Weichselian Late Pleniglacial surface winds over northwest and central Europe: a model–data comparison

Reconstructions of the Weichselian Late Pleniglacial wind direction in northwest and central Europe are reviewed and compared with palaeoclimate simulations performed with an atmospheric general circulation model. These reconstructions are based on proxy data containing information on former wind directions, such as relic dune forms, sediments and wind‐polished rock surfaces. The objective is to investigate whether: (1) the proxy information is internally consistent; and (2) in agreement with the model simulations. We find a general consensus in the proxy‐based reconstructions, indicating a dominant westerly to northwesterly wind in winter during the Late Pleniglacial. The model results indicate over the study area an atmospheric circulation in winter that is dominated by southwesterly to west‐northwesterly winds, which are stronger than the southwesterly winds in the present‐day climate. The main driving factors behind the anomalous atmospheric circulation in the Late Pleniglacial are the Laurentide Ice Sheet and a colder North Atlantic Ocean with a relatively extensive sea‐ice cover, leading to an eastward relocation of the Icelandic Low and an enhanced pressure gradient over northwest Europe. The minor difference in Late Pleniglacial wind direction between the reconstructions and model can be explained by a combination of uncertainties in the proxy data and the relatively low spatial resolution of the applied climate model. Copyright © 2006 John Wiley & Sons, Ltd.     

Late Weichselian fluvio‐aeolian sands and coversands of the type locality Grubbenvorst (southern Netherlands): sedimentary environments,climate record and age

The Weichselian Late Pleniglacial and Lateglacial aeolian stratigraphy (Older Coversand I, Beuningen Gravel Bed, Older Coversand II, Younger Coversand I, Usselo Soil, Younger Coversand II) in the southern Netherlands has been reinvestigated in its type locality (Grubbenvorst). Sedimentary environments have been reconstructed and related to their climatic evolution based on periglacial structures. In addition, 22 optically stimulated luminescence (OSL) ages have been determined that provide an absolute chronology for the climatic evolution and environmental changes of the coversand area. From this work it appears that, prior to 25 ka fluvial deposition by the Maas dominated. After 25 ka fluvial activity reduced and deposition occurred in a fluvio‐aeolian environment with continuous permafrost (Older Coversand I). This depositional phase was dated between 25.2 ± 2.0 and 17.2 ± 1.2 ka. The upward increase of aeolian activity and cryogenic structures in this unit is related to an increase of climatic aridity and a decrease in sedimentation rate during the Last Glacial Maximum (LGM). The Beuningen Gravel Bed, that results from deflation with polar desert conditions and that represents a stratigraphic marker in northwestern Europe, was bracketed between 17.2 ± 1.2 and 15.3 ± 1.0 ka. Based on this age result a correlation with Heinrich event H1 is suggested. Permafrost degradation occurred at the end of this period. Optical ages for the Older Coversand II unit directly overlying the Beuningen Gravel Bed range from 15.3 ± 1.0 ka at the base to 12.7 ± 0.9 ka at the top. Thus this regionally important Older Coversand II unit started at the end of the Late Pleniglacial and continued throughout the early Lateglacial. Its formation after the Late Pleniglacial (LP) maximum cold and its preservation are related to rapid climatic warming around 14.7 ka cal. BP. The Allerød age of the Usselo Soil was confirmed by the optical ages. Copyright © 2007 John Wiley & Sons, Ltd.     

Sediment budget and tectonic evolution of the Meuse catchment in the Ardennes and the Roer Valley Rift System

The Meuse river system is located in the northeastern part of the Paris Basin, the Ardennes, and the Roer Valley Rift System (RVRS). The Meuse river system developed during the uplift of the Ardennes since the Eocene and it was affected by renewed rifting of the RVRS starting in the Late Oligocene. In response to the uplift of the Ardennes, the river system incised and a terrace sequence developed during the Plio–Pleistocene. The sediments generated by erosion in the catchment were transported into the RVRS and further to the north, into the Zuiderzee Basin and the North Sea Basin. Using a digital terrain model, the amount of eroded rock volume versus time for the Meuse catchment has been computed using the Paleogene and older planation surfaces and the fluvial terraces. Comparison of the amount of eroded material with the volume of sediment preserved in the RVRS for the early Middle Pleistocene shows that about 17.5% of the sediment volume transported into the RVRS remained there, the rest being transported further into the Zuiderzee Basin and the North Sea Basin. The Quaternary tectonic uplift of the Ardennes inferred from the incision history of the Meuse river system is characterized by a long-term uplift, on which a Middle Pleistocene acceleration is superimposed. The accelerated uplift is contemporaneous with an uplift event in the RVRS and in the neighbouring Eifel area, and with the onset of the youngest phase of volcanism in the Eifel area. The areal distribution of this uplift is characterized by a dome shape centered around the Eifel area.     

