Steven M. Hill

Termite species variations and their importance for termitaria biogeochemistry: towards a robust media approach for mineral exploration

ABSTRACT Termitaria (termite mounds) are a widespread and abundant component of tropical savannah ecosystems in northern Australia. Despite their abundance very little systematic research has been carried out on the application of termitaria sampling to mineral exploration in this region. Multi-element biogeochemistry of termitaria from species with the most abundant epigeal mounds (Nasutitermes triodiae (N. triodiae), Drepanotermes rubriceps (D. rubriceps) and Amitermes vitiosus (A. vitiosus)) is characterized and compared. Differences in the biogeochemistry of termitaria built by different species are identified in this biogeochemical study of the termitaria at the Titania Au Prospect, situated proximal to a palaeochannel system in a highly prospective area in northern Australia. In particular, elevated levels of Mo and Au in the coarse sand fraction of the D. rubriceps mounds are observed. Mineralization is expressed in the biogeochemical characteristics of termitaria through up to 15 m of transported regolith, particularly in the fine, silty-clay fraction of the mound samples. This is particularly obvious for Au, As, Zn and Ni, which all show relatively high analytical concentrations within material sampled from termitaria of N. triodiae. These findings show that termitaria can successfully delineate buried mineralization, reinforcing the role that soil biota, such as termites, play in forming surface geochemical anomalies above mineralization buried by transported regolith.

Biogeochemical expression of buried gold mineralization in semi-arid northern Australia: penetration of transported cover at the Titania Gold Prospect, Tanami Desert, Australia

ABSTRACT Gold mineralization at the Titania Prospect in the Tanami Desert Region is buried by transported regolith including mixed aeolian and sheetflow deposits over palaeodrainage sediments. This prospect is the only example of discovery through significant thickness of transported regolith and therefore provides an important site for developing an understanding of geochemical pathways from buried mineralization. Plant sampling for biogeochemical analysis was conducted over this prospect in October 2005 with the aims of characterizing the expression of the mineralization and in particular what species best expressed the chemical signature of the buried mineralization. The multi-element chemical compositions of leaves or phyllodes were compared across the mineralized and adjacent ‘background’ areas as well as between adjacent plants at the same sites to directly compare the uptake properties of different plant species. The nine most widespread and abundant plant species at the prospect were sampled, of which three are of particular interest. The soft spinifex (Triodia pungens) expressed all of the key ore indicator elements (Au, As, Zn, S) and best delineated the buried mineralization. Melaleuca lasiandra and Acacia bivenosa also delineated the mineralization but their usefulness is reduced because of their more restricted distributions. Baseline elemental levels varied among species, and it is suggested that these differences largely relate to differences in rooting depth and thereby the plants ability to access different parts of the regolith profile.

‘Of droughts and flooding rains’: an alluvial loess record from central South Australia spanning the last glacial cycle

Abstract Deposits of proximal dust-derived alluvium (alluvial loess) within the catchments of the now semi-arid Flinders Ranges in South Australia record regionally synchronous intervals of fluvial entrainment, aggradation and down-cutting spanning the last glacial cycle. Today, these floodplain remnants are deeply entrenched and laterally eroded by ephemeral traction load streams. The north–south aligned ranges are strategically situated within the present-day transitional zone, receiving both topographically enhanced winter rainfall from the SW and convectional downpours from summer monsoonal incursions from the north. We develop a regional chronostratigraphy of depositional and erosional events emphasizing the Last Glacial Maximum (LGM). Based on 124 ages (94 accelerator mass spectrometry radiocarbon and 30 optically stimulated luminescence) from the most significant terrace remnants on both sides of the Ranges, we conclude that the last glacial cycle including the LGM was characterized by major environmental changes. Two pronounced periods of pedogenesis between c. 36 and 30 ka were followed by widespread erosion and reworking. A short-lived interval of climatic stability before c. 24 ka was followed by conditions in which large amounts of proximal dust (loess) were deposited across the catchments. These loess mantles were rapidly redistributed and episodically transported downstream by floods. The termination of this regime c. 18–16 ka was marked by rapid incision.

