Tesi sul tema "Luminescence dating"

Luminescence dating is a widespread dating method used in the fields of archaeology and Quaternary science. As an experimental method it is subject to various uncertainties in the determination of parameters that are used to evaluate age. The need to express these uncertainties fully, combined with the prior archaeological knowledge commonly available, motivates the development of a Bayesian approach to the assessment of age based on luminescence data. The luminescence dating procedure is dissected into its component parts, and each is considered individually before being combined to find the posterior age distribution. We use Bayesian multi-sample calibration to find the palaeodose in the first stage of the model, consider the problem of identifying a plateau in the data, and then use this, along with the annual dose, to estimate age. The true sample age is then modelled, incorporating any prior information available, both for an individual sample and for a collection of samples with related ages.

This work aims to contribute to the solution of a problem relevant to archaeology and microdosimetry, namely the TL dating of destratified archaeological ceramics. It is apparent that museums hold a large body of archaeological material excavated from important sites during the early part of this century. Absolute dating of this corpus of material would be extremely valuable to archaeology in allowing historic hypotheses to be tested. The background to this problem has been presented within the context of the historical development of thermoluminescence dating and of dosimetry concepts. A critical review of previously proposed strategies for dating material from unknown gamma contexts is presented, and then a general model using an isochron approach is introduced. The isochron model is then developed explicitly and theoretical simulation is used to explore different microdosimetric systems. Two main isochron solutions have been identified, the grain size (or alpha-beta attenuation) and alpha efficiency isochrons. An experimental approach was designed, to evaluate the validity of the grain size isochron predictions, using model matrices. Isochron behaviour was clearly observed in both cases. The first system, based on microcline feldspar grains in a high dose rate matrix, produced an age estimate consistent with the known age. The second experiment, using fluorite grains in a lower dose rate matrix, produced a highly coherent data set. However, the age estimate obtained was greater than the expected value by a factor of approximately 3. The possible reasons for this are discussed in detail. A brief experiment carried out subsequently on duplicate portion of this matrix gave results that are consistent with predicted values. Thus, it would appear that the original experimental design and method were valid and that the isochron approach does indeed deserve further investigation.

Essex is a county rich in significant historic brickwork spanning the medieval period. A great deal of earlier archaeological study has focused on the development and use of brick during this period, providing a framework of understanding as to how this material was employed in Essex through the medieval period. However, the common approaches adopted to date historic brick have several caveats that can potentially limit the amount of information they can provide. This presented an opportunity to apply the scientific dating technique of optically stimulated luminescence in order to derive absolute dates for important medieval brick sites in Essex. This in turn would allow this framework of understanding surrounding medieval brick to be critically examined and revised where necessary. A series of important brick buildings that spanned the 11th through to the 16th century were selected for inclusion in this thesis. The buildings were studied from an archaeological perspective, deriving likely dates for their erection and development, before samples of the brickwork were taken. These were subsequently dated by luminescence. In light of the luminescence dates, the archaeological evaluations of the buildings were reviewed and revised where necessary. The results have shown that medieval brick was introduced much earlier than had previously been suspected. This has refuted the long held notion that the Cistercians were responsible for introducing brick in the 12th century and has led to suggestions of a small scale, late Saxon brick industry. It was also apparent that, whilst being manufactured, brick was also being re-used to a large extent throughout the medieval period, especially in the 16th century. Whilst this is likely to be largely due to practical motivational factors, other esoteric social aspects are also likely to have played a role, such as the Great Rebuilding.

