Luminescence Profiling Research Articles

Multi-method geochronological approach to reconstruct post-1800 floodplain sedimentation in the upper Rhine plain, France

The precise dating of sedimentary archives covering the last 200 years in floodplains massively impacted by human activities is a major challenge. A combination of geochronological approaches is necessary to accurately date post-1800 sedimentary deposits. Here, we use a combination of a wide range of methods to unravel floodplain sedimentary dynamics, through the example of the Upper Rhine which is a highly regulated river. This comprises short--lived radionuclides (137Cs, 210Pbxs) and Infrared Stimulated Luminescence (IRSL) single-grain dating. Luminescence profiling methods (IRSL screening, portable luminescence reader) were also used to further characterise sedimentation dynamics. These were combined with a hydrogeomorphological approach based on historical planimetric and hydrological data, the knowledge of engineering works as well as the morpho-sedimentary adjustments they induced. Our study demonstrates the value of historic maps as well as historical hydrological data, which provide precise time markers for dating the sedimentary archive under study. We illustrate different assumptions, validity domains and limitations inherent to each method, especially the complexity of 137Cs to date floodplain sediments and the potential of luminescence methods for dating and estimating sedimentation continuity. We finally show the advantage of combining geochronological approaches in the construction of robust age models for young floodplain sedimentary archives in highly anthropized fluvial environments.

Coupled luminescence and cosmogenic nuclide dating of postglacial deflation surfaces and sand drift on a raised ice-contact delta at Veinge, SW Sweden

Wind-abraded cobbles (ventifacts) and aeolian sand are known from the sandy-gravelly coastal areas of south-western Sweden, especially in association with raised deltas. Ventifacts are recorded on at least two different stratigraphic levels, at some sites atop glaciofluvial sediment, at other sites atop littoral deposits, and in some places at both levels, while aeolian sand usually forms a surficial cover. The formation of ventifacts has usually been coupled to abrasion due to katabatic winds from the retreating ice sheet or with periglacial climate during the Younger Dryas stadial (12.8–11.7 ka).To determine the timing of these deflation events, we have applied a combination of dating methods to ventifacts and associated sediments on top of an ice-contact delta at Veinge, south-western Sweden. Quartz and feldspar luminescence dating as well as portable luminescence profiling has been used for littoral and aeolian sediments over- and underlying deflation surfaces, while rock surface luminescence burial dating and paired 14C–10Be cosmogenic nuclide dating were conducted on ventifacts. The results show that a first deflation event occurred c. 16.5 ka, just after deglaciation and prior to a regional transgression that peaked around 15.7 ka. At 12.4–11.4 ka, during the Younger Dryas stadial, a new set of ventifacts formed on the surface of the exposed littoral sands and gravels. Some wind abrasion also occurred in the early Holocene, but at c. 8.5 ka the surface was covered by aeolian sand, up to 2.5 m thick.The combination of different dating methods have allowed us to draw more informed conclusions on the timing and duration of these wind abrasion/transport events than would have been possible from the use of only single-method dating. It has also made it possible to infer some environmental conditions during deposition. For example, both glaciofluvial and littoral deposits show evidence of incomplete bleaching of the luminescence signal. This suggests short subaerial transport and brief reworking by waves, respectively, though bleaching conditions improved during shore regression. Rock surface burial luminescence profiles reveal that some ventifacts were repeatedly exposed, but that later event(s) were shorter in duration as indicated by quartz-feldspar age comparisons.

