User Guide for Luminescence Sampling in Archaeological and Geological Context

Luminescence dating provides a direct age estimate of the time of last exposure of quartz or feldspar minerals to light or heat and has been successfully applied to deposits, rock surfaces, and fired materials in a number of archaeological and geological settings. Sampling strategies are diverse and can be customized depending on local circumstances, although all sediment samples need to include a light-safe sample and material for dose-rate determination. The accuracy and precision of luminescence dating results are directly related to the type and quality of the material sampled and sample collection methods in the field. Selection of target material for dating should include considerations of adequacy of resetting of the luminescence signal (optical and thermal bleaching), the ability to characterize the radioactive environment surrounding the sample (dose rate), and the lack of evidence for post-depositional mixing (bioturbation in soils and sediment). Sample strategies for collection of samples from sedimentary settings and fired materials are discussed. This paper should be used as a guide for luminescence sampling and is meant to provide essential background information on how to properly collect samples and on the types of materials suitable for luminescence dating. La datación por luminiscencia proporciona una estimación directa de la edad del último momento en el que el cuarzo o los minerales de feldespato se expusieron a la luz o al calor y que se ha aplicado exitosamente a depósitos, superficies rocosas y materiales expuestos al fuego en distintos contextos arqueológicos y geológicos. Las estrategias de muestreo son diversas y pueden ser individualizadas dependiendo de las circunstancias locales, aunque todas las muestras de sedimentos deben incluir una muestra segura que no haya sido expuesta a la luz y material para calcular la tasa de la dosis. La exactitud y precisión de los resultados de la datación por luminiscencia están directamente relacionadas con el tipo y la calidad de los materiales muestreados y los métodos de recolección de muestras en el campo. La elección del material de estudio para su datación debe incluir las siguientes consideraciones en torno a la idoneidad de poder reposicionar la señal de luminiscencia (blanqueador óptico y térmico), la capacidad de caracterizar el ambiente radiactivo que rodea la muestra (la tasa de la dosis) y el que no exista evidencia de una alteración posdeposicional (bioperturbación en suelos y sedimentos). Se discuten las estrategias de muestreo para la recolección de muestras de contextos sedimentarios y de materiales expuestos al fuego. Este artículo debe utilizarse como una guía para el muestreo por luminiscencia y tiene la intención de proveer información básica de cómo recolectar muestras y sobre los tipos de materiales apropiados para la datación por luminiscencia

Application of OSL Dating to Middle to Late Holocene Arroyo Sediments in Kanab Creek, Southern Utah, USA

Middle to late Holocene alluvium, identified as Quaternary alluvial unit 4 (Qa4), along Kanab Creek in southern Utah, USA was dated using optically stimulated luminescence (OSL) on quartz sand, and by radiocarbon dating of detrital charcoal. Entrenchment beginning in 1882 AD created arroyo walls that expose up to 35 m of the Qa4 alluvium. The stratigraphy and sedimentology suggest that fluvial aggradation along the study reach occurred rapidly. Due to the high sediment supply, short transport distances and semi-arid climate with flashy discharge, partial bleaching (zeroing) of the luminescence signal was expected to be a problem for OSL dating. We approached this problem by first using small-aliquot (∼20 grains) and single-grain dating of quartz sand to reduce the number of grains contributing to the OSL signal. Second, we used statistical parameters based on single-grain and small-aliquot equivalent dose (De) distributions of bleached sediment to help identify partial bleaching and to inform if a minimum age model (MAM) should be used for age calculation. Comparison of results with radiocarbon ages demonstrates the success of OSL dating on Kanab Creek arroyo-fill deposits, although careful attention should be paid to the sedimentary facies and stratigraphy of the targeted sample horizon to minimize the effects of partial bleaching. Thin, decimeter-scale plane-bedded and ripple cross-bedded sandy lithofacies were found to be the best target for OSL dating, as these sediments showed minimal evidence for incomplete solar resetting. Additionally, results generally indicate that better-bleached sediments are found in downstream reaches. Age control from these arroyo-fill deposits was acquired in order to fulfill larger research goals of understanding regional arroyo incision and aggradation cycles

Using Grain-Size Distribution to Calculate Soil Water Content: Application to Dose-Rate Calculation for Luminescence Dating

Soil moisture is an important factor for dose-rate determination in luminescence and other dating methods as soil water content impacts sediment bulk density, alters rates of chemical reactions and attenuates effective exposure to nuclear radiation from the surrounding sediments and incoming cosmic rays. Given its importance in dose-rate calculation, methods for measuring and modeling soil water content are discussed, with special focus on semi-arid environments and other situations where modern in situ values are unlikely to be representative of mean soil moisture conditions. We present an alternative method for calculating sediment water content based on grain-size characteristics using the freely available Rosetta Lite v.1.1 software. Modeled outputs include saturation, residual and other water retention curve (WRC) parameters. WRCs were generated from model outputs using the van Genuchten (1980) equation, and mean annual water state was determined using soil moisture regime maps and classifications. Dose-rate values using modeled outputs and laboratory-measured in situ and saturation water content are compared in a test case using Holocene alluvial sediments from Kanab Creek in southern Utah, USA. Best practices for how to estimate mean annual water state for different soil moisture regimes and past soil moisture content in situations where in situ values are not representative of the burial history are discussed