Neotectonic disruption of silicified palaeovalley systems in an intraplate, cratonic landscape: regolith and landscape evolution of the Mulculca range-front, Broken Hill Domain, New South Wales

The landscape expression of a wide range of ancient and contemporary regolith materials in the vicinity of the Mulculca Fault demonstrates two important points: (i) tectonism can be a significant factor in the evolution of landscapes in some parts of the Australian craton; and (ii) ancient and young regolith‐landform features can coexist within a tectonically active landscape. Tectonic activity along the Mulculca Fault has created a range‐front near the Broken Hill Domain ‐ Murray Basin margins. This tectonism defeated a now silicified palaeodrainage system that flowed from the area now occupied by the Barrier Ranges towards the present area of the Murray Basin. Stream defeat led to the development of lacustrine‐overbank conditions within the area of the fault‐angle depression, which was later breached by stream incision across the range‐front. The area of lacustrine‐overbank deposition is now dominated by alluvial (channel and overbank) deposits with minor colluvial and aeolian deposition. Silicification of palaeovalley sediments and adjacent saprolite has been occurring over a broad range of times during landscape development, including several stages of palaeovalley evolution and as minor red‐brown hardpan development in the contemporary landscape. Ferruginised regolith has been developing at many different times during the evolution of the landscape, including: (i) prior to the defeat of the palaeodrainage system; (ii) during the sedimentary infilling of the fault‐angle depression; and (iii) within the contemporary landscape. The variable preservation and, therefore, landscape expression of a wide range of regolith materials that formed over a long period of landscape evolution has persisted even though there has been tectonic activity along the Mulculca Fault. For example, topographically inverted, and therefore ancient, silicified alluvial deposits occur alongside contemporary colluvial and alluvial deposits along the tectonically active range‐front. This is in contrast to simple models invoking long‐term tectonic stability to account for the expression of ancient regolith and landforms in Australian cratonic landscapes.

Sr-isotopes as a tracer of Ca sources and mobility in profiles hosting regolith carbonates from southern Australia

Regolith carbonates are common in soil profiles in the arid to semiarid areas of southern and central Australia. Extrinsic sources are now inferred to be the dominant source of Ca even as far inland as Alice Springs in central Australia. This study of Ca sources in a near coastal 2 m deep profile at Clarendon, South Australia, and two inland 4- and 3 m-deep profiles near Olary, South Australia uses Sr isotopes as a proxy for Ca. Our results show that up to 90% of Sr (and by association Ca) in both labile fractions and in soil carbonate is sourced from atmospheric input. The silicate weathering input is minor (<10%) and independent of the influence of different bedrock types. The Sr isotope composition throughout the profiles is relatively homogeneous with most values between 0.714 and 0.717, increasing only when in the saprolith, indicating that a process of continual reworking and mixing of the Sr (and Ca) goes beyond the near surface and continues throughout the profile.

A terminal Last Glacial Maximum (LGM) loess-derived palaeoflood record from South Australia?

