Search

The extinction of large-bodied terrestrial ‘megafauna’ during earlier phases of the Quaternary had a significant impact on the transforming structure of ecosystems. However, the causes of such losses remains difficult to determine in part because of a paucity of reliable geochronological information about the taxa involved. This is especially true for continents such as Australia where the majority of extinct species have never been dated using radiometric and/or luminescence methods. Here we add new understanding about the geochronology of the world's largest-ever marsupial, the giant wombat-like Diprotodon optatum, an iconic member of the large herbivore guild of Pleistocene Australia. We present 28 new direct U-series ages (dentine) and 10 luminescence ages (sediments) for D. optatum fossils from three sites in tropical north and subtropical eastern Australia. The luminescence ages lie close to saturation for the tropical northern site of Floraville and therefore indicate minimum ages, and sediments from Gowrie Creek in the Darling Downs were mixed and can only be stated as a likely age range. Nevertheless the results assist in our broader understanding of the timing of persistence of the species. Our results demonstrate that the species roamed the northern tropics at least until the mid-Pleistocene (ca. 420 ka). They likely remained widespread during Marine Isotope Stage 5 (ca. 110 ka) and were abundant on the Darling Downs of eastern Australia. The youngest of the new ages that we report (ca. 60 ka) are from Neds Gully on the Darling Downs, a catchment previously considered by some to contain among the last survivors of the now-extinct megafauna. The new dated record demonstrates that deposits of varying ages occur within the catchment. Consequently, existing species lists that treat Neds Gully as a single faunal assemblage are likely significantly time-averaged and overinflated in terms of palaeo-diversity.

Degradation of inshore water quality associated with catchment modification is threatening global coral reef ecosystems. Coral trace element proxies are widely applied to document the magnitude and timing of historical changes in river runoff and other disturbances. However, conflicting interpretations of commonly used coral proxies (Ba/Ca, Y/Ca and Mn/Ca) complicate their application for examining historical changes in coastal water quality. The exploration of other coral trace element proxies (such as rare earth elements, REE) is limited in space and time, and to few coral genera. This study examined the dynamics of dissolved REE and yttrium (REEY) in the Fitzroy and Burdekin river tributaries and estuaries, Queensland, Australia. In addition, monthly-resolution long-term temporal records of Ba/Ca, Mn/Ca, Y/Ca and REEY proxies were investigated in two Porites and one Cyphastrea coral colonies from the central and southern Great Barrier Reef in order to test the reliability of these proxies to record the variability of river runoff and local anthropogenic disturbances. The results showed large scale removal of REEY (55–86%) in the low salinity mixing zones of both estuaries with significant fractionation of Nd-Yb and Y-Ho, confirming the ability of coral REEY to act as a terrestrial runoff proxy. Coralline Ba/Ca, Y/Ca and Mn/Ca records generally lack coherence with proximal discharge. However, temporal fluctuations of REEY proxies, irrespective of geographic location and coral genus, showed consistent behaviour relative to regional discharge with progressive increase of total REE/Ca and shale normalized Nd/Yb and decrease of Y/Ho during high-flow summer periods. The shifting baselines of REEY proxies in Cyphastrea grown in the turbid water setting of Rat Island effectively captured the timing of Gladstone Port dredging activities. Our findings suggest that shale normalized coral REEY distributions outperformed other commonly used trace element proxies and are robust indicators of changing inshore water quality. Longer-term records of coral REEY, even covering the period before European settlement from the 1850s, may provide a means to identify shifting baselines and evaluate and quantify the impacts of catchment alteration on coastal water quality and specific coral reef communities.

The Wufeng and Longmaxi organic-rich shales host the largest shale gas plays in China. This study examined the petrography, rare earth element (REE) and other trace-element geochemistry, Sm-Nd geochronology, and isotope geochemistry (87Sr/86Sr, δ18O, δ13C) of fracture-cementing minerals within core samples of the Wufeng and Longmaxi Formations from the Jiaoshiba shale gas field in order to (1) characterize the mineral phases occurring in the veins (mineralized fractures); (2) determine the ages of the calcite by the Sm-Nd isochron dating method; (3) understand the sources of calcite-precipitating fluids; and (4) explore the possible mechanisms responsible for calcite vein formation in shale gas systems. The fractures hosted in the Longmaxi Formation are mineralized with quartz as the predominant fracture cement, and calcite as an intracementation phase postdating the earlier quartz cement. In contrast, the fractures hosted in the Wufeng Formation are dominantly mineralized by calcite, which occurs either as the only cement present or as a cement phase predating later quartz cement. Calcite veins within the Longmaxi Formation have a Sm-Nd isochron age of 160 ± 13 Ma and δ13C values of –4.71‰ to –3.11‰, δ18O values of 17.1‰–17.4‰, and 87Sr/86Sr values of 0.72437–0.72869. Calcite veins within the Wufeng Formation yielded a Sm-Nd isochron age of 133 ± 15 Ma and are characterized by δ13C values of –2.29‰ to –1.03‰, δ18O values of 17.3‰–17.7‰, and 87Sr/86Sr values of 0.72202–0.72648. The similarity between 87Sr/86Sr values of the calcite and those of their respective surrounding host rocks (0.72670–0.72875 of the Longmaxi shales; 0.72030–0.72648 of the Wufeng shales), combined with relatively depleted δ13C and uniform fluid δ18O isotopic features, indicates that the calcite-precipitating fluids within the Wufeng and Longmaxi Formations were derived largely from their respective surrounding host-rock sources. REE data equally indicate that the distinguishable Eu anomalies (6.20–19.35; 4.45–11.91), Y anomalies (1.03–1.50; 1.44–1.70), and Y/Ho ratios (28.80–39.16; 38.86–45.18) of calcite veins within the Longmaxi and Wufeng Formations were controlled by their respective surrounding host rocks. The Sm-Nd isochron ages and fluid inclusion data of fracture cements suggest that fracture opening and calcite precipitation in composite veins within the Wufeng and Longmaxi Formations were triggered by gas generation overpressurization.

