College of Science and Engineering CSE publications Recent publications in Earth and Environmental Sciences

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Recent publications in Earth and Environmental Sciences

Law, Lisa, Azzali, Simona, and Conejos, Sheila (2021) Planning for the temporary: temporary urbanism and public space in a time of COVID-19. Town Planning Review, 92 (1). pp. 65-74.
It is a cliché to say we live in strange times: COVID-19 has focused our attention on schedules of lockdowns and long-term economic effects, and has even slowed down our experience of time due to increased cognitive loads. But as planners or urban designers it is our urban places that have also become strange: COVID-19 is altering our use of, and behaviour in, public space – from physical and social distancing to staying at home or even leaving the city altogether. We are concerned with how long we will tolerate state encroachments in public space, especially new techniques of surveillance and control, but we also see local governments opening up streets to give more public spaces back to pedestrians. In this Viewpoint we explore these paradoxes of public space in a time of COVID-19, from its temporary disappearance to the potential for temporary changes to underpin lasting strategies for liveable, economically viable and resilient public space. Although some link temporary urbanism to neo-liberal urban development and austerity policies (Stevens et al., 2019), we ponder how the COVID-19 moment critiques the status quo by providing new openings for shifting temporary urbanism into the mainstream planning toolkit. Does COVID-19 present an opportunity to make temporariness more deliberate and programmatic,thereby catalysing long-term change?

Poblete, Jaime A., Dirks, Paul H.G.M., Chang, Zhaoshan, Huizenga, Jan Marten, Griessmann, Martin, and Hall, Chris (2021) The Watershed tungsten deposit, Northeast Queensland, Australia: Permian metamorphic tungsten mineralization overprinting Carboniferous magmatic tungsten. Economic Geology. (In Press)
The Watershed tungsten deposit (49.2 Mt avg 0.14% WO3) lies within the Mossman orogen, which comprises deformed Silurian-Ordovician metasedimentary rocks of the Hodgkinson Formation intruded by Carboniferous-Permian granites of the Kennedy Igneous Association. The Hodgkinson Formation in the Watershed area comprises skarn-altered conglomerate, psammite, and slate units that record four deformation events evolving from ductile, isoclinal, colinear folding with transposition (D1–D3) to brittle ductile shear zones (D4). Multiple felsic to intermediate dikes cut across the metasedimentary rocks at Watershed including: (1) Carboniferous, monzonite dikes (zircon U/Pb age of 350 ± 7 Ma) emplaced during D1–2; and (2) Permian granite plutons and dikes (zircon U/Pb ages of 291 ± 6, 277 ± 6, and 274 ± 6 Ma) and diorite (zircon U/Pb age of 281 ± 5 Ma) emplaced during D4. Tungsten mineralization is largely restricted to skarn-altered conglomerate, which preserves a peak metamorphic mineralogy formed during ductile deformation and comprises garnet (Grt40–87 Alm0–35Sps1–25Adr0–16), actinolite, quartz, clinopyroxene (Di36–59Hd39–61Jhn1–5), and titanite. A first mineralization event corresponds to the crystallization of disseminated scheelite in monzonite dikes (pre-D3) and adjacent units, with scheelite grains aligned in the S1–2 fabric and affected by D3 folding. This event enriched the Hodgkinson Formation in tungsten. The bulk of the scheelite mineralization formed during a second event and is concentrated in multistaged, shear-related, quartz-oligoclase-bearing veins and vein halos (muscovite 40Ar-39Ar weighted average age of 276 ± 6 Ma), which were emplaced during D4. The multistage veins developed preferentially in competent, skarn-altered conglomerate units and formed synchronous with four retrograde alteration stages. The retrograde skarn minerals include clinozoisite after garnet, quartz, plagioclase, scheelite, and phlogopite with minor sodium-rich amphibole, which formed during retrograde stages 1 and 2, accompanied by later muscovite, calcite, and chlorite formed during retrograde stage 3. Retrograde stage 4 was a late-tectonic, noneconomic sulfide stage. The principal controls on scheelite mineralization at Watershed were the following: (1) early monzonite dikes enriched in scheelite; (2) D4 shear zones that acted as fluid conduits transporting tungsten from source areas to traps; (3) skarn-altered conglomerate lenses that provide a competent host to facilitate vein formation and a source for calcium to form scheelite; and (4) an extensional depositional environment characterized by vein formation and normal faulting, which provide trapping structures for tungsten-bearing fluids, with decompression being a likely control on scheelite deposition. The coexistence of scheelite with oligoclase in monzonite dikes and veins suggests that tungsten was transported as NaHWO4⁠. Exploration in the area should target Carboniferous monzonite, associated with later syn-D4 shear zones cutting skarn-altered conglomerate.