Submarine canyons are major geomorphic features, transporting large quantities of sediments from land to the deep sea. These sediments contain nutrients, enabling life in the deep sea and potentially forming hydrocarbon reservoirs. The transport of sediments towards the deep sea is also important as it links into fundamental concepts of the Earth’s system, such as the global carbon cycle and land surface denudation. Concepts based on the assumption of direct transport of sediments from land to the deep sea. However, how this transport occurs, on what timescales, and if there is potential storage of sediments along the way, is actually poorly known. The current theory is that gravity flow events, such as turbidity events, are the main mechanism behind canyon formation and maintenance. Luminescence dating, an absolute dating method, has been used in an earlier study to look at sediment transport via turbidity currents down the Monterey Canyon, off the coast of California, USA (Stevens et al., 2014). An active upper canyon was found at 1093 metres depth, with frequent events. At 3555 and 3612 metres depth the turbidity events dated were older and indications of major reworking of sediments were found. To pinpoint this change in environments, the present study used luminescence dating in order to get an age estimate of sediments at 2920 meter depth, creating a sequence of ages in the canyon. These cores have captured sediments that have been transported via sand waves, not turbidites. Sand waves are related to the frequent passing of turbidity events, but exact understanding of the mechanisms at hand is poorly understood. Single grain analysis on quartz is used to obtain the individual properties and ages of grains. This gives representative canyon entry ages of the sediments in addition to intrinsic grain properties. The data shows a skewed distribution of grain ages with a narrow, dominant peak between 180 and 240 years within a single core, indicating frequent flushing events and minor reworking of sediments. This is a similar pattern to the core at 1093 meter depth, albeit with increased age, suggesting temporary storage of sediment to at least a depth of 2920 metres. It is proposed that there is a gradual increase in ages down canyon towards 2900 meters depth with a more abrupt transition in environments with increased storage of sediments between 2900 and 3500 meter depth. Sand waves, and the exact relation to turbidites, remain a poorly understood transport mechanisms, but are potentially capable to transport vast amounts of sediments towards the deep sea.
Marina raviner transporterar stora mängder sand från land till havets botten. Men hur sker detta? I nuläget förklaras sandtransport med gravitationsflöde, att gravitationen drar ner sandkornen mot bottnen. Men sker detta vid ett enda stort skede eller i små gradvisa steg? Och kan det vara så att sand, på sin väg till botten, lagras i ravinerna? Det är dessa frågor som jag försöker att kasta ljus på i och med detta projekt.Målet var att komplettera vår kunskap om hur sand förflyttar sig från land till havsbotten genom att studera ifall det har skett en gradvis eller en abrupt transport av sand i ravinen Monterey Canyon vid Kaliforniens kust. Detta har jag gjort genom att datera åldern av sand vid ett djup av 2 920 meter, som i det här fallet deponerats av sandvågor, och sedan jämfört denna ålder med åldrarna på sanden från ett mindre (1 100 m) och större (3 500 m och djupare) djup, vilka analyserades i en tidigare studie (Stevens et al., 2014). Transportmekanism i den studien skiljer sig med min då det rör sig om gravitationsflöden.Med endast några få sandkorn av annan ålder så var den dominerande åldern på kornen i mitt prov mellan 180 till 240 år gamla. Provet vid 1 100 m djup visade sig också ha en liten spridning av ålder vilket tyder på att det skett återkommande utspolning av gammal sand som istället ersatts av ny. Man kan se att det ändå sker en tillfällig lagring av sediment mellan det minsta, studerade djupet och det nyligen tagna provet på 2 900 m, då en svag ökning i ålder kan mätas. Åldern på sandkornen i proven som kom från ett större djup var istället mycket spridd och generellt mycket högre än de från mindre djup. Att det finns en mix av ålder vid ett och samma djup tyder på att sanden vid återkommande tillfällen omfördelats i ravinen.Denna studie antyder att ravinen i fråga är aktiv upp till ett djup av minst 2 920 meter, med bara en svag stegring i ålder med ökande djup. Mellan 2 920 och 3 500 meter ändras miljön vilket gör att sprid-ningen av ålder ökar. Därutöver var det nya provet taget från en plats med ett annorlunda transport-mekanism, sandvågor istället för gravitationsflöde. Sandvågor, och dess relation till gravitationsflöden, är fortsättningsvis en dåligt förstådd transportmekanism som potentiellt är kapabel till att flytta stora mängder sediment till havets botten.