Tungsten is a critical element used in the industry with increasing global demand. There are millions of tons of current and legacy mineral processing tungsten tailings worldwide that can potentially contaminate the environment and pose human health risks. These tailings could also potentially turn into valuable resources if we thoroughly characterise their geochemical composition. In this study, an innovative method was developed to achieve the complete digestion of tungsten tailings. We tested three different digestion methods (hotplate digestion, bomb digestion, and ColdBlockTM digestion) and compared the results. Additionally, an alkali fusion for major element analysis was also applied and tested. The results showed that alkali fusion is the best method for major elements analysis, while bomb digestion is the best method for tungsten and trace element analysis, but volatile chlorite loss was also observed. The hot plate digestion method for tungsten mine tailings was not recommended, because of poor recoveries of trace elements compared to the bomb digestion method. The quick and safer ColdBlockTM digestion method could be used for Bismuth (Bi), Molybdenum (Mo), and several rare earth element analyses indicated by their recoveries being close to the bomb digestion method.

Volcanic-hosted iron deposits of the eastern Awulale metallogenetic belt in Central Asia possess a reserve of over 1.2 billion tons of iron ores and constitute one of the most important basements for high-grade iron resources in China. Skarns are widespread in these deposits and closely associated with iron mineralization. The ages of these skarns are unclear, and their genesis remains debated, preventing further investigation into their metallogenic processes. We focused on garnets in nine ore-bearing skarns from three large-scale iron deposits (Chagangnuoer, Dunde, and Beizhan) in the eastern Awulale belt. U-Pb dating was conducted on these garnets using our in-house reference material, the Taochong garnet (TC-13, Pb-Pb isochron age: 126.2 ± 2.3 Ma, initial 207Pb/206Pb ratio: 0.845 ± 0.022). Laser-ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) was employed in the garnet U-Pb dating, and high-precision U-Pb ages (0.3%–1.6%) were obtained, highlighting the advantages of LA-MC-ICP-MS in dating low-U minerals. The garnet U-Pb ages of the nine skarn samples fall into three groups, i.e., 329.0 ± 5.1–326 ± 3.3 Ma (two samples), 316.3 ± 2.9–311.2 ± 2.4 Ma (six samples), and 295.6 ± 1.0 Ma (one sample), implying three episodes of skarn alteration in the volcanic-hosted iron mineralization system. The first and second episodes of skarns formed as a result of contact metasomatism between coeval volcanic rocks and limestone, and they have economically important iron mineralization. The third was likely caused by a local postcollision granitic intrusion, but its metallogenic potential deserves further assessment.

Modern water quality gradients on the inner-shelf of the Great Barrier Reef (GBR) are influenced by catchment modification and increased terrigenous suspended sediment delivery. Proxy-based reconstructions of terrestrial sediment discharge are critical to trace the environmental drivers that modulate inshore water quality and to quantify the magnitude and timing of major changes. In this study we present high-resolution Porites coral rare earth element (REE) data over the period 1987–2012 from inshore Magnetic Island, GBR. Shale-normalized REE distributions in coral samples effectively captured the major features of seawater. Terrigenous sediment derived characteristics of shale-normalised REE and Y (e.g., higher ΣREE, reduced LREE depletion, and lower Y/Ho ratios) show linear relationships with each other on annual to multi-annual timescales thus providing a specific fingerprint for terrestrially derived turbidity. Temporal variation of the proxies generally shows spikes associated with increased water turbidity during strong summer floods. However, anomalous spikes coinciding with negligible river discharge during dry periods were also observed and highlight that data from non-flood year summers and winters show less predictable relationships possibly related to wind driven resuspension events, channel dredging and other as yet undetermined factors. Regardless, temporal variability of the proxies show synchronicity with tested environmental drivers (e.g., river discharge and rainfall) on multi-annual timescales with greater terrigenous influence during wet periods from the late-1980s to early-1990s, late-1990s to early 2000s and late 2000s to early-2010s, consistent with increased delivery of terrestrial sediment at those times. Cerium (Ce) anomalies showed complex behaviour during lower discharge seasons but have enhanced negative anomalies during strong flood-year summers when large flood plumes enriched in terrigenous nutrients were likely to reach waters around Magnetic Island. We speculate that higher abundance of Ce-oxidizing bacteria during strong flood events modulate local nearshore marine Ce anomalies. Based on these findings, we demonstrate that robust, time-resolved shale-normalized REE distributions in coral skeletons, not just elemental concentrations, provide very useful proxies for monitoring terrigenous sediment discharge related changes in inshore water quality and for tracing coastal biological activities, particularly at annual and multi-annual timescales.