Controls on luminescence signals in lake sediment cores: A study from Lake Suigetsu, Japan

The luminescence characteristics of sediments are driven by a range of environmental factors and can be used as indicators of both local and regional environmental shifts. Hence, rapid luminescence profiling techniques are increasingly employed during multiproxy analysis of sediment cores, overcoming the practical limitations of traditional (dating) methods. One emerging application of luminescence profiling is in the palaeoenvironmental investigation of lake cores. This study demonstrates the versatility of rapid core profiling using portable optically stimulated luminescence and laboratory profiling techniques for appraising the luminescence characteristics of the Lake Suigetsu (Japan) sediment cores. These techniques were employed across four key time periods, each selected for their unique environmental context and significance on either a local or global scale, in order to identify relationships between down-core luminescence and environmental change. We demonstrate that the luminescence characteristics of the cores are susceptible to a range of environmental perturbations and can therefore act as proxies of past change. Additionally, the quantification of these luminescence signals, alongside an assessment of dose rate variations down-core, supports the notion that future luminescence dating is feasible. The results of this analysis contribute to the wider understanding of the application of luminescence techniques – both profiling and dating – to lake sediment cores. • Rapid down-core profiling techniques are applied to sediment cores from Lake Suigetsu, Japan. • Down-core luminescence signals are sensitive to a range of catchment-scale environmental changes. • Estimates of dose rate are made from elemental concentrations and provide an assessment of chronometric accuracy.

Characterization of (paleo)lacustrine landforms using sedimentological and portable OSL investigations at Schweriner See, north‐eastern Germany

AbstractWe investigated four subaerial (paleo)lacustrine landforms at the north‐eastern shoreline of Schweriner See, north‐eastern Germany. These included two beach ridges, one subaerial nearshore bar and a silting up sequence located close to a fossil cliff, which marks the former maximum extent of Schweriner See. We used luminescence profiling with a SUERC portable OSL device (POSL) on all four sediment sequences in combination with sedimentological investigations such as grain size, loss‐on‐ignition and magnetic susceptibility to provide information on the various formations in a lacustrine depositional environment. The POSL reader was used on pre‐treated polymineral samples to gain an insight into luminescence distribution within the individual sediment sequences, but also among the four sequences. POSL proved valuable to understand depositional processes, which were not visible in lithology or sedimentological parameters. With somewhat larger uncertainty this method provides relative chronologies of the sediment sequences. Additionally, we carried out radiocarbon dating and full optical stimulated luminescence (OSL) dating to establish a chronological framework. OSL ages proved to be more reliable to date beach ridges in this setting than radiocarbon samples, which were severely influenced by sediment reworking. This combined approach of sedimentological analyses, luminescence profiling and absolute age determinations revealed details in depositional processes at Schweriner See which otherwise would have remained undetected. Furthermore, it helped to set these subaerial (paleo)lacustrine landforms in a chronological framework.

High-resolution portable-OSL analysis of Vegetated Linear Dune construction in the margins of the northwestern Negev dunefield (Israel) during the late Quaternary

Abstract Vegetated Linear Dunes (VLDs) are elongated dunes whose construction is controlled by vegetation and wind. Common in southern hemisphere drylands, they were mainly active in the late Pleistocene. VLDs vertically accumulate sand during elongation episodes and their internal stratigraphy thus serves as a proxy for major periods of strong winds. However, the framework of VLD buildup and elongation is constrained by low-resolution luminescence chronology. To overcome this gap this study applies high-resolution Portable Optically Stimulated Luminescence (POSL) profiling coupled with OSL dating and sedimentology of an exposed VLD section, combined with successive sections along a fluvially truncated downwind elongation trace of the dune at the margin of the stabilized northwestern Negev dunefield, Israel. POSL profiling of the VLD section revealed three statistically distinct stratigraphic units. Winnowing of very fine sand and silt grains can explain a higher ratio between quartz and heavy minerals in the upper VLD unit. This winnowing decreased dose rates and, consequently, reduced bulk POSL luminescence signals and De values in the upper unit. The two upper units of the VLD section date to the Younger Dryas while the basal unit dates to the Heinrich-1 event. OSL ages at the lower unit and at the section bases along the downwind elongation trace of the dune indicate initial elongation during the Heinrich-1 event, and even prior. The study demonstrates that beyond delineating accumulation stages and assigning stratigraphic units, POSL is a sensitive sensor of sedimentological and mineralogical differences within a dune profile, enabling correlation with OSL measurements.

