School of Earth Sciences - Theses

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The Variation of atmospheric carbon dioxide,methane and nitrous oxide during the holocene from ice core analysis

MacFarling Meure, Cecelia. (University of Melbourne, 2004)

Recent studies have demonstrated that the atmospheric concentrations of radiatively important greenhouse gases, including methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O) and carbon monoxide (CO), have significantly increased during the past 200 years due to anthropogenic emissions. Analysis of air trapped in polar ice cores allows for past atmospheric variations due to natural climate conditions to be investigated, placing recent changes in a historical context. In this thesis new high- precision, multispecies measurements of atmospheric trace gas concentrations during the Holocene have been produced by analysing the air trapped in the ice at Law Dome, East Antarctica (66�46'08"E, 112�48�28�S). The ice core records are well-dated, have high age resolution and overlap with modem instrumental records due to the high accumulation rate at the drilling sites. The combination of high age resolution, precise dating and high precision measurements allows for subtle, decadal-scale variability to be detected. The multispecies measurement technique allows for biogeochemical causes of variations to be identified. The first part of this study focused on the late Holocene period (AD 0 to 1975). New high-precision records of CH4, CO2, N2O and CO have been produced for this period. The CH4 and CO2 measurements are used to build upon the existing Law Dome records of these gases during the last 1000 years, to validate and further define previously observed variations. The new measurements extend the records of these gases by another 1000 years. As a consequence of the multispecies measurement technique it has been possible to also measure N2O and CO during this period. These new measurements highlight the atmospheric response to the Little Ice Age (LIA) cooling (AD 1550 to 1800), particularly a 10 ppm decrease in atmospheric C02 between AD 1550 and 1600. A stabilization of CO2 during the 1940s was also confirmed in the Law Dome record. Increased data density during this period shows that the atmospheric CO2 mixing ratio stabilized at ~310 ppm between 1937 and 1955. New signals were observed in the extended records, including a 100 ppb increase in the CH4 concentration between AD 0 and 1800, which is probably the result of increasing pre-industrial anthropogenic emissions. The second part of this study focussed on the CO2 and CH4 response to a rapid, abrupt cooling at 8,200 years BP. The Law Dome (DSS) measurements are complemented by four measurements of NorthGRIP (Greenland) ice core. A decrease of at least 52 ppb CH4 is observed in the DSS record, and a decrease of at least 62 ppb is observed at NorthGRIP during the same period. A smaller CO2 response of 4 to 5 ppm is seen in both the records. The CH4 signal is used to improve the chronologies of these ice cores by synchronising with other well-dated CH4 records, specifically GRIP (Greenland) and Dome C (Antarctica).
The geology, petrology and geochemistry of the granitic rocks of Victoria

Rossiter, Allan G. (University of Melbourne, 1973)

In the field the granitic rocks of Victoria show a wide variety of characteristics but chemically all are related and are the result of similar processes that occurred cyclically during the Palaeozoic. The granites may be divided into two groups on the basis of whether or not primary hornblende is present in the more basic members of the suite. Rocks of the hornblende-free series concentrate mainly in central Victoria and usually contain biotite that is red-brown in colour. In the granites of the hornblende-bearing group green-brown biotite is generally present. The two different colours appear to indicate unlike oxygen fugacities in the magmas from which the micas crystallized. The rocks of the hornblende-bearing and hornblende-free provinces also vary slightly in chemistry - the most important difference being that the basic members of the first group contain slightly more Ca than those of the second having comparable silica content. The compositions of the Victorian granites is consistent with their derivation by anatexis of a mixture of basic igneous rocks and sedimentary material. The conclusion is drawn that a combination of Cambrian basalts and dolerites and Cambro-Ordovician sediments constitute the source. The explanation of the fact that two chemical trends are observed in the granites may lie in the possible existence of two chemically distinct groups in the Cambrian igneous rocks - the one having lower Ca predominating under central Victoria.
Antarctic sea ice and its interactions with high latitude weather and climate

Watkins, Andrew Bruce ( 1998)