Legacy: Hugh French and his significance for periglacial environment and permafrost studies

正Hugh French passed away unexpectedly on May 11, 2019, at the age of 76. His influence on the research and teaching in the fields of periglacial environment, permafrost and civil engineering can hardly be overstated. Out of his numerous international contacts, impressive publication records, memberships of international organizations and committees, and awards(Guglielmin and Murton, 2019),     

Mössbauer study of the thermal decomposition of lepidocrocite and characterization of the decomposition products

The lepidocrocite (-FeOOH) to maghemite (-Fe₂O₃), and the maghemite to hematite (-Fe₂O₃) transition temperatures have been monitored by TGA and DSC measurements for four initial -FeOOH samples with different particle sizes. The transition temperature of -FeOOH to -Fe₂O₃ and the size of the resulting particles were not affected by the particle size of the parent lepidocrocite. In contrast, the -Fe₂O₃ to -Fe₂O₃ transition temperature seems to depend on the amount of excess water molecules present in the parent lepidocrocite. Thirteen products obtained by heating for one hour at selected temperatures, were considered. Powder X-ray diffraction was used to qualify their composition and to determine their mean crystallite diameters. Transmission electron micrographs revealed the particle morphology. The Mössbauer spectra at 80 K and room temperature of the mixed and pure decomposition products generally had to be analyzed with a distribution of hyperfine fields and, where appropriate, with an additional quadrupole-splitting distribution. The Mössbauer spectra at variable temperature between 4.2 and 400 K of two single-phase -Fe₂O₃ samples with extremely small particles show the effect of superparamagnetism over a very broad temperature range. Only at the lowest temperatures (T55 K), two distributed components were resolved from the magnetically split spectra. In the external-field spectra the m_I=0 transitions have not vanished. This effect is an intrinsic property of the maghemite particles, indicating a strong spin canting with respect to the applied-field direction. The spectra are successfully reproduced using a bidimensional-distribution approach in which both the canting angle and the magnetic hyperfine field vary within certain intervals. The observed distributions are ascribed to the defect structure of the maghemites (unordered vacancy distribution on B-sites, large surface-to-bulk ratio, presence of OH^- groups). An important new finding is the correlation between the magnitude of the hyperfine field and the average canting angle for A-site ferric ions, whereas the B-site spins show a more uniform canting. The Mössbauer parameters of the two hematite samples with MCD₁₀₄ values of respectively 61.0 and 26.5 nm display a temperature variation which is very similar to that of small-particle hematites obtained from thermal decomposition of goethite. However, for a given MCD the Morin transition temperature for the latter samples is about 30 K lower. This has tentatively been ascribed to the different mechanisms of formation, presumably resulting in slightly larger lattice parameters for the hematite particles formed from goethite, thus shifting the Morin transition to lower temperatures.Senior Research Associate, National Fund for Scientific Research (Belgium)     

On the origin of the folding in the Namurian strata at the Namur Citadelle,Belgium

A number of the features of folding at the Namur Citadelle, a classical outcrop of Namurian strata, can be interpreted in terms of penecontemporaneous deformation induced by sandstones overlying shales of lighter density. Variscan tectonics has then overprinted already folded rocks.     

Method for Stochastic Inverse Modeling of Fault Geometry and Connectivity Using Flow Data

This paper focuses on fault-related uncertainties in the subsurface, which can significantly affect the numerical simulation of physical processes. Our goal is to use dynamic data and process-based simulation to update structural uncertainty in a Bayesian inverse approach. We propose a stochastic fault model where the number and features of faults are made variable. In particular, this model samples uncertainties about connectivity between the faults. The stochastic three dimensional fault model is integrated within a stochastic inversion scheme in order to reduce uncertainties about fault characteristics and fault zone layout, by minimizing the mismatch between observed and simulated data.