Late Quaternary paleoclimatic and geomorphological evolution at the interface between the Menyuan basin and the Qilian Mountains, northeastern Tibetan Plateau

The Tibetan Plateau is regarded as an amplifier and driver of environmental change in adjacent regions because of its extent and high altitude. However, reliable age control for paleoenvironmental information on the plateau is limited. OSL appears to be a valid method to constrain the age of deposits of glacial and fluvial origin, soils and periglacial structures in the Menyuan basin on the northeastern Tibetan Plateau. Dating results show glaciers advanced extensively to the foot of the Qilian mountains at ~. 21. ka, in agreement with the timing of the global Last Glacial Maximum (LGM) recorded in Northern Hemisphere ice cores. Comparison with results from the eastern Tibetan Plateau suggests that the factor controlling glacial advance in both regions was decreased temperature, not monsoon-related precipitation increase. The areas of the Menyuan basin occupied by glacio-fluvial deposits experienced continuous permafrost during the LGM, indicated by large cryoturbation features, interpreted to indicate that the mean annual temperature was ≥. 7. °C lower than at present. Glacio-fluvial systems in the Menyuan basin aggraded and terraces formed during cold periods (penultimate glaciation, LGM, and possibly the Younger Dryas) as a response to increased glacial sediment production and meltwater runoff then. © 2013 University of Washington

Revising the Gent Formation : a new lithostratigraphy for Quaternary wind-dominated sand deposits in Belgium

In Belgian lithostratigraphy, the Gent Formation was previously introduced to encompass all Quaternary sandy aeolian sediments. It has been difficult to apply, however, as it was incomplete, regionally biased, and not based on sediment properties alone. To solve this problem the Gent Formation is revised both in terms of definition and subdivision. Morphological and chronological criteria were omitted to allow ranking strata on the basis of visible lithological properties. The Belgian sand belt is newly introduced to designate the area where these sediments were deposited. The Gent Formation is subdivided into five members based on distinct lithological properties, and as a consequence reflecting different palaeoenvironmental conditions during deposition. Whenever feasible, each member is put in a chronostratigraphical and geomorphical context. The new subdivision is discussed and compared with earlier Belgian lithostratigraphical frameworks, as well as to the most recent one for comparable deposits in the Netherlands

Grèzes litées and their genesis: the site of Enscherange in the Rhenish-Ardennes Massif as a case study

The freeze-thaw cycles in periglacial areas during the Quaternary glacials increased frost weathering, leading to a disintegration of rock formations. Transported downslope, clasts allowed in some areas the formation of stratified slope deposits known as "grezes litees". This study reviews the existing theories and investigates the grezes litees deposits of Enscherange and Rodershausen in Luxembourg. This process was reinforced by the lithostructural control of the parent material expressed by the dip of schistosity (66 degrees) and its orientation parallel to the main slopes in the area. This gave opportunities to activate the frost-weathering process on top of the ridge where the parent material outcropped. As the stratified slope deposits have a dip of 23 degrees and as there is no significant lateral variation in rock fragment size, slope processes that involve only gravity are excluded and transportation in solifluction lobes with significant slopewash and sorting processes is hypothesized. The Enscherange formation, the biggest known outcrop of grezes litees in north-western Europe, shows evidence of clear layering over the whole profile depth. A palaeolandscape reconstruction shows that ridges must have been tens of metres higher than presently. The investigation of the matrix composition shows Laacher See tephra in the overlying periglacial cover bed with infiltrations of the minerals in the reworked upper layer of the grezes litees deposit. Chronostratigraphic approaches using the underlying cryoturbation zone and Laacher See heavy minerals in the overlying topsoil place the formation of grezes litees deposits in the Late Pleistocene

Site-selective mapping of metastable states using electron-beam induced luminescence microscopy

