Description: Publication date: Available online 24 December 2014 Source: Quaternary Geochronology Author(s): M.D. Bateman , S. Stein , R.A. Ashurst , K. Selby 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.

Description: Publication date: Available online 15 December 2014 Source: Quaternary Geochronology Author(s): O. Trandafir , A. Timar-Gabor , C. Schmidt , D. Veres , M. Anghelinu , U. Hambach , S. Simon Previous works focused on optically stimulated luminescence dating of quartz extracted from Romanian and Serbian loess reported significant discrepancies between ages obtained on fine (4-11 μm) and coarse (63-90 μm) quartz. The present study is directed at expanding these investigations. The SAR-OSL and double SAR-OSL protocols are applied on quartz of different grain sizes belonging to 9 samples extracted from a newly identified archaeological site at Bistricioara-Lutărie III on the Bistrița Valley (NE Romania). Radiocarbon ages are also obtained for the 3 uppermost cultural layers hosted in the loess-like deposit. Discrepant ages are obtained between fine (4-11 μm) and coarse (63-90 and 90-200 μm, respectively) quartz for equivalent doses higher than ∼80-100 Gy. However, a very good agreement is achieved for the youngest sample, with an age of ∼8 ka (with a D e of 38 Gy for fine and 35 Gy for coarse grains, respectively). The comparison with independent control provided by radiocarbon dating suggests better agreement of ages calculated for coarse quartz. Our results are once again proof that concerns should be raised regarding the reliability of the equivalent doses obtained on quartz samples for which the laboratory dose response cannot be fitted by a single saturating exponential function. Further systematic investigations are required regarding the very different saturation characteristics of fine and coarse grained quartz.

Description: Publication date: Available online 15 December 2014 Source: Quaternary Geochronology Author(s): Guillaume Guérin , Mayank Jain , Kristina Thomsen , Andrew Murray , Norbert Mercier Single grain OSL has become a widely used approach in Quaternary geochronology. However, the origins of D e distributions and the sources of variation in individual dose estimates are still poorly understood. The amount of scatter in these distributions on top of the known uncertainties in measurement and analysis is defined by overdispersion and this quantity is generally used for weighting individual D e values to calculate a central equivalent dose. In this study, we address the nature and amount of different sources of dispersion in quartz single grain D e estimates, by (i) using appropriate statistical tools to characterize D e populations and (ii) modelling, with a specifically designed Geant4 code, dose rate distributions arising from the presence of potassium feldspar grains in well-sorted sands. The model uses Monte Carlo simulations of beta emissions and interactions in a random close packing of quartz and feldspar spheres representing a sand sample. Based on the simulation results, we explain the discrepancy between intrinsic and natural overdispersion values in a well-bleached sample, thus validating the model. The three parameters having the most influence on dispersion in dose rate distributions, and modelled in this study, appear to be grain size, potassium content and total dose rate. Finally an analysis of measurement uncertainties and other sources of variations in equivalent dose estimates leads us to conclude that all age models (both logged and unlogged) which include an overdispersion value to weight individual D e values rely mainly on unknown parameters; this ignorance may lead to an inadvertent bias in D e estimates. Assuming counting statistics make a small contribution to dispersion (as is often the case), we suggest that in some cases it is most appropriate to use unweighted averages of equivalent doses when dividing by commonly measured average dose rates.

Description: Publication date: Available online 11 December 2014 Source: Quaternary Geochronology Author(s): Christina M. Neudorf , Olav B. Lian , Ian J. Walker , Dan H. Shugar , Jordan B.R. Eamer , Libby C.M. Griffin The Quaternary geology of British Columbia’s central coast contains a rich and complex record of glacial activity, post-glacial sea level and landscape change, and early human occupation spanning the last ∼10,000 years. At present, however, this region remains a largely understudied portion of coastal North America. This study describes the luminescence characteristics of quartz and K-feldspar from coastal dune and beach sands on Calvert Island and develops a suitable luminescence dating protocol that will allow for a more rigorous chronology for post-glacial landscape evolution and human occupation on BC’s central coast. Luminescence signals from Calvert Island quartz are dim, and appear to lack the so-called “fast” component that is most desirable for optical dating. K-feldspar signals are sufficiently bright for optical dating. We test and refine a single-aliquot regenerative-dose (SAR) protocol for K-feldspar specific to Calvert Island samples through a series of dose recovery and preheat plateau tests. Two approaches for correcting a sample age for anomalous fading are compared and a correction for phototransfer is introduced and applied. Measured fading rates vary from sample to sample implying that, in this region, it is not sufficient to rely on two or three representative fading rates as has sometimes been done elsewhere. Refined age estimates show consistency with independent radiocarbon dating control and help identify radiocarbon-dated organic-rich sediments that have been reworked.

