma, directly correlates to the lower part of the Kockatea Shale in the Perth Basin, the so-called Inertinitic Interval. We demonstrate that the extinction of Permian Glossopteris forests observed in the Perth Basin had an immediate impact on the marine faunas due to the massive buildup of organic matter, leading to euxinia in the photic zone and ultimately pushing the marine faunas to an ecological extinction. The last lingering occurrence of marine invertebrates of Permian aspect occur in layers that may tentatively mark the Permian–Triassic boundary, positioned just below the appearance of Triassic floras of the Kraeuselisporites saeptatus Zone (equivalent to the Lunatisporites pellucidus Zone). A striking feature at the base of the Early Triassic Sapropelic Interval of the Hovea Member is the sudden and synchronous appearances of anomalously abundant acritarchs and lycophyte spores, alongside the mass occurrence of the bivalve Claraia, allowing correlation with the rise of the eastern Australian post-extinction pioneer floras in the Early Triassic. This demonstrates a significant lag time between the recovery of the terrestrial versus the marine pioneer biota in high-latitude Gondwana, with a significant delay for the faunal recovery.

Multivariate examination of the sediment-deficient southeast Australian continental shelf

Continental shelves are the most morphologically variable element within the source-to-sink system owing to the numerous processes that influence their formation. A recent multivariate analysis of a global compilation of modern continental shelf data showed that much of the variability is related to tectonic setting, the degree to which the shelf has been glaciated, and carbonate production. While these factors play first-order roles in determining the morphology of shelves, other controlling mechanisms such as siliciclastic sediment supply, wave and tidal energy, bedrock lithology, and sea-level fluctuations are not as well understood. Here, we report findings from a detailed investigation of the southeast Australian shelf that explored how sediment distribution, wave energy, and bedrock lithology influence shelf morphology. The high-resolution analysis suggests that the southeast Australian shelf has 11 distinct shelf types. No strong relationships exist between the shelf attributes or shelf type with their onshore catchments. However, a substantial section boundary correlates with a bedrock contact between the Sydney Basin in the south and the New England Orogen to the north. South of this boundary, we propose that the shelf morphology reflects transgression with low sediment supply, whereas to the north, the morphology reflects transgression with higher sediment input. Although several factors contributed to this difference in shelf morphology, we suggest that sediment distribution and retention due to the active wave climate during the most recent transgression likely played a vital role.

The Sydney Basin in the Triassic—a review of the geology, flora and fauna, and ecosystems. The Narrabeen Group

The aim of this report is to provide a framework within which future earth science researchers of the Sydney Basin in the Triassic Period can work to rapidly access information relevant to their particular field of study. Information on the geology, flora and fauna and ecosystems has been extracted and summarized from an extensive range of papers published from the late 1800s to present day. In many cases the taxonomic classification of specimens has changed over the years as more data has come to light. The history of these changes has been noted. This information is backed by specimen lists and illustrated by images of selected specimens sourced from the extensive palaeontological collection of the Australian Museum, augmented by additional images from the collection of the Geological Survey of New South Wales. The major Triassic geological structures of the Sydney Basin are the Narrabeen Group, the Hawkesbury Sandstone and the Wianamatta Group. This report provides a consolidated review of data presently available for the Narrabeen Group. Future reports will cover the Hawkesbury Sandstone and the Wianamatta Group in a similar manner.

In-situ gas contents of a multi-section coal seam in Sydney basin for coal and gas outburst management

The gas content is crucial for evaluating coal and gas outburst potential in underground coal mining. This study focuses on investigating the in-situ coal seam gas content and gas sorption capacity in a representative coal seam with multiple sections (A1, A2, and A3) in the Sydney basin, where the CO2 composition exceeds 90%. The fast direct desorption method and associated devices were described in detail and employed to measure the in-situ gas components (Q1, Q2, and Q3) of the coal seam. The results show that in-situ total gas content (QT) ranges from 9.48 m3/t for the A2 section to 14.80 m3/t for the A3 section, surpassing the Level 2 outburst threshold limit value, thereby necessitating gas drainage measures. Among the gas components, Q2 demonstrates the highest contribution to QT, ranging between 55% and 70%. Furthermore, high-pressure isothermal gas sorption experiments were conducted on coal samples from each seam section to explore their gas sorption capacity. The Langmuir model accurately characterizes CO2 sorption behavior, with fit coefficients (R2) greater than 0.99. Strong positive correlations are observed between in-situ gas content and Langmuir volume, as well as between residual gas content (Q3) and sorption hysteresis. Notably, the A3 seam section is proved to have a higher outburst propensity due to its higher Q1 and Q2 gas contents, lower sorption hysteresis, and reduced coal toughness f value. The insights derived from the study can contribute to the development of effective gas management strategies and enhance the safety and efficiency of coal mining operations.

Provenance of a Late Permian retroarc foreland basin along the eastern Gondwanan margin: northern Sydney Basin, eastern Australia

Abstract The Upper Permian sedimentary successions in the northern Sydney Basin have been the subject of several stratigraphic, sedimentological and coal petrographic studies, and recently, extensive U-Pb zircon dating has been carried out on tuffs in the Newcastle Coal Measures. However, detailed petrographic and geochemical studies of these successions are lacking. These are important because a major change in tectonic setting occurred prior to the Late Permian because of the Hunter-Bowen Orogeny that caused the uplift of the Carboniferous and Devonian successions in the Tamworth Group and Tablelands Complex adjacent to the Sydney Basin. This should be reflected in the detrital makeup of the Upper Permian rocks. This study provides data that confirms major changes did take place at this time. Petrographic analysis indicates that the source area is composed of sedimentary, felsic volcanic and plutonic and low-grade metamorphic rocks. Conglomerate clast composition analysis confirms these results, revealing a source region that is composed of felsic volcanics, cherts, mudstones and sandstones. Geochemical analysis suggests that the sediments are geochemically mature and have undergone a moderate degree of weathering. The provenance data presented in this paper indicate that the southern New England Orogen is the principal source of detritus in the basin. Discrimination diagrams confirm that the source rocks derive from an arc-related, contractional setting and agree with the provenance analyses that indicate sediment deposition in a retroarc foreland basin. This study offers new insights on the provenance and tectonic setting of the Northern Sydney Basin, eastern Australia.

An Aboriginal presence in the Sydney basin prior to the LGM; further investigations into the age and formation of the Parramatta Sand Body

The Parramatta Sand Body (PSB) in Parramatta, New South Wales, Australia is an ancient sedimentary sand deposit bordering parts of the Parramatta River which today flows into Sydney Harbour. Whilst the lower portions of the sand deposit pre-date human occupation, some locations with near surface sand deposits contain dense Aboriginal archaeological sites with a profusion of stone tools and remains of hearths. We explored the timing of human occupation in Parramatta by applying optically stimulated luminescence (OSL) ages to archaeological evidence from site AT14. Interpretation of the OSL data was guided by particle size analysis and the resulting age estimates agreed with the radiocarbon dating of charcoal sampled from archaeological deposits at AT14, to provide a secure age for human occupation evidence in the Sydney region at 31 ± 2 ka. Results link the single grain overdispersion found in quartz OSL samples to trampling actions resultant of Aboriginal occupation and forms a future consideration for the effective dating of archaeological sites.

Wildfire and Climate Impacts Tree Hollow Density in a Temperate Australian Forest

Tree hollows are an important landscape resource used by fauna for shelter, nesting, and predator avoidance. In fire-prone landscapes, wildfire and climate may impact hollow dynamics; however, assessments of their concurrent impacts are rare. We conducted a field survey at 80 sites in the Sydney Basin bioregion (Australia) to understand how fire frequency, fire severity, mean annual temperature, and mean annual precipitation concurrently impacted the site-density of small- (&lt;5 cm entry width), medium- (5–10 cm entry width) and large-size (&gt;10 cm entry width) tree hollows and tree basal scars (which mediate hollow formation via invertebrate access to heartwood), when tree-size and dead/live status were considered. A unimodal relationship occurred between medium- and large-sized hollow densities and fire frequency and severity, respectively, with hollow densities greatest at intermediate frequencies/severities. Increases of 1.82, 1.43, and 1.17 hollows per site were observed between the 1 (reference) and 2, 2 and 3, and 3 and &gt;3 fire frequency categories. Increases of 1.26, 1.75 and 0.75 hollows per site were observed between the low (reference) and moderate, moderate and high, and high and very high fire severity categories. Fire severity was also positively associated with basal scar density, with increases of 2.52, 8.15, and 8.47 trees per site between the low (reference) and moderate, moderate and high, and high and very high categories. A weak positive and stronger negative association was observed between mean annual temperature and small-sized hollow and basal scar density, respectively. Dead and medium-sized tree density was positively associated with medium-sized hollow and basal scar tree density, respectively. Collectively, our results suggest that wildfires, and in some cases climate, have diverse and size-specific impacts on tree hollow and basal scar density. Our results imply that fire regimes that allow for moderately severe wildfire will promote larger-sized tree hollows, which are a limiting resource for many fauna species.

Limited change in silicate chemical weathering intensity during the Permian–Triassic transition indicates ineffective climate regulation by weathering feedbacks

Vast emissions of volcanogenic greenhouse gases resulted in rapid global warming during the latest Permian mass extinction (LPME, ∼252 Ma), the impact of which on continental chemical weathering conditions was complex. Here, we compile Chemical Index of Alteration (CIA) records from 25 terrestrial and 12 marine sections with a near-global paleogeographic distribution to reconstruct the evolution of chemical weathering intensity of silicates during the LPME. This compilation shows that the CIA profiles, except those from the Australian Sydney and Bowen basins of the high-latitude Southern Hemisphere, exhibit either indiscernible changes or decreases through the LPME interval, contrary to previous inferences of increased silicate chemical weathering intensity. The lack of major changes in silicate chemical weathering intensity is further supported by the near uniformity of clay mineral assemblages through the LPME interval, with only minor increases of illite and chlorite and, if present, decreases in kaolinite content in some terrestrial sections. We infer a shift from dominantly transport-limited to kinetic-limited weathering regimes, likely caused by environmental climate factors such as widespread devegetation, river-flow changes (i.e., toward flashier and more intense discharge), and aridification during the earliest Triassic that effectively reduced water availability on land for water/rock reactions. Combined with limited changes in chemical weathering fluxes from previous estimates, our data imply possibly ineffective climate regulation by silicate chemical weathering at a (near-)global scale, despite high erosion rates, amid the intense global warming that followed the LPME.

The organic geochemistry of Permian high latitude sediments in two boreholes in the southern Sydney Basin, New South Wales, Australia

Twenty six samples of Permian high latitude sedimentary rocks from the southern Sydney Basin were analysed using organic geochemical methods for their thermal maturity, organic matter inputs, and depositional environment. Fourteen samples are from the Elecom Clyde River (ECR) DDH01 borehole (inland; Southern Highlands), and 12 are from the ECR-DDH07 borehole (coastal; near Nowra). The analysed formations are the Berry Siltstone, the Nowra Sandstone, the Wandrawandian Siltstone, the Snapper Point Formation and the Pebbley Beach Formation. This study is the first organic geochemical study of samples from the Berry Siltstone and Nowra Sandstone. The formations mostly have total organic carbon varying from 1 to 2 wt%, but the Snapper Point Formation is leaner in TOC (0.2–0.7 wt%). The samples vary from low to very high thermal maturity. The samples from the ECR-DDH01 borehole are in the early to middle of the oil window (vitrinite reflectance equivalent = 0.60–0.80%), based on hopane, sterane, alkylnaphthalene, alkylphenanthrene, alkylbiphenyl, and alkyldibenzothiophene thermal maturity parameters. The samples from the ECR-DDH07 borehole are much more thermally mature, in the late part of the oil window to the early gas window (vitrinite reflectance equivalent = 1.2–1.7%). This high thermal maturity has led to the loss of nearly all polycyclic biomarkers, and the thermal rearrangement of many groups of compounds, including monomethylalkanes. The ECR-DDH01 borehole location and time-equivalent outcrop samples south-west of Ulladulla have similar thermal maturities and are close to the margins of the Sydney Basin, and it is estimated to have previously been covered by about 3 km of overburden. In contrast, the samples in the ECR-DDH07 borehole were buried much deeper, with about 4–5 km of overburden, which means that only limited information about their source inputs and depositional environment could be recovered. Aliphatic biomarker, n-alkane and aromatic data are consistent with an overall strong terrigenous organic matter input for the samples from the ECR-DDH01 borehole. Sterane/hopane ratios are mostly low, but only a few compounds diagnostic of specific source inputs were identified. There is a microbially-dominated sample near the base of the Snapper Point Formation (high C29 αβ hopane/C30 αβ hopane ratio and 2α-methylhopanes), and high amounts of parent polycyclic aromatic hydrocarbons in some samples from the Berry Siltstone, likely reflecting an occasional pyrogenic signature from palaeo-forest fires. Several parameters, including sterane carbon number distributions, terpane ratios and the relative abundance of dibenzofuran compared to phenanthrene show that the samples from the ECR-DDH01 borehole have a more strongly terrigenous signal than the previously analysed outcrop samples. This is inferred to be because the ECR-DDH01 location was closer to the palaeo-shoreline than the likely more distal outcrop samples. Based on the pristane/phytane ratio and hopane distributions, deposition of the sediments was under varying oxicity conditions, from highly oxic to suboxic. The inferred environments are marine shale/lacustrine and fluvial/deltaic, so the organic geochemical data agrees with the Permian depositional history of the southmost part of the Sydney Basin previously inferred from sedimentological and palaeogeographic studies.

Structural characterization and mass spectrometry fragmentation signatures of macrocyclic alkanes isolated from a Sydney Basin torbanite, Australia

Structural characterization and mass spectrometry fragmentation signatures of macrocyclic alkanes isolated from a Sydney Basin torbanite, Australia

Reproductive characteristics, population genetics, and pairwise kinship inform strategic recovery of a plant species in a fragmented landscape

AbstractPopulation genetics and understanding of mating systems provide fundamental information for conservation planning. Pairing these methods is a powerful tool in the study of threatened species, however, they are rarely applied in concert. We examined the mating system and used molecular genetics to measure pairwise kinship and the potential for inbreeding inHibbertia spanantha, a critically endangered long‐lived shrub endemic to the Sydney Basin, Australia, as a model for conservation planning of species in highly fragmented populations. In situ hand pollination experiments demonstrated that the species is preferentially outcrossing, with limited ability to self‐pollinate (either autogamously or geitonogamously). Although population genetics confirmed high levels of kinship and clonality, there is currently enough population heterozygosity for successful open pollination, primarily through buzz pollination by Sweat Bees (Lasioglossum [Chilalictus]). High levels of clonality and population kinship in one population may be the cause of reduced fitness, identified because our outcrossing pollination treatment produced significantly more seeds with greater viability and seed mass than the open treatments. Differences in weight of filled (viable) seeds were identified between populations, although not treatments, where clonal dominance may be swamping pollinator foraging activities. Identification of species mating system, population reproductive capacity, and impacts of fragmentation on population genetic health provides a robust basis for strategic planning and conservation of this critically endangered species, including establishment of an ex situ population and genetic rescue through population augmentation. These methods are easily applicable and particularly relevant to other plant species with small populations or those occurring in fragmented systems.

Mercury evidence from southern Pangea terrestrial sections for end-Permian global volcanic effects

The latest Permian mass extinction (LPME) was triggered by magmatism of the Siberian Traps Large Igneous Province (STLIP), which left an extensive record of sedimentary Hg anomalies at Northern Hemisphere and tropical sites. Here, we present Hg records from terrestrial sites in southern Pangea, nearly antipodal to contemporaneous STLIP activity, providing insights into the global distribution of volcanogenic Hg during this event and its environmental processing. These profiles (two from Karoo Basin, South Africa; two from Sydney Basin, Australia) exhibit significant Hg enrichments within the uppermost Permian extinction interval as well as positive Δ199Hg excursions (to ~0.3‰), providing evidence of long-distance atmospheric transfer of volcanogenic Hg. These results demonstrate the far-reaching effects of the Siberian Traps as well as refine stratigraphic placement of the LPME interval in the Karoo Basin at a temporal resolution of ~105 years based on global isochronism of volcanogenic Hg anomalies.

Kungurian (Cisuralian/Early Permian) brachiopods from the Snapper Point Formation, southern Sydney Basin, southeastern Australia

Elements of a high-latitude (∼60–70°S) and low-diversity early Kungurian (Cisuralian/Early Permian) brachiopod fauna have been sporadically reported from the sandstone-dominated Snapper Point Formation (SPF) in the southern Sydney Basin of southeastern Australia for more than a half-century, but a detailed description of this fauna is not yet available. In this paper we describe 12 brachiopod species and an indeterminate ingelarellid from the SPF, including one new species (Tasmanospirifer jervisbayensis sp. nov. Waterhouse & Lee). Though this brachiopod fauna is evidently associated with an interglacial stratigraphic interval, its taxonomic characteristics overall resemble those from stratigraphically bounding glacial intervals. This association is interpreted to indicate persistence and the strong endemic nature of the Permian Eastern Australian biogeographic province in high-latitude eastern Gondwana, regardless of glacial/interglacial climate states during the Cisuralian. Biostratigraphically, the SPF brachiopod fauna is divisible into two distinctive stratigraphic assemblages: the Notospirifer cf. triplicata–Simplicisulcus sp. Assemblage in the lower part of the formation and the Johndearia brevis–Sulciplica transversa Assemblage in the upper part, each distinguished by a set of unique species. Sangmin Lee [sangminlee76@gmail.com] and G. R. Shi [guang@uow.edu.au] School of Earth, Atmospheric and Life Sciences, University of Wollongong Faculty of Science Medicine and Health, Northfields Avenue, Wollongong, NSW 2522, Australia Bruce Runnegar [runnegar@ucla.edu] Earth, Planetary and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095-1567, USA J. B. Waterhouse [permia@xtra.co.nz] Oamaru, Oamaru, New Zealand.

Indigenous Knowledge of seasons delivers a new way of considering annual cycles in atmospheric dispersion of pollutants

Poor air quality is recognised as the most important environmental health issue of our time. Meteorological variables like temperature and wind speed can strongly influence air quality and these variables often show clear annual cycles. It is therefore common to analyse atmospheric pollutants within a seasonal framework. However, the commonly used seasons in Australia do not align well with all of the most important annual weather patterns that influence air quality in the Sydney Basin. We used Indigenous perspectives on ‘seasons’ as identified by the co-authors and combined these with statistical analysis of the local climatology. This enabled us to create a set of locally informed ‘quasi-seasons’ that we named IKALC-seasons (Indigenous Knowledge Applied to Local Climatology). Engaging with the IKALC-seasons improved our understanding of temporal variability of air pollution in western Sydney, mainly due to a better identification of the time of year when cold, still weather conditions result in higher levels of fine particulate pollution, carbon monoxide and nitrogen oxides. Although the IKALC seasons identified in this study are intrinsically local in nature, the methodology developed has broadscale application. This approach can be used to identify the times of year when micrometeorological conditions are most likely to drive poor air quality thereby helping to inform effective decision-making about emission controls.