Metastable states created by electron or hole capture in crystal defects are widely used in dosimetry and photonic applications. Feldspar, the most abundant mineral in the Earth's crust (> 50%), generates metastable states with lifetimes of millions of years upon exposure to ionizing radiation. Although feldspar is widely used in dosimetry and geochronometry, the creation of metastable states and charge transfer across them is poorly understood. Understanding such phenomena requires next-generation methods based on high-resolution, site-selective probing of the metastable states. Recent studies using site-selective techniques such as photoluminescence (PL), and radioluminescence (RL) at 7 K have revealed that feldspar exhibits two near-infrared (NIR) emission bands peaking at 880 nm and 955 nm, which are believed to arise from the principal electron-trapping states. Here, we map for the first time the electron-trapping states in potassium-rich feldspar using spectrally-resolved cathodoluminescence microscopy at a spatial resolution of similar to 6 to 22 mu m. Each pixel probed by a scanning electron microscope provides us a cathodoluminescence spectrum (SEM-CL) in the range 600-1000 nm, and elemental data from energy-dispersive x-ray (EDX) spectroscopy. We conclude that the two NIR emissions are spatially variable and, therefore, originate from different sites. This conclusion contradicts the existing model that the two emissions arise from two different excited states of a principal trap. Moreover, we are able to link the individual NIR emission peaks with the geochemical variations (K, Na and Fe concentration), and propose a model that explains the quenching of the NIR emission by Fe4+. Our study contributes to an improved understanding of charge storage in feldspathic minerals, with implications for developing sub-single grain (micrometer scale) measurement techniques in radiation dosimetry

The almost hidden role of deep traps when measuring afterglow and thermoluminescence of persistent phosphors

Although the luminescence characteristics of persistent phosphors have been extensively investigated, the physical mechanism underlying their afterglow is not yet fully understood. Many variables influence the outcome of thermoluminescence, charging and afterglow experiments, hampering a correct interpretation. Here we investigate the role of deep, thermally stable traps in SrAl2O4:Eu2+,Dy3+ which received little attention in previous studies. We demonstrate that these traps have a considerably higher trapping cross-section than the shallow traps, which are responsible for the persistent luminescence. This affects the charging dynamics of the shallow traps significantly and should therefore be considered in behavioral studies of these phosphors

Reconstructing the history of the silva carbonaria, an enigmatic charcoal-burners-forest in Central Belgium

The Sonian forest, situated south of Brussels, is one of the last remnants of a vast forest that is believed to have covered the larger part of central Belgium up to at least the end of the Early Medieval period and which is mentioned as the silva carbonaria (Latin for ‘charcoal burners forest’) in several historical texts. The strict reserves within the forest, together with several other European old growth beech forests, were listed as a UNESCO world heritage site since 2017. Extensive archives allow us to reconstruct its history over the last 500 years, yet, little is known however on the extent, composition and exploitation of this forest before that time.. We now present the preliminary results of an interdisciplinary study of archaeological remains of charcoal and metal production sites from this forest, which provide a lot of new information on its history and evolution. This study includes the detection of charcoal and metal production sites using LIDAR and geophysical methods, radiocarbon and OSL-dating of different types of features from these sites and anthracological analysis. In addition, the results also provide new information on the role of beech in the natural forest vegetation in the lowlands of NW-Europe

A comprehensive study of three different portable XRF scanners to assess the soil geochemistry of an extensive sample dataset

The assessment of soil elemental concentrations nowadays mainly occurs through conventional laboratory analyses. However, proximal soil sensing (PSS) techniques such as X-ray fluorescence (XRF) spectrometry are proving to reduce analysis time and costs, and thus offer a worthy alternative to laboratory analyses. Moreover, XRF scanners are non-destructive and can be directly employed in the field. Although the use of XRF for soil elemental analysis is becoming widely accepted, most previous studies were limited to one scanner, a few samples, a few elements, or a non-diverse sample database. Here, an extensive and diverse soil database was used to compare the performance of three different XRF scanners with results obtained through conventional laboratory analyses. Scanners were used in benchtop mode with built-in soil calibrations to measure the concentrations of 15 elements. Although in many samples Cu, S, P, and Mg concentrations were up to 6, 12, 13, and 5 times overestimated by XRF, and empirical recalibration is recommended, all scanners produced acceptable results, even for lighter elements. Unexpectedly, XRF performance did not seem to depend on soil characteristics such as CaCO3 content. While performances will be worse when expanding to the field, our results show that XRF can easily be applied by non-experts to measure soil elemental concentrations reliably in widely different environments