Antarctic sea ice plays a major role in the earth system by greatly influencing the high latitude exchanges of heat, moisture and momentum between the ocean and atmosphere, as well as profoundly effecting the salt budget of the ocean, and thus the production of Antarctic Bottom Water, one of the driving mechanisms of worldwide oceanic circulation. With such considerable and far reaching impact, it is important to document its climatology, understand its variability and quantify its influence. Climatologies and trends of the Southern Ocean sea ice pack are presented using the most recent satellite observations available from the Defense Meteorological Program’s (DMSP) Special Sensor Microwave Imager (SSM/I). The analysis of these data show that Antarctic sea ice is highly variable in both time and space. Statistically significant increases in the sea ice extent, open water and ice areas have been determined from the SSM/I data for the 9 year period 1987 to 1996, a result which differs from the Scanning Multichannel Microwave Radiometer (SMMR) observations (1978-1987). The increasing trend in the SSM/I observations can be attributed to the large increases in sea ice observed in 1994-1995, as confirmed by an analysis of data from the ERS-1 satellite. The mean season length during these years has remained relatively unchanged. Regional trends, both in the sea ice concentration and in season length, showed vast spatial inhomogeneity. SSM/I data displayed increasing season length in the central Weddell Sea, Bellingshausen Sea and Balleny Islands regions, with decreasing length in the Amundsen Sea, eastern Ross Sea and in the coastal areas off Wilkes Land. Similar trends are observed in the seasonal sea ice concentration. In most cases, these trends are opposite to those observed in the SMMR data, which may be linked to the shift observed in the Amundsen Sea low after 1990. Comparisons with historical data would suggest that no large scale anomalous change has occurred in the Antarctic sea ice limits over the course of human observation. Furthermore, the degree of variability suggests great care is needed in interpreting large scale changes in sea ice conditions, and hence atmospheric or oceanic change, from locally observed anomalies. Case studies of the effect of individual cyclones upon the sea ice concentration show small but definite modification of the ice conditions. To further diagnose aspects of the thermodynamic and dynamic forcing upon the Antarctic pack, detailed analysis of the sea ice concentration variability has been conducted using spectral techniques, and the spectra have been compared to those of the European Centre for Medium Range Weather Forecasts (ECMWF) temperature and wind data. In all cases, and with the seasonal cycle removed, the sea ice concentration shows a bias towards longer timescales of variability than either the wind stress or surface air temperature. This “red shift” in its frequency spectrum is strongest with the wind stress, and weakest with the temperature. For longer period waves, this may be due to the formation of new ice by surface cooling or the moderation of melting by the cold surface water, whereas for shorter period waves, where wind stress dominates temperature and ice concentration respectively, time is required for winds to draw in warmer or cooler air, as well as to overcome the ice masses inertia and keel friction to open or close leads. Strong intraseasonal variability of the sea ice concentration is observed in the 20-25 day period, reflecting similar timescales of the temperature variability, as well as that of the energetic eddies of the Antarctic circumpolar current. Examination of the latitudinal variation of the sea ice concentration, temperature and wind stress spectra showed not only the importance of the north-south temperature gradient in influencing the variability, but also the seasonal changes in the semi annual oscillation of the circumpolar trough. Regional spectra showed clear differences between location, and reflected the influences of the atmosphere and ocean upon the sea ice pack. This is clearly shown in the Weddell Polynya region and off East Antarctica, with high variability in the synoptic timescales, and in the western Ross Sea where changes occur in timescales of greater than 20 days. In order to determine if satellite derived, real time sea ice concentration and distribution would be of benefit to operational numerical weather prediction (NWP) schemes, the effect of sea ice concentration change upon the atmosphere in synoptic timescales was examined using a general circulation model in conjunction with the Australian Bureau of Meteorology’s GASP analyses. Experiments were conducted with a typical July sea ice concentration and distribution, as well as slab concentrations of 0, 10, 25, 50, 80 and 100%. Results from 5-day numerical weather forecasts show that the central pressure, structure and tracks of individual cyclones are sensitive to the ‘switch on’ of different sea ice conditions. Composites of all forecasts made with each concentration showed considerable, and mostly statistically significant, anomalies in the surface temperatures and turbulent heat fluxes over the sea ice. The magnitudes of these changes varied monotonically with the area of open water. The largest changes were simulated closest to the coast for all concentrations except for the typical July sea ice run, which displayed maxima over the outer pack. Significant westerly anomalies were induced over the ice in all cases, as were reductions in mean sea level pressure. The July sea ice runs displayed a distribution of the mean sea level pressure anomaly different from all others, with maxima occurring in the central to outer pack. All other forecasts displayed maxima at the coast. The results suggest that sea ice concentration does induce anomalies in the atmospheric parameters in timescales of less than five days. Further, the use of a realistic distribution of sea ice concentration produces results distinct from the constant concentration forecasts. Hence it is suggested that real time Antarctic sea ice data may be of considerable benefit to numerical weather prediction models.
Covariances in the weather and the influence on an Australian large-scale renewable electricity system

