Boreas最新文献

The present-day landscape of the northern Alpine foreland is marked by the cumulated impact of weathering during interglacial, and of erosion and deposition during glacial periods of the Quaternary. Direct traces of the earliest phases of ice advance, as well as thorough studies thereof, exist only sporadically. Here, a succession of diamictic deposits, which has been interpreted as the infill of an Early Pleistocene overdeepened basin, is investigated with a combined sedimentological-geotechnical approach including analysis via μCT scans, and standard tests of the water uptake, consistency, and compaction properties. The diamicts are exposed along a 4.5-m-deep profile, and are subdivided into a yellowish-brown lower unit with a variable, carbonaceous, silty to sandy matrix, and a reddish-brown upper unit that is free from carbonate and appears largely homogeneous. Although the lower unit is rather loose and surficially bioturbated, it contains microstructures indicative of subglacial deformation, which are lacking in the compact and clay-rich upper unit. The lower part is interpreted as a secondary glacial deposit (i.e. it has been affected by limited sorting in water) that was overridden and sheared by a glacier briefly after deposition, and recently bioturbated. The upper part is less sorted, more massive and compact, and thus likely of a primary glacial nature. It is further characterized by a strong pedogenetic overprint typical of prolonged warm periods. This suggests that it is separated from the overlying glacifluvial gravel, which has an equivalent petrographic composition, by a full interglacial at least. Thus, the combination of geotechnical testing and CT-based micromorphology offers a new, practical and cost-effective approach to the characterization of glacially derived sediments.

The Greenland Ice Sheet is highly sensitive to climate change, leading to significant retreat along its edges. This rapid ice loss contributes to rising sea levels and impacts the Earth's climate stability. Understanding the extent of recent glacier retreat is crucial in order to determine if it is unprecedented or within ranges of natural variability. Palaeoenvironmental studies aim to identify past glacial phases and landscape changes using advanced dating methods such as cosmic ray exposure (CRE) dating. In NE Greenland, CRE dating has helped establish the timing of glacial oscillations, yet a comprehensive understanding of glacial fluctuations during specific periods still needs to be developed. This study aims to chronologically constrain the postglacial landscape evolution of two NE Greenland valleys from the Young Sund–Tyrolerfjord area (74°N, 20–25°E) from the onset of deglaciation and throughout the Holocene to better understand glacial and postglacial changes. The chronological framework relies on 27 ¹⁰Be cosmic-ray exposure ages that constrain our interpretation of the geomorphological features in both valleys. Inconsistencies were observed in the ages dataset, highlighting potential bias associated with nuclide inheritance and post-glacial dynamics. Despite limitations, the CRE results confirm the general pattern observed in NE Greenland: (i) major deglaciation and disconnection of glaciers from the main glacial systems during the Lateglacial and Early Holocene with a rapid but not homogeneous deglaciation within the range from ~14.3 to 11.9 ka; (ii) no evidence of glacial activity during the Middle Holocene, probably associated with the withdrawn position of the ice masses’ fronts; and (iii) glacier expansion during the Late Holocene, with a Little Ice Age advance as the last significant period of glacial regrowth.

We investigate how luminescence signals imprinted on fluvial sediments vary depending on the depositional environment and vary through time in the same river. We collected sediment samples from four geomorphically distinct locations on the modern floodplain and modern point bar on the Buffalo River in northwest Arkansas, USA, in order to determine if different depositional environments are associated with distinct bleaching characteristics in the sediments. Our analysis revealed that all samples from different depositional environments yielded ages consistent with modern deposition. The samples collected from the floodplain and bar head contained a higher proportion of grains with residual doses, indicative of incomplete bleaching during transport, while samples from the mid-bar and bar tail appeared well bleached. Our results are particularly intriguing for two significant reasons. First, they highlight distinct equivalent dose distributions in different depositional environments. Second, they shed light on an intriguing relationship: despite generally well-bleached modern floodplain samples, ancient sediments from corresponding terraces displayed equivalent dose (D_e) distributions that suggest partial bleaching in some cases. This research contributes to the growing body of work that seeks to establish a relationship between luminescence properties and sediment transport processes and offers valuable insight into how luminescence signals vary locally in modern fluvial deposits, which can help guide the interpretation of older fluvial deposits.

