Weichselian palaeoenvironments at Kobbelgård, Møn, Denmark

Lithostratigraphical and palynological investigations of a coastal cliff section at Kobbelgård, Møn (Denmark) reveal a sedimentary sequence of Weichselian age. Bedded clayey sediments are overlain by stratified silt, sand and occasional beds of clay and gravel. The clay was deposited in water, and most of the silt and sand is aeolian, forming fairly thick units of loess and sand-loess. The lower part of the sequence forms an anticlinal structure, probably of glacio-tectonic orìgìn. The upper part of the sequence appears to represent a depression filling. In the lower part of this, clayey layers alternating with loess deposits suggest wet conditions periodically. In the upper part, loess and fine sand were deposited, interfingering with slope sediments in a periglacial environment from around 24,000 BP almost until the Weichselian glacial maximum. Pollen investigations at the site point to three periods of vegetation. The lowest pollen sequence contains much Ericales, Empetrum and occasionally also Pinus , and is thought to be of Early Glacial or Lower Pleniglacial age. Overlying pollen-bearing strata with high proportions of herbs, including Artemisia , antedate a TL dating of c. 27,000 BP. An upper pollen sequence, derived from slightly organic layers in the depression fill, points to a palaeovegetation almost exclusively of herbs, with Artemisia as an important component. This vegetation is thought to represent a relatively moist site, and is TL dated to c. 24,000 P.     

Aspects of the Weichselian chronology in central East Greenland

From central East Greenland, C₁₄ ages between 19,500 > 40,000 years B.P. have been obtained for six samples of marine bivalve shells. The ages seem to be consistent with geological observations and form the basis for a tentative chronology for the Weichselian ice age in the region. It appears that the maximum glaciation during Weichselian times was attained more than 40,000 years ago, and that since then ice-free areas have existed. This assumption agrees with evidence of botanical refugia in the region, and the restricted glacier activity especially during the Upper Pleniglacial (ca. 30,000–15,000 years B.P.) is explained by a reduced supply of moisture. A comparison with evidence from other parts of Greenland indicates that different glacial histories can be expected for different sectors of the Greenland Inland Ice.     

Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea

Graham, A.G.C., Lonergan, L. & Stoker, M.S. 2010: Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea. Boreas, Vol. 39, pp. 471–491. 10.1111/j.1502‐3885.2010.00144.x. ISSN 0300‐9483. Geological constraints on ice‐sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here, we present a detailed interpretation of depositional environments from a new 30‐m‐long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British–Fennoscandian Ice Sheet. Seven units characterize a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeoregimes. These are: a period of advance and ice‐sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine‐to‐marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overriding by the SE–NW‐flowing Witch Ground ice stream. AMS ¹⁴C dating confirms ice‐stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 ¹⁴C ka BP. Sediments overlying the ice‐compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 ¹⁴C ka BP. A re‐advance of British ice during the last deglaciation, dated at 13.9 ¹⁴C ka BP, delivered ice‐proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally pervasive iceberg‐ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 ¹⁴C ka BP, and may correspond to oscillating ice‐sheet margins during final, dynamic ice‐sheet decay.     

Palaeoecology of a Late Weichselian vertebrate fauna from Nmre Lyngby, Denmark

Investigations at a Late Weichselian freshwater basin in northwestern Jutland, Denmark, yielded a fairly rich assemblage of vertebrate remains, mostly bones and teeth of small mammals. The remains are primarily allochthonous and the bones have been subjected to different taphonomic pathways and agents. AMS ¹⁴C-dates on terrestrial organic remains provided ages of Middle to Late Allerød time. Identifications revealed the first fossil record in Scandinavia of Rana arvalis, Sorex minutus, Ochotona cf. pusilla, Microtus gregalis, Microtus oeconomus , and Sicista cf. betulinu. Spermophilus cf. major and Desmana moschata , previously found only once and twice respectively, were retrieved, and Sorex araneus and Arvicola terrestris were recovered for the first time beyond the Atlantic chronozone. Ecologically, the Nørre Lyngby small mammal fauna can be characterized by its very high and almost equal proportions of boreal forest and steppe elements followed by a relatively high proportion of tundra elements. The fossil species share a modern area of sympatry north of the Caspian Sea from the river Volga in the west to the southern and western slopes of the Urals. If, however, the large Allerød mammals are added, the fauna is without modern analogues. The Nørre Lyngby fauna can be seen as a last expansion of the North European glacial fauna. Provided that an absolute chronology and a differentiated sea-level curve for the area can be established, the Nsrre Lyngby fauna could become important for studies in mammalian dispersal and migration rates.     

