Manfred Frechen

Malacological and sedimentological evidence for “warm” glacial climate from the Irig loess sequence, Vojvodina, Serbia

Four loess units and three paleosol layers are preserved in the Irig brickyard, Vojvodina, Serbia. Amino acid geochronology provides stratigraphic correlations between loess units V-L1 and V-L2 at the Irig section with loess of glacial cycles B and C, respectively, described from other central European localities. Luminescence dating results for the upper loess layers V-L1L1 and V-L1S1L1 confirm the geological interpretations, although in samples below paleosol V-L1S1S2, the age increase with depth is less than in our proposed age model. Magnetic susceptibility and sedimentological evidence from the Irig loess-paleosol sequence show general similarities with the MIS 6-1 pattern of the SPECMAP oxygen-isotope curve. Malacogical investigations at the Irig site reveal the continuous presence of the Chondrula tridens and Helicopsis striata faunal assemblages throughout the last glacial and final part of the penultimate glacial loess. The loess snail fauna, which is characterized by the complete absence of cold-resistant species, suggests a stable, dry, and relatively warm glacial climate, compared with other central European loess localities. Furthermore, these data suggest that the southern slope of Fruska Gora was a refugium for warm-loving and xerophilus mollusc taxa during the otherwise unfavorable glacial climates of the Late Pleistocene.

Loess chronology of the Last Interglacial/Glacial cycle in Bohemia and Moravia, Czech Republic

Abstract Combined infrared and green light stimulated luminescence and thermoluminescence dating applied to the extensively studied Bohemian and Moravian loess/palaeosol sequences from Sedlec Suchdol, Kutna Hora, Dolni Věstonice, Lechovice, Modřice, Bulhary and Cervený Kopec provides a reliable chronological framework for the last interglacial/glacial cycle. Based on this luminescence dating study a new chronology is proposed for the last interglacial/glacial loess/palaeosol sequences from the Czech Republic. IRSL and TL dating suggests that the Bt horizon of a truncated brown forest soil (lower PK III) formed during the Last Interglacial, equivalent to Oxygen Isotope Substage 5e. The upper chernozem of PKII belongs to oxygen isotope stage 3, if the combined IRSL and TL age estimates are taken into account, although from geological estimates an age range within OI Substage 5a is most likely. The Upper Weichselian loess accumulated at a very high rate. Owing to the high accumulation rate there is no time difference in sedimentation ages between the tundra gley palaeosols above PK I, which include the Upper Weichselian sediments in Central Europe.

Aeolian dust dynamics in central Asia during the Pleistocene: Driven by the long‐term migration, seasonality, and permanency of the Asiatic polar front

Loess-paleosol sequences preserve detailed archives of climate change, reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere. The detailed investigation of particle size distributions (PSDs) of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics. The central Asian loess belt offers the potential to reconstruct Pleistocene atmospheric circulation patterns along an adjacent west-east transect within interior Eurasia through granulometric studies. In this study we present the aeolian dust record of the loess sequence at Remisowka (SE Kazakhstan), which reflects a detailed signal of glacial-interglacial climate and atmospheric dynamics in central Asia. On the basis of radiocarbon and amino acid geochronologic data, long-term semicontinuous trends in the aeolian dust record of the Last Glacial Cycle are observed and interpreted to reveal their paleoclimate signal. In consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central Asia, it is likely that the observed trends reflect the long-term migration, seasonal duration, and permanency of the polar front during the late Pleistocene. Previously published models, which focused on the reciprocal glacial-interglacial influence of the zonal Westerlies and the Asiatic high on the aeolian dust transport in central Asia, were overly simplified and should be modified to include the major influence of the Asiatic polar front. As the polar front activity is intimately connected with the development and position of the interhemispherically active, high-level planetary frontal zone (HPFZ), the presented data give insight to long-term aeolian dust dynamics and climate variability of interior Eurasia, which are linked with interhemispheric climates.