Evidence of global climate change is expected to be first seen in polar regions, where subtle changes in climate may have large impacts on fragile geomorphic systems. Polar dunes are one such system for which there is little precise information available. For example, the extent to which polar aeolian deposits are stabilized by ice-bonded sands is unknown. As a first step towards a better understanding of the response of polar desert aeolian systems, we have mapped the sand dunes in Victoria Valley, Antarctica over the past four decades. The dune field is located at the confluence of the Packard and Victoria Valleys and has been the focus of field measurement programs for more than 40 years. Previous studies indicate that dune mobility has been limited to the crests shifting over ice-cemented sand layers within the dune in response to the Valley’s bi-direction wind regime. This is believed to impede net migration of the dune field. Short-term field studies have shown erratic movement of the dunes with the range between –14 and 62 m. However, no study has been made of longer term change in the morphological character of the dune field. In this study we use vertical air photographs and LIDAR data to map dune change over a 43 year period. We assess change in dune position and morphology over time. We find that the dunes have migrated (up to 75 m), and that dune form has changed, principally by lateral coalescing and limb extension. Movement of the dunes suggests that migration is possible despite the presence of ice and snow within the dune core. In addition, these changes support earlier observations that indicate a net (westerly) migration driven by topographically channeled thermally generated easterlies and gradient southeasterly winds. We infer this to indicate that the region has not undergone significant change in weather patterns in the last four decades. This is in agreement with the findings of Ayling and McGowan (2006) who investigated dust deposits on the adjacent Victoria Lower Glacier. Accordingly, it would appear that neither change in weather or climate due to global warming has caused significant change to the meteorology of the Victoria Valley, Antarctica and in-turn its aeolian geomorphic system.Plant macrofossils from permafrost deposits at the Bolshoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic were studied aiming at the revelation of climatic similarities and distinctions between the last and the current interglacial. The plant remains revealed the existence of a shrubland dominated by Alnus fruticosa, Betula nana, and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Pollen-based climatic reconstructions using the best modern analogue (BMA) approach suggest a mean temperature of the warmest month (MTWA) range of 914.5 °C during the warmest interval of the last interglacial. Reconstructions from plant macrofossils based on thermal minimum needs of included plants, representing more local environments, gained MTWA values above 12.5 °C in contrast to todays 2.8 °C. We explain this contrast in summer temperature and moisture conditions with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial. The project was funded by the German Research Foundation (DFG).Over two-thirds of northern and central Britain has been glaciated during the Quaternary, and the present landscape is a relict of the glacial processes that have acted to erode and redistribute large quantities of geological material. The landscape of Southern Britain by contrast, which lay largely beyond the maximum ice extent, was not subjected to such processes. Instead the present form of the landscape reflects approximately 2.5 million years of subaerial weathering under a climate regime, characterized since the onset of the Middle Pleistocene, by a long-term trend of periglacial-Interglacial-periglacial cycles operating with 100ka cyclicty. The effect of this, as preserved with the geological record, has been the extensive in-situ weathering of bedrock materials and the development of thick regolith. Since the region became populated, deforestation and cultivation has progressively removed the vegetation that once acted to stabilize the regolith, and the regolith material is now highly susceptible to erosion by hillwash and solifluction processes. This represents a significant ground stability hazard especially in relation to the subsidence and collapse of roads and property. In addition, large valley accumulations of regolith material can liquefy under prolonged periods of intense rainfall and can result in catastrophic flooding and landslide events, such as those that occurred in Lynmouth in 1952 and more recently, in Boscastle on the north Cornwall coast in 2004. This abstract reports the findings of research undertaken both to map the spatial extent of these regolith deposits, and also to understand what controls their local and regional distribution. The research, based upon field analysis and NEXTMAP digital terrain models from two test areas in southwest England, reveals that the spatial distribution of in-situ and soliflucted regolith material is largely controlled by lithological variability and structural complexity of the bedrock. It is hoped that these models will prove an invaluable to planners to enable informed decision making and the prediction of natural geohazards.QUAVIDA is a new project which aims to understand the interactions among vegetation structure and function, climate and fire regimes during the Late Quaternary. The project targets Australasia as a critical area in the development of a global picture of environmental change. Australasia has experienced major wet/dry, temperature and atmospheric CO2 fluctuations in the past; human arrival and occupation have also had a substantial environmental influence. Much of the vegetation within the region is fire-prone (and fire-adapted), with fire management long and widely practised. We need to understand the natural