Investigating post-depositional sediment mixing at an archaeological site on the northern Plains using a portable optically stimulated luminescence (OSL) reader

The Bodo Archaeological locality is a major multicomponent site located in east-central Alberta, Canada, in a fossil aeolian dune landscape. About five decades ago, oilfield-related pipeline construction activity resulted in the post-depositional stratigraphic disturbance of some parts of the site. However, the absence of easily discernible signs of anthropogenic disturbances makes visual identification of the disrupted sequences difficult. As a result, identifying sequences that yield accurate reconstructions of the archaeological occupations is problematic. In an effort to differentiate between areas at the site that are intact from those that have been disturbed, this study employed a portable optically stimulated luminescence reader to construct luminescence profiles that show the variation of luminescence signal intensities with depth. The results show that depositional sequences that have undisrupted stratigraphy display signal intensities that decrease up the sequence, correlable with depositional age. Conversely, areas with disrupted stratigraphy are characterized by signals that fluctuate with depth, which results from mixing of strata of dissimilar age. Luminescence profiling also allows the approximation of relative ages of depositional units and these show that, in the undisturbed sites, sediments at the base of the sequences are about three to four times older than sediments in the upper parts. Overall, the ability to identify stratigraphic sequences that are intact enables investigators to expend time and resources on stratigraphic records that yield accurate archaeological reconstructions.

The development of historic field systems in northern England: a case study at Wallington, Northumberland

ABSTRACT Wallington in central Northumberland is a late seventeenth- and early eighteenth-century country house with associated pleasure grounds. Much of the surrounding estate is agricultural land, though there are also expanses of moorland and conifer plantation. The character of Wallington’s landscape, now divided into fifteen separate farm holdings, was to a large extent shaped by estate management practices and improvements in the eighteenth– nineteenth centuries. Today’s settlement pattern is made up largely of dispersed farmsteads, with field systems which reflect the orderly rectilinear layout of planned enclosure, being separated mainly by long and fairly straight stonefaced banks. In medieval and early modern times, by contrast, the landscape is thought to have been quite different, with nucleated villages set amidst irregular open fields which were farmed collectively. The process of long-term landscape change from open to enclosed field systems has been inferred across the whole of Northumberland but it can be difficult to understand in detail. Absolute dating evidence for field systems before the eighteenth century is generally lacking and the origins and development of historic earthworks including boundary banks and the remains of arable farming are poorly understood. This paper presents results of research which used retrogressive landscape analysis (based on documentary evidence, archaeological data, aerial photographs, and historic cartography) to identify five areas for detailed geoarchaeological investigation and sampling with optically stimulated luminescence profiling and dating (OSL-PD). The results provide new perspectives on the development of landscape character at Wallington which have wider relevance for north-east England and beyond.

Optically stimulated luminescence profiling and dating of earthworks: the creation and development of prehistoric field boundaries at Bosigran, Cornwall

Abstract

Geochemistry, luminescence and innovative dose rate determination of a Chalcolithic calcite-rich negative feature

An interdisciplinary approach comprising archaeological, chemical, mineralogical, and luminescence data was applied to a better understanding of the fill dynamic and chronologies of a calcite-rich negative archaeological feature from Southern Portugal. This work aims to contribute to the assessment of the human involvement in the backfilling actions of a negative archaeological feature from a Chalcolithic site, thus better defining the moments of its destruction and/or abandonment. There are well-known limitations of luminescence dating of calcite-rich materials, particularly in the dose rate determination. In this work, a proposal of two innovative protocols to determine the dose rate of calcite-rich contexts is discussed. A clear improvement of the dose rate estimation was obtained by using the “radionuclide weighed” protocol. The comprehensive used methodologies enabled to define the infill phases and the sources of the infill materials. The luminescence profiling studies were also useful to describe the infill processes, highlighting their discontinuity and pointing to different deposition rates. The luminescence ages obtained, when using the “radionuclide weighed” protocol proposed in this work, are closer to the archaeological evidence of a Chalcolithic occupation.

