Gregory E. Webb

A novel high‐resolution, non‐destructive method for diagenetic screening of fossil corals for geochronologic and paleoclimatic studies using neutron computed tomography (NCT) is proposed. NCT circumvents limitations of traditional techniques, such as destructive sampling and 2‐D imaging by providing detailed 3‐D visualizations of coral structure and carbonate mineral phases. This method differentiates aragonite and calcite phases in fossil coral, crucial for identifying well‐preserved sections suitable for dating and paleoclimatic reconstructions. A key advantage of NCT is its ability to map hydrogen content, providing a reliable indicator for identifying regions of well‐preserved skeletal aragonite, since aragonite typically retains more water organic‐matter than calcite. NCT scans conducted on a Holocene Porites coral (ca. 1.36–1.87 ka BP) from Muschu Island, Papua New Guinea, successfully distinguished between secondary low‐magnesium calcite and aragonite skeletal material. This technique was also applied to an Isopora palifera fossil coral (ca. 39.4 to 44.8 ka BP) from Ashmore Reef, Northwest Shelf, Australia, which presented a more complex diagenetic history. Comparisons were made with results from hyperspectral imaging, X‐Ray CT, scanning electron microscopy, and geochemical and petrological analyses, following calibration using a modern Porites coral from One Tree Reef, Southern Great Barrier Reef, Australia. Additionally, NCT was applied to an altered Acropora humilis coral (ca. 600 ± 280 ka BP) from Ribbon Reef 5, Great Barrier Reef, revealing small, hidden aragonite sections undetected by surficial hyperspectral imaging. This study demonstrates the advantages of combining NCT with traditional screening methods in identifying well‐preserved aragonite for accurate geochronologic and paleoclimatic reconstructions. Recommendations for applying NCT in fossil coral screening are provided.

Coral reefs are among the most important marine habitats but face significant threats from anthropogenic sources, including climate change. This paper reviews and compares the modern Great Barrier Reef Province and the 360-million-year-old Devonian Great Barrier Reef of western Australia. Despite occurring at times with different climates, biota (both marine and terrestrial), weathering processes and marine chemistry, similar reefs were constructed under certain circumstances. Major differences in global temperature, marine carbonate saturation, sea level behavior and reef community constituents were evaluated. The comparison highlights the integration of, and interdependencies within, reef communities and the need for both carbonate producers and significant binders, whether skeletal or microbial, to construct a reef in a high-energy setting. Devonian communities with abundant corals and skeletal sponges were incapable of making modern reef types without competent binders to unify framework into rigid substrate. The current strong focus on corals and bleaching in modern reef conservation may be obscuring the equally significant issue of ocean acidification, which impacts on equally crucial framework unification, i.e., hard binding by coralline algae and microbialites and early cementation. The comparison also supports the idea that ‘empty bucket’ carbonate platform morphologies require increased accommodation from high-amplitude icehouse sea level oscillations.

Context: Examining Australia’s late Quaternary subfossil record can be valuable in assessing whether the current diversity of small-bodied mammals seen across some parts of northern Australia is ‘normal’. Such records are important for establishing baselines for measuring historic changes in communities today and into the future. These datasets are becoming increasingly important, given trajectories in current global climate change, and predicted habitat losses and other potential anthropogenic impacts. Aims: The main aim of this study is to utilise the local subfossil record from north-eastern Australia to establish a natural baseline for assessing changes in small mammal communities post-European colonisation. Methods: Subfossils of vertebrates and other taxa were recovered from surface deposits adjacent to cave entrances at Broken River, near Greenvale in north-eastern Queensland, and were subjected to taxonomic, taphonomic and statistical analyses. These were then compared with local faunal records from modern surveys to compare differences in faunal communities between past and present. Key results: Radiocarbon dating showed that these subfossils are geologically young, dating to approximately the time of European colonisation. We provide evidence for the former presence of extinct species of hopping mice (Notomys spp.) and rabbit rats (Conilurus spp.) in the region. Additional locally extirpated taxa such as Cape York bandicoot (Isoodon peninsulae) and Shark Bay mouse (Pseudomys gouldii) demonstrated considerable range contractions since the deposits accumulated, compared with their current distribution. Independent evidence from subfossil land snails recovered from these deposits is, with two exceptions, all modern-day vine thicket, karst-dwelling species indicating a long-term maintenance of vine thicket habitat. Thus, the loss of several mammal species is unlikely to be the result of habitat loss. Conclusions: Analysis of the surface deposits showed that local historic small-mammal communities were much more diverse than are the region’s extant faunas recorded by modern surveys. Many extinctions and extirpations evidently occurred prior to such faunas being recorded as local inhabitants of the region. Implications: Our data suggested that post-European colonisation small-mammal losses are likely to be substantially worse than previously realised.