High‐precision uranium‐thorium (U‐Th) dating of dead branching corals from Luhuitou reef, Sanya, northern South China Sea indicates that the reef framework grew episodically over the past 7,000 years. Episodes of coral reef growth (“switch‐on”phases) occurred in response to regional warming during the mid‐Holocene Climate Optimum, Medieval Warm Period, and Current Warm Period, when the East Asian summer monsoon was strong and the East Asian winter monsoon was weak. In contrast,episodes when reef growth dramatically slowed or ceased (“switch‐off”phases) occurred during comparatively cold periods (e.g., Dark Age Cold Period and Little Ice Age) and are linked to abrupt weakening of the East Asian summer monsoon and concurrent strengthening of the East Asian winter monsoon. In the context of global warming, the northern South China Sea may become an important refugium for coral reef growth of up to 2 °C above present, but only if local anthropogenic pressures are reduced.

Reconstructing coral reef histories provides a window of understanding into reef response to changing environmental and climatic conditions over various temporal scales. Here we present the results of 117 U-Th dates from emergent reef flat and slope cores and surface death assemblages, combined with previously published fossil microatoll data, to capture the entire sequence of reef growth at Mazie Bay, inshore Southern Great Barrier Reef (GBR). Coral U-Th dates indicate that Mazie Bay reef initiated ~6,900 years before present (yr. BP) quickly filling accommodation space. While rates of vertical reef accretion (5.3 ± 1.0 mm year⁻¹) were comparable to the GBR average during the mid-Holocene (~5.0 mm year⁻¹), reef flat progradation occurred at a rate 1.5- to 6-fold previous GBR rates until 5,100 yr. BP (~70.4 cm year⁻¹). Average progradation slowed to ~7.1 cm year⁻¹ in the subsequent ~4,000 years and reef slope cores indicate this reef had largely "turned-off" by 400 yr. BP, with modern coral communities existing as a veneer over the largely senescent framework. Death assemblage dates highlight coral disturbance and recovery regimes in response to increased cyclone activity 1960-1985 AD and recent extreme sea surface temperature and flood events post 2000 AD. U-Th dating of mid-Holocene to modern coral deposits from Mazie Bay reef provides a unique insight into past reef development, response to recent disturbance regimes, and potential for future reef growth. In the case of Mazie Bay, our data suggest limited accommodation space and increased occurrence of sea surface temperature extremes will restrict future reef growth at this site.

Improved understanding of subsurface paleo-fluid circulation history can assist in reconstructing associated pore evolution of carbonate reservoirs. Multi-stage dolomite cements generated by basinal fluids over time were investigated using a combination of petrography, geochemistry, fluid-inclusion studies, LA-ICP-MS U-Pb geochronology, and seismic interpretation. This study aims to gain clues about diagenetic, hydrothermal and paleo-oil filling events within the Ediacaran Dengying Formation, Sichuan Basin, China. Four main phases of dolomite cementation were petrographically, geochemically and geochronologically distinguished that can be ascribed to major tectonic events throughout the basin evolution. The earliest dolomite generation occurs as fibrous dolomite crust (FDC) growing along the karst vug wall, interpreted as marine diagenetic cement formed in a submarine environment during the Late Ediacaran, most likely from the influx of seawaters following the uplift and subaerial exposure related to the Tongwang movement. In situ U-Pb ages obtained from the other three generations of cement dolomites are interpreted to coincide with the timing of repeated strike-slip fault movements as indicated by the seismic data, suggesting a direct link between cement emplacement and regional tectonic-thermal events. Sub-vertical extension dolomite veins (EDV), representing the second generation, are considered as being syntectonic, generated from slightly modified connate seawaters at a shallow to moderate burial depth in a transtensional stress regime during the Cambrian taphrogenesis. Two generations of saddle dolomite cements, SD1 and SD2, have recorded two major episodes of hot fluids circulating in the Dengying Formation. The SD1, filling in hydraulic fractures and vugs, formed during the third phase of cementation, as a result of a hydrothermal event associated with Caledonian exhumation. Deep-seated hot brines squeezed into the Dengying reservoirs along the sub-vertical strike-slip faults combined with some meteoric waters that percolated downward, are deemed responsible for precipitating SD1. The SD2 is the youngest cement present, which is interpreted to have formed during the ingress of deeper, hot, hypersaline brines arising from the late Permian hydrothermal activity likely triggered by the eruption of Emeishan flood basalts. Cross-cutting relationships between bitumen phases and different dolomite generations indirectly define the dates of two paleo-oil charging events. The first episode of paleo-oil charging occurred during the Late Ediacaran to Early Cambrian, likely sourced from underlying Ediacaran Doushantuo shales. Late oil emplacement occurred after the Late Permian, in agreement with the reported bitumen Re-Os age and the age inferred through fluid-inclusion analysis. Primary source rocks generating this phase of oil were considered as the Cambrian Qiongzhusi shales, because basin modeling-derived date of oil window matches with the second oil filling time.