Middle to Late Holocene Chronostratigraphy of Alluvial Fill Deposits Along Kanab Creek in Southern Utah

Kanab Creek in southern Utah flows through three geomorphically defined reaches between the White Cliffs and the town of Kanab, Utah. The upper reaches, particularly the middle (canyon) reach, are characterized by three topographically distinct terraces. Alluvial deposits that underlie these terraces are chronometrically associated with inset aggradational packages downstream in basin-fill alluvium. The town of Kanab is located in the basin-fill reach at the base of the Vermillion Cliffs, where Kanab Creek enters a broad alluvial valley. Historical records document that the floodplain of Kanab Creek was at the level of the second highest terrace in the upstream reaches and near the height of the basin-fill surface in the lower reach prior to the most recent arroyo cutting. Today, Kanab Creek occupies a 20-40-meter-deep arroyo that formed following a series of large-magnitude floods in the early 1880s. Surficial mapping and detailed stratigraphy of terrace and arroyo-wall exposures reveals evidence for past arroyo cut-fill dynamics along Kanab Creek. Results from optically stimulated luminescence (OSL) dating of quartz sand and radiocarbon dating of charcoal collected within fine-grained alluvial sediments suggest at least four periods of fluvial aggradation occurred along Kanab Creek since the mid-Holocene: 6.2-3.6 ka (Qa4), 3.2-2.6 cal ka BP2010 (Qa3’- basin-fill only), 1.9-1.2 ka (Qa3), and 0.8-0.2 ka (Qa2), each separated by arroyo entrenchment (Summa, 2009; Summa-Nelson and Rittenour, 2012). The lowest terrace (Qat1) and alluvium (Qa1) formed in the arroyo bottom following early 1880s entrenchment. The uppermost terrace (Qat4) is underlain by a single alluvial fill package (Qa4), while the middle terrace (Qat2/3) is underlain by multiple fills (Qa4, Qa3, Qa2) and in places is a fill-cut (alluvial strath) terrace. These middle to late Holocene alluvial packages are primarily composed of broadly lenticular, fine-grained silty sand with interbedded clay beds and weakly developed soil horizons. Gravel facies are rare to non-existent in Qa4, Qa3, and Qa2 but can be found in Qa1 and are confined to small lenticular channel bodies in the basin-fill (Qabf) stratigraphy. While not the focus of this study, mapped units also include historic and late Pleistocene deposits and landforms

OSL Chronology of Middle to Late Holocene Aeolian Activity in the St. Anthony Dune Field, Southeastern Idaho, USA

Late Quaternary aeolian dune systems in the Great Plains and western U.S. are valuable archives of past climate variability. This study investigates the St. Anthony dune field, located in the eastern portion of the Snake River Plain in southern Idaho. The current semi-arid climate of the region allows for a central core of active dunes that is approximately 450 km2 in area and includes compound crescentic, blowout, falling, and climbing dunes that range in height from 15 to 121 m. The surrounding region is characterized by ∼20,000 km2 of relic parabolic, linear, and complex linear dunes that are currently fixed by vegetation. This study examined nine samples collected from the fixed dunes that surround the active core of the St. Anthony dune field. Optically stimulated luminescence (OSL) dating results indicate that these fixed dunes were mobile and actively accreting ∼6.6 ka (middle Holocene) and 1.0–2.0 ka (late Holocene). Evidence for activation of a large region currently occupied by stable dunes suggests these periods were characterized by hydrologic deficit and/or warmer climate conditions than currently exists. This research provides new information regarding the depositional timing of the St. Anthony dunes and assists in providing evidence of palaeo-climatic conditions for the eastern Snake River Plain during the middle to late Holocene

Luminescence Dating of Late Pleistocene Proximal Glacial Sediments in the Olympic Mountains, Washington

Late Pleistocene glacial sediments from the South Fork Hoh River valley in the Olympic Mountains, Washington, USA, were dated using optically stimulated luminescence (OSL) on quartz sand. High sediment supply typical of glacial environments, short transport distances, and sediment newly eroded from bedrock sources were expected to pose problems for luminescence dating. Samples were collected from five distinct sedimentary facies, using approximated distances from the ice-front, to assess how luminescence results varied due to these factors and to determine which samples produced the most reliable age estimates. Results from the South Fork Hoh highlight the importance of transport environment and sedimentary facies on solar resetting. Sediments from better-sorted, ice-distal environments were determined to be more completely bleached and more reliable for OSL dating. Samples were collected as part of larger research goals to improve understanding of the glacial history of the South Fork Hoh River valley

Guide to Luminescence Dating Techniques and Their Application to Paleoseismic Research