Since the introduction, in 1985, of optically stimulated luminescence (OSL) for age determination, the technique has become increasingly common as a method of dating. Light emitting diodes (LEDs) are a convenient and economical light source for the optical stimulation of luminescence. However for work with quartz, green light stimulation with an argon ion laser as light source is usual, particularly because of the low light intensity of light emitting diodes. Replacement of the original green light emitting diodes by newly developed high intensity green light emitting diodes allowed this limitations to be overcome. The new arrangement was shown to be of comparable sensitivity to the traditionally used argon ion laser system. The optically stimulated luminescence dating method has been advanced with the introduction of the "single aliquot method", which uses one disc prepared from the sample to carry out all the measurements to determine the equivalent dose. A method based on a single aliquot has the advantages of avoiding normalization problems and reducing effort. The original version of this method concerned the infrared stimulation of feldspar and showed success with an additive dose method, in which correction was made for less of luminescence signal due to repeated preheating and reading of the same aliquot. A similar single aliquot approach has been applied to the stimulation of quartz by green light, involving an alternative method of analysis of single aliquot data. This approach provides comparable accuracy to conventional equivalent dose determination by the multiple aliquot technique.

The objective of this study is to perform Optically Stimulated Luminescence (OSL) dating on the ceramic samples from different parts of the Laodikeia by using Infra Red Stimulated Luminescence (IRSL) on polyminerals. As a first step, a literature survey has been done about the dating system and the methodology of dating. The calibration of the system was done before carrying out the experiments. The six ceramic samples were collected from the site and dated. The mineral compositions of the samples were examined by X-ray Diffraction Analysis, which showed that all samples contain quartz, feldspars, calcites and together with other minerals. The equivalent dose was found by using Multiple Aliquot Additive Dose (MAAD) and Multiple Aliquot Regenerative Dose (MARD) techniques using Infra Red diode array of the system that gave the IRSL ages for samples. Alpha counter measured the dose components of uranium and thorium contributions to the annual dose. The potassium concentration was determined by Atomic Emission Spectrometry. The cosmic ray component of annual dose was evaluated by the Al2O3:C Thermoluminescence Dosimeter (TLD) discs which have been placed and kept for 8 and 11 months in the site. From the data the IRSL ages were calculated for six ceramic samples LDKY-1, LDKY-2, LDKY-3, LDKY-4, LDKY-5 and LDKY-6 with the help of the OSL system software. The IRSL ages for these samples, in the given order, are 737 ±
60, 1563 ±
120, 1445 ±
110, 1602 ±
120, 1034 ±
80 and 1034 ±
80 years by using MAAD technique. The IRSL ages for the same samples are 870 ±
60, 1550 ±
120, 1440 ±
110, 1600 ±
120, 1030 ±
80 and 1030 ±
70 years by using MARD technique.

This thesis presents new research on the luminescence dating of burnt mounds in the Orkney and Shetland Islands. Through an examination of available evidence for Scottish burnt mounds, a number of key problematic areas have been identified in relation to our understanding of these sites and their place within the archaeological record. Previous chronological investigations of burnt mounds have so far provided little information on the likely duration of individual sites. Site information processes are likewise poorly understood. Luminescence dating has been outlined as a method suited to determining the age of both excavated and unexcavated sites, and to tackling issues of site formation. A combination of stratigraphic and surface sampling at sites on the island of Eday, Orkney and at coastally eroding sites across Shetland has provided suitable material for study. In addition, detailed sampling during excavation of Cruester burnt mound, on Bressay, Shetland has enabled the collection of a series of samples directly linked with the formation of the mound and structures at the site. Fieldwork is reported together with detailed characterisation of the external and internal dose rates of samples collected. Additive dose thermoluminescence dating techniques have been applied to extracted feldspar grains. A procedure for correcting temperature-shift due to thermal contact variation has been developed and implemented, leading to improvements in data processing. Problems have been identified relating to unequal sensitisation at different stages of equal-predose additive dose run which cause normalisation errors leading to incorrect dose estimates. Whilst the underlying physical origins of such changes are not yet firmly understood, a correction method based on modelling of the sensitisation behaviour has been applied. When both sets of corrections are applied, satisfactory plateau responses are obtained, and data from controlled experiments are consistent with external controls.