Deposits of biodegraded heavy oils are commonly encountered within the Eocene reservoir units in the North Slope of the Biyang Sag, Nanxiang Basin, eastern China. Oil physical property data and biomarkers show that these biodegraded oils occur only above burial depth equivalent to about 62 °C. This is much cooler than the cutoff temperature of biodegradation (about 80 °C), which has been interpreted within a complex petroleum evolution history that includes an early oil filling, significant uplift, a second phase of filling, and late-stage biodegradation. We use a new combination of fluid-inclusion analysis and calcite LA-ICP-MS U–Pb dating to obtain a temporal constraint on oil migration in the siliciclastic reservoirs. Two generations of oil inclusions, each showing a distinct fluorescence color (yellow and blue-green), were trapped before and after quartz cementation, respectively, which indicates multi-stage oil charge events. The early oil charge, marked by hydrostatic conditions and low-salinity pore waters, occurred during the late Eocene to early Oligocene burial period, corresponding to peak oil generation by basin modeling. The reservoirs were then refilled at a moderate-overpressure regime by higher maturity oils accompanied by high-salinity waters during the early Miocene exhumation. Reservoir sandstone-hosted, yellowish calcite veins, characteristic of 13C depletion and oil odor, contain primary blue-green fluorescent oil inclusions and bitumens, consistently pointing to precipitation from petroleum-derived fluids. LA-ICP-MS U–Pb dating of these vein calcites yields a U–Pb age of 19.6 ± 1.2 Ma, representing the latest timing of the second oil charge event in the North Slope. The isotope age of the fissure calcites near fault zones coincides well with the indirect age estimate based on fluid-inclusion homogenization temperature and the regional uplift stage. This scenario suggests that the Miocene tectonic compression not only triggered the recharge of oils but also facilitated the initiation or re-activation of faults that acted as conduits for oil migration. Reconstructed burial models show a continuous burial followed by significant uplift and erosion in this region. Since some reservoirs with maximum paleotemperature less than 80 °C were not sterilized during burial, the contained oils suffered from extensive biodegradation, presumably during the middle Miocene to present day. Thus, the shallower shutoff depth of biodegradation in this region was most likely ascribed to the paleo-pasteurization during burial, as opposed to later fresh oil replenishment or influx of shallow aquifers.

A robust marine radiocarbon (14C) reservoir correction (ΔR) is essential for calibrating14C dates of marine mollusks and fish bones routinely found in archaeological sites as discarded food remains and bones of terrestrial animals (including humans) with an appreciable marine diet. New ΔR values are reported for the atoll archipelago of the Marshall Islands, eastern Micronesia. Atolls consist of biogenetic material—mostly coral and foraminifera—that can be directly dated for establishing sequences of atoll emergence and islet development. After sectioning and examination using scanning electron microscopy (SEM) to screen for sample diagenesis, 6 pristine branch coral samples were selected from the modern oceanside beach, 3 archaeological sites, and islet developmental facies from Ebon Atoll (4º34′N, 168º41′E). Each sample was analyzed by U-series and accelerator mass spectrometry (AMS)14C showing no substantial temporal ΔR variations and yielding a weighted mean ΔR of 41±42 yr1spanning ~500 yr before earliest human colonization (the period when islets first became habitable) through the entire 2000-yr occupation sequence. Reliable published ΔR values for Micronesia and Δ14C data for Palmyra Island, together with our results for Ebon Atoll, indicate that the Pacific North Equatorial Counter Current is almost stable for the past 2500 yr.