Ziegler, Alan D., Lim, H.S., Wasson, Robert J., and Williamson, Fiona C. (2021) Flood mortality in SE Asia: can palaeo‐historical information help save lives? Hydrological Processes, 35 (1). e13989.
[Excerpt] Asia is one of the world's most flood-prone regions by many metrics: high flood magnitudes, frequency, severity; the number countries affected, the area of inundation; the number of people at risk; and importantly, flood-related fatalities (AIR, 2014; Luo, Maddoks, Iceland,Ward, & Winsemius, 2015; Table 1). With respect to mortality, nearly all the countries with more than 5,000 flood-related deaths since 1985 are from Asia (11 of 13; Table 1; Figure 1). As we write this commentary, flooding associated with tropical storm Nangka has caused more than 40 deaths in Laos, Cambodia, and Vietnam(Floodlist, 2020).

Spence, Joshua S., Sanislav, Ioan V., and Dirks, Paul H.G.M. (2021) 1750–1710 Ma deformation along the eastern margin of the North Australia Craton. Precambrian Research, 353. 106019.
In this contribution, we present field-based evidence that in the Mary Kathleen Domain from the Eastern Fold Belt of the Mount Isa Inlier the 1790–1750 Ma metasediments of the Leichhardt Superbasin were sheared and folded between 1750 and 1710 Ma. The Mary Kathleen Domain consists of a series of anastomosing high and low strain domains intruded syn- to late-tectonically by a series of 1740–1710 Ma felsic and mafic plutons and dykes. The timing relationships in the high strain domains are unclear due to mylonitisation and transposition but in the lower strain domains are well-preserved. The earliest deformation, D1, consists of a series of low angle truncation surfaces and shear zones that are folded around large scale N-S trending upright folds during D2. The D2 folds were refolded during D3 along NW to EW trending fold axes. An undeformed granitic pluton from the Mt Godkin area dated at ~1710 Ma that crosscuts the D2-D3 folds and the youngest detrital zircon population of ~1750 Ma constrains the timing of D1-D3 deformation between 1750 and 1710 Ma. Later, N-S (D4) and N-E (D5) trending brittle-ductile shears are interpreted to indicate a late Isan Orogeny overprint. The occurrence of contemporaneous folding in the Western Fold Belt suggests that between 1750 and 1710 Ma the eastern margin of the North Australia Craton was experiencing a significant deformation event that can be correlated with similarly aged deformation events from other parts of the North Australia Craton, from South Australia Craton and from East Antarctica. Following the assembly of most of the Nuna Supercontinent by 1.8 Ga, we postulate that the 1750–1710 Ma deformation and plutonism observed in Mount Isa Inlier is part of a series of worldwide orogenic events that contributed to the final configuration of the Nuna Supercontinent.

Palma, Ana C., Goosem, Miriam, Fensham, Roderick J., Goosem, Steve, Preece, Noel D., Stevenson, Pablo R., and Laurance, Susan G.W. (2021) Dispersal and recruitment limitations in secondary forests. Journal of Vegetation Science. e12975. (In Press)
Aims: Secondary forests are expanding rapidly in tropical regions and could play an important role in conserving native biodiversity and stabilising global climate. The recovery rate of plant communities in secondary forests varies considerably due to mechanisms associated with seed dispersal and recruitment dynamics. We explored these mechanisms along a chronosequence of tropical secondary forests in an agricultural landscape that was extensively cleared. Location: We explored these mechanisms along a chronosequence of secondary forests in tropical Australia. Methods: We used selected plant traits to characterise plant species and compared community composition between demographic stages (i.e. soil seedbank, understorey and overstorey) and forest age categories. We collected soil samples to assess seedbank composition and used quadrants and transects to assess understorey and overstorey plant community composition at each site. Results: For all demographic stages, we found that young (4-12 years) and intermediate-aged forests (16-20 years) were dominated by early successional, small-seeded species and traits associated with disturbed forests. In old secondary forest (23-34 years) some traits associated with late successional stages were present (e.g. large seeds, trees). However, the traits and species composition of mature forests remained distinct from all secondary forests. Across the chronosequence, forest age and demographic stage were significant factors in discriminating species and trait composition between forest sites. We found clear plant community similarities within demographic stages, despite the forest age differences. This suggests stronger limitations to dispersal and recruitment between demographic stages than between forest ages. Conclusions: Our results show that secondary forests in this region assemble slowly with dispersal and recruitment limitations constraining their recovery. Although a successional transition in species and plant traits composition along the chronosequence is clear, similarities to mature forests remain low. The slow recovery of late successional and large-seeded species in these secondary forests suggests that active restoration of such species may be necessary if we want to enhance the capacity of these forests to conserve native biodiversity.