Changes and continuities in a Mediterranean landscape: a new interdisciplinary approach to understanding historic character in western Catalonia

To understand why historic landscapes changed in the past researchers need to identify when and where changes took place, but in rural landscapes, the origins and development of many historic elements including field systems, roads, terraces and other earthworks remain poorly understood. This paper outlines a practical interdisciplinary method using GIS-based historic landscape characterisation (HLC) to integrate data from different sources and model how historic character varies in space. It pilots an innovative approach using luminescence profiling and dating that can underpin the HLC with significantly improved knowledge of historic processes of change. We focus on four case studies of terraced agricultural landscapes in western Catalonia and demonstrate for the first time that existing terrace systems often have medieval or early modern origins.

The terrestrial Eemian to late Weichselian sediment record at Beckentin (NE-Germany): First results from lithostratigraphic, palynological and geochronological analyses

Over recent decades a growing number of well-documented records from terrestrial last interglacial sites across central Europe have substantially improved our understanding of Eemian climate and landscape dynamics. Despite this progress, there are also large areas from which little information is available, thus constituting significant paleo-geographic gaps in the last interglacial record. Among the regions with still inadequate paleo-environmental information is the maritime-influenced area of NE-Germany at the southern margin of the Eemian (Baltic) Sea. Here we present first results from a geological investigation of a new last interglacial site, recently discovered during archaeological excavations near Beckentin (SW-Mecklenburg). The study area is located approximately 25 km to the south of the maximum MIS-2 ice limit of the Scandinavian Ice Sheet in NE-Germany, and thus lies outside the Weichselian belt of glaciation. Based on lithostratigraphic and sedimentological logging, complemented by geochemical (XRF) and palynological investigations, we divide the local succession into three sections: (1) a basal facies comprising Saalian till and associated glaciofluvial sand, overlain by section (2) consisting of a fen peat which grades into laminated organic to minerogenic mud. The organic deposits of section (2) preserve a near complete Eemian pollen inventory, encompassing pollen zones (PZ) I to VI (Menke and Tynni 1984). Above this rest poorly sorted periglacial sands (section 3) with ventifacts and evidence for cryogenic deformation. Geochronological results from 230Th/U dating of the buried organic-rich deposits at Beckentin, show that these units accumulated in a former dead ice depression between 118 ± 7/6 ka and 114 ± 6/5 ka during the Eemian Interglacial. High-resolution optically stimulated luminescence (OSL) profiling, undertaken with a portable luminescence reader, reveals a significant hiatus between the lacustrine fines and overlying periglacial cover sand. Five OSL ages obtained from these cover sediments and the sand-filling of an ice-wedge cast show that these strata formed between during the last glacial - interglacial transition.

Optically-stimulated luminescence profiling and dating of historic agricultural terraces in Catalonia (Spain)

Dating agricultural terraces is a notoriously difficult problem for archaeologists. The frequent occurrence of residual material in terrace soils and the potential for post-depositional disturbance mean that conventional artefactual and lab-based dating methods often provide unreliable dates. In this paper we present a new technique using luminescence field profiling coupled with OSL dating to produce complete (relative) sequences of dates for sedimentary stratigraphies associated with agricultural terraces and earthworks. The method is demonstrated through a series of case-studies in western Catalonia, Spain, in which we reconstruct the formation sequence of earthwork features from the Middle Ages through to the present day. OSL profiling at the time of archaeological survey and excavation permitted spatially and temporally resolved sediment ‘chronologies’ to be generated, and provides the means to interpret the environmental and cultural archives contained in each. The case-studies presented here show that luminescence approaches are a valuable tool to reconstruct landscape histories.