Direct evidence for fault reactivation is crucial for understanding long-term fault behavior and reconstruction of fluid circulation and hydrocarbon migration and accumulation during active tectonics. However, absolute dating of fault reactivations and fluid circulation is still challenging due to dissolution and recrystallization of fault zone materials and obliteration of previous events by the latest deformation/hydrothermal event. The lower Ordovician limestone strata at 3.8 km depth in the Central Uplift of the Tarim Basin, northwest China experienced multi-stage regional tectonic activities that developed a series of NW–SE striking reverse faults and NE–SW oriented strike-slip faults. In this study, we performed in situ laser-ablation ICP-MS U Pb dating and trace element characterization of calcites collected from borehole cores within one of the main fault zones in the Central Uplift of the Tarim Basin. A new in-house calcite standard AHX-1A (209.8 ± 1.3 Ma), collected from the Tarim Basin, calibrated against well-calibrated WC-1 and ASH-15 calcite standards, is used for mass-bias correction. We obtained in situ U Pb ages of 9 calcite samples from two wells within a Paleozoic fault zone in the Tarim Basin. They are 456 ± 11 Ma, 454.7 ± 7.2 Ma, 450.4 ± 6.2 Ma, 435.2 ± 9.7 Ma, 328.0 ± 9.2 Ma and 307.6 ± 7.1 Ma from well TZ2, and 371 ± 18 Ma, 390.6 ± 6.0 Ma and 395 ± 14 Ma from well TZ4 (all reported uncertainties are 2σ). Combined with petrographic evidence, these results define at least six generations of secondary calcite precipitations in the fault zone, that occurred during 456 ± 11 to 450.4 ± 6.2 Ma (weighted mean 452.8 ± 4.3 Ma), 435.2 ± 9.7 Ma, 395 ± 14 to 390.6 ± 6.0 Ma (weighted mean 391.3 ± 5.5 Ma), 371 ± 18 Ma, 328.0 ± 9.2 Ma and 307.6 ± 7.1 Ma. Chondrite-normalized rare earth element (REE) + yttrium (Y) patterns of these calcite samples show prominent positive Gd and Y anomalies, lack of negative Ce anomaly, and enrichment in light REE but depletion in heavy REE, similar to the shallow marine platform host-rock limestone. The results suggest multi-stage fluid circulation under shallow burial, low temperature, and non-oxidizing environments along the fault zone, with the secondary calcite precipitating from a similar fluid source that originated from dissolution of host-rock carbonate or early-stage diagenesis. The detail petrographical and mineralogical analysis of this study, combined with the new interpretation of high-resolution seismic data, constrains two main episodes of faulting and related uplift during 456–435 Ma and 395–371 Ma, as well as a younger faulting episode with weaker intensity during 328–308 Ma. This study demonstrates that the central fault zone of the Tarim Basin experienced ~150 Ma of episodical reactivation during the Paleozoic, which has important implications for hydrocarbon exploration.

The history of thermal and fluid flow events is of crucial importance to understand the mechanism of hydrocarbon maturation. The northern South China Sea (SCS) contains abundant hydrocarbon resources with high heat flow anomalies, but the mechanisms responsible for modification of thermal regimes are poorly understood. Here we conducted the first high-precision Rb-Sr isochron dating and geochemical analyses of authigenic illites separated from the Palaeogene sandstones in the Beibuwan Basin, northern SCS. Eight high-precision Rb-Sr isochron ages reveal three major thermal and fluid flow events in the Beibuwan Basin, northern SCS. The 34.5 ± 0.9 Ma and 23.6 ± 0.8 Ma events occurred in the western area are probably related to the Eocene-Oligocene transition characterised by a significant regional unconformity resulted from intensive uplift of Hainan Uplift and Oligocene-Miocene transition marked by a post-rift unconformity, respectively. By contrast, the 31.2 ± 0.6 Ma event affecting the eastern area appears to be closely associated with the igneous intrusion dated by zircon U/Pb to 32.3 ± 0.7 Ma. REE and stable isotope characteristics indicate that the illites from the western area formed within a meteoric-hydrothermal system, whilst those from the eastern area were likely precipitated from fluids heated by the large-scale igneous intrusion at higher water/rock ratios. Moreover, our data in conjunction with palaeo-temperature reconstructions show that the fluid flow events had profound effects on the rapid organic maturation in the northern SCS.

Primary gas accumulation with trillions of cubic meters of gas volumes was discovered recently in the Precambrian Dengying Formation of the Gaoshiti-Moxi block, Central Sichuan Basin, China. In this study we investigated the pervasive saddle dolomite cements and solid bitumens within karst vugs in the Dengying dolomite reservoirs. Using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in situ U-Pb dating, we obtained a high-precision absolute age of 259.4 ± 3.0 Ma for the saddle dolomite cementation, consistent in timing with the eruption of Emeishan flood basalts (262–251 Ma). Combined with high homogenization temperatures (Th) and salinities of primary fluid inclusion, as well as rare earth element (REE) compositions, we consider that the saddle dolomite precipitation was likely related to hydrothermal activity driven by the Emeishan mantle plume. The identification of rare surviving oil inclusions and extensive solid bitumens within the dolomite vugs is indicative of the presence of paleo-oil reservoirs. These bitumens are characterized by high equivalent vitrinite reflectance (Requ), no fluorescence, and deformed fibrous textures, typical of highly mature pyrobitumens. Gas geochemistry data indicates that only minor thermochemical sulfate reduction (TSR) has occurred. Thus the pyrobitumen was interpreted to result mainly from the thermal cracking of paleo-oils, and its associated Re-Os isochron age of 154 ± 21 Ma, representing the timing of dry gas formation. Petrographical evidence suggests that the paleo-oil charge must have taken place after sparry dolomite cementation but prior to pyrobitumen generation. This, combined with coeval aqueous inclusion Th data and published thermal-burial models, constrains the time of paleo-oil emplacement to ca. 222–205 Ma, suggesting an oil-filling event related to the Indosinian Orogeny. This study documented the first chronological data constraining the complex evolution history of a petroleum system in one of the oldest primary gas reservoirs in the world.