Huva, Robert Gordon ( 2014)

Sometime in the future Australia’s demand for electricity will undoubtedly need to rely on significant amounts of Renewable Electricity (RE). Fossil fuels are inherently non-renewable and their dwindling supply will force investment in alternatives. There is therefore a need to research how such increased penetrations of RE resources will be managed. Installed across large areas, a National Electricity Market (NEM) with increased contributions from RE will be affected by large-scale meteorological variability. The synoptic scale (100s-1,000s of km and days-weeks) weather systems are of particular interest. This thesis examines how synoptic scale weather variability might affect a future highly RE dependent Australia using two approaches. Approach one (Part 1 of the thesis) identifies the common synoptic scale weather systems from a reanalysis data set (ERA-Interim) and then analyses the availability of wind and solar associated with each weather type. Approach two (Part 2) utilises data from a regional model (ACCESS-R) as part of an electricity model that maximises the contribution of wind and solar electricity in meeting the demand of Australia. The influence of the weather systems identified in Part 1 on the optimised electricity network is then analysed. Part 1 of this thesis utilises the European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis product ERA-Interim from 1989-2009 and for the Austral region (6S,105E) → (49.5S,165E). The Self-Organising Map (SOM) technique is then used to identify commonly occurring features in the ERA-Interim Mean Sea-Level Pressure (MSLP) field. The SOM technique converts the time series of MSLP to a time series of commonly occurring MSLP patterns, or weather types. The weather types are then analysed for their tendency to be associated with either high or low wind and solar potential. Some autumnal MSLP patterns are shown to be associated with very low wind speeds and solar irradiance for most of the Australian continent, while other summertime patterns show good potential for extracting wind and solar electricity. Following this an analysis of just the wind field demonstrates that decorrelation in the wind field is reached at a distance of approximately 1,300km. Part 2 of this thesis focuses on optimising renewable electricity capacity to meet electrical demand, using data from the Bureau of Meteorology’s high resolution regional weather model, ACCESS-R, for the period 2010-2011. The ACCESS-R data, in tandem with electrical demand data from the Australian Electricity Market Operator and a Genetic Algorithm, are utilised to investigate the influence of synoptic scale variability on a largely RE-based network. Wind and solar installations from locations across the ACCESS-R grid are optimally placed to maximise their contribution to meeting the electrical demand of 2010-2011. A gas-fired back-up system is deployed to cover moments when the combination of wind and solar cannot meet demand. The gas usage is made expensive to minimise its use, yet it is found that gas is still needed throughout the 2010-2011 period to cover moments when both the wind and solar are low. An investigation is then undertaken to determine any large-scale links to the minima in renewable generation. The common weather types identified in Part 1 are utilised in Part 2. By assigning SOM weather types to the 2010-2011 period it is shown that some regimes either adversely or favourably affect the net output of the optimised system. In particular, a late autumn and a summer weather type are shown to be significantly associated with very low RE output. The persistence and re-occurrence of low RE events shows that most episodes of low RE last for less than six hours and such low RE events have a mean return period of more than a week. Increasing the cost of transmission results in installed RE capacity contracting to four large wind stations and it is shown that the NEM region exhibits four distinct wind regimes. The wind regimes are highly uncorrelated and the minimum distance between regime locations reflects an approximate, but identical to Part 1, optimisation-based decorrelation length of 1,400km. In combination, Parts 1 and 2 of this thesis illustrate some of the issues that a future high penetration RE network might need to overcome. Knowledge of the influence of detrimental/favourable weather phenomena will be critical when designing and/or maintaining a large-scale renewable electricity network for Australia—in particular, knowledge of the decorrelation length-scale in the wind field.
Investigating potential pathways to remediate thiocyanate-contaminated groundwater and wastewater at a Victorian gold mine