Towards increasing the spatial resolution of luminescence chronologies – Portable luminescence reader measurements and standardized growth curves applied to a beach-ridge plain (Phra Thong, Thailand)

Abstract Since optically stimulated luminescence (OSL) dating is time-consuming and cost-intensive, the quantity of ages available for individual study sites is usually restricted significantly. In particular the interpretation of complex depositional systems with temporally and spatially diverse sedimentation histories may suffer from the effects of a poor spatial resolution or an ineffective distribution of chronological data. In these cases, time and cost efficient approaches that provide reasonable dating accuracy are required to substitute or complement full luminescence dating. In this study, we evaluate the potential (i) of luminescence profiling using a portable luminescence reader, and (ii) of standardized growth curves applied to quartz extracts and bulk samples in a standard luminescence reader for functioning as age proxies. Since both proxies save time for processing and/or measurements, they would be applicable to larger datasets in future studies and, by this, may allow to improve the spatial resolution and sampling strategy of OSL dating in coastal settings. Both approaches are applied to a set of approximately 50 samples from the sandy beach-ridge plain of Phra Thong Island, Thailand, for which age control is given by regular quartz luminescence dating from previous studies. Results show that although standardized growth curves are also associated with shortcomings in dating accuracy, and luminescence profiling in general does not equal full luminescence dating, both approaches are capable of reproducing some of the main chronostratigraphic features of the island. This includes the differentiation between the Holocene and Last Interglacial parts of the ridge plain, as well as the identification of the general east-west progradation of the Holocene ridges. On the other hand, several pronounced hiatuses of 1500–2000 years within the Holocene sediment succession, were not identified at all or with a poor precision. More robust absolute age estimates can only be achieved by considering the highly variable dosimetry, which is the main contributing factor to bulk luminescence signals apart from deposition age on Phra Thong Island. Thus, for the beach ridges on Phra Thong portable reader signals as a proxy for palaeodoses combined with sample-specific dose rates seem to be the best compromise between rapid data acquisition and adequate dating accuracy. In future studies, this will allow for processing significantly larger numbers of samples compared to regular luminescence dating while keeping dating accuracy at a level that should be adequate for many research questions, which in the end could enable an increased spatial resolution of chronological information.

Feldspar SARA IRSL dating of very low dose rate aeolian sediments from Sandwick South, Unst, Shetland

Young sediments, with low sensitivity and low dose rates, are challenging for luminescence dating. Here, we present work on the site of Sandwick South, a Norse settlement, in which these challenges were present. Field gamma dose rates below 0.1 mGy a−1, and total dose rates of 0.4–0.5 mGy a−1, combined with expected ages of less than 1ka, resulted in a requirement for quantitative determination of equivalent doses of 0.2–0.4 Gy. The bedrock geology of the area are metagabbros, which explain both the exceptionally low dose rates and the lack of autochthonous quartz. Luminescence profiling during fieldwork revealed stratigraphically progressive OSL and IRSL signals, indicating phases in the sediments with dating potential. While laboratory characterisation recovered some quartz, its low yields and luminescence sensitivity precluded application of quartz methods. Electron microscopy confirmed the presence of feldspars, which were separated and used for IRSL Single Aliquot Regeneration Additive (SARA) analysis. Counting times for both high resolution gamma spectrometry (HRGS) and thick source beta counting (TSBC) measurements were extended by 1 order of magnitude, resulting in overall uncertainties of <6% for these low dose rates. Dose estimates were obtained using an adapted SARA protocol, incorporating long overnight preheats before first measurement, with the aim of mitigating short-term fading effects. Using these procedures, archaeologically meaningful dates were obtained from this difficult material, which are internally consistent, coherent with stratigraphy, and concordant with the radiocarbon constraints of the associated archaeological settlement. The dates demonstrate sand accumulation in the early to mid-13th century AD and also in the 18th century AD, which are contemporary with disruptive sand movements registered in other coastal regions of the Northeast Atlantic and North Sea regions. The approaches adopted here have provided solutions to the challenging conditions of this young, insensitive material and can therefore be considered to extend the range and applicability of luminescence dating methods.

