Morteza Fattahi

Dating volcanic and related sediments by luminescence methods: a review

Abstract Applications of luminescence dating of geological materials have undergone extensive development and refinement since 1974 when Wintle first attempted to date volcanic lava using thermoluminescence (TL). Today, luminescence techniques are potentially highly useful methods for dating volcanic and related materials and events over timescales ranging from 10 2 to 10 6 years. While luminescence approaches generally do not possess the precision afforded by techniques such as 40 Ar/ 39 Ar and 14 C methods, they offer a useful alternative approach with advantages in terms of age range and scope of material. Although the application of luminescence methods has in some cases been successfully described, a comprehensive study outlining and defining protocols for routine luminescence dating of volcanic materials has not been forthcoming. This review surveys previous attempts to develop luminescence techniques to date volcanic products and discusses the state of knowledge of the luminescence behaviour of the four principal materials currently used for luminescence dating of volcanic events. Particular attention is paid to the red luminescence emissions, primarily because of previous successes in using Red Thermoluminescence (RTL) of quartz and feldspar for dating volcanic products, for which the upper age limit may extend beyond a million years. Proposals are made for future research directions; these include: technological developments in the measurement of optically stimulated red luminescence, the systematic characterization of RTL and optically stimulated red luminescence as key luminescence parameters in volcanic quartz, feldspar, glass and polymineral sample fractions, and optimization of luminescence dating methods to define a comprehensive protocol for routine dating of volcanic materials.

Extending the time range of luminescence dating using red TL (RTL) from volcanic quartz

Abstract The potential of red thermoluminescence (RTL) emission from quartz, as a dosimeter for baked sediments and volcanic deposits, has received some attention over the past decade. While there have been some important observations relating to signal stability, saturation characteristics and emission wavebands, there has not been a systematic analysis of RTL properties of older (i.e., >1 Ma), quartz-bearing known age volcanic deposits. We have undertaken such an analysis using independently-dated silicic volcanic deposits from New Zealand, ranging in age from 300 ka through to 1.6 Ma. We observed a complex RTL emission in most volcanic quartzes, which consists of a number of discrete high temperature (i.e, >220°C) TL peaks. Isothermal analysis indicates a stable dating trap ( E =2.03 eV; S =4.20×10 15 ) which is stable at ambient (c. 20°C) temperatures for >10 9 a. We confirm the slow onset of saturation with dose, and the limited extent of sensitivity changes due to dosing and TL readout. As such, there is much potential for exploiting the dosimeter in dating studies and we present the results from a modified single aliquot regenerative (SAR) procedures which indicate that there is a good agreement between RTL dating and other methods over time scales 10 5 –10 6 a. This paper presents a summary of the most important related results of our findings and outlines the configuration of photomultiplier and filter combinations which maximizes RTL detection for temperatures up to 500°C.

Red emission luminescence from quartz and feldspar for dating applications: an overview

Abstract In dating applications, detection of thermal or optically stimulated (IR & visible) luminescence is overwhelmingly biased towards the UV-blue portions of the electromagnetic spectrum. This bias is based on a number of factors including the generally good performance of UV-blue emission luminescence as an integrating dosimeter for quartz over the time range ca. 0– 150 ka , the historical development of blue-sensitive photomultiplier tubes and problems in the separation of longer wavelength emissions from thermal and other background contributions. Research into the use of orange-red and far-red luminescence emissions has, however, also progressed. Applications to quartz have been limited to investigating the thermoluminescence (TL) dating of volcanic sediments. Application of red TL to known age volcanic demonstrated that the dosimeter may have potential for routine dating of burnt or fired quartz back to more than 1 Ma . The potential advantages of using feldspathic minerals as integrating dosimeters for utilization in TL and optically stimulated luminescence research have been complicated by the widespread observation of anomalous fading. Red TL from feldspar (λ∼600– 750 nm ) has been demonstrated not to exhibit anomalous fading. The far-red IRSL is bleachable by IR (λ=830 nm ) or via polychromatic daylight; the measured IRSL being accurately described by the sum of three exponential components. Experimentation using the single-aliquot regeneration (SAR) protocol demonstrates, in contrast to some studies using the UV-blue IRSL emission, that it is possible to use a test dose to accurately monitor sensitivity changes in the course of experimental procedures, and that synthetic doses may be reconstructed. Short-term fading experiments on samples that exhibit significant anomalous fading in the UV-blue portion of the emission spectrum suggest that anomalous fading is absent or significantly reduced.