Bosnjak, Angelina ( 2014)

Thiocyanate (SCN-) is toxic to higher organisms, affecting the central nervous system, to cause irritability, nervousness, hallucinations, psychosis, mania, delirium and convulsions. This contaminant is commonly associated with gold mining activities and forms when cyanide, used for extraction of gold, reacts with reduced sulphur species in wastewater. Significant concentrations of thiocyanate have been detected in groundwater bores around the No. 2 Tailings Dam at Stawell Gold Mine in Victoria, with concentrations steadily increasing over time. Thiocyanate can be eliminated from groundwater and wastewater by oxidation to less harmful products such as ammonia and sulphate through chemical oxidation and biodegradation. Certain bacterial strains indigenous to thiocyanate-contaminated sites have demonstrated the ability to degrade thiocyanate and can be used to remediate contaminated land and water. Chemical and biological oxidation of thiocyanate was explored in this study through synthetic abiotic laboratory redox optimisation experiments and field-based injection experiments to determine the controls on thiocyanate degradation and potential pathways which could be implemented to remediate thiocyanate-contaminated groundwater and wastewater at the site. Analysis of site groundwater chemistry and aquifer properties revealed the presence of a plume of thiocyanate in acidic to near-neutral groundwater outside the tailings dam wall at monitoring bores SE12 and SE14 confined to the upper unconsolidated aquifer with low hydraulic conductivity (0.001-0.004 m/d) and low transmissivity (0.01-0.05 m2/d). The source of thiocyanate at the site was determined as the tailings dam. Inconclusive results from the nitrate reduction-thiocyanate oxidation experiments in synthetic and actual groundwater and wastewater suggests that nitrate may not form a redox couple with thiocyanate. However, in acidic solutions (pH 2) of Fe-EDTA and thiocyanate heated to 80°C, the Fe2+ was generated from thermal degradation of the Fe-EDTA compound, while thiocyanate was completely hydrolysed within 22 days. Catalysis of thiocyanate hydrolysis by iron reduction was not determined. However, solution pH and temperature were important factors, as thiocyanate hydrolysis did not proceed at pH 5.5 and 80°C. At pH 2, the hydrolysis of thiocyanate was faster at 80°C compared to 70°C. Thiocyanate-degrading microorganisms were not successfully stimulated in simulated injection (push-pull) experiments, as no appreciable decrease in thiocyanate concentrations was observed in groundwater or wastewater replicates.
The palaeovegetation, palaeoclimate and biostratigraphy of South-eastern Australia during the Eocene Greenhouse to Oligocene Icehouse transition

Nguyen, Ngoc ( 2014)