Younes, Nicolas, Joyce, Karen E., and Maier, Stefan M. (2021) All models of satellite-derived phenology are wrong, but some are useful: a case study from northern Australia. International Journal of Applied Earth Observation and Geoinformation, 97 (102285).
Satellite-derived phenology (or apparent phenology) is frequently used to illustrate changes in plant phenology (i.e. true phenology) and the effects of climate forcing. However, each study uses a different method to detect phenology. Plant phenology refers to the relationship between the life cycle of plants and weather and climate events. Phenology is often studied in the field, but recently studies have transitioned towards using satellite images to monitor phenology at the plot, country, and continental scales. The problem with this approach is that there is an ever-increasing variety of earth observation satellites collecting data with different spatial, spectral, and temporal characteristics. In this paper we ask if studies that detect phenology using different sensors over the same site produce comparable results. Mangrove forests are one example where different methods have been used to examine their apparent phenology. In general, plant phenology, including mangroves, is described using few individual plants, but continental-scale descriptions of phenological events are scarce or inexistent. Few attempts have been made to describe the phenology of mangroves using satellite imagery, and each study presents a different method. We hypothesize that apparent phenology changes with: 1) areal extent; 2) site location; 3) frequency of observation; 4) spatial resolution; 5) temporal coverage; and 6) the number of cloud contaminated observations. Intuitively, one would assume that these hypotheses hold true, yet few studies have investigated this. For example, one would expect that clouds change the observed phenology of vegetation, that the number of species captured at spatial resolution will impact the apparent phenology, or that mangroves in different places display different phenologies, but how are these changes represented in the apparent phenology? We use the Enhanced Vegetation Index (EVI) to examine the changes in the start of season and peak growing season dates, as well as the shape and amplitude of the apparent phenology in each hypothesis. We use Landsat and Sentinel 2 imagery over the mangrove forests in Darwin Harbour (Northern Territory, Australia) as a case study, and found that apparent phenology does change with the sensor, site, and cloud contamination. Importantly, the apparent phenology is comparable between Landsat and Sentinel 2 sensors, but it is not comparable to phenology derived from MODIS. This is due to differences in the spatial resolution of the sensors. Cloud contamination also significantly changes the apparent phenology of vegetation. In this paper we expose the complexity of modelling phenology with remote sensing and help guide future phenology investigations.

Zhao, Xu, Fu, Lebing, Wei, Junhao, Huizenga, Jan, Liu, Yan, Chen, Jiajie, and Wang, Dianzhong (2021) Generation and structural modification of the giant Kengdenongshe VMS-type Au-Ag-Pb-Zn polymetallic deposit in the East Kunlun Orogen, East Tethys: constraints from geology, fluid inclusions, noble gas and stable isotopes. Ore Geology Reviews, 131. 104041.
The Kengdenongshe giant Au-Ag-Pb-Zn polymetallic deposit is located in the East Kunlun Orogen (EKO). It contains about 42.2 t of Au, 608.6 t of Ag and 1.05 Mt of Pb and Zn with an average grade of Au 2.31 g/t, Ag 19.29 g/t and Pb + Zn 3.49 wt% (Pb: 1.23 wt%, Zn: 2.26 wt%). The NWW-trending ore bodies are predominantly hosted in Late Permian to Triassic rhyolitic tuff, which formed during Late Permian back-arc extension to Triassic arc-continental collision. The ore bodies are subdivided into Pb-Zn rich ore bodies on the top with high grades of Pb and Zn and low grades of Au and Ag, and Au-Ag rich ore bodies below with high grades of Au and Ag and low grades of Pb and Zn. The Pb-Zn rich ore bodies occur as vein, stockwork, and in breccia, and comprise quartz, pyrite, galena, sphalerite, and small amounts of chalcopyrite. The Au-Ag rich ore bodies consist of auriferous barite-sulfide-oxide veins and contain barite, pyrite (early strawberry and oolitic pyrite and later eu- to subhedral pyrite), galena, sphalerite, chalcopyrite, tetrahedrite and covellite. Gold is present as electrum, kustelite and native gold and silver is present as polybasite, pearceite, kongsbergite, and as minor native silver in microfractures in sulfides. The hydrothermal alteration minerals include, from bottom to top, quartz + barite + calcite around the Au-Ag rich orebodies, quartz + chlorite + epidote around the Pb-Zn rich orebodies, and quartz + K-feldspar within the tuff. Fluid inclusions from both the Pb-Zn rich and the Au-Ag rich orebodies consist of two phases (V–L-type) fluid inclusions of which the vapor phase has a size of 10–40 vol%. Fluid inclusions microthermometry reveal homogenization temperatures of fluid inclusions in Pb-Zn rich and Au-Ag rich ore bodies of 128–230 °C and 110–320 °C, with corresponding salinities of 0.7–9.9 and 0.2–18.3 wt% NaCl equivalent, respectively. H-O-S-Pb stable isotope and He-Ar noble gas isotope data indicate a mixed magmatic water-seawater source for both the Pb-Zn and Au-Ag rich ore bodies, and an additional meteoric water component for the Au-Ag rich ore bodies. The Pb-Zn and Au-Ag rich ore bodies share the same sulfur and lead sources, i.e. sulfur is derived from crustal magma and seawater/marine sulfate, and the lead originated from a mixed magmatic-ancient crustal sedimentary source. Collectively, the regional geology, mineralogy, alteration, and geochemistry indicate that the Kengdenongshe Au-Ag-Pb-Zn polymetallic deposit can be characterized as a VMS-type (volcanic-associated massive sulfide) deposit. Formation of the ore-hosting rhyolite tuff and mineralization are associated with Late Permian to Triassic marine volcanic exhalation. Middle to Late Triassic basin closure and arc-continent collision modified the deposit and resulted in the location inversion of the Pb-Zn and Au-Ag rich orebodies.

Huang, Han‐Xiao, Dai, Zuo-Wen, Liu, Hong, Li, Guang‐Ming, Huizenga, Jan Marten, Zhang, Lin‐Kui, Huang, Yong, Cao, Hua‐Wen, and Fu, Jian‐Gang (2021) Zircon U–Pb ages, geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern Qiangtang of Tibet, western China: implications for the evolution of the Bangong Co‐Nujiang Meso‐Tethyan Ocean. Geological Journal. (In Press)
We present in-situ zircon laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb ages, whole-rock geochemistry, and Sr–Nd–Pb–Hf isotopes of the Mugagangri monzogranite in the southern margin of the Qiangtang Block, Tibet, western China. The zircons yield a U–Pb age of ca. 123 Ma. The hornblende-bearing monzogranite shows metaluminous to weak peraluminous and high-K calc-alkaline characteristics exemplified by high silica (SiO2 = 67.57–70.57 wt%), high aluminium (Al2O3 = 14.68–15.78 wt%), high potassium (K2O = 4.00–5.14 wt%), high alkali (K2O + Na2O = 7.88–8.62 wt%), and low calcium contents (CaO = 1.72–2.17 wt%), with the aluminium saturation index (A/CNK) ranging from 0.98 to 1.09, suggesting that the Mugagangri monzogranite is a metaluminous to weak peraluminous I-type high-K calc-alkaline granite. Geochemically, similar to the arc magmas, the monzogranite is enriched in large-ion lithophile elements, and relatively depleted in high-field-strength elements. The monzogranite displays relatively high(87Sr/86Sr)i values (0.70972–0.71240), uniform εNd(t) values (−2.24 to −3.40), variable zircon εHf(t) values (−14.1 to +8.0), and high radiogenic Pb isotopic values (206Pb/204Pb = 18.588–18.790, 207Pb/204Pb = 15.616–15.642, and 208Pb/204Pb = 38.838–39.053). These geochemical characteristics indicate that the monzogranite was derived from a mixed source comprising ancient crustal and mantle materials, and experienced frac- tional crystallization during emplacement. We propose that the parental magma of the Mugagangri monzogranite was most likely generated during northward subduction of the Bangong Coujiang Meso-Tethys Ocean.

Koci, Jack, Wilkinson, Scott N., Hawdon, Aaron A., Kinsey-henderson, Anne E., Bartley, Rebecca, and Goodwin, Nicholas R. (2021) Rehabilitation effects on gully sediment yields and vegetation in a savanna rangeland. Earth Surface Processes and Landforms. (In Press)
Gully rehabilitation can contribute to catchment management by stabilising erosion and reducing downstream sediment yields, yet the globally observed responses are variable. Developing the technical basis for gully rehabilitation and establishing guidelines for application requires studies that evaluate individual rehabilitation measures in specific environments. An eight-year field experiment was undertaken to evaluate sediment yield and vegetation responses to several gully rehabilitation measures. The rehabilitation measures aimed to reduce surface runoff into gully head cuts, trap sediment on gully floors and increase vegetation cover on gully walls and floors. The study occurred in a savanna rangeland in northeast Australia. Two gullies were subject to treatments while four gullies were monitored as untreated controls. A runoff diversion structure reduced headcut erosion from 4.3 to 1.2 m2 y-1. Small porous check dams and cattle exclusion reduced gully total sediment yields by more than 80 percent, equivalent to a reduction of 0.3–2.4 t ha-1 y-1, but only at catchment areas less than 10 ha. Fine sediment yields (silt and clay) were reduced by 7 and 19 percent from the two treated gullies, respectively. The porous check dam deposits contained a lower percentage of the fine fraction than the parent soil. Significant regeneration of gully floor vegetation occurred, associated with trapping of organic litter and fine sediment. Increases in vegetation cover and biomass were comprised of native perennial grasses, trees and shrubs. In variable climates, long-term gully rehabilitation will progress during wetter periods, and regress during droughts. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.

Po, Sovinda, and Sims, Kearrin (2021) The myth of non-interference: Chinese foreign policy in Cambodia. Asian Studies Review. (In Press)
The discourse of “non-interference” features prominently in China’s so-called “peaceful rise” and “win – win” approach to international diplomacy. This article contests Beijing’s non-interference rhetoric through a case-study analysis of Cambodia. We make two core arguments: first, interference by foreign powers is not limited to actions that challenge a regime’s leadership, but can also include the reinforcement of regimes that lack popular support. Second, Beijing’s “non-interference” rhetoric is not demonstrated in the context of Cambodia, where it has repeatedly interfered to reinforce Prime Minister Hun Sen’s leadership during times of political contestation. To make these arguments, the article offers a historical summary of Chinese interference in Cambodia followed by an analysis of the key domains in which Hun Sen’s regime supports Chinese geostrategic interests. These are: support for Beijing’s One China Policy and its Belt and Road Initiative; support for Beijing in negotiations with ASEAN; and support for Chinese economic interests. Collectively, we argue that these domains contribute to the advancement of China’s “core national interest”, and it is therefore a myth to suggest that China has not interfered in Cambodia’s domestic politics.

Sims, Kearrin (2020) Laos set its own debt trap. East Asia Forum.
[Excerpt] On 23 September the Fitch Ratings agency downgraded Laos’ credit rating to CCC — the second downgrade in 2020, having dropped to B- in May. Much of the blame lies with COVID-19, which has seen Laos’ economic growth drop from 5.5 per cent in 2019 to a projected 0.5 per cent for 2020. This represents the country’s slowest economic growth recorded since 1990.

Rowe, Cassandra, David, Bruno, Mialanes, Jerome, Ulm, Sean, Petchey, Fiona, Aird, Samantha, McNiven, Ian J., Leavesley, Matthew, and Richards, Thomas (2020) A Holocene record of savanna vegetation dynamics in southern lowland Papua New Guinea. Vegetation History and Archaeobotany, 29 (1). pp. 1-14.
The southern lowlands of Papua New Guinea (PNG) are biogeographically distinct. Vast tracts of savanna vegetation occur there and yet most palaeoecological studies have focused on highlands and/or forest environments. Greater focus on long-term lowland environments provides a rare opportunity to understand and promote the significance of local and regional savannas, ultimately allowing non-forested and forested ecosystem dynamics to be compared. This paper examines palaeoecological and archaeological data from a lowland open savanna site situated on the south-central PNG coastline. The methods used incorporate pollen and micro-charcoal analyses, artefact recovery and sediment descriptions. We conclude with an environmental model of sedimentation and vegetation change for the past c. 5,800 years, revealing a mid to late Holocene savanna interchange between herbaceous and woody plant growth, with fluctuating fire occurrence increasing toward the present day. Increased silt deposition and modified regional hydrology are also recorded. Environmental changes correspond in timing with the start of permanent settlements and human use of fire. In particular, landscape burning for hunting and gardens for agriculture have helped create the open ecosystem still evident today.

Niu, Si-Da, Li, Sheng-Rong, Huizenga, Jan Marten, Santosh, M., Zhang, De-Hui, and Li, Zheng-Da (2020) ⁴⁰Ar/³⁹Ar geochronology, fluid inclusions, and ore‐grade distribution of the Jiawula Ag–Pb–Zn deposit, NE China: implications for deposit genesis and exploration. Geological Journal, 55 (2). pp. 1115-1127.
The Jiawula Ag–Pb–Zn deposit is located in the northern part of the Great Xing'an Range metallogenic belt within the eastern segment of the Central Asian Orogenic Belt. Here, we report results from muscovite ⁴⁰Ar/³⁹Ar geochronology and fluid inclusion study and formulate a vertical projection map of the ore grade in this deposit. The muscovite from the Jiawula deposit yields a plateau age of 133.27 ± 0.66 Ma and a ⁴⁰Ar/³⁹Ar isochron age of 131.88 ± 0.83 Ma. The muscovite ⁴⁰Ar/³⁹Ar data indicate a discrete second hydrothermal event postdating the mineralization, which we correlate with post‐collisional extension after the subduction direction of the Palaeo‐Pacific Plate changed. Low‐salinity aqueous fluid inclusions in quartz from the Jiawula deposit represent meteoric water or groundwater. Based on the fluid inclusion study, the fluids were trapped during cooling and decompression, which may have resulted in metal precipitation. We envisage that the copper precipitated from a high‐temperature fluid in the southern domain whereas lead, zinc, and silver precipitated at a lower temperature in the north. The spatial distribution of the ore‐forming elements, therefore, reflects the ore fluid migration‐cooling path from the south to north.

Preston, Robyn, Gratani, Monica, Owens, Kimberley, Roche, Poornima, Zimanyi, Monika, and Malau-Aduli, Bunmi (2020) Exploring the impact of assessment on medical students’ learning. Assessment and Evaluation in Higher Education. (In Press)
What and how students learn depend largely on how they think they will be assessed. This study aimed to explore medical students’ perception of the value of assessment and feedback on their learning, and how this relates to their examination performance. A mixed methods research design was adopted in which a questionnaire was developed and administered to the students to gain their perceptions of assessments. Perceptions were further explored in focus group discussions. Survey findings were correlated with students’ performance data and academic coordinators’ perceptions. Students’ perceptions of the level of difficulty of different assessments mirrored their performance in examinations, with an improvement observed in clinical assessments as students progressed through their degree. Students recognised that feedback is important to allow improvements and seek more timely, better quality and personalised feedback. Academic coordinators identified that some of the students’ suggestions are more realistic than others. Students had a positive attitude towards assessment, but emphasised the need for educators to highlight the relevance of assessment to clinical practice.

Munksgaard, Niels C., Zwart, Costijn, Haig, Jordahna, Cernusak, Lucas A., and Bird, Michael I. (2020) Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales. Hydrological Processes, 34 (1). pp. 111-124.
High-frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here, we present a near-continuous 6-month record of O- and H-isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both wet and dry seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near-continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales, and cross-wavelet analysis identified significant regions of common power for hourly averaged water vapour isotopic composition and relative humidity, wind direction, and solar radiation. Relative humidity had the greatest subdiurnal influence on isotopic composition. On longer timescales (weeks to months), isotope variability was strongly correlated with both wind direction and relative humidity. The high-frequency records showed diurnal isotopic variations in O- and H-isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean, whereas moisture transport from northerly directions occurred mainly during the wet season monsoonal airflow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.

Wiersma, Jelle P., Roberts, Eric M., and Dirks, Paul H. G. M. (2020) Formation of mud clast breccias and the process of sedimentary autobrecciation in the hominin-bearing (Homo naledi) Rising Star Cave system, South Africa. Sedimentology, 67 (2). pp. 897-919.
Unconsolidated mud clast breccia facies in the hominin-bearing (Homo naledi) Rising Star Cave, Cradle of Humankind, South Africa, are interpreted to have formed through a process termed sedimentary autobrecciation in this study. This process, by which most of the angular mud clast breccia deposits are thought to have formed autochthonously to para-autochthonously via a combination of erosion, desiccation, diagenesis and microbial alteration of laminated mud deposits, is thought to have taken place under relatively dry (i.e. non-flooded) conditions inside the cave. Subsequently, gravitational slumping and collapse was the dominant mechanism that produced the mud clast breccia deposits, which commonly accumulate into debris aprons. The mud clast breccia is typically associated with (micro) mammal fossils and is a common facies throughout the cave system, occurring in lithified and unlithified form. This facies has not been described from other cave localities in the Cradle of Humankind. Additionally, sedimentary autobrecciation took place during the deposition of some of the fossils within the Rising Star Cave, including the abundant Homo naledi skeletal remains found in the Dinaledi Subsystem. Reworking of the mud clast breccia deposits occurs in some chambers as they slump towards floor drains, resulting in the repositioning of fossils embedded in the breccias as evidenced by cross-cutting manganese staining lines on some Homo naledi fossil remains. The formation of the unlithified mud clast breccia deposits is a slow process, with first order formation rates estimated to be ca 8 x 10(-4) mm year(-1). The slow formation of the unlithified mud clast breccia facies sediments and lack of laminated mud facies within these deposits, indicates that conditions in the Dinaledi Chamber were probably stable and dry for at least the last ca 300 ka, meaning that this study excludes Homo naledi being actively transported by fluvial mechanisms during the time their remains entered the cave.

Van Ryt, M.R., Sanislav, I.V., Dirks, P.H.G.M., and Huizenga, J. (2020) Trace element associations in magnetite and hydrothermal pyrite from the Geita Hill gold deposit, Tanzania. Journal of Geochemical Exploration, 209. 106418.
Gold mineralization in the Geita Hill deposit is associated with pyrite formed along microfracture networks and sulfidation fronts together with K-feldspar and biotite. The sulfidation fronts are best developed in magnetite-bearing ironstone. The gold is present mainly as electrum and gold tellurides along grain boundaries, and as inclusions in pyrite, quartz, biotite and K-feldspar. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of pyrite and magnetite grains reflect complex fluid-host rock interactions. Magnetite textures and chemistry change with alteration intensity, indicating the progression of the alteration front into the host rock. Pyrite textures are uniform across all rock types and reflect late-tectonic growth linked to multi-staged infiltration of hydrothermal fluids. Trace element distribution patterns in pyrite are locally complex and influenced by host rock chemistry. Gold distribution patterns in pyrite correlate closely with Te, Ag, Bi and Pb, indicating that gold occurs in micro- and nano-inclusions of telluride minerals. This is especially so for gold in quartz veins, whereas gold in ironstone and diorite also occurs as electrum with an average Au/Ag ratio of 0.41. As, Co and Ni in pyrite are lattice bound and occur in high concentrations in ironstone and diorite where they show characteristic growth zoning patterns. Pyrite in quartz veins has As, Co and Ni concentrations that are low and variable. Cr, Cu, Mo, Mn and Zn are present in all rock types in isolated inclusions in pyrite grains, whilst Pb, Bi and Sb occur in more dispersed patches of fine clustered inclusions. The Se content in pyrite is typical for Archean gold deposits, and reflects an average temperature of ~340 °C for the mineralizing fluid. The Co/Ni ratio of pyrite grains varies between 0 and 5.2 in ironstone and diorite, and most likely reflects the equilibration Co/Ni ratio of the host rock. The Co/Ni ratio of pyrite grains in quartz veins varies between 1 and 12, and is consistent with a magmatic-hydrothermal origin for the ore fluid. Trace element distribution patterns in magnetite and pyrite indicate that As, Ni, Co, Cr, Mn and Cu were mostly locally derived, and remobilised into the pyrite during sulfidation of the host rock. The concentrations of these elements are strongly lithologically controlled, and they are not consistently incorporated into the pyrite after initial stages of growth. Au, Ag, Te, Bi and Pb were externally derived, and closely correlate in all varieties of pyrite as well as strongly altered magnetite. The alteration footprint of the Geita Hill deposit is limited in extent, and does not involve As and Sb that are typically enriched in Archaean lode-gold systems. Instead, Te and Bi are most characteristic for the deposit and could be of use as path finder elements together with altered magnetite grains.

Puga-Bernabéu, Ángel, Webster, Jody Michael, Beaman, Robin Jordan, Thran, Amanda, López‐Cabrera, Javier, and Daniell, James (2020) Submarine landslides along the mixed siliciclastic-carbonate margin of the Great Barrier Reef (offshore Australia). In: Ogata, Kei, Festa, Andrea, and Pini, Gian Andrea, (eds.) Submarine Landslides: subaqueous mass transport deposits from outcrops to seismic profiles. Geophysical Monograph, 246 . Wiley, Washington, DC, USA, pp. 313-337.
Submarine landslides on modern mixed siliciclastic-carbonate margins are poorly understood compared to their counterparts in other settings. We present a synthesis of four representative submarine landslides types along the Great Barrier Reef margin, the largest extant mixed siliciclastic-carbonate province in the world. The investigated examples are 5–31 km in length, extend over 18–528 km2, and have remobilized an estimated 0.025–32 km3 of sediments. They display morphological features corresponding to debris avalanches and slides. The estimated timing of two dated landslides is coincident with deglaciations corresponding to the transitions MIS 12–11 and MIS 2–1. Large seismic events were the most likely triggering mechanism for the landslides, where high pore water pressure in examples close to paleo-deltaic systems could also have preconditioned the eventual failure. A potential preconditioning factor, yet to be confirmed, is the geologic control associated with alternating mixed siliciclastic and carbonate sediments in the failed lithologies. The Gloria Knolls Slide is large enough to have significant tsunamigenic potential. Tsunami simulations show that this landslide would produce a sizable tsunami under present-day sea level conditions, with coastal run-up heights of 0.5–2 m. We highlight a reef buffering effect due to broader-scale shelf bathymetry and the complex structure of coral reefs.

Liu, Guangxian, Yuan, Feng, Deng, Yufeng, Wang, Fangyue, White, Noel, Huizenga, Jan, Li, Yue, Li, Xiaohui, and Zhou, Taofa (2020) Ore-fluid geochemistry of the Hehuashan Pb–Zn deposit in the Tongling ore district, Anhui province, China: evidence from REE and C–H–O isotopes of calcite. Ore Geology Reviews, 117. 103279.
Calcite is the main gangue mineral of the Hehuashan lead–zinc deposit, which is located in the Tongling ore district, Anhui Province, East China. The ore bodies of the Hehuashan deposit are hosted by dissolution breccia of the Lower Triassic carbonate sediments. We report petrography, rare earth elements (REE), and C–H–O isotope data of four generations of calcite recognized in the Hehuashan deposit, namely the pre-ore stage calcite (Cal-1), early ore-forming stage calcite (Cal-2), late ore-forming stage calcite (Cal-3) and post-ore stage calcite (Cal-4). In addition, we also report C–H–O isotopes data of dolostone from the Lower Triassic carbonate sediments. All four calcite generations show a low ∑REE content (13–50 ppm on average), indicating that the related ore-forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines. Low LREE/HREE ratio (1.1–6.1 on average) of all four calcite generations implies that no significant REE fractionation happened during the mineralizing processes. The wide distribution of Y/Ho ratios (17–70) of calcite indicates a result of fluids mixing. The δ¹³C values of calcite (1.4‰ to 4.2‰) are comparable to marine carbonates, but the δ¹⁸O values are lower, indicating possibly a result of carbonates dissolution. Calculated δ¹⁸O of the fluid in equilibrium with calcite vary from –3.1‰ to –0.1‰, combining the δDV-SMOW (–100‰ to –81‰), implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the Hehuashan deposit.