Dating of Las Mesas Copper Age walled enclosure (La Fuente, Spain)

The site of Las Mesas is located in the west bank of the Guadajira river (La Fuente, Badajoz, Spain). It covers a half hectare and is enclosed by a stone wall. Previous assessments based on site surveys suggested a general chronological span from Late Neolithic period (ca. 3600-2900 BC) through the Copper Age (3rd millennium BC). Excavations revealed a well-constructed wall with bastions and a domestic space at the centre of the site with three occupational phases. Several functional areas and a votive pit are ascribed to the second phase. A deer antler located in a re-cut ritual pit associated to the second phase was dated by AMS-14C. Samples from a living floor assigned to the second phase (SU-9/10) and the basement of a kiln associated with the first phase (SU-18) was dated by optically stimulated luminescence (OSL) using the single aliquot regenerative dose (SAR) protocol on 90-160 m quartz grains. Luminescence profiling analysis of 7 samples taken throughout the archaeological stratigraphy was used to assess variations in luminescence behaviour and relative age through the sequence, using infrared-, optically –and thermally– stimulated luminescence (IRSL, OSL, TSL) on poly-mineral and etched samples. Luminescence dating and profiling indicates that the upper archaeological layer (SU-1B) probably dates to the Late Bronze Age (ca. 1000 BC), but that the sediments in the remainder of this section accumulated during the late Neolithic-Copper Age: the site was most probably inhabited between 3300 and 2900 BC. There were gaps in occupation between the Late Neolithic-Cooper Age phases (I & II), and between the Late Neolithic-Cooper Age phases and Late Bronze Age phase (II & III), indicating that the site was abandoned and reoccupied twice. The AMS-14C date on deer antler of 4254 ± 45 BP (3010-2675 cal BC) is consisten with the OSL results for phase II, indicating that the pit was excavated at the beginning of the second occupational phase. Combined OSL and AMS-14C dating shows that Las Mesas site was first occupied during Late Neolithic farming colonization, abandoned during the Copper Age and occupied again during the Late Bronze Age. The occupational gap recorded during the Copper Age relates to evidence for burning of the site and the partial destruction of the wall, followed by its reconstruction and consolidation.

Instant luminescence chronologies? High resolution luminescence profiles using a portable luminescence reader

Establishing a robust chronology is fundamental to most palaeoenvironmental studies. However, the number and positioning of dated points is critical. Using a portable luminescence reader, it is possible to rapidly generate high resolution down core relative age profiles. Profiles of portable luminescence data from two coastal dunes were evaluated and compared with the results of particle size analysis, stratigraphy, and an independent historical chronology. Results show that, even in young samples, portable luminescence data is dominated by an age related signal which in homogeneous sediment need not be corrected for moisture, feldspar content changes or grain size. Profiles therefore provide relative chronologies from which accumulation phases can be established, and from which better targeted sampling and comparison to other sites could be undertaken. Even though they do not provide instant absolute chronologies, field-based portable luminescence profiling of Late Quaternary sites hold much potential to improve the resultant chronologies.

Delineating stratigraphic breaks at the bases of postglacial eolian dunes in central Alberta, Canada using a portable OSL reader

ABSTRACTTemporal constraints for the Late Pleistocene deposition of eolian dunes that occur in central and northern Alberta, Canada can be provided by dating sediments from the dune bases using luminescence techniques. In places, however, the postglacial dunes overlie glaciofluvial sands that resemble the eolian deposits in texture such that demarcating the bases of the dunes is often problematic. In this study we address the problem by employing a portable optically stimulated luminescence (OSL) reader to construct luminescence profiles that depict luminescence signal variation with depth. With the portable OSL reader, measurement can be performed on bulk sediments, negating the need for laborious separation procedures to isolate pure mineral fractions, as is required in regular luminescence dating. Measurements can also be carried out in the field, permitting quicker decision making during sample collection. Results from this study, presented as depth variations of feldspar derived infrared stimulated luminescence (IRSL) signals and predominantly quartz‐generated post‐IR blue OSL signals, show that luminescence profiling enables one to distinguish between eolian deposits that make up the dunes from the underlying non‐eolian sands. The identification of such cryptostratigraphic interfaces is made possible by differences in the dosimetric histories of the sediments. The delineation of the dune bases allows targeted sampling that yields best luminescence age approximations for the initiation of postglacial eolian deposition in the region. Luminescence profiling of eolian sequences would also, in theory, permit the identification of depositional breaks of extended duration. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Survey of Palaeolithic sites by luminescence profiling, a case study from Eastern Europe