A high-resolution palynological record from northwest Belgium is presented. The record encompasses the second part of the Younger Dryas and the Early Holocene. The basal part of the pollen record reflects a relatively open landscape, characteristic for the Younger Dryas. The transition to the Holocene is marked by an expansion of birch woodland, followed by an expansion of pine in the Late Preboreal (~11.2–10.7 cal. ka BP). Subsequently, the record shows an expansion of mixed deciduous forest with hazel, elm and oak, characteristic for the Boreal (~10.7–8.6 cal. ka BP). Early Holocene forest expansion was interrupted by a number of short-lived fluctuations, presumably driven by climatic changes. The most distinct event is the Rammelbeek phase (~11.4–11.2 cal. ka BP), during which forest development was temporarily interrupted in favour of grasses, while wildfires increased. Following this climatic event, hunter-gatherers returned to the area after a period of almost 1.5 millennia of low population density. They most likely were attracted by the increased temperatures and abundance of edible plants present in the birch-pine forests and on the banks of the river Kale/Durme. A temporary expansion of pine during the Boreal (~10.7–8.6 cal. ka BP) may correspond with the 9.3-ka event. At this time, superimposed on a trend of gradual infilling of the channel, a temporary change to drier conditions is observed. The significant drop in the number of prehistoric sites in the Moervaart region clearly cannot be attributed to this short-term climatic event alone but was most likely caused by a combination of environmental changes, such as the decreasing availability of hazelnuts as well as freshwater and edible (semi-)aquatic plants as the Kale/Durme river gradually turned dry. The study provides insight into, partly climate-driven, Early Holocene environmental changes and the effect this may have had on human occupation.

The low field magnetic susceptibility (χ_LF) measured in the 1116-m-long Dévaványa core (Pannonian Basin) is a quasi-continuous record of the Plio–Pleistocene Mid-European mountain permafrost development. The continuity of fluvial conditions is confirmed by seismic data, and the detrital origin of magnetite is indicated by frequency-dependent susceptibility measurements, scanning electron microscope, and hysteresis investigations. The χ_LF record is correlated to the δ¹⁸O curve (LR04) supported by palaeomagnetic data. The colour of samples documents precession and obliquity cycles in local facies variations, but the χ_LF indicates the dominance of 100-ka eccentricity cycles in the linked mountainous permafrost events. Comparison with orbital solutions revealed that the long-term development of permafrost occurs as a result of amplitude modulation of the 100-ka eccentricity cycles. Increases in amplitude of the 100-ka cycles inhibits permafrost development due to shortened winters. Thus, if extremes are present, the permafrost regions are limited or disappear, but if the 100-ka eccentricity cycles are attenuated, permanent frost can extend into the temperate zone. This amplitude modulation may also be responsible for the early glaciations during the Pliocene, for the intensification of Northern Hemisphere glaciation, foreshadows cooling in the forthcoming 405-ka term, and allows the change from 41-ka cycles to 100-ka ones in the Mid-Pleistocene Transition to be explained. The 41-ka cycles are the result of obliquity-controlled changes close to the polar cycles, while 100-ka cycles occur when the amplitude attenuation of the 100-ka eccentricity cycles enables extended glaciations that suppress the regular 41-ka cycles. Higher mountains in the catchments enable higher resolution of permafrost records documenting even smaller glaciations. However, the similarities in the overall trends in χ_LF records of catchment areas with 1500-m difference in their altitude is a potential counter-argument when considering the role of tectonic elevations in the expansions of mountainous permafrost.

Southeastern France occupies a key biogeographical position on the lower Rhone corridor, at the interface between southern and northern Europe. It is also at the heart of long-standing ecological debates about the respective roles of natural and human drivers in shaping the Mediterranean landscape. Molluscan analysis may represent a valuable contribution to this issue. In this paper, land snail assemblages from three calcareous tufa deposits in the Luberon mountain were used to reconstruct Lateglacial and Holocene palaeoenvironments. The Lateglacial communities only differ from the Pleniglacial ones by the development of hygrophilic snails. We note a high moisture budget at the end of the Lateglacial Interstadial (LGI). A patchy, steppe landscape is attested. A time lag in recolonization by woodland species during the LGI is conceivable. The postglacial woodland assemblages then trace a laborious reassembly of forest snail communities. It takes place mainly between c. 8000 and c. 6600 cal. a BP with spatial disparities and delayed recruitments. The French Mediterranean region has not benefitted from the macrorefugia that it would have sheltered or with which it would have been close. Woodlands, however, appear progressively more closed and complex c. 8000 cal. a BP. They reached their optimum c. 7500 to 7400 cal. a BP although their canopy seems to have stayed quite open. Anthropization remained weak during the Early Neolithic. A significant woodland opening is observed in the Early–Middle Neolithic. Human impact becomes clear from the Late Neolithic. Nevertheless, there are substantial differences compared with Basse-Provence, where a more marked openness of the landscape from 7000 cal. a BP was accompanied by the development of Mediterranean synanthropic snails. The molluscan successions of the Luberon mountain should be a reference for the development of the Lateglacial and Holocene malacofauna in the SE of France, at the northern boundary of the western Mediterranean domain.

We, the editors, are grateful to all reviewers for their help in processing volume 53 of Boreas.

Jan A. Piotrowski

Nicolaj Krog Larsen

The Vimmerby Moraine is the only significant ice-marginal moraine on the eastern side of southern Sweden, but no detailed studies exist on its formation during the final deglaciation of the Fennoscandian Ice Sheet. Through ground-penetrating radar surveys and detailed sediment logging, we provide evidence for an active, oscillating ice margin during the formation of the Vimmerby Moraine, suggesting that the deglaciation of the South Swedish Uplands was, at least in some regions, dynamic. Ground-penetrating radar surveys enabled imaging of internal sediment and delineation of the bedrock surface. These were complemented by common mid-point surveys and sediment logging, as well as lithofacies analysis at three exposures in agravel pit. This approach revealed multiple subglacial till units partially separated by intercalated glacifluvial deposits. The glacifluvial sediments exhibit evidence of glaciotectonism, suggesting active overriding by the last ice sheet. Further evidence of an active ice margin is provided by the ground-penetrating radar profiles collected perpendicular to the moraine crest. These contain a series of northerly dipping reflectors, which we interpret as evidence of repeated basal freeze-on and melt-out of sediment slabs during ice margin oscillations, as has been observed at contemporary glacier margins in Iceland, Norway, and the Alps. The data presented here demonstrate that the last Fennoscandian Ice Sheet remained active around the time of the Vimmerby Moraine formation. This work highlights the benefits of including detailed sediment logging and near-surface geophysical surveys in the interpretation of deglaciation dynamics.

The detailed chronostratigraphy of the Saalian Stage sensu lato (Marine Isotope Stage: MIS 11b-6) in Europe is far from being clarified and with the exception of the Late Saalian glaciation (MIS 6), there are in fact two separate schemes. One is for the northern, glaciated part of the continent, which is full of stratigraphical hiatuses that make interregional correlation difficult. The other one is for the extraglacial area, based on sites with fluvial, lake, and loess sequences, and this scheme is much more complete. Combining these two schemes remains a challenging field in the European stratigraphy. Among the main problems, there is a lack of reliable dating methods that can be applied to this part of the Middle Pleistocene. Correlation of terrestrial sequences with high-resolution deep-sea oxygen isotope curves seems to be a good way forward for future progress. Such correlation is crucial for identifying and understanding the interactions between orbital parameters, global ice volume, and greenhouse gas concentrations, which are responsible for the various expansions and contractions of the ice sheets throughout the Saalian Stage.

The following collection of contributions presents both unique and synthesized regional evidence that provides considerable clarification regarding this part of the European Quaternary stratigraphical sequence. It is a reliable step forward to overcome an over-simplistic view, because progress over recent years in many different fields has led to significant advances in our understanding regarding the interactions between environmental processes and climate.

We have here articles related to the late Middle Pleistocene stratigraphy including several topics, among them MIS 10-7 palaeoclimate, Early Saalian (= MIS 9) and Late Saalian (= MIS 7) interglacials, glacial evidence, loess and fluvial stratigraphy, as well as correlation of terrestrial and marine stratigraphy. The contributions are multidisciplinary and provocative, being focused on the main challenges to stimulate further scientific discussion.

The contribution of Candy et al. (2024) is a review of the Holsteinian Stage and its equivalents (= MIS 11c; c. 426 000 to 396 000 years ago) to climate reconstructions across Europe, based on varved lake records from the northern part of the continent, long pollen records of southern Europe and the comparison of both with marine, including pollen, records from the North Atlantic. This review is especially focused on evidence of abrupt climate changes and the result is a discussion of the evidence for millennial and centennial scale climate change noted in the European records, the patterns of warming across this interglacial and the discrepancy in duration between the marine and terrestrial records.

The contribution by Antoine & Limondin-Lozouet (2024) is a review of loess–palaeosol sequences and fluvial terrace records from the late Middl

As in most chalk river valleys in NW Europe, the sedimentary fill of the Somme valley is mainly composed of fluviogenic alkaline peat. The site of Morcourt exhibits a thick and well-preserved fluvial sequence (10 m, including 6 m of peat). This sequence provides the framework for reconstructing fluvial and palaeoenvironmental dynamics from the end of the Upper Weichselian Pleniglacial (~20 000 cal. a BP) to the High Middle Ages (~700 cal. a BP). The palaeoenvironmental reconstruction is based on a high-resolution stratigraphic study of 60 transect cores, 36 radiocarbon dates and sedimentological, geochemical, pollen and plant macrofossil analyses. There are three main phases in the development of the valley floor: (i) after the incision of the abandoned Pleniglacial braided river channels, a first generation of localized peat developed during the Bølling and the Allerød interstadial (<1 m thick); (ii) at the beginning of the Holocene, a peat formation phase began in the deepest parts of the valley and then spread over the valley floor by the end of the Middle Holocene (~4700 cal. a BP), with the limited runoff shifting to a small lateral channel; and (iii) at the transition to the Late Holocene, environmental changes, driven by the intensification of human activities and perhaps accentuated by climatic modifications, caused the incision of the peat system as a result of the formation of a channel. This channel drained the valley, and then mixed a detrital load into the peat. By the Low Middle Ages, the system had been altered to such an extent that the peat was completely covered by organic silty alluvium. The water table was lower, which definitively inhibited peat formation. The Morcourt sedimentary record (thickness and continuity) and the resumption of turfigenesis during the Late Holocene are remarkable in NW Europe, making this site a model of continuous morpho-fluvial evolution since the Lateglacial.