Upper Pleistocene loess stratigraphy in Southern Germany

Abstract The detailed loess/paleosol sequences of Southern Germany provide a highly sensitive record of the regional climate and environmental changes of the Upper Pleistocene. Combined infrared stimulated luminescence (IRSL) and thermoluminescence (TL) dating was carried out on loess and loess derivatives at Upper Pleistocene-type sections from the Mainz Basin, the Middle Neckar Valley and the Alpine Foreland with the aim of setting up a reliable chronological framework for the past 130 000 years. The IRSL and TL age estimates are in agreement with the geological estimates up to 70 000 years. However, the chronostratigraphic position of the first truncated brown forest soil in the sections at Bockingen, Bonnigheim and Bobingen, considered to be the Eemian soil or equivalent to oxygen isotope (OI) substage 5e, remains uncertain. The methodological results indicate that IRSL dating is the more advantageous technique for the Upper and Middle Weichselian periglacial deposits, as demonstrated for the loess/paleosol sequence in Mainz-Weisenau.

Dry early Holocene revealed by sand dune accumulation chronology in Bayanbulak Basin (Xinjiang, NW China)

Understanding the Holocene climate changes (especially moisture variation) and their mechanisms in the semiarid–arid Central Asia (SCA) is very important, as water availability is crucial for sustainable developments in this area. This study presents chronostratigraphy of an aeolian sedimentary sequence from Bayanbulak Basin (Xinjiang, NW China), aiming to infer the Holocene moisture history in the SCA. Luminescence dating technique was selected to construct the age framework of the study section. Since the luminescence signal intensity of quartz from the samples was too low to be detected, feldspar was used as an alternative dosimeter. A newly developed post-infrared (IR) IR-stimulated luminescence (IRSL) (pIRIR) dating protocol on K-feldspar was applied to determine the ages of samples. A set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable. Combined with the stratigraphic investigation on the sand dune/palaeosol section, the results imply a very dry climatic condition characterized by sand dune accumulation at ~9–8 kyr, and a wet interval of 5–1.6 kyr when a soil layer was formed. This moisture variation pattern is consistent with that inferred from many lacustrine records in the SCA, suggesting a widespread dry period at 11–8 kyr. The present results appear to challenge a new stalagmite δ18O sequence, located nearby to Bayanbulak Basin, which instead suggested a humid early Holocene.

Chronology of upper Quaternary offshore successions from the southeastern Mediterranean Sea, Israel

Pleistocene and Holocene transgressions advancing over the shelf that was exposed during glacial maxima drowned any continental and shallow marine sediments deposited during low sea level stands. To complement records from sequences exposed on land, core material from the shallow continental shelf is needed to reconstruct climatic and sea level fluctuations. Two cores drilled offshore Ashqelon off the southern Mediterranean coast of Israel, in a water depth of 10 and 25 m, were analyzed. Sedimentary facies and faunal analyses indicate that most of the sediments were deposited in nearshore environments, with only short intervals of continental episodes. Luminescence dating of alkali feldspar and quartz, as well as 14 C ages of mollusks, date the cores to marine oxygen isotopic stages 6–1, between B140 and 5 ka. Comparison between the dating methods shows that most alkali feldspar ages agree with independent sea level and sedimentological constraints while quartz ages are overestimated. r 2003 Elsevier Science Ltd. All rights reserved.

A new massive deposit of allophane raw material in Ecuador.

In Ecuador, DINAGE (known today as the Servicio Geológico Nacional) and the German Federal Institute for Geosciences and Natural Resources have discovered a huge allophane deposit covering an area of >4000 km2. This study presents the results from an investigation of a 16-m thick vertical sequence from this deposit, supposedly the weathering product of two different volcanic ash deposits. In particular, the distribution of alkali metals within the uppermost layer indicates that the weathering process is still ongoing.According to the mineralogical composition, an allophane-rich layer (allophane facies) could be distinguished from the underlying halloysite-rich layer (halloysite facies). A 2-m thick transition zone is characterized by the presence of gibbsite and intermediate specific surface area values. Only a few imogolite fibers could be identified (by scanning electron microscopy), indicating the dominance of allophane over imogolite in the allophane facies. Single allophane particles were investigated by atomic force microscopy, though this method was less accurate than transmission electron microscopy with respect to the determination of the primary particle diameter. Carbon isotope analysis (14C) suggested an age of ∼20,000 y for the allophane layer.Within the allophane facies, a 4-m thick layer occurs containing 70–80 wt.% allophane with an N2-BET specific surface area of >300 m2/g. Based on infrared and energy-dispersive X-ray diffraction measurements, an Al/Si ratio of 1.3–1.4 was established for this allophane, which is between Al-rich and Si-rich allophane. The allophane layer may be of economic value due to the large allophane content, the small amount of organic matter, and the significant thickness of the deposit.