The shift from the Eocene 'Greenhouse' to Oligocene 'Icehouse' conditions is a globally significant event. The Eocene – Oligocene boundary (33.9 million years ago) marks the onset of permanent large-scale glaciation in Antarctica and the onset of the current global climatic 'Icehouse‘ state. In the Austral-Antarctic region, the transition is well recorded in deep water marine carbon and oxygen isotopes, however in the terrestrial realm little is known of the nature of environmental change associated with this event. In Australia, this is partly due to a lack of precise methods of dating Paleogene terrestrial strata. The most common practice of dating terrestrial sediments is the application of Gippsland Basin‘s spore-pollen biostratigraphy. This research assessed the applicability of the Gippsland Basin‘s spore-pollen biostratigraphy to the Otway Basin. Results demonstrated Gippsland Basin‘s spore-pollen biostratigraphy provides inaccurate ages when applied to samples from the Otway Basin. In addition, results from pollen analyses combined with foraminifera, dinoflagellate, and calcareous nannofossils and other stratigraphic data were used to create a detailed climate history of this high palaeolatitude region (~60°S). The spore-pollen assemblage indicates the palaeovegetation of the Otway Basin was dominated by Nothofagidites spp., with an abundance of species from the families Myrtaceae, Casuarinaceae and Proteaceae. The Nothofagus-dominated mesothermal rainforest probably had an emergent layer of Podocarpaceae and Araucariaceae species and a diverse understorey of ferns. The palynological record of the Otway Basin shows no vegetation change occurred during the time prior to and across the Eocene-Oligocene boundary even though there is evidence of permanent continental–scale glaciation on Antarctica.
Biogeochemical arsenic cycling in the hydrothermal acid-sulfide springs at Waiotapu, New Zealand: implications for the evolution of arsenic resistance

HUG, KATRIN ( 2014)

Active acid-sulfide hot springs provide modern analogs for the geothermal systems of the early Earth where microbial metal(loid) resistance may have first evolved. One metal(loid) that potentially presented a critical geochemical challenge to the earliest biological processes is arsenic, present at high concentrations in the hot springs at Waiotapu on the North Island of New Zealand. Particularly of interest is the moderately acidic sulfidic Champagne Pool that features dissolved arsenic concentrations of up to 4.2 mg L-1. The biogeochemical arsenic cycle in Champagne Pool follows reaction paths that are not yet fully understood with respect to biotic versus abiotic contributions, but involve strong coupling to the biogeochemical sulfur cycle. In this PhD study, I quantified arsenic species at Champagne Pool via HPLC-ICPMS and detected arsenic oxyanions, arsenic thioanions and methylated arsenic species. Arsenite was the dominant species at Champagne Pool’s inner pool, rim and outflow channel (55% – 75% of total arsenic concentration), with dithio- and trithioarsenates forming 18% – 25% of total arsenic concentration. In the outflow channel, dimethylmonothioarsenate comprised up to 9% of total arsenic concentration, while on the highly siliceous outflow terrace „Artist’s Palette“, thioarsenates were the dominant species at 55% of total arsenic concentration. I also quantified the redox sensitive sulfur species sulfide, thiosulfate, sulfate and elemental sulfur via UV-VIS and HPLC-UV spectrometry. Sulfide and sulfate were measured at their maximum concentration in Champagne Pool and at the adjacent outflow terrace, respectively; whereas sulfite, not quantified in this study, could possible contribute up to 30% to the total sulfur concentration at the individual sites. Elemental sulfur, not included in the sulfur mass balance, reached its measured maximum concentration at the outflow terrace. Phylogenetic analysis of 16S ribosomal RNA genes of the whole microbial community obtained via metagenomic sequencing revealed the dominance of Sulfurihydrogenibium at all sites, with an elevated archaeal population including Thermofilum and Sulfolobus at the rim and outflow channel of Champagne Pool. This analysis revealed several phylotypes closely related to known sulfur oxidizing as well as sulfur reducing microorganisms. Functional gene analysis linked sulfur metabolizing genes to sulfur speciation results, supporting the potential for microbially mediated sulfur-dependent transformation of arsenite to thioarsenate species. Metagenomic analysis revealed genes encoding for the arsenate reductase ArsC at all sites, which, given the wide thioarsenate species distribution, suggests a possible early evolution for arsenate resistance in the absence of oxygen. Furthermore, the absence of the arsenite oxidase encoding gene aio at all sites suggests the priority of an arsenite detoxification mechanism over the energy conserving arsenite oxidation. Finally, the detection of methylated arsenic, a solely biogenic arsenic species, only at the outflow channel, and in conjunction with a significant increase in Aquificaceae, indicates a potential role for methyl transferases from this lineage in the evolution of thermophilic arsenic resistance. My PhD study highlights microbial contributions to coupled arsenic and sulfur cycling in an acid-sulfide hot spring that have implications for understanding the evolution of microbial arsenic resistance in sulfidic geothermal environments.
The structural evolution, tectonics and hydrocarbons of the offshore Otway Basin, SE Australia