Neotectonic deformation of a Late Weichselian outwash plain by deglaciation‐induced fault reactivation of a deep‐seated graben structure

The Late Weichselian Tinglev outwash plain in southwestern Denmark slopes gently from east to west, but certain areas of the topography show unusual irregularities. Analysis of LiDAR data reveals a mosaic of smaller areas with pronounced changes in slope magnitude and orientation between neighbouring areas. The outwash plain also features notable changes in elevation across kilometre‐long lineaments and areas lying lower and higher than the expected level. The depressions in the area have previously been interpreted as the result of melting dead‐ice blocks left by the Late Weichselian ice sheet. However, borehole samples from Lake Tinglev on the outwash plain show that lake sedimentation did not start until the early Holocene (9000 years ago), which is more than 9000 years after the ice sheet had retreated. The topographical irregularities are located above the Tønder Graben structure, and we interpret these as the result of Holocene strike‐slip movements along the graben faults resulting in areas of both subsidence and uplift. The deformations of the outwash plain are interpreted as the effect of deglaciation tectonics acting within a limited time frame at the beginning of the Holocene. As the event can be related to stress release from the weight of the Scandinavian Ice Sheet, we expect that other fault zones in northern Europe would be equally prone to reactivation. Tectonic events related to deglaciation would most likely be recurrent, and the stress changes appear to have been able to induce short‐lived tectonic instability to areas normally considered tectonically stable. We conclude that this type of tectonics has had a significant impact on topography and sedimentation throughout the Quaternary.     

Sedimentary features of a Weichselian glaciolacustrine delta

Inclined beds of sand, granules, pebbles and cobbles resembling a glacio-tectonically tilted sequence were shown by sedimentological studies to constitute the 10–12 m thick foreset beds of a glaciolacustrine Gilbert-type delta in Kyndby, North Sjælland, Denmark. The foreset beds are slightly curved, dip 10–28 SE, and display a bundlewise structure with alternating coarse-grained cobble-rich and fine-grained sandy units. The occurrence of ascending megaripple cross-bedding and climbing ripple cross-lamination in the sandy foresets can be ascribed to strong backflow currents formed by the lee-side vortice. The foreset beds are underlain by flat-lying fine-grained sand, silt and clay (bottomset beds), and are overlain transitionally or erosively by 2–3 m of flat-lying sand, pebbles and cobbles (topset beds). In the transition zone between foreset beds and topset beds, various delta distributary channel units occur. The delta probably formed in a partly ice-dammed lake in connection with the general retreat of a Weichselian advance from the north ('Norwegian ice')     

Sedimentology of Wartanian outwash near Bełchatów, central Poland

The braided outwash of Wartanian age near Bełchatów, central Poland, was formed synchronously by two river systems: glacier streams flowing from the northwest and west and periglacial rivers flowing from the south and southwest. An extensive alluvial fan was formed which later developed into a highly aggrading fan due to a rising water level in the proglacial lake to the north. Braided streams were represented by relatively low-energy systems with shallow-channel and/or transverse bar deposition. Sporadically, rapid inflows of meltwater caused more energetic conditions and formation of large scours. The latter were found only in the glacier streams and this was confirmed by palaeocurrent measurements and analyses of quartz roundness.     

A Late Saalian, Eemian and Weichselian marine sequence at Nørre Lyngby, Vendsyssel, Denmark

A 120 m thick marine Quaternary sequence resting on Upper Cretaceous chalk at Nørre Lyngby has been stratigraphically analysed on the basis of its foraminiferal content. The foraminiferal zones in the Nørre Lyngby boring are compared with corresponding zones from borings and outcrops in adjacent areas in Vendsyssel and Kattegat, and a general zonation covering the whole area is proposed. The lower part of the marine sequence at Nørre Lyngby represents deposits of pre-Eemian, