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Hydrochemical and isotopic fingerprinting of the Walloon coal measures and adjacant aquifiers in the Clarence-Moreton and Eastern Basins in Southeast Queensland
No full textThe Clarence-Moreton and the Surat basins in Queensland and northern New South Wales contain the coal-bearing
sedimentary sequences of the Jurassic Walloon Coal Measures, composed of up to approximately 600 m of
mudstone, siltstone, sandstone and coal. In recent years, the intensification of exploration for coal seam gas (CSG)
resources within both basins has led to concerns that the depressurisation associated with future resource
development may have adverse impacts on water resources in adjacent aquifers.
In order to identify the most suitable tracers to study groundwater recharge and flow patterns within the Walloon
Coal Measures and their degree of connectivity with over- or underlying formations, samples were collected from
the Walloon Coal Measures and adjacent aquifers in the northern Clarence-Moreton Basin and eastern Surat Basin,
and analysed for a wide range of hydrochemical and isotopic parameters. Parameters that were analysed include
major ion chemistry, δ13C–DIC, δ18O, 87Sr/86Sr, Rare Earth Elements and Yttrium (REY), 14C, δ2H and δ13C of CH4 as well
as concentrations of dissolved gases (including CH4).
Dissolved CH4 concentrations range from below the reporting limit (10 μg/L) to approximately 50 mg/L in
groundwaters of the Walloon Coal Measures. However, the high degree of spatial variability of methane
concentrations highlights the general complexity of recharge and groundwater flow processes, especially in the
Laidley Sub-Basin of the Clarence-Moreton Basin, where numerous volcanic cones penetrate the Walloon Coal
Measures and may form pathways for preferential recharge to the Walloon Coal Measures. Interestingly, dissolved
CH4 was also measured in other sedimentary bedrock units and in alluvial aquifers in areas where no previous CSG
exploration or development has occurred, highlighting the natural presence of CH4 in different aquifers.
Radiocarbon ages of Walloon Coal Measure groundwaters are also highly variable, ranging from very young (~82
pMC) to very old (0.43 pMC). While groundwaters sampled in close proximity to the east and west of the Great
Dividing Range are mostly young, suggesting that recharge to the Walloon Coal Measures occurs through the basalts
of the Great Dividing Range; there are otherwise no clearly discernable spatial patterns and no apparent
relationships with depth or distance along inferred flow paths in the Clarence-Moreton Basin.
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In contrast to this strong spatial variability of CH4 concentrations and groundwater ages, REY patterns and 87Sr/86Sr
isotope ratios of Walloon Coal Measure groundwaters appear to be very uniform and clearly distinct from
groundwaters contained in other bedrock units. This difference is attributed to the different source material of the
Walloon Coal Measures (mostly basalts in comparison to other bedrock units which are mostly composed of
mineralogically more variable Paleozoic basement rocks of the New England Orogen).
This study suggests that REY and 87Sr/86Sr ratios may be suitable tracers to study the hydraulic connectivity of the
Walloon Coal Measures with over- or underlying aquifers, although more studies on the system are required. In
addition, this study also highlights the need to conduct detailed water chemistry and isotope baseline studies prior
to the development of coal seam gas resources in order to differentiate between natural background values of CH4
and potential impacts of coal seam gas development
Estimating the inundation limits of small historical tsunamis
No full textThere has been considerable progress in tsunami research in recent years, yet most work has been focussed on
identifying and understanding the evidence of large events. This talk discusses the evidence for small historical
tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by numerous relatively small
historical tsunamis without depositing any notable sedimentary evidence. However, excavations of shallow soil
profiles revealed discontinuous layers of small grey mud clasts, most likely transported from the nearby harbour, at
various depths across the study area. The origin of these mud clast layers was investigated using a multi-proxy
approach comprising sedimentological, geochemical and diatom analyses complemented by radiometric dating and historical data. Subtle variations consistent with inclusions of marine mud, such as a decrease in organic content and
magnetic susceptibility and increases in geochemical markers (e.g. potassium, calcium) were found in the
sedimentary profile. Variations in diatom assemblages suggesting marine influence were also recorded at similar
depths, aligning with layers of mud clasts. Using 137Cs dating and historical data, these deposits were attributed to
the 1960 Chile and possibly 1964 Alaska tsunamis. Sedimentary evidence for the 2010 Chile tsunami was not found
at the study site, but geochemical analysis of surface samples revealed marked changes in calcium, chlorine,
strontium and titanium concentrations, indicative of a change from terrestrial to marine influence. This was used to
identify the landward extent of inundation. Ultimately, this study shows that a broad multi-roxy analysis can
distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © Geological Society of Australia In
How weather cand climate influences speleothem growth and paleo-climate isotopic records
No full textSpeleothem growth band variations in chemical and isotopic composition are used to infer paleo-climatic conditions.