The sheltered bays of the Orkney Islands are backed by extensive dune systems that commonly contain archaeological sites, many of which now protrude from cliffed sections due to coastal erosion. In an area where other dating techniques are often precluded due to a lack of organic dating material, this research establishes that optically stimulated luminescence (OSL) dating can provide a viable and robust alternative by dating wind blown sands within the sites to constrain the archaeological age. Since this is the case, the OSL chronology can also be applied to natural sites where no archaeological chronology exists and so be used in palaeoenvironmental reconstruction. Six periods of increased sand movement are recorded in the Orkney Islands at the sites sampled; the Neolithic, the Bronze Age, two periods in the Iron Age, the Viking/Medieval period and the Little Ice Age. The phases of sand movement identified using OSL in the Orkney Islands are also identified at other sites in Scotland and north-east Europe and support the chronologies derived from other environmental indicators such as tree rings and peat bogs. It is suggested that at least two events may be related to the deterioration in climate subsequent to the eruption of Hekla 4 in the late Neolithic and Hekla 3 in the late Bronze Age. However, OSL dating requires that the latent luminescence signal within quartz and feldspar is rapidly reduced to near zero by exposure to light, yet the rate and extent of bleaching depends on the length of time that the grains are exposed and the light intensity at the time of exposure. Bleaching experiments used here confirmed that not only is there a difference in the rate of bleaching between quartz and feldspar depending on the light intensity, but that there is also a difference in the rate of bleaching between samples from different geological areas and this needs to be taken into account in future research. The residual levels from the Orcadian modern beach sands (<0.5 Gy) suggest that some samples collected for OSL dating may be partially bleached and a new technique, the psi (?) ratio, is proposed here to identify partially bleached sediments.

Thesis (Ph.D.) - University of Glasgow, 2007.
Ph.D. thesis submitted to the Department of Geographical & Earth Sciences, University of Glasgow, 2007. Includes bibliographical references. Print version also available.

The objective of this project is to apply the Optical Stimulated Luminescence (OSL) technique to date the palaeo sediment from Mu Us Desert, part of the Inner Mongolia in northern China and reconstruct the palaeo environment. Five OSL samples were collected from Dagouwan, Salawusu River Valley at Inner Mongolia by Dr S. H. Li and his team in 2009. Extraction of 150μm to 180μm silt-size feldspar from collected dune sand, lacustrine facies and fluvial facies samples and running of luminescence dating therefore to obtain the age from 50ka to 90ka. Climate proxies - magnetic susceptibility, grain size, fossil vertebrates and fossil pollens have been analyzed and it is concluded that significant climate change occurred within this period, which change from domination of warm, humid and rainy summer monsoons (before 70ka) to cold, wind, windy strengthened dry winter wind and back to warm and humid again after 55ka.
published_or_final_version
Applied Geosciences
Master
Master of Science

The thesis follows an interdisciplinary approach combining sediment analysis and luminescence dating of sediments from selected archaeological sites. The work aims to assess the role of sediment analysis for luminescence dating, and the potential of TL and IRSL for dating waterlain material of Holocene age. A comparative chronology based on radiocarbon, stratigraphic and archaeological grounds is important. However, the viability of comparing different dating techniques is considered in the light of the dating results. The novel IRSL and established TL techniques were shown to successful for dating waterlain sediments, provided that a suitable light source is used for laboratory bleaching. Age comparisons between the luminescence techniques was excellent. Disparities between luminescence and C-14 ages is largely explained on a sedimentological basis. The role of sediment analysis is shown to be of great importance for luminescence dating. Certain sedimentological and luminescence characteristics are shown to be closely linked. The relationship between undated sediments affected by instability or low intensity of signals, and weathering in the strata from which the samples were taken is tested by experiment. This demonstrates that weathering of feldspars in the stratum severely affects the luminescence signals and therefore the potential for dating these samples. This represents a step towards the recognition of problematic samples in the field. In conclusion, it is shown that luminescence is suitable as an absolute dating technique for a wide variety of inorganic sedimentary material between 0-200 000 years old. This exceeds the C-14 technique both in range of material and in age limits. The main source of error is associated with variations in water content, which with the recognition of the significance of weathering, demonstrates the importance of sediment analysis in support of luminescence dating studies.

The work presented in this thesis details the design, construction, and calibration of a high-sensitivity multispectral thermoluminescence (TL) imaging system, with applications in geophotonics and luminescence dating. The system delivered enhanced spatially-resolved detection capabilities and sufficient sensitivity to accurately quantify the faint spectral emissions from single grains of quartz across multiple detection bands. Such measurement was previously unavailable using current techniques; with existing instrument architecture lacking the targeted detection, required sensitivity, and wavelength resolution made possible by the spatially-resolved imaging of thermoluminescence emissions. The advances presented herein provide i) a viable means of obtaining trapped-charge dose measurements from samples with luminescence emission characteristics for which current techniques are unsuited, and ii) a valuable research tool for investigating the temperature- and wavelength-resolved kinetic processes of thermoluminescence production and the mechanisms which govern these interactions. A design science research approach was adopted; requiring a comprehensive synthesis and understanding of the key elements underpinning instrument development and imaging techniques in luminescence dating applications. These elements included 1) luminescence production mechanisms and models, 2) the kinetic parameters of quartz governing these processes, 3) the current techniques in luminescence dating and existing instrument architecture used to detect and quantify the thermally and optically stimulated luminescence emissions of quartz, and 4) the application of advanced optical imaging systems and techniques to these areas. A comprehensive and systematic evaluation of the instrumentation used in luminescence dating was first undertaken, with a primary focus on the devices used for light collection and the spectral separation of luminescence emissions. These findings, along with fundamental considerations in optical imaging techniques, were used to inform the design and construction of the multispectral thermoluminescence imaging system. The key operational objectives relating to system performance were all met or exceeded, including specifications for quantum efficiency, optical throughput, spectral response, noise performance and sensitivity, as well as unit price and system integration cost. The resultant system delivered enhanced spatially-resolved multispectral detection capabilities previously unavailable using current techniques and existing instrument architecture. The system was developed around a Santa Barbara Instrument Group (SBIG) STT-8300M charge-coupled device (CCD) camera utilizing a Kodak KAF-8300 sensor, with peak quantum efficiency of 56% at approximately 550 nm. The sensor was thermo-electrically cooled to -20 oC during measurement to reduce thermal readout noise, producing dark current threshold values of 0.02e-/pixel/sec. A high-throughput custom-built lens configuration was designed for light collection and imaging, with lenses constructed from uncoated fused silica providing strong transmission (≥95%) across the visible spectrum and deep ultraviolet (UV). An Astrodon Sloan SDSS filter set was chosen for spectral separation of TL emissions, providing five discrete narrow bands of detection with extremely high peak transmission (≥95%), steep wavelength rejection characteristics and deep out-of-band blocking (≤0.03 %). Individual filters were mounted in a SBIG FW8S-STT filter wheel mounted below the STT-8300M camera. In addition, a single Hoya U-340 filter (25.4 mm diameter, 2 mm thickness) was mounted in a custom adapter within the filter wheel to be used for ‘standard’ signal detection analogous to current instrumentation. Total system transmittance was found to exceed 85% utilising the Astrodon SDSS filters (>80% for the SDSS u’2 ultraviolet filter), with approximately 70% transmittance when using the Hoya U-340 filter. The optical column and STT-8300M camera were interfaced to the RISO DA-15 automated luminescence reader by means of a custom mounting plate and turret adapter. The RISO unit is equipped with a 90Sr/90Y beta irradiation source and facilities for the thermal and optical stimulation of mineral grains, allowing repeated luminescence measurement from quartz samples. Multiple calibration and evaluation cycles were undertaken in developing the high-sensitivity multispectral thermoluminescence imaging system. The relative detection efficiency and system response was evaluated, with an investigation of the signal:noise ratio (SNR) between the CCD imaging system and the standard EMI 9235QB photomultiplier tube (PMT) arrangement used on the RISO DA-15 automated luminescence reader. The noise performance of the PMT arrangement exceeded that of the CCD-based imaging system, with approximately twice the SNR measured at all given doses. A marginal improvement (approximately 20%) was observed in the SNR when using the SDSS u’2 filter compared to the Hoya U-340 for the imaging system, and overall detection efficiency increased slightly at higher administered radiation doses. The system was used to successfully recover a known irradiation dose from a calibration quartz sourced from the RISO Denmark Technical University (DTU) National Laboratory. The clear delineation of the luminescence signal required the development of novel image processing techniques. An aperture photometry tool was used for signal intensity calculations; a method typically used to determine stellar magnitudes in astrophotometry. The software is designed to measure point-source intensity and its uncertainty by summing all pixel values within a constrained region-of-interest (i.e. the aperture) and subtracting the background contribution. This is estimated from a nearby imaged region that surrounds, but excludes, the observed radiance from the TL emission (i.e. the source signal). An innovative suite of imaging and analysis protocols were also developed to maximize signal collection efficiency in high-sensitivity luminescence imaging applications. The well-known effects of varying heating ramp temperatures as a means to increase signal intensity was investigated, along with the potential to shift TL peak position relative to the detection band constrained by the optical filter; thereby providing a further proxy to test system response and calibration. This method was further adapted to maximize clean photon yield in the narrow UV detection band, with overall photon yield shown to increase at lower ramp temperatures (below 1.0 °C s-1) for both large-aliquot and single-grain samples. System noise performance was improved with the development of a calibrated background correction, which suppressed the signal arising from blackbody radiation emitted by the heater plate of the RISO luminescence reader. Ultraviolet thermoluminescence (UV-TL) photon yield was compared between the industry-standard Hoya U-340 optical filter and the high-transmittance SDSS astrophotometry optical filter set. Exposure correction techniques to mitigate the thermal and readout noise associated with charge-transfer processes in CCD sensors were also investigated. These approaches are vital in maximizing signal collection efficiency and are a necessary precursor for the use of advanced imaging systems in routine luminescence dating applications. The multispectral thermoluminescence imaging system was then used to characterize the spectral signature of individual quartz grains, allowing the inter- and intra-sample spectral diversity of quartz grains from contrasting geological context to be analysed. Luminescence emission behaviour was characterised for quartz grains (180-212 μm) for three samples of contrasting geological context, from which spectral profiles were collated. A clear distinction in the spectral signatures of individual grains originating from single deposits were identified within each provenance. This is a key finding of the work undertaken; and represents a significant advance in the understanding of the spectral variation in TL emissions from quartz, as well as in the characterization of geological provenance for individual quartz grains through luminescence studies. By better understanding the full spectral signature of individual grains, information on specific trapping sites (through temperature-resolved signal peaks) and on recombination centres (through wavelength-resolved signal peaks) may be extrapolated. Such findings demonstrate not only the viable collection of the luminescence dating signal beyond the detection range of current commercial instrumentation, but also highlights the potential for thermoluminescence imaging technique to be developed as a routine dating method, providing a new approach for extracting valuable provenance information from mineral grains natively with the luminescence dating signal. A key set of challenges that must be overcome in bridging current detection and analysis methods with spatially-resolved luminescence imaging techniques is the ability to generate accurate and precise equivalent dose (De) estimates and dose distributions in quartz. An innovative suite of imaging and analysis protocols were developed, which allowed investigation into the multispectral dose-response behaviour for natural quartz samples. This allowed, for the first time, the ability to generate multispectral equivalent dose distributions for quartz using solid-state luminescence imaging techniques. Dose response curves and De estimates were successfully generated across all four detection bands under investigation; providing encouraging results for the efficacy and validity of the TL system and luminescence imaging methods presented herein. The dose estimates compared favourably with the independent known dose of the sample in the UV emissions band, with overestimation of De in other detection bands. The overestimation was attributed to extrinsic factors such as the functional differences in detection efficiency and noise performance of solid-state imaging systems, and intrinsic factors relating to luminescence production such as the kinetic behaviour of TL traps and colour centres in quartz. The latter factors relating to luminescence production may be addressed with the development of advanced luminescence imaging and analysis protocols, which seek to account for the variability in the spectral emissions from natural quartz samples. While the development of such comprehensive analysis protocols is beyond the scope of the present work, much of the success in attempting to bridge routine detection and analysis methods with spatially-resolved luminescence imaging techniques is reliant on the further development and optimization of such procedures. A single-grain method for generating De estimates for quartz supergrains using in-situ luminescence imaging techniques was also presented. This technique investigated the viability of extracting luminescence signals from extremely bright individual grains contained within large-aliquot samples. Dose response was found to vary considerably between grains, with large errors in signal intensity measures attributed to sub-optimal background subtraction parameters in dense-field imaging applications. Such artefacts serve to further highlight the need for a true single-grain luminescence imaging method, providing increased accuracy and precision in dose estimates compared to large-aliquot and in-situ luminescence measures. This was achieved by the present study. A single-grain De distribution was successfully generated in the red detection band using dose estimates from twenty-six individual grains, providing a central De value in good agreement of the known independent dose of the sample. However, single-grain TL dose distributions could not be generated in detection bands other than the red transmission window constrained by the SDSS r’2 optical filter. This was attributed to a combination of 1) instrument limitations; namely those relating to detection efficiency, noise performance and spectral resolution, 2) sub-optimality of analysis protocols for specific detection windows and routine dating, and 3) the complexity and variability of the kinetic response and recombination processes which give rise to TL spectra in natural quartz samples. These limitations may be addressed with improved automation and the use of single-photon sensitive, back-illuminated, UV-enhanced electron-multiplying charge-coupled device (EM-CCD) cameras with appropriate high-throughput custom optics. Such a system was devised by the Author as the subject of a funding proposal under the Australian Research Council (ARC) Linkage, Equipment, Infrastructure and Facilities (LIEF; LE180100148) grant scheme in 2018. This proposal is currently pending resubmission. The work contained in this thesis has made significant advances in geophotonics and the multispectral imaging of quartz thermoluminescence. Despite the considerable and complex challenges inherent to the process of instrument development, particularly within the temporal and financial constraints of a PhD project, this work has overcome significant challenges in moving toward the routine use of spatially-resolved imaging systems and techniques in luminescence dating applications. With ongoing research and improvements in these key areas, the use of solid-state detectors for routine signal collection and age determinations will prove an invaluable tool in luminescence dating applications.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

Reconstruction of former Central Asian glaciers extents can provide valuable information about past atmospheric circulation variations. These extents, often marked by terminal moraines, need to be chronologically constrained. Cosmogenic nuclide exposure (CNE) dating is widely used to directly date moraines. In addition, there is increasing interest on using optically stimulated luminescence (OSL) techniques for dating glacial landforms. This thesis focuses on the methodological aspects of directly dating glacial landforms to perform paleoglacial reconstructions in Central Asia, with an emphasis on OSL dating. For OSL dating of sediments from glacial settings, it is important to measure the luminescence signal at the single grain scale, because the sediments are likely affected by partial bleaching due to short light exposure during glacial or glaciofluvial transport. The use of an Electron Multiplying Charges Coupled Device (EMCCD)-based imaging system for single grain OSL measurements would offer larger flexibility in light stimulation and sediment type, compared to the current Single Grain Risø reader. An automated image processing procedure has been developed to compensate for sample carrier displacement over repeated measurements and for attributing pixels to each grain for signal integration when using this imaging system. However, significant cross talk contamination, demonstrated by laboratory and simulation experiments, prohibits accurate single grain luminescence measurements. Preliminary experiments using a basic image processing algorithm show good potential for software correction solutions. Paleoglacial reconstructions conducted in the Altai Mountains, Central Asia, using both CNE and OSL dating demonstrate that luminescence measurements of glaciofluvial sediments performed at the multi-grain scale result in large age overestimates, and that single grain measurements allow for more accurate dating of glacial landforms. However, uncertainties remain that are related to the model used for extracting equivalent doses for well-bleached grains and to fading corrections when using feldspar minerals. The timing of glaciation can be inferred from scattered CNE moraine boulder ages if most of the ages are concentrated within a few thousand years, with only few ages clearly older or younger. Overall, combining CNE and OSL techniques for dating a glacial landform is a powerful approach for producing robust glacial chronologies, despite uncertainties inherent to each technique. Paleoglacial reconstructions from the Altai Mountains indicate Marine Isotope Stage (MIS) 2 and MIS 4/late MIS 5 local Last Glacial Maximums. In Central Asia, in addition to a regional MIS 2 glaciation, previous studies indicate a period of major glacial advances during MIS 3 that is out of phase with global ice volume records. However, most MIS 3 glacial chronologies from Central Asia are based on too few or too heavily scattered CNE data sets, or on OSL or Electron Spin Resonance (ESR) ages for which partial bleaching has not been properly investigated. Hence, at this stage, chronological evidence is insufficient to demonstrate a regional MIS 3 glaciation in Central Asia. Surge-related glacial features identified in the Russian Altai also highlight the importance of conducting detailed geomorphology and sedimentology studies to understand former ice dynamics, which is essential for inferring appropriate paleoclimate information from paleoglacial reconstructions.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

At the turn of the century, Kanab Creek incised 30-meters into its alluvium, leaving behind fluvial terraces and thick basin fill sediments exposed along arroyo walls. Research objectives were to determine the timing and causes of past valley-filling and arroyo-cutting episodes along a 20 km-long reach of Kanab Creek in southern Utah. Fluvial deposits were mapped at the 1:12,000 scale and sediments were described and dated using Optically Stimulated Luminescence (OSL) and radiocarbon dating. The Kanab Creek valley can be divided into a narrow, upper terraced reach and a broad lower basin fill reach near Kanab, Utah. The most prominent terrace in the upper reach is Quaternary alluvial terrace 4 (Qat4), followed by Qat3, Qat2/3, and Qat2 map units. These are composed of tabular-bedded, fine-grained sand, silt, and clay layers. The Qat2/3 map unit is a both a fill and fill-cut terrace underlain by Qa4, Qa3, and Qa2 alluvium and is used when the Qat3 fill-cut (fill-strath) terrace can not be differentiated from the Qat2 fill terrace due to their similar geomorphic position. The Qat3 fill-cut terrace upstream correlates to ~8 meters of aggradation downstream. The youngest terrace, Qat1, is a minor terrace, composed of coarse-grained channel facies. More recent channel and floodplain deposits were deposited over the last century following arroyo cutting. OSL and radiocarbon results suggest at least four cycles of fluvial cutting and filling: >6-3.5ka (Qa4), ~3->1ka (Qa3), 0.7-0.12ka (Qa2), and post-1880 AD (Qa1). Correlation to regional climate records suggests major periods of aggradation correlate to regionally cooler and wetter climatic intervals. Periods of arroyo cutting occurred at >6ka, ~3ka, 1-0.7ka, and during historic arroyo cutting (1882-1914 AD), and correlate to regionally warmer, drier intervals. These periods of aggradation and incision are roughly contemporaneous with regional drainages, except for the large aggradation seen in Kanab Creek 6-3.5ka (Qa4). Analysis of terrace longitudinal profiles indicates Qat4 has the lowest concavity suggesting that Qat4 aggraded during a period of greater sediment supply and/or reduced flood regime. Although OSL samples exhibited some degree of incomplete zeroing, calculated ages using a minimum age model are consistent with radiocarbon results.