Over the past 25 years, luminescence dating has become a key tool for dating sediments of interest in paleoseismic research. The data obtained from luminescence dating has been used to determine timing of fault displacement, calculate slip rates, and estimate earthquake recurrence intervals. The flexibility of luminescence is a key complement to other chronometers such as radiocarbon or cosmogenic nuclides. Careful sampling and correct selection of sample sites exert two of the strongest controls on obtaining an accurate luminescence age. Factors such as partial bleaching and post-depositional mixing should be avoided during sampling and special measures may be needed to help correct for associated problems. Like all geochronologic techniques, context is necessary for interpreting and calculating luminescence results and this can be achieved by supplying participating labs with associated trench logs, photos, and stratigraphic locations of sample sites

Single-Grain Optically Stimulated Luminescence Dating of Quartz Temper From Prehistoric Intermountain Ware Ceramics, Northwestern Wyoming, USA

This study applies single-grain optically stimulated luminescence (SG OSL) dating of quartz sand temper to Intermountain Ware ceramics recovered from four archaeological sites in northwestern Wyoming, USA. We show that SG OSL dating can strengthen and further refines existing archaeological site chronologies in certain settings. The SG OSL results are compared to multi-grain infrared stimulated luminescence (IRSL) dating of the polymineral (feldspar and quartz) silt fraction in the ceramic paste of the same sherds. Results from the two methods are statistically indistinguishable, although coarse-grained quartz SG OSL ages have consistently lower standard error terms due to higher relative sensitivity and avoidance of anomalous fading calculations. Moreover, the SG OSL results produced precision at two-sigma standard error greater than or equal to associated calibrated radiocarbon ages. SG OSL dating of quartz temper from Intermountain Ware ceramics provides more reliable site occupation timing than radiocarbon dating, which can be conditioned by incorporation of old wood and contamination from young soil carbon. This study highlights the importance of SG OSL dating on sherds from buried contexts when exposure to wildfires may have occurred, as ceramics recovered from the ground surface of one site after a high-intensity fire produced near-modern apparent ages, suggesting they were thermally reset during the fire. We suggest SG OSL should be applied to date similar ceramics with quartz temper to determine site age and bolster regional chronologies

Anatomy and Evolution of a Dynamic Arroyo System, Kanab Creek, Southern Utah, USA

Many alluvial valleys in the American Southwest are entrenched within continuous arroyos, and stratigraphic evidence indicates that these fluvial systems experienced repeated periods of entrenchment and aggradation during the mid- to late-Holocene. Previous research suggests arroyo dynamics were regionally quasi-synchronous, implying that they were driven by allogenic forcing due to hydroclimatic fluctuations. However, several of these interpretations rely on records with limited age control and include distal correlations across the American Southwest. While hydroclimatic variability must exert some role, autogenic mechanisms related to catchment-specific geomorphic thresholds are hypothesized to partially control the timing of arroyo dynamics. If driven by autogenic processes, episodes of arroyo cutting and filling may not be regionally contemporaneous. Recent improvements in dating methods permit more detailed reconstructions of the timing and evolution of arroyo dynamics, allowing for a more nuanced assessment of these competing hypotheses. Here we present a uniquely large and focused chronostratigraphic data set from two alluvial reaches of Kanab Creek, located in the Grand Staircase region of southern Utah. Episodes of prehistoric arroyo cutting and filling are reconstructed from 27 sites through recognition of soils and buttressed unconformities in the arroyo-wall stratigraphy, and age control derived from 54 optically stimulated luminescence (OSL) ages and 50 radiocarbon ages. Our chronostratigraphic data set indicates five periods of channel aggradation occurred since ca. 6.0 ka, with each interrupted by an episode of arroyo entrenchment. Repeated aggradation to a similar channel elevation suggests attainment of a threshold profile, and comparison of the pre-entrenchment longitudinal profile with the modern arroyo channel demonstrates that changes between end-member entrenched and aggraded states are expressed in channel concavity and slope. We propose that arroyo dynamics are partially driven by sediment supply and the rate of channel aggradation, and that these systems must approach complete re-filling before they become sensitive to incision. Entrenchment itself appears to be associated with rapid transitions from pronounced decadal-scale aridity to pluvial (wetter) periods. Not all such hydroclimatic fluctuations are associated with arroyo entrenchment, which highlights the importance of threshold controls on the behavior of these systems. The collective period of “dynamic instability” characterized by epicycles of arroyo entrenchment and aggradation did not initiate until the mid-Holocene, when a climatic shift toward warmer and drier conditions likely increased fine-grained sediment supply to the fluvial system

The 9th New World Luminescence Dating Workshop: Aim of the Community and Scope of the Conference Proceedings

The New World Luminescence Dating Workshop (NWLDW) is a nearly annual conference held in the Americas for the purpose of bringing together the luminescence and electron spin resonance dating community to discuss current research, share ideas about new laboratory or field methods, and to introduce the next generation of students to the techniques and their applications by those who have pioneered and are developing them. The debut of the workshop series took place November 2001 on the Tulsa Campus of Oklahoma State University under the guidance of Drs. Steve McKeever, Regina Kalchgruber (now DeWitt), Ken Lepper, Michael Blair, and Eduardo Yukihara; all from the Stillwater, Oklahoma luminescence lab