PALMOWSKI, DANIEL BRUNO ( 2003)

The offshore Otway Basin is part of Australia's passive southern margin, in which two separate rift-phases between the Tithonian? and Maastrichtian formed numerous depocentres. The research presented has analyzed and described the structural styles in the offshore Otway Basin and constructed a model of the basin's evolution since the Late Jurassic. The Otway Basin has been divided into four structural zones from north to south. Zone I comprises the onshore area and most of the shelf along the margin. Deep halfgraben developed during the first rift phase with characteristic horst and graben in Palaeozoic basement. To the south, zone I is bound by the Hinge Zone. Structural zone II covers the entire deepwater part of the Otway margin, characterized by a very thick Late Cretaceous section with pervasive Turonian faulting in the east and saucer-shaped depocentres in the west. Large halfgraben controlled deposition of the post-Turonian sedimentation in the eastern Otway Basin. Negative flower structures document strike-slip faulting. Strongly thinned lower laminated continental crust underlies this zone, limited to the south by the Outer Margin Highs. Domino faulting formed halfgraben and less commonly graben in Structural Zone III, the Outer Margin Highs. The base of the Outer Margin High sediments represents a regional decollement surface and domino faulting occurred along a second-generation decollement. Structural zone III is limited to the south by the continent-ocean-boundary with oceanic crust in structural zone IV. In the Shipwreck Trough, halfgraben died out against an accommodation zone which developed into the Shipwreck Fault with strike-slip offset .The regional stress regime indicate sinistral strike-slip movement along this fault zone. In the southwest Shipwreck Trough, four Turonian to early Coniacian syn-rift phases can be distinguished formed through footwall collapse to the north of the Hinge Zone. Differences in the amount of extension in the basin are accommodated along strike-slip faults such as the Shipwreck Fault. Sedimentation rates between 89 and 83 Ma increased whilst extension rates declined. Since approximately 83Ma sedimentation rates declined exponentially in phase with extension rates. Regionally, rapid Turonian extension formed a wide graben system between Antarctica and Australia. With the serpentinization of exhumed mantle peridotite in the Outer Margin Highs during the Coniacian in the east and Turonian in the west, the crustal deformation mechanism changed from mainly pure shear to simple shear along the newly established decollement. Fast spreading since the Mid Eocene caused gravitational collapse of the margin. Changes in heat flow possibly correlate with a change in deformation style in the continental crust. Parallel developments of sedimentation-rate and extension-rate suggest that most of the subsidence was structurally related. The Shipwreck Trough hydrocarbon fairway probably continues south into the Sorrell Basin. Possible stagnant conditions in deeper water offshore across the Hinge Zone might have enhanced the organic content of the Belfast Mudstone creating potential oil source rocks. Deepwater lntra-Paaratte reservoirs are not proven, but the alternating reflective to non-reflective seismic facies might indicate interbedded sands and shales. Large rollover anticlines would make excellent traps in the deepwater Otway Basin.
Thermochronological and structural insights into the Mesozoic-Cenozoic tectonic evolution of the eastern Tibetan Plateau

Tian, Yuntao ( 2013)