The application of optically stimulated luminescence (OSL) dating to desert sand dunes has allowed accumulation histories to be used as tools to infer past environmental change. In response to issues facing the interpretation of these records, two research questions are addressed in this thesis. (i) Are dune chronologies representative of dune stratigraphies? And (ii) how can we most appropriately interpret dune chronologies as records of Quaternary environmental conditions? Five dune profiles were sampled for OSL dating at two sites in the northeastern Rub’ al Khali in the southern Arabian Peninsula. The visible stratigraphy was used to guide sampling for three of the profiles and the effectiveness of this approach is assessed. A key finding is that bounding surfaces are not always identifiable as chronological hiatuses by OSL dating, given the level of precision that can be achieved. Using hierarchical relationships visible in two-dimensional exposures is therefore not guaranteed to identify the depositional units necessary to reconstruct dune histories. Comparison of the depositional records from three sampled profiles shows that there is significant variability in chronologies at both the dune and dunefield scales. In light of these findings, the use of ‘range-finder’ OSL dating was investigated as a method of increasing sample throughput in the laboratory. It is concluded that the use of partially prepared samples and shortened measurement techniques can be used to rapidly assess the chronological context of samples and target those units most useful in constructing dune profiles. A new method of presenting dunefield OSL datasets as net accumulation rates, incorporating accumulation thickness rather than relying on the frequency of ages, is presented. Within the last 30 ka, regional accumulation and preservation occurred at ~30-26, 22.5-18, 16-9, 6-2.7, 2.1-1.6, 1.1 and 0.7 ka. In conjunction with numerical model results and a review of other palaeoenvironmental archives, the regional aeolian record is interpreted as a response to changing forcing factors. High rates of net accumulation between ~16-9 ka are attributed to coeval increases in sediment supply and transport capacity. A hiatus in accumulation between ~9-6 ka is interpreted as a result of reduced sediment availability due to high moisture levels. The importance of both external forcing factors and local controls on dune accumulation processes is recognised, and therefore the importance of sampling at multiple locations to distinguish these factors is emphasised.