Interpretation of speleothem paleoclimatic records may be improved by matching analysed subsamples to the
represented elapsed time and prevailing weather or climatic conditions. Analysed subsamples may represent a
month for rapid growth speleothems or many years for slow speleothem growth. Speleothem growth may also be
seasonally biased affecting the paleo-climate record. To better understand the temporal fine scale of speleothem
growth patterns we have principally used CO2 concentration in cave air. As CaCO3 is precipitated to accrete a new
speleothem layer, CO2 is released into the atmosphere. However, CO2 may also come from other sources. To
discriminate between different sources a real-time isotopic CO2 analyser, located near the entrance to Chifley Cave,
is used. Cave air is sequentially sampled for 10mins from 4 internal and 2 external locations and analysed for H2O,
CH4, CO2, and 13CCO2. The 3 principal sources of CO2 are external air, speleothem growth and soil-air. The proportion
of each CO2 source contributing to the total cave air CO2 is calculated for each sampled Chifley Cave location. CO2
exhaled from passing tour groups is often recorded as a minor rapid increase before subsiding to the previous
background levels over 10–15 mins. Cave air CO2 shows a seasonal (summer maximum) and often a diurnal cycle,
from a minimum late morning to a maximum in the late evening caused by ventilation of external low CO2 air.
Differences between the external temperature and the near constant cave air temperature causes a buoyancy
contrast which drives bidirectional cave air ventilation. On hot days cool cave air (11°C) sinks into the Grand Arch and
is replenished by sucking external air from the Plughole cave opening. The slightly lower cave atmospheric pressure
on hot days also causes soil-air rich in CO2 to seep into Chifley Cave, notably at the bottom of Katies Bower. On cold
winter days relatively buoyant warm cave air escapes via the Plughole 70 m above and through minor fissures
reversing the summer pattern. A detailed description (10 min sampling for 2 years) of the speleothem growth
pattern in response to external temperature variation is presented
IBA methods for characterisation of fine particulate atmospheric pollution: a local, regional and global research problem
No full textThe IBA techniques of PIXE, PIGE, RBS and PESA have been used simultaneously to analyse fine particle pollution collected on Teflon filters. This provided a suite of 23 elements from hydrogen to lead which can be used to characterisation and fingerprint pollution sources and estimate their contributions to the total mass loading. These methods have been demonstrated to be applicable for aerosol pollution studies on a local, regional and even globe scale on time frames from a few days to decades. © 2020 Elsevier B.
Environmental impact of radiotracer studies: biota dose assessment
No full textThe intentional release of short lived radioisotopes to trace transport and partitioning processes in the environment has been in decline in recent decades due to negative regulatory and public perceptions of the associated risks. Radiotracing is subject to significant regulatory requirements; in some jurisdictions one of these requirements is to demonstrate that radiation exposure to ecosystems is limited to ensure protection of populations of species.
Radiation exposures from radiotracer studies are localised, transient and infrequent by nature, making it difficult to apply guidelines and biota dose assessment tools that are designed for chronic and widespread exposure scenarios. We will discuss the limitations of available guidelines and dose assessment methodologies when applied to radiotracer studies. A range of case studies for biota dose assessment will be presented using a variety of available tools including the ERICA Assessment Tool, the methodology of Copplestone et al. (2001) and a dynamic dose assessment model (Vives I Batlle et al., 2008). These case studies demonstrate that steady state, spatial homogeneity and bioavailability assumptions inherent in available dose assessment tools may lead to an over-estimate of dose to biota from radiotracer studies, and that many radiotracer studies can be conducted with minimal dose to biota
Radiotracer applications: case studies from four continents
No full textCase studies are a simple way to demonstrate how radiotracers can be successfully used in the environment in addressing water resources contaminant transport and coastal management issues. This paper presents ten case studies from Korea, France, Brazil, Hong Kong, Australia, Belgium and Sweden using a variety of radiotracers including 99mTc, 198Au, 3H, 82Br, 32P, 175+181Hf, 160Tb, 51Cr(III), 65Zn, 54Mn and 35S. These studies address physical transport processes such as dispersion and mixing, reactive transport and adsorption and contaminant uptake. Traced components include water, effluent, nutrients, contaminants and mud in rivers, lakes, wetlands and coastal waters.International Atomic Energy Agenc
A new continuum regression model and its application to climate and rainfall isotope relationships
No full textClimate field reconstruction using networks of rainfall-isotope proxies is an example
of a problem that requires the estimation of a model that aims to predict one field (Y) using
another field (X). The general problem is to estimate a subspace of X that retains useful
information for predicting Y. Methods to estimate such subspaces include principal
components regression (PCR), partial least squares (PLS), redundancy analysis (RDA), and
canonical correlation analysis (CCA), but these methods typically do not estimate the same
subspace. One solution is to treat these different methods as end members of a continuous
manifold of regression subspaces. By weighting the end member solutions in some way, we
can search for the best regression subspace over the manifold.
In this study, a new continuum regression model is developed by extending an earlier
method known as Principal Covariates Regression (PCovR). PCovR has two end members:
PCR and RDA. Here, PCovR is extended by shrinking the covariance matrix of X. As a
result, our new method regPCovR includes three end members (PCR, RDA and PLS) and is
particularly suited to climate data, where the spatial dimension is larger than the temporal
dimension, and where there are missing values in the response field (Y). regPCovR includes
both a weighting parameter and shrinkage parameter, which are estimated using crossvalidation.
The benefits of regPCovR are illustrated using two examples. In the first example, the
problem of predicting the southern Australian winter rainfall (P) field from the regional
winter sea level pressure (SLP) field is investigated. The best rank two regression subspace
found by regPCovR explains over 50% of the variance in the rainfall field. This subspace
thus estimates the relationship between SLP and P better than the end member subspaces. In
the second example, PCovR is used to investigate the relationships between the winter SLP
and P fields, and rainfall isotope (d18O) data from Australia and New Zealand. Two main
patterns are identified, which explain about half the variance in the southern GNIP d18O sites.
Subspace projection is used to relate these patterns to various regional and Southern
Hemisphere climate indices. regPCovR will be useful for finding subspaces that better capture the relationships
between climate and rainfall isotopes, which is a necessary step for quantitative
palaeoclimatology. © The Author
Accelerator Mass Spectrometry on SIRIUS: new 6MV spectrometer at ANSTO
No full textAs a part of Australian Federal Government funding in 2009 to establish a centre for
accelerator science a new 6 MV state of the art accelerator – SIRIUS – was purchased. The
system is now commissioned and comprises ion sources and beam lines to cater for a wide
variety of both IBA and AMS applications. The ion source used for AMS (MC-SNICS) is
the latest incarnation followed by 45 degree spherical ESA(R=0.3 m) and double focusing
injection magnet (R=1 m, ME=20) prior the accelerator. At the terminal we have a choice
of 2 stripper gasses and/or stripper foils. The high-energy spectrometer for AMS consists
of a 1.27 m radius analyzing magnet with ME=176, 45 degree ESA (R=3.81m), followed
by a switching magnet and 3 beam lines: one with a standard multianode ionization
chamber; one with an absorber cell in front of the detector; whereas the third beam line
has a time-of- ight detector. Details of the instrument design and performance data for
10Be, 26Al and 36Cl will be presented. © The Author
Late Holocene climate variability In the Australian Alps: can sedimentary and geochemical tracers track fine scale paleo-environment change?