Investigations of the performance of quartz single aliquot DE determination procedures

Abstract Over the past few years a variety of equivalent dose ( D E ) determination techniques for quartz, which are truly single aliquot-based, have been proposed. Such methods avoid the need for inter-aliquot normalisation, and provide considerable improvements in the precision of equivalent dose ( D E ) estimates. Much of the research leading to these developments have been based on detailed investigations of a few samples, primarily from Australia. All ’protocols’ developed have performed impressively. It is necessary, however, to verify the consistency of the single aliquot D E determination methods on a wide range of samples before they can be considered as prescribed or standard. We have analysed approximately 100 samples from a range of sedimentary environments and geological provinces in an attempt to confirm the robustness of the single aliquot techniques. Up to 65% of samples measured in our laboratory were not suited to analysis via application of single aliquot additive dose (SAAD) procedures. This relates to a range of factors, including lack of sample sensitivity and dose dependent sensitivity changes. Furthermore, we have observed some problems in dating young sediments using single aliquot regeneration (SAR) methods. Critically, we observe that sample to sample variability on quartz luminescence (thermally- and optically-stimulated) behaviour is considerable, and many samples are found to exhibit behaviour which contrasts greatly from that described in recent phenomenological studies.

Holocene settlement shifts and palaeoenvironments on the Central Iranian Plateau : Investigating linked systems

For thousands of years, humans have inhabited locations that are highly vulnerable to the impacts of climate change, earthquakes, and floods. In order to investigate the extent to which Holocene environmental changes may have impacted on cultural evolution, we present new geologic, geomorphic, and chronologic data from the Qazvin Plain in northwest Iran that provides a backdrop of natural environmental changes for the simultaneous cultural dynamics observed on the Central Iranian Plateau. Well-resolved archaeological data from the neighbouring settlements of Zagheh (7170—6300 yr BP), Ghabristan (6215—4950 yr BP) and Sagzabad (4050—2350 yr BP) indicate that Holocene occupation of the Hajiarab alluvial fan was interrupted by a 900 year settlement hiatus. Multiproxy climate data from nearby lakes in northwest Iran suggest a transition from arid early-Holocene conditions to more humid middle-Holocene conditions from c. 7550 to 6750 yr BP, coinciding with the settlement of Zagheh, and a peak in aridity at c. 4550 yr BP during the settlement hiatus. Palaeoseismic investigations indicate that large active fault systems in close proximity to the tell sites incurred a series of large (MW ~7.1) earthquakes with return periods of ~500—1000 years during human occupation of the tells. Mapping and optically stimulated luminescence (OSL) chronology of the alluvial sequences reveals changes in depositional style from coarse-grained unconfined sheet flow deposits to proximal channel flow and distally prograding alluvial deposits sometime after c. 8830 yr BP, possibly reflecting an increase in moisture following the early-Holocene arid phase. The coincidence of major climate changes, earthquake activity, and varying sedimentation styles with changing patterns of human occupation on the Hajiarab fan indicate links between environmental and anthropogenic systems. However, temporal coincidence does not necessitate a fundamental causative dependency.

Red luminescence from potassium feldspar for dating applications: a study of some properties relevant for dating

Abstract Aspects of the red thermoluminescence (RTL) and IR (833±5 nm ) stimulated red ( λ emission =600– 750 nm ) luminescence (orange-red IRSL) of potassium feldspar from different origins are described. Anomalous fading of RTL (300–500°C) from a selection of potassium feldspar samples was tested. High temperature RTL (300–450°C) exhibits less anomalous fading in comparison to UV luminescence, for the samples under study. The result supports the contention of Zink and Visocekas (1997) that the red TL emission from feldspar does not fade. It was found that RTL is bleachable due to IR exposure, and the relationship between RTL lost and orange-red IRSL produced is linear. It is shown that around one third of the trapped charge responsible for the orange-red IRSL signal gives rise to an RTL signal, indicating that some traps and luminescence centres are shared for RTL and orange-red IRSL. Specific characteristics of orange-red IRSL from feldspar were identified. It was found that the orange-red IRSL decay curve is bleachable by IR and daylight and can be described by the sum of three exponential components. Orange-red IRSL fading was tested. Short-term storage tests (up to 2 weeks) showed no fading. Longer-term (ca. months) storage of orange-red IRSL do in fact indicate fading, though at levels considerably lower than for the UV emission. The contradictory result is possibly due to the detection wavelength. As such, it is highly likely that the long-term fading experiment is strongly influenced by the feldspar emission centred at ca. 570 nm , which exhibits anomalous fading, while the short-term fading experiment is more greatly influenced by the far red emission centred at ca. 710 nm that in comparison to UV emission shows no or less fading.

Absorbed dose evaluation in feldspar using a single-aliquot regenerative-dose (SAR) infrared-stimulated red luminescence protocol

Abstract The potential of the IR (833±5 nm ) stimulated red emission (λemission=600– 750 nm ) luminescence (red IRSL) from potassium feldspar, as a dosimeter is discussed. A series of experiments are presented to examine the performance of single-aliquot regenerative dose (SAR) protocol for equivalent dose determination using red IRSL signal. Outlines of the SAR protocols are presented, and tests of their performance are discussed. It is shown that, for the samples under study, SAR can successfully and accurately recover a known laboratory dose in red IRSL from potassium feldspar separates. It has additionally been demonstrated that reconstruction of a laboratory dose is easily achieved using a SAR protocol. Equivalent doses (Des) for natural samples examined give results that are consistent with the far-red emission circumventing the effects of anomalous fading.