To extend the range of materials that can be used to provide chronological constraint in archaeological and palaeontological settings, we explore the use of cave pearls that form in shallow pools. Here, we present U-series dating results of cave pearls found in cave sediments with mammal fossils collected from systematic excavations at the Diaozhongyan Cave (“DZY”), located in Guangxi Zhuang Autonomous Region, southern China. Similar to soda straw stalactites, cave pearls can be transported after formation and subsequently incorporated into sediments. Thus, the U-series ages of the outermost layers of cave pearls are expected to be older than their host sediments and associated archaeological and paleontological materials. In conjunction with U-series dating of mammal teeth, which can provide a reliable minimum age, U-series ages of cave pearls can provide a maximum age limit of the deposits. Thus, dating of the mammal teeth and cave pearls from DZY reasonably constrains the first occurrence of the DZY Ailuropoda-Stegodon fauna to a period between 205.6 ± 1.4 ka and 231.0 ± 12.8 ka. These age constraints agree well with previous estimates for the time range of the late Middle Pleistocene Ailuropoda-Stegodon fauna in southern China. We propose that greater attention should be paid to cave pearls, which are commonly found in cave deposits that were laid down at least in part due to fluvial activity, and can be used for U-series dating to better constrain the age of the associated cave deposits.

In the face of changing global climate the future of corals reefs is uncertain. High latitude reefs may offer potential refugia for corals under projected increasing sea surface temperatures (SSTs). To understand the reef growth potential of modern high latitude reefs it is first necessary to understand past reef growth and response to climatic and environmental changes. The history of the Great Barrier Reef (GBR) has been shown to be punctuated by a multi-millennial Mid-Holocene reef “turn-off” or initiation hiatus in the Northern and Southern GBR (∼5500–2500 years before present [yr. BP]). Here we present the results of chronologically constrained reef matrix cores from five continental island fringing reefs and coral communities in the Keppel Islands to revaluate the timing, extent and possible drivers of the Mid-Holocene hiatus in the Southern GBR. Earliest initiation occurred at Wedge and Halfway Islands at 7773 ± 19 yr. BP and 7455 ± 20 yr. BP, respectively. Following initiation, vertical reef accretion at Halfway was comparable to previously reported rates for the GBR of ∼3.4 mm yr−1, increasing to ∼8.0 mm yr−1 between 6100 and 5500 yr. BP. Conversely, the coral community at Wedge Island, located closer to mainland terrestrial influence, accreted

Halogens are critical elements for transporting metals in hydrothermal solution and tracing the sources of fluids and volatiles in subduction zones. This study tested the suitability of LA-ICPMS for simultaneous measurement of Cl, Br and I with selected trace elements in altered gabbros recovered from the Atlantis Bank core complex close to the SW Indian Ridge. The aim was to better understand the causes of I-enrichment in low temperature carbonate and Fe-oxyhydroxide alteration, which is intensely developed in core recovered from between ~100 and ~600 mbsf down Hole U1473A drilled during Expedition 360 of the International Ocean Discovery Program (IODP). The analysis of reference materials including scapolites, Durango apatite, USGS and NIST reference glasses and volcanic glasses demonstrate Cl, Br and I can be measured in most minerals, but accuracy is limited by matrix dependent laser backgrounds (false signals of Cl, Br and I generated during sample ablation). Silicate reference glasses define reproducible ‘laser backgrounds’ of ~320 μg/g Cl and ~1.7 μg/g Br that point to limits of quantification of ~200 μg/g Cl and ~1 μg/g Br in silicate glasses after correction for laser backgrounds. In contrast, laser backgrounds are much lower and possibly negligible for carbonate, suggesting limits of quantification as low as ~50 μg/g Cl and 0.1 μg/g for Br, dependent on instrument sensitivity. Laser backgrounds for I varied between minerals and analytical sessions, there was no laser background for I in apatite and under favourable conditions silicate glasses have laser backgrounds of

Catchment modification and increased sediment loads in coastal regions are impacting many of the world's coral reefs, yet relevant water quality data are limited by the availability of instrumental records. Massive Porites spp. corals offer the potential to reconstruct water quality by use of the geochemical proxies that are incorporated into their skeleton. Here we present ∼ monthly resolved rare earth element (REE), yttrium (Y) and barium/calcium (Ba/Ca) concentrations obtained from four Porites corals collected across a known water quality gradient from the Great Barrier Reef, Australia. Sub-annual REE time series patterns were comparable among corals despite having significantly different concentrations. Whilst Ba/Ca did not reflect the known water quality gradient of the region, Y/holmium ratios reflected broad cross shelf water quality gradients and REE concentrations reflected local scale variance in water quality. This study demonstrates that REE analysis of Porites corals offers great potential for assessing changes in water quality in reef environments.