No full textThe Australian Alps have experienced some of the most dramatic change in any Australian landscape
over the last glacial cycle, i.e. shifting between cold-climate conditions, glacial growth and
dominance of periglacial processes and present day (warm) conditions. While these large scale
changes are well documented, less is known about how the Alps have responded to more minor
palaeo-climate change during the Holocene. Minor temperature changes may result in a measurable
landscape response because they would be expected to manifest in changes to the occurrence of
cold-climate processes, such as freeze thaw or solifluction, or conversely, increased vegetation cover
and landscape stability. Sedimentary records from cirque lakes, therefore offer the potential to
examine palaeo-environmental change in the alpine region during the late Holocene. In this study
we examine recent (late Holocene) changes in the Alpine region of Kosciuszko National Park using
cores extracted from Blue Lake and Club Lake. The two short cores date from 3,500 and 1,900 cal. yr
BP, respectively. At Blue Lake, there is relatively little change recorded over most length of the core
with the exception of a minor period of changing sedimentation rates and increased charcoal at
2,200-2,800 cal. yr BP, implying possible increased fires and associated landscape instability.
Similarly, the Club Lake core also records little variability, although a change in sediment
geochemistry implies the addition of less weathered material to the lake during the Little Ice Age,
implying a potential increase in physical weathering. The most substantial change in both cores
occurred within the last 200 years, with the addition of finer, less organic and significantly more
chemically weathered material to the lakes. This coincides with the onset of grazing in the alpine
region. This change implies that there has been increase in the contribution of sediment derived
from soil to the lakes and, in particular, an increased contribution from subsoil (which in the case of
the Australian Alps are more weathered). Finally, there is evidence of recovery in the top few
centimetres of the cores implying conditions in the Alps have recovered from the dramatic grazing
era perturbation, with conditions now similar to those over most of the late Holocene. © Author(s
Holocene record of gradual, catastrophic and human influenced environmental change at Moashitu wetland, D'Urville Island, New Zealand
No full textActive tectonism, sea level fluctuation and human arrival have moulded the present day physical
environment of New Zealand. Coastal wetlands are recognised archives of Holocene environmental changes.
By applying sedimentological, geochemical and chronological techniques to coastal wetlands, natural and
anthropogenic changes can be observed. Moawhitu Wetland, located on D’Urville Island, New Zealand, is
home to a Maori oral tradition that describes a giant wave destroying a community in the 15th century. Little
geological work has been carried out to investigate the evidence of the event and no studies have researched
the palaeoenvironmental history of the area. This research was therefore aimed at reconstructing the
Holocene environmental record at Moawhitu Wetland to determine if there was evidence of severe changes
to the landscape as described in Maori oral traditions. Three sedimentary sequences from Moawhitu Wetland were used to reconstruct a 7500 year record that
incorporated gradual, catastrophic and human influenced changes. The record was established by using
multiple sedimentary proxies (grainsize, organic matter content, geochemistry and mineralogy) at three
different sites that were temporally aligned with dating techniques (14C and 210Pb) . Barrier formation, lake
and wetland formation, erosion, human influences and a tsunami ~3000-3300 yr BP were identified in the
sedimentary record. These changes were applied to a broader spatial context from which inferences of sea
level rise, regional faulting and potential climate change were drawn. The central west coast of New Zealand
has undergone an array of short and long term environmental changes throughout the Holocene and can be
identified as an area susceptible to potential tsunami events