The loess record in sections at Koblenz–Metternich and Tönchesberg in the Middle Rhine Area

Abstract The loess–palaeosol sequences of the Middle Rhine Area provide a relatively detailed and continuous terrestrial record of climate and environment change for the past 200,000 years. Loess–palaeosol sequences are generally well preserved in inter- and intra-crater depressions of late Middle Pleistocene scoria cones in the East Eifel Volcanic Field and on fluvial terraces of the lower middle terrace of the rivers Rhine and Moselle. Stratigraphic and chronological investigations of loess–palaeosol sequences from sections at Tonchesberg and Koblenz–Metternich in the Middle Rhine Area indicate that the last interglacial and glacial cycle is preserved in much more detail than previously thought. In both sections, the last interglacial soil is covered by at least ten palaeosols, postdating the Eemian (oxygen isotope (sub)stage, OIS 5e) brown forest soil.

The Last Interglacial palaeosol in the Belgian loess belt: TL age record

Abstract In the Belgian loess plateau, the Rocourt soil is a well-known luvisol horizon that is regarded as representing the Last Interglacial. The name of the soil comes from the locality of Rocourt in the east of the country, where it has been observed for the first time. Later, exposures of a similar soil were found in other localities. Most typically, a sequence of three horizons is observed: a red-brown illuvial Bt horizon, overlain by a bleached horizon and a compound dark horizon. In this paper, we present the results of TL age determinations obtained on sediments directly bracketing the soil at the type locality of Rocourt and at the locality of Momalle more to the west, together with some supplementary data for the exposures at Kesselt to check a controversial result that was obtained earlier (J. Quaternary Sci. 13 (5) (1998) 487). The TL analyses involved both the (total bleach) additive dose and regeneration methods. Our TL ages confirm the assumed chronostratigraphic position (oxygen isotope stage 5) of the soil exposed at the type locality. The ages obtained at Momalle and Kesselt indicate that we are dealing with the same soil here but the palaeodose data are less consistent. This is probably due to the fact that the loess has been disturbed by post-depositional processes such as solifluction, surface run-off, cryo- and bioturbation. This seems to be a major problem with the sediments in the eastern part of the Belgian loess belt.

Chronology of Cauvery Delta Sediments from Shallow Subsurface Cores Using Elevated-Temperature Post-IR IRSL Dating of Feldspar

Chronology of Cauvery Delta Sediments from Shallow Subsurface Cores Using Elevated-Temperature Post-IR IRSL Dating of Feldspar We present the results of luminescence dating of sediments from two cores from the Cauvery Delta in south-east India. Since all natural quartz OSL signals except one sample were in saturation, the elevated temperature post-IR IRSL protocol for K-feldspar was applied to establish a chronology. Internal dose rates of K-feldspar grains were calculated from the measured internal content of potassium, uranium, thorium and rubidium in the bulk of K-feldspar grains using solution ICP-OES and ICP-MS analysis. A substantial scatter in single-aliquot De values was observed which is most probably due to the effect of incomplete bleaching of fluvial sediments before burial. A minimum age model was applied to extract possible depositional ages. The study revealed that except an upper layer of Holocene sediments (< 5m), the majority of the upper ~50m of Cauvery delta sediments were deposited between marine isotope stage MIS-5 and MIS-10 or older. The feldspar luminescence ages also indicate the existence of a period of non deposition or erosion in the upper part of the cores.