Description: Publication date: Available online 3 December 2014 Source: Quaternary Geochronology Author(s): Eva Panagiotakopulu , Thomas F.G. Higham , Paul C. Buckland , Jennifer A. Tripp , Robert E.M. Hedges Results from AMS dating applied to insect chitin from a variety of contexts and different preservation conditions and retrieval methods are presented. Secure contexts, which include other dated organic material from different geographic locations ranging from Egypt to Greenland and different chronological periods, from Lateglacial to Medieval, have been used. In addition, insect species with different dietary requirements have been selected for dating purposes in order to provide an understanding as to whether diet plays a role in the chitin dating results. Dates from each context/site are discussed separately in the context of their stratigraphy and/or archaeology. Our research concentrates on the results from pre-treatment methods which require small quantities of chitin as these could be applied in a variety of Quaternary and archaeological contexts. The dates from carbonised and desiccated remains where no chemicals had been involved in storage fell within the range of dates from other organics or the archaeology. Although some of the dates from waterlogged contexts were successful, problems were encountered and these have been linked with long term storage in various alcohols of uncertain provenance. Whilst short term immersion in paraffin (kerosene) and alcohols during processing probably has no impact, it is recommended that chitinous material for dating be stored in acidified distilled water. Our results demonstrate the potential of chitin as a dating medium and provide a basis for its wider application.

Description: Publication date: February 2015 Source: Quaternary Geochronology, Volume 25 Author(s): W. Derek Hamilton , Jane Kenney In recent years, the use of Bayesian statistical analysis for modelling radiocarbon dates has become much more commonplace within archaeology, however there remains very little literature to aid new practitioners with understanding the archaeological assumptions that underpin many of the modelling choices. Using a suite of radiocarbon dates from a sample of seven ovens, from the 18 excavated across the site at Ysgol yr Hendre, Caernarfon, North Wales, this paper explores the various methods of modelling this group of features. It stresses the underlying archaeological assumptions of each model, while also highlighting some of the tools that should especially be considered when developing very precise models. Finally it compares the results of the models.

Description: Publication date: February 2015 Source: Quaternary Geochronology, Volume 25 Author(s): Barbara Fiałkiewicz-Kozieł , Piotr Kołaczek , Adam Michczyński , Natalia Piotrowska The main aim of this paper is to present the pitfalls connected with the construction of reliable chronologies for anthropogenically disturbed peatlands over the last two millennia based on 210 Pb and 14 C dating, i.e. the period of the strongest human impact on these ecosystems. The following hypotheses have been formulated: i) parts of peatlands suspected to be affected by peat extraction may possess traces of mechanical disturbances undetectable using different analyses based on biota proxy; ii) failure to consider information included in radionuclide date inversions may contribute to the establishment of misleading chronologies. To test these hypotheses, different scenarios of chronology based on high resolution 210 Pb and 14 C dating from a peat core retrieved from the Puścizna Krauszowska bog (southern Poland) have been analysed. Nowadays, this mire is intensively exploited by humans; however, it contains remains of dome considered undisturbed, from which the core presented in this paper was collected. The set of dates revealed the presence of marked 14 C date inversions (mechanical disturbances) which, if inappropriately interpreted before the age–depth modelling process, may lead to the establishment of misleading chronologies, and thus an incorrect interpretation of biota proxy records, e.g. pollen. Those sections of peat profiles with prominent age inversions and/or strong discrepancies between the peat accumulation rate and bulk density should be rejected from age–depth modelling, even if interpretable chronologies can be obtained.