climate variability, disentangle the role of humans in past changes and investigate how plant types, vegetation and fire regimes will respond to future climate changes. QUAVIDA will do this by using state-of-the-art earth system models in hypothesis-testing mode, running simulations for specific times in the past but with different model components operative and using different scenarios of external and internal forcing. In order to evaluate and interpret these simulations, comprehensive data sets describing palaeoenvironmental conditions at key times in the past will be required. Thus, the first major focus of activity within QUAVIDA has been the creation of a comprehensive database of palaeoenvironmental information from Australasia, covering the last 70,000 years. The database contains radiometrically-dated pollen, phytolith, plant macrofossil, stickrat midden, carbon isotope and charcoal records. Interrogation of this database will yield benchmark reconstructions of vegetation patterns and fire regimes for the evaluation of the model simulations. Using more than one source of palaeoenvironmental information allows differences in the temporal and spatial scale of different kinds of observations to be taken into account in making reconstructions. It also allows for the fact that different sources record different aspects of climate and/or environmental changes. This presentation will introduce QUAVIDA, the methods and preliminary results of the palaeo-data synthesis, and discuss the project’s contribution to the international earth-modelling community.In February 2004, a 4 m core spanning the last ~ 40 ka was retrieved from Native Companion Lagoon (NCL), southeast Queensland, Australia using a Russian D-section corer. Analysis of the top 1 m of the core, which represents the Holocene, identified a pronounced increase in aeolian sedimentation commencing at ~5700 cal BP with peaks in the deposition of wind transported sediment of 12.5 g m−2a at 4690 cal BP and 10.8 g m−2a at 3890 cal BP before decreasing to 0.3 g m−2a at ~2000 cal BP. The increase in aeolian sedimentation ~5700 cal BP was coincident with a pronounced increase in charcoal content of the core, thereby indicating that fire was most likely a key agent in the destabilisation of the local dunes. Geochemical provenance of the long traveled dust component of the record identified western Queensland and southwestern New South Wales as the dominant source areas. Analysis of pollens from the core indicate a reduction in aquatics similar to that reported by Donders et al. (2006) for Lake Allom, Fraser Island, while there was also a reduction in rainforest and pteridophytes. As a result, we believe that this period of increased aeolian sedimentation was caused by prolonged and severe drought possibly linked to the onset of ENSO type conditions in the mid-Holocene as reported by Moy et al. (2002) and Gagan et al. (2004). Through analogy with contemporary ENSO events, precipitation bearing southeasterly trade winds would have been suppressed and replaced by more frequent and dry west to southwesterly winds as indicated by the provenance of far traveled dust to west and southwestern source areas. Importantly, the NCL record identifies southeast Queensland as a region susceptible to prolonged and severe drought as a consequence of more persistent ENSO type conditions. Recent modeling studies suggest that ENSO type conditions may transform from their current interannual variability into the mean climate as a consequence of global warming. Our results suggest that if this was to occur, then southeast Queensland may experience the onset of another arid phase.A high resolution pollen record from the ODP 820 marine core for the last million years is presented. It is chronologically controlled by marine stratigraphic data.This record provides a picture of substantial vegetation and environmental change for the humid tropics region of northeastern Australia. It is the first largely continuous record in Australia to cover this length of time in any detail, although sediment accumulation rates decrease with increasing age. The influence of orbital forcing (particularly eccentricity and obliquity) is clearly present in the record providing good support for the proposed age model based on the marine stratigraphy, but each isotope stage contains some distinctive features. Superimposed on these cyclical patterns are abrupt and sustained changes in the representation of many taxa and community types that may be explained by a combination of regional changes in oceanic and atmospheric circulation systems throughout this time period, along with the impacts of people in the later part of the record (i.e. last 45,000 years BP).

Riparian eucalypt biogeochemical expression of groundwater salinity, Murray River, South Australia

Salinisation of floodplains along the Murray River is a significant environmental and social problem in south-eastern Australia that can be expensive and time-consuming to monitor. The potential of plant biogeochemistry as an environmental monitoring tool, specifically its innovative application to groundwater salinity detection, is explored in this paper. Major and trace element biogeochemical data were compared to data from three geophysical surveys in the study area as well as field observations of the underlying stratigraphy. The result is an understanding of how groundwater chemistry can be characterised by plants, specifically river red gum (Eucalyptus camaldulensis) and black box (Eucalyptus largiflorens) leaves. From the survey it is evident that E. camaldulensis and E. largiflorens were both successful in expressing high salinity levels in the subsurface. Molybdenum was the most suitable pathfinder element for high salinity groundwater. The study has important implications for interpreting biogeochemical mineral exploration results; anomalous element concentrations need to be interpreted in relation to salinity levels.