Early marine diagenetic processes are affected by a variety of physical, chemical, and biological processes that can alter their composition and properties at micrometre scales, in part due to microbial organisms. Compared to later stage meteoric diagenesis that can be more pervasive in effect but still results in fabric selective textures and heterogeneity at micron to centimeter scales. Diagenetic analyses inform biogeochemical and lithification processes and alteration which affects the reliability of the geochemical data used for paleoenvironmental proxies and isotopic dating to minimize geochemical anomalies. Electron microscopy (EM)-based techniques have been useful as tool to visually demonstrate textures at high resolutions and indicate mineralogy with elemental analysis but have lacked the broad perspective and speed of light microscopy. New-generation EM offers high-quality chemical composition data maps, with the potential to generate mineralogical and textural information over comparable spatial scales. Core material from the Southern Great Barrier Reef, Australia, was used to explore the utility of automated mineral (AM) analysis in characterizing the microtextural, elemental, and mineralogical features in biominerals from Holocene reefs. High-resolution, large-area mapping of carbonate minerals (down to 0.5 μm pixel spacing) was performed using a TESCAN Integrated Mineral Analyzer (TIMA) Field Emission Scanning Electron Microscope at the Central Analytical Research Facility, QUT (Brisbane, Australia). The combined use of back-scattered electron (BSE) imagery and multiple EDX detectors provided detailed insights into both textural and compositional aspects of the samples, aiding in phase differentiation across various cements and skeletal components. BSE allowed for precise visualization of microtextural features, while EDX enabled rapid, fine-scale collection of spectral data to confirm elemental composition and mineral phases with minimal surface damage to beam-sensitive materials. Collected spectra were used to confirm the presence of elements and mineral phases.

Late Pleistocene to Holocene-aged microfaunal assemblages are rarely reported in Australia despite their critical importance for palaeoecological studies, as well as their bearing on the megafaunal extinction debate. Capricorn Caves, central-eastern Queensland, hosts three Late Pleistocene to Holocene deposits containing significant faunal records. Excavations were conducted on these deposits over several seasons, with analyses of recovered material ongoing. Here, we report interim results and explore their implications for our understanding of the microfaunal record of central eastern Queensland. Fern Chamber was previously dated using U-series to the Holocene (>7.6 ± 0.2 ka). Honeymoon Suite was dated to >6.4 ± 0.2 ka using U-series. However, new charcoal dates from the deposit span approximately 7.5–15.5 ka, although the association between charcoal and fauna is unresolved. The fauna is likely Holocene. Colosseum Chamber is the oldest of the deposits, and new single-grain luminescence ages and age-depth modelling suggest that the deposit likely spans MIS 1–4. We use abundant fragmentary rodent remains to examine palaeoenvironmental change over this period. Carbon and oxygen isotope analyses of rodent incisor fragments reveal broad diets within the rodent community, and significant differences in precipitation between glacial and interglacial conditions. Rodent long bone histological analyses indicate significant differences in bone metabolism at the family level between the MIS 3 and 2 samples, but not MIS 1. We suggest that these data support evidence for a mid-Holocene arid anomaly in the region, and increased aridity through the Holocene relative to the terminal Pleistocene. The sites contain at least 10 small mammal species either globally extinct or locally extirpated, including the Capricorn rabbit-rat (Conilurus capricornensis), the white-footed rabbit-rat (Conilurus albipes), the plains mouse (Pseudomys australis), Gould’s mouse (Pseudomys gouldii), Forrest’s mouse (Leggadina forresti), the long-tailed hopping mouse (Notomys longicaudatus), swamp rat (Rattus lutreolus), the white-tailed rat (Uromys caudimaculatus), the narrow-nosed planigale (Planigale tenuirostris), the Liverpool Plains striped bandicoot (Perameles fasciata), the Cape York brown bandicoot (Isoodon peninsulae), and the southern brown bandicoot (Isoodon obesulus). We also record significant range contractions for frogs (Philoria sp., Neobatrachus sp.) and earless dragons (Tympanocryptis sp.). This study demonstrates that significant changes in the microfaunal community of tropical Queensland occurred between the Late Pleistocene and the late Holocene. It also reinforces how poorly recorded native faunas are from the late Holocene through the historical period, to today. Such records underpin and are thus vital for modern biodiversity conservation efforts. Julien Louys [j.louys@griffith.edu.au], Australian Research Centre for Human Evolution, Griffith University, Brisbane, Australia; Jonathan Cramb [jonathan.cramb@qm.qld.gov.au], Queensland Museum, Brisbane, Australia; Kyle Ferguson [k.ferguson81@outlook.com.au], School of Earth and Environmental Science, The University of Queensland, Brisbane, Australia; Justine Kemp [j.kemp@griffith.edu.au], Australian Research Centre for Human Evolution, Griffith University, Brisbane, Australia; Rachel Wood [rachel.wood@arch.ox.ac.uk], School of Archaeology and Anthropology, Australian National University, Canberra, Australia and Oxford Radiocarbon Accelerator Unit (ORAU), University of Oxford, Oxford, UK; Justyna J. Miszkiewicz [j.miszkiewicz@uq.edu.au], School of Social Science, University of Queensland, Brisbane, Australia and Naturalis Biodiversity Center, Leiden, the Netherlands; Nathalia R. Dias Guimarães [ndg0601@gmail.com], School of Archaeology and Anthropology, Australian National University, Canberra, Australia; Penny Higgins [pennilyn.higgins@gmail.com], EPOCH Isotopes, 6606 E Townline Road, Williamson, NY 14589, USA; Kenny J. Travouillon [Kenny.Travouillon@museum.wa.gov.au], Western Australian Museum, Perth, Australia; Scott A. Hocknull [scott.hocknull@qm.qld.gov.au], Geosciences, Queensland Museum, Brisbane, Australia; Gregory E. Webb [g.webb@uq.edu.au], School of Earth and Environmental Science, The University of Queensland, Brisbane, Australia; Gilbert J. Price [g.price1@uq.edu.au], School of Earth and Environmental Science, The University of Queensland, Brisbane, Australia.

We employ high-throughput thermal-neutron tomographic imaging to visualise internal diagnostic features of dense fossiliferous breccia from three Pleistocene cave localities in Sumatra, Indonesia. We demonstrate that these seemingly homogeneous breccias are an excellent source of data to aid in determining taphonomic and depositional histories of complex depositional sites such as tropical caves. X-ray Computed Tomographic (CT) imaging is gaining importance amongst palaeontologists as a non-destructive approach to studying fossil remains. Traditional methods of fossil preparation risk damage to the specimen and may destroy contextual evidence in the surrounding matrix. CT imaging can reveal the internal composition and structure of fossils contained within consolidated sediment/rock matrices prior to any destructive mechanical or chemical preparation. Neutron computed tomography (NCT) provides an alternative contrast to X-rays, and in some circumstances, is capable of discerning denser matrices impenetrable to or yielding no contrast with CT imaging. High-throughput neutron imaging reduces neutron fluence during scanning which means there is less residual neutron-induced radioactivation in geological samples; allowing for earlier subsequent analyses. However, this approach remains unutilised in palaeontology, archaeology or geological surveys. Results suggest that the primary agents in the formation of the breccias and concentration of incorporated vertebrate remains are several rapid depositional phases of water and sediment gravity flow. This study highlights the potential for future analyses of breccia deposits in palaeontological studies in caves around the world.

Measuring the amount of carbon captured in deep-sea limestones is fundamental to understanding the long-term carbon cycle because pelagic limestones represent Earth’s largest carbon sink since the mid-Mesozoic. However, their contribution to the long-term carbon cycle is poorly quantified. Here, we use X-ray fluorescence and scanning X-ray diffraction microscopy for high-resolution chemical and structural analysis of pelagic limestone from the Paleocene Kaiwhata Formation in New Zealand. We identify densely packed diagenetic micro-dissolution seams that are invisible to light and electron-beam microscopes in most cases. Mass-balance calculations indicate that individual seams remove ~50% of the calcite mud matrix while their bulk-sample carbon loss adds up to ~10%. The liberated carbon is trapped in situ as calcite cement or returned to the ocean during physical compaction or soft-sediment deformation. We suggest micro-dissolution structures may play an important role in the long-term carbon cycle by modulating carbon exchange between the geosphere and hydrosphere.

Taxonomic utility of Early Cretaceous Australian plesiosaurian vertebrae