Description: Publication date: Available online 28 November 2014 Source: Quaternary Geochronology Author(s): Nathaniel Lifton , Marc Caffee , Robert Finkel , Shasta Marrero , Kunihiko Nishiizumi , Fred M. Phillips , Brent Goehring , John Gosse , John Stone , Joerg Schaefer , Bailey Theriault , A.J. Timothy Jull , Keith Fifield Well-dated bedrock surfaces associated with the highstand and subsequent catastrophic draining of Pleistocene Lake Bonneville, Utah, during the Bonneville flood are excellent locations for in situ cosmogenic nuclide production rate calibration. The CRONUS-Earth project sampled wave-polished bedrock and boulders on an extensive wave-cut bench formed during the Bonneville-level highstand that was abandoned almost instantaneously during the Bonneville flood. CRONUS-Earth also sampled the Tabernacle Hill basalt flow that erupted into Lake Bonneville soon after its stabilization at the Provo level, following the flood. New radiocarbon dating results from tufa at the margins of Tabernacle Hill as part of this study have solidified key aspects of the exposure history at both sites. Both sites have well-constrained exposure histories in which factors such as potential prior exposure, erosion, and shielding are either demonstrably negligible or quantifiable. Multi-nuclide analyses from multiple labs serve as an ad hoc inter-laboratory comparison that supplements and expands on the formalized CRONUS-Earth and CRONUS-EU inter-laboratory comparisons (Blard et al., 2014, this volume; Jull et al., 2013, this volume; Vermeesch et al., 2012, this volume). Results from 10 Be, 26 Al, and 14 C all exhibit scatter comparable to that observed in the CRONUS-Earth effort. Although a 36 Cl inter-laboratory comparison was not completed for Jull et al. (2013, this volume), 36 Cl from plagioclase mineral separates exhibits comparable reproducibility. Site production rates derived from these measurements provide valuable input to the global production rate calibration described by Borchers et al. (this volume). Whole-rock 36 Cl concentrations, however, exhibit inter-laboratory variation exceeding analytical uncertainty and outside the ranges observed for the other nuclides (Jull et al., 2013, this volume). A rigorous inter-laboratory comparison studying the systematics of whole-rock 36 Cl extraction techniques is currently underway with the goals of delineating the source(s) of this discrepancy and standardizing these procedures going forward.

Description: Publication date: Available online 18 October 2014 Source: Quaternary Geochronology Author(s): David C. Argento , John O. Stone , Robert C. Reedy , Keran O'Brien Characteristics of the spallogenic component of nuclide production are investigated through the use of a physics-based model. Calculated production rates for commonly used nuclides indicate differences in scaling up to 15% at very high altitude. Angular distribution of nuclide forming particles suggests the current method of shielding correction, which is neither altitude nor latitude dependent, can be improved on. Subsurface production profiles suggest that erosion corrections should be performed with non-constant attenuation lengths. Results are parameterized for easy application.

Description: Publication date: Available online 24 November 2014 Source: Quaternary Geochronology Author(s): Patrick Chiroiu , Markus Stoffel , Alexandru Onaca , Petru Urdea Snow avalanches are a widespread natural phenomenon in steep mountain environments, where they modulate landscapes and frequently disturb forest stands. Such disturbances in trees have been used since the 1970s to retrospectively date avalanches, study their extent and reach, as well as to document their triggers. Although virtually every dendrogeomorphic paper is still based on the concepts established by Shroder (1978), important methodological improvements have been achieved in the field ever since and more particularly over the last decade. This study therefore reports on recent methodological progress and employs three different approaches (i.e. Shroder index value and Kogelnig-Mayer weighted index value) and different sets of signals in trees (i.e. inclusion of tangential rows of traumatic resin ducts as evidence of past avalanching) to record snow avalanche activity. Using 238 increment cores from 105 Picea abies (L.) Karst trees which colonize a snow avalanche path in the Romanian Carpathians, we illustrate possibilities and limitations of the different approaches for the period covered by the chronologies (1852–2013). In addition, we sampled 30 undisturbed P. abies trees from a forest stand north of the avalanche path, where no geomorphic disturbance was identified, so as to build a reference tree-ring chronology. The three avalanche chronologies constructed with the disturbed trees allow identification of past process activity, but results differ quite considerably in terms of avalanche frequency, number of reconstructed events and their temporal distribution. Depending on the approach used, 15 to 20 snow avalanches can be reconstructed, with the best results being obtained in the dataset including tangential rows of traumatic resin ducts. The addition of this anatomical feature, formed after mechanical impact enlarges the number of growth disturbances by 43.5%, and can thus explain the increase of reconstructed avalanches by one-third as compared to the results of the chronology using the “conventional” Shroder approach.