Sahlström, Fredrik, Chang, Zhaoshan, Arribas, Antonio, Dirks, Paul, Johnson, Craig A., Huizenga, Jan Marten, and Corral, Isaac (2020) Reconstruction of an early Permian, sublacustrine magmatic-hydrothermal system: Mount Carlton epithermal Au-Ag-Cu deposit, Northeastern Australia. Economic Geology, 115 (1). pp. 129-152.
The Mt. Carlton Au-Ag-Cu deposit, northern Bowen basin, northeastern Australia, is an uncommon example of a sublacustrine hydrothermal system containing economic high-sulfidation epithermal mineralization. The deposit formed in the early Permian and comprises vein- and hydrothermal breccia-hosted Au-Cu mineralization within a massive rhyodacite porphyry (V2 open pit) and stratabound Ag-barite mineralization within volcano-lacustrine sedimentary rocks (A39 open pit). These orebodies are all associated with extensive advanced argillic alteration of the volcanic host rocks. Stable isotope data for disseminated alunite (δ34S = 6.3–29.2‰; δ18OSO4 = –0.1 to 9.8‰; δ18OOH = –15.3 to –3.4‰; δD = –102 to –79‰) and pyrite (δ34S = –8.8 to –2.7‰), and void-filling anhydrite (δ34S = 17.2–19.2‰; δ18OSO4 = 1.8–5.7‰), suggest that early advanced argillic alteration formed within a magmatic-hydrothermal system. The ascending magmatic vapor (δ34SSS ≈ –1.3‰) was absorbed by meteoric water (~50–60% meteoric component), producing an acidic (pH ≈ 1) condensate that formed a silicic → quartz-alunite → quartz-dickite-kaolinite zoned alteration halo with increasing distance from feeder structures. The oxygen and hydrogen isotope compositions of alunite-forming fluids at Mt. Carlton are lighter than those documented at similar deposits elsewhere, probably due to the high paleolatitude (~S60°) of northeastern Australia in the early Permian. Veins of coarse-grained, banded plumose alunite (δ34S = 0.4–7.0‰; δ18OSO4 = 2.3–6.0‰; δ18OOH = –10.3 to –2.9‰; δD = –106 to –93‰) formed within feeder structures during the final stages of advanced argillic alteration. Epithermal mineralization was deposited subsequently, initially as fracture- and fissure-filling, Au-Cu–rich assemblages within feeder structures at depth. As the mineralizing fluids discharged into lakes, they produced syngenetic Ag-barite ore. Isotope data for ore-related sulfides and sulfosalts (δ34S = –15.0 to –3.0‰) and barite (δ34S = 22.3–23.8‰; δ18OSO4 = –0.2 to 1.3‰), and microthermometric data for primary fluid inclusions in barite (Th = 116°– 233°C; 0.0–1.7 wt % NaCl), are consistent with metal deposition at temperatures of ~200 ± 40°C (for Au-Cu mineralization in V2 pit) and ~150 ± 30°C (Ag mineralization in A39 pit) from a low-salinity, sulfur- and metal-rich magmatic-hydrothermal liquid that mixed with vapor-heated meteoric water. The mineralizing fluids initially had a high-sulfidation state, producing enargite-dominated ore with associated silicification of the early-altered wall rock. With time, the fluids evolved to an intermediate-sulfidation state, depositing sphalerite- and tennantite-dominated ore mineral assemblages. Void-filling massive dickite (δ18O = –1.1 to 2.1‰; δD = –121 to –103‰) with pyrite was deposited from an increasingly diluted magmatic-hydrothermal liquid (≥70% meteoric component) exsolved from a progressively degassed magma. Gypsum (δ34S = 11.4–19.2‰; δ18OSO4 = 0.5–3.4‰) occurs in veins within postmineralization faults and fracture networks, likely derived from early anhydrite that was dissolved by circulating meteoric water during extensional deformation. This process may explain the apparent scarcity of hypogene anhydrite in lithocaps elsewhere. While the Mt. Carlton system is similar to those that form subaerial high-sulfidation epithermal deposits, it also shares several key characteristics with magmatic-hydrothermal systems that form base and precious metal mineralization in shallow-submarine volcanic arc and back-arc settings. The lacustrine paleosurface features documented at Mt. Carlton may be useful as exploration indicators for concealed epithermal mineralization in similar extensional terranes elsewhere.

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