This thesis explores the evolution of the eastern Tibetan Plateau (TP) in select areas, i.e. Yidun Arc, eastern Songpan-Ganze terrane (SGT), Longmen Shan (LMS) and Sichuan Basin (SB) using a combination of structural and thermochronological techniques. Results highlight the role of: (i) flat subduction of the Meso-Tethys in triggering crustal refrigeration and exhumation in the Yidun Arc; (ii) crustal strength discontinuities in transferring deformation in central Asia; (iii) inherited crustal architecture in forming the eastern TP margin; (iv) crustal extrusion in forming the post-collisional stress-regime and high elevations in the eastern TP; and (v) Late Cenozoic onset of the Asian monsoon in enhancing river incision in the southeastern TP. Thermochronology data from the Yidun Arc indicate a distinct phase of Late Jurassic-Early Cretaceous crustal refrigeration and exhumation, which is interpreted as resulting from flat subduction of the Meso-Tethys and subsequent Lhasa-Qiangtang collision along the Bangong suture. Such an interpretation is consistent with lithospheric features imaged by seismic data. Thermochronology data from the eastern SGT (including a deep >7 km borehole) point to a ubiquitous phase of Late Jurassic-Early Cretaceous cooling. This cooling is best explained by regional post-orogenic denudation, as a far-field response to Lhasa-Qiangtang collision to the south and extensive sinistral shearing along major faults bounding the SGT. Projecting these aforementioned events onto an Early Cretaceous paleogeographic terrane reconstruction, results in a new tectonic model, where shearing along the faults transferred strain related to the Lhasa-Qiangtang collision into central Asia. Structural and geochronological results from the southern LMS suggest that Early Cretaceous-Early Paleogene deformation of the LMS included a phase of crustal extension along its hinterland, and a phase of crustal shortening along its front, forming ~2-3 km thick foredeep deposits in the southwestern SB. This deformation assemblage is interpreted as the combined effect of failure of the LMS crustal wedge and clockwise rotation of the SGT. These results indicate that the pre-Cenozoic LMS was underlain by a thickened crust, which was further thickened by Late Cenozoic crustal shortening along a series of listric reverse-faults merging into a detachment seated at a depth of ~20-30 km. Thermochronology data from deep boreholes across a W-dipping reverse fault in the eastern SB point to a distinctive cooling episode in the hanging wall commencing at ~28 ± 3 Ma. This age constrains the timing of a Cenozoic shortening component along this structural belt corroborating that a phase of W-E shortening occurred in the eastern TP and SB. This finding is consistent with evidence supporting extrusion of the eastern TP. Enhanced river incision in the Yidun Arc (part of the southeastern TP) was initiated in the Early Miocene (~15-22 Ma). This timing is older than previous proposals for Late Miocene plateau formation and river incision elsewhere in the same region. It is concluded that the Early Miocene inception of river incision heralds the onset of surface uplift by continental subduction and extrusion, whereas Late Miocene incision was triggered by commencement of the Asian monsoon.
Investigations into diamond drilling and rock drillability: microscale and fullscale impregnated bits

Siribumrungsukha, Boonsom ( 1980)

Drill bits having cutting edges formed of a matrix of sintered metal powder impregnated with diamond bort (the so called "impregnated" diamond bits) have the potential to greatly increase the economy of diamond drilling, due to low production costs and long bit life resulting from reconditioning of the cutting edges. However, little detailed research into the performance of impregnated bits has been conducted, and the capacity to predict their field behaviour is limited. As a contribution to the knowledge of impregnated bit performance, this project has studied basic relationships between thrust, rotational speed and the penetration of diamond bits into rock, with particular attention paid to the development of techniques suitable for laboratory testing using miniature impregnated bits. A conventional bench drill and a radial arm drill were modified and instrumented to enable operating conditions to be controlled and drilling parameters to be measured and monitored, for microscale and fullscale drilling using impregnated drill bits. Bit performance and drilling characteristics were studied for four rock types, and rock drillability studies were carried out on seven rock types. Statistical relationships between penetration rate, specific energy, torque and drilling distance that were determined enable projection of drilling data from a standard "sharp" condition. A wear measuring device was developed to assess matrix wear of the impregnated microbits. Reconditioning was done by drilling medium-strength, abrasive Stawell sandstone. Initial penetration rate increases linearly with increases in thrust and/or rotational speed, but only within a limited range, depending on rock type and the other operating parameters. Matrix contact with the rock surface, "clogging" of the diamonds, time-dependency, and strength of diamonds and the diamond-matrix bond play important roles in these phenomena. Comparison of rock drillability between that of microscale and fullscale bits shows a straight-line relationship indicating the possibility to predict drilling performance in the field. Uniaxial compressive strength, tensile strength, and Sklerograf hardness can be used as a preliminary, but not reliable guide, to predict drillability. Petrographic characteristics and the relative scale of diamond size to grain size of minerals affect rock drillability.

School of Earth Sciences - Theses

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