A new chigutisaurid (Brachyopoidea, Temnospondyli) with soft tissue preservation from the Triassic Sydney Basin, New South Wales, Australia

ABSTRACT Compared with other Mesozoic tetrapod groups, chigutisaurid fossils from Australia are rare, with only three named taxa described from the continent. From Queensland, Keratobrachyops australis is known from the Triassic, and Siderops kehli from the Jurassic. Koolasuchus cleelandi, from the Cretaceous of Victoria, represents the youngest-known temnospondyl globally. Here we describe the first chigutisaurid from New South Wales, from the Early–Middle Triassic Terrigal Formation. The specimen (AM F125866) comprises an articulated, near-complete skeleton, presented in ventral aspect, as well as outlines of soft tissue. The new taxon preserves features that indicate an affinity with Chigutisauridae, confirming previous hypotheses on the presence of large-bodied chigutisaurids in the Triassic of Australia. The new Terrigal chigutisaurid is only the second chigutisaurid known from the Lower Triassic and fourth from Australia overall. The distribution of brachycephalic temnospondyls throughout the Mesozoic suggests specific adaptations led to the long-term survival of chigutisaurids, especially across the end-Triassic extinction event.

Segmentation and fault–monocline relationships in the Lapstone Structural Complex, Sydney Basin, New South Wales

The 95 km-long Lapstone Structural Complex is a segmented structural association consisting of north-trending faults and monoclines in the western Sydney Basin between the Cumberland Basin to the east and lower Blue Mountains to the west. It has developed in a compressional regime. At depth, the Lapstone Structural Complex is most likely a deeply penetrating, west-dipping thrust fault that is seismogenic in the brittle middle crust. This structure has propagated upwards into the overlying Sydney Basin in the top ∼3 km of the crust and formed a suite of distinct fault and fault–monocline structures, including: (a) in the north, inferred imbricate faults at depth in the lower Sydney Basin dying out upwards into a well-displayed, major east-facing monocline (central limb has an overall consistent <20°E dip); (b) in the middle part of the complex, an east-facing monocline with dips increasing from west to east formed as a fault-propagation fold; and (c) as found in the south, a single thrust fault (Bargo and Nepean faults). The complex has a probable late Cenozoic age and has played a role in landscape development as shown by topography, uplifted river gravels and knick points along lower order streams. Therefore, it has formed late in the uplift history of the southeastern Australian highlands postdating uplift in the Cretaceous and uplift associated with basaltic eruptions in the Cenozoic. KEY POINTS The Lapstone Structural Complex is an association of segmented faults and monoclines formed at the tip of a deep-seated thrust fault. The largest structure in the complex is a gently east-dipping monocline formed above an inferred imbricate fault system in the lower Sydney Basin succession. Much of the middle and southern parts of the complex are single faults and a fault-propagation monocline related to a thrust fault at depth. The Lapstone Structural Complex is of late Cenozoic age and is most likely seismogenic.

The Hornsby Quarry Geosite, NSW, Australia—A Geoheritage Treasure

Quarrying for aggregate material at Hornsby in New South Wales (Australia) exposed a &gt;100 m-deep cross-section of the volcanic neck of a Jurassic diatreme, which extruded through the Sydney Basin deposits. The cross-section reveals volcanic features at many scales. Globally, there are very few instances of such excellent 3D exposure. It is arguable that this exposure alone makes it a geosite of international value. However, evaluation of the Hornsby Diatreme using a geoheritage toolkit shows that it meets various geoheritage conservation criteria, being a reference site, and an historically and culturally important site, as well as hosting important archival material. It has significant features at various scales: at the macroscale, where dish beds are visible on all quarry walls, preserving the structure formed during volcanic accretion and later caldera collapse; at the mesoscale, where breccia and surge layers are visible, providing insight into how magma interacted with various host rock types; and at the microscale, where lapilli, chilled margins on host rock blocks, and carbon-rich xenoliths are visible in hand specimens. As such, the Hornsby Quarry hosts a world-class array of volcanic features and preserves an important period of volcanic and post-volcanic history within the Sydney Basin, fostering geoeducation and geotourism.