A luminescence-based approach to the rapid characterisation of sites in terms of their datability and sedimentary history is described (luminescence profiling), and contrasting results presented for three Palaeolithic archaeological sites in Russia. Three mineral/grain-size fractions (polymineral silt-sized, polymineral sand-sized, quartz-enriched sand-sized) were separated from each of many small samples taken through the sites’ stratigraphies. Luminescence signals from the different fractions were measured using infra-red light, blue light, and thermal stimulation. Patterns in luminescence sensitivity and equivalent dose values are used to indicate which sites, samples, fractions and/or signals may yield meaningful luminescence ages, and the experimental effort that may be required to obtain said ages. Case studies range from a site where a detailed chronostratigraphy might be produced using a limited number of full luminescence dates to tie in the profiling results, to a site where profiling indicates there is little chance of producing useful luminescence dates. These interpretations are based on dialogue between the luminescence profiling results and archaeological, palaeoenvironmental, and geomorphological evidence. Luminescence profiling is shown to be a useful tool for understanding sedimentological process at each site, independent of full luminescence dating.

OSL and radiocarbon dating of a pre-Angkorian canal in the Mekong delta, southern Cambodia

This study presents preliminary results of research on pre-Angkorian canals near the ancient settlement of Angkor Borei in the southern Mekong delta of southern Cambodia. The canals have been mapped by aerial photograph interpretation and investigated in the field by hand auger drilling of two canal traces and trenching of one of these. Luminescence profiling through the canal infill successfully identified the base of the canal as well as revealing disturbance and mixing of the canal infill that was not apparent from visual inspection or sedimentological analyses of the infill sediments. OSL dating of the canal bed indicates excavation (or re-excavation) of the canal bed between the first millennium BC and the middle of the first millennium AD. This date is consistent with the time of initial occupation of Angkor Borei in the fourth century BC. Multiple charcoal samples with a pooled age of early fourth to early fifth century AD probably signal the onset of canal infilling. The apparent demise of the canal coincides with a major change in land-use signalled in pollen and diatom data from Angkor Borei, but this change cannot be taken to indicate de-population of the region. This tentative chronology will be refined when more canals are investigated and greater precision is achieved in OSL dating of the canals. The latter will necessitate clearer identification and separation of unbleached (older, pre-archaeological) components and bleached (younger and dating the canal digging and/or operation) components in the OSL stored dose.

Luminescence dating of anthropogenically reset canal sediments from Angkor Borei, Mekong Delta, Cambodia

This paper presents a case study in the analysis of anthropogenically reset sedimentary materials, through work undertaken to identify and date sediments in an ancient canal in the Mekong Delta, Cambodia. The emergence of rice cultivating communities, utilising canals for both hydraulic management and transport, represents an important stage in the social evolution of southeast Asia. The emergence of complex polities in the region, which may have depended on both international trade and intensified agriculture, led ultimately to the formation of the famous Khmer empires which dominated the region on several occasions through the 1st and 2nd millennia AD. French colonial scholars identified possibly ancient canals in the region that may have played roles in trade, agriculture, or both. This series of ancient canal features near Angkor Borei has been the subject of recent investigations in a collaboration between the Universities of Glasgow and Hawaii. Luminescence profiling measurements were used to identify the canal bed, by exploiting the contrast between a regional substrate of some 50 ka depositional age and more recent archaeological sediments. In this manner it has been possible to identify the sedimentary substrate, undisturbed canal sediments, and redeposited material. Ages have been estimated for substrate and canal infill sediments. The work represents the first convincing demonstration of luminescence dating of one of these important regional features, and indeed the first confirmation of the presumed antiquity of the canal system around Angkor Borei.