Carbonate successions are principal geochemical archives of the extraordinary environmental changes that occurred during the Neoproterozoic Era. In this study, we present a stratigraphic record of carbonate rare earth element (REE) compositions from Neoproterozoic and Cambrian strata in central and southern Australia. The new REE results provide insight into the redox conditions of the Neoproterozoic-Cambrian ocean, the influence of glacial meltwater on carbonate precipitation, and Neoproterozoic-Cambrian paleoenvironmental changes. High Ce/Ce* and low Y/Ho suggest that the major Neoproterozoic and Cambrian carbonate accumulations of central and southern Australia formed in restricted marine environments that were largely dysoxic. Elevated ∑REE of mid-Cryogenian and early Ediacaran carbonate from the Amadeus Basin (central Australia) and King Island (Tasmania), respectively, are interpreted to reflect increased detrital mineral flux following periods of Cryogenian glaciation. REE data from the basal Ediacaran Cumberland Creek Dolostone of King Island suggest a transient episode of ocean oxidation in the wake of the terminal Cryogenian glaciation, but the balance of evidence suggests dominantly low oxygen ocean conditions during carbonate deposition in the remainder of the Neoproterozoic Era. An apparent mismatch in timing between carbonate deposition in central and southern Australia versus previously proposed mid-to-late-Ediacaran oxygenation events based on geochemical results from strata of South China highlights what may be important factors in reconciling varied geochemical records of Neoproterozoic-Paleozoic ocean oxygenation.

Extensive catchment modification since European settlement on the eastern coast of Australia results in poor coastal water quality, which poses a major threat for near shore coral communities in the iconic Great Barrier Reef (GBR). Long lived inshore corals have the potential to provide long-term temporal records of changing water quality both pre- and post-anthropogenic modification. However, water quality proxies require more study and validation of the robustness of coral-hosted geochemical proxies for a specific site is critical. This study investigated the long-term (1958–2010) influence of environmental drivers on high-resolution Ba/Ca and Y/Ca proxies obtained from Porites sp. coral from Great Keppel Island, southern GBR, Australia. Geochemical proxy records were influenced by environmental change on a seasonal to decadal scale. Although seasonal oscillations of Ba/Ca and Y/Ca were related to rainfall and discharge from the Fitzroy River catchment, some uncorrelated anomalous peaks were evident throughout the time series. Regardless, the behaviour of these proxies was significantly consistent over the longer time scale. Most long-term drought-breaking floods, including one that occurred in winter, resulted in significant increase in the targeted elemental ratios owing to higher terrigenous sediment flux to the near shore marine environment from a catchment with reduced groundcover. Following this intense flushing event, elemental ratios were reduced in subsequent wet periods as a result of less sediment being available for transport to coastal seawater. Ba/Ca and Y/Ca proxies can be valuable tools in reconstructing multiyear variations in terrestrial runoff and associated inshore water quality. As these proxies and their regional and local controls are better understood they will aid our understanding of how reefs have responded and may respond to changing water conditions.

An obvious but key prerequisite to testing hypotheses concerning the role of humans in the extinction of late Quaternary ‘megafauna’ is demonstrating that humans and the extinct taxa overlapped, both temporally and spatially. In many regions, a paucity of reliably dated fossil occurrences of megafauna makes it challenging, if not impossible, to test many of the leading extinction hypotheses. The giant monitor lizards of Australia are a case in point. Despite commonly being argued to have suffered extinction at the hands of the first human colonisers (who arrived by 50 ka), it has never been reliably demonstrated that giant monitors and humans temporally overlapped in Australia. Here we present the results of an integrated U–Th and 14C dating study of a late Pleistocene fossil deposit that has yielded the youngest dated remains of giant monitor lizards in Australia. The site, Colosseum Chamber, is a cave deposit in the Mt Etna region, central eastern Australia. Sixteen new dates were generated and demonstrate that the bulk of the material in the deposit accumulated since ca. 50 ka. The new monitor fossil is, minimally, 30 ky younger than the previous youngest reliably dated record for giant lizards in Australia and for the first time, demonstrates that on a continental scale, humans and giant lizards overlapped in time. The new record brings the existing geochronological dataset for Australian giant monitor lizards to seven dated occurrences. With such sparse data, we are hesitant to argue that our new date represents the time of their extinction from the continent. Rather, we suspect that future fossil collecting will yield new samples both older and younger than 50 ka. Nevertheless, we unequivocally demonstrate that humans and giant monitor lizards overlapped temporally in Australia, and thus, humans can only now be considered potential drivers for their extinction.

Studies on the growth response of corals to changing climate have largely focused on long-lived corals with relatively distinct density bands such as massive Porites corals. Little is known about the climatic response of other more abundant growth forms, such as branching Acropora corals, largely because of the absence of a clear annual density banding pattern. Using a combination of X-radiography, gamma densitometry, Sr/Ca analysis, and Uranium–Thorium (U-Th) dating, we quantified patterns of annual growth in the robust branching coral Isopora palifera from the central Great Barrier Reef (GBR), Australia (18°16′S 147°22′E) collected in May 2013. While visual analysis of the positive X-radiographs revealed alternating patterns of high- and low-density bands along the central growth axis, gamma-densitometry analysis suggests that these bands do not exhibit a clear annual cycle. In contrast, skeletal Sr/Ca ratios consistently revealed clear patterns of seasonality matching local sea surface temperatures (SST), and provided a growth chronology to calculate linear extension rate, skeletal density and calcification rate. Comparisons between SST-Sr/Ca calibrations derived from our I. palifera samples with (i) massive Porites from the same location and (ii) Isopora spp. from the GBR and Papua New Guinea revealed significant differences of up to 3.5 °C, implying palaeoclimate reconstructions should use site-specific and species-specific Sr/Ca-SST calibrations. Our approach provides a robust method for assessing changes in growth for a common Indo-Pacific branching coral, and provides a valuable framework for quantifying past and future changes in skeletal growth in response to climate change.

Long-term data with high-precision chronology are essential to elucidate past ecological changes on coral reefs beyond the period of modern-day monitoring programs. In 2012 we revisited two inshore reefs within the central Great Barrier Reef, where a series of historical photographs document a loss of hard coral cover between c.1890–1994 AD. Here we use an integrated approach that includes high-precision U-Th dating specifically tailored for determining the age of extremely young corals to provide a robust, objective characterisation of ecological transition. The timing of mortality for most of the dead in situ corals sampled from the historical photograph locations was found to coincide with major flood events in 1990–1991 at Bramston Reef and 1970 and 2008 at Stone Island. Evidence of some recovery was found at Bramston Reef with living coral genera similar to what was described in c.1890 present in 2012. In contrast, very little sign of coral re-establishment was found at Stone Island suggesting delayed recovery. These results provide a valuable reference point for managers to continue monitoring the recovery (or lack thereof) of coral communities at these reefs.

Nha Trang Bay (NTB) is located on the Central Vietnam coast, western South China Sea. Recent coastal development of Nha Trang City has raised public concern over an increasing level of pollution within the bay and degradation of nearby coral reefs. In this study, multiple proxies (e.g., trace metals, rare earth elements (REEs), and Y/Ho) recorded in a massive Porites lutea coral colony were used to reconstruct changes in seawater conditions in the NTB from 1995 to 2009. A 14-year record of REEs and other trace metals revealed that the concentrations of terrestrial trace metals have increased dramatically in response to an increase in coastal development projects such as road, port, and resort constructions, port and river dredging, and dumping activities since 2000. The effects of such developmental processes are also evident in changes in REE patterns and Y/Ho ratios through time, suggesting that both parameters are critical proxies for marine pollution.

Speleothem-based stable isotope records are valuable in sub-humid and semi-arid settings where many other terrestrial climate proxies are fragmentary. The Eastern Mediterranean is one such region. Here we present an 80-kyr-long precisely-dated (by U-series) and high-resolution oxygen (δ18O) and carbon (δ13C) records from Dim Cave (~36°N) in SW Turkey. The glacial-interglacial δ18O variations in the Dim Cave speleothem are best explained in terms of changes in the trajectories of winter westerly air masses. These are along a northerly (European) track (isotopically less depleted) during the early last glaciation but are gradually depressed southward closer to the modern westerly track along the North African coast (more depleted) after c.50 kyr and remain in the southern track through the Last Glacial Maximum. The southward displacement of the westerly track reflects growth of the Fennoscandian ice sheet and its impact on westerly wind fields. Changes in δ13C are interpreted as reflecting soil organic matter composition and/or thickness. δ13C values are significantly more negative in interglacials reflecting active carbonic acid production in the soil and less negative in glacial times reflecting carbonate rock values. Several Heinrich events are recorded in the Dim record indicating intensification of westerly flow across this part of the EM.

Speleothem-based stable isotope records are valuable in sub-humid and semi-arid settings where many other terrestrial climate proxies are fragmentary. The Eastern Mediterranean is one such region. Here we present an 80-kyr-long precisely-dated (by U-series) and high-resolution oxygen (δ18O) and carbon (δ13C) records from Dim Cave (~36°N) in SW Turkey. The glacial-interglacial δ18O variations in the Dim Cave speleothem are best explained in terms of changes in the trajectories of winter westerly air masses. These are along a northerly (European) track (isotopically less depleted) during the early last glaciation but are gradually depressed southward closer to the modern westerly track along the North African coast (more depleted) after c.50 kyr and remain in the southern track through the Last Glacial Maximum. The southward displacement of the westerly track reflects growth of the Fennoscandian ice sheet and its impact on westerly wind fields. Changes in δ13C are interpreted as reflecting soil organic matter composition and/or thickness. δ13C values are significantly more negative in interglacials reflecting active carbonic acid production in the soil and less negative in glacial times reflecting carbonate rock values. Several Heinrich events are recorded in the Dim record indicating intensification of westerly flow across this part of the EM.

Seasonal two-way migration is an ecological phenomenon observed in a wide range of large-bodied placental mammals, but is conspicuously absent in all modern marsupials. Most extant marsupials are typically smaller in body size in comparison to their migratory placental cousins, possibly limiting their potential to undertake long-distance seasonal migrations. But what about earlier, now-extinct giant marsupial megafauna? Here we present new geochemical analyses which show that the largest of the extinct marsupial herbivores, the enormous wombat-like Diprotodon optatum , undertook seasonal, two-way latitudinal migration in eastern Sahul (Pleistocene Australia–New Guinea). Our data infer that this giant marsupial had the potential to perform round-trip journeys of as much as 200 km annually, which is reminiscent of modern East African mammal migrations. These findings provide, to our knowledge, the first evidence for repetitive seasonal migration in any metatherian (including marsupials), living or extinct, and point to an ecological phenomenon absent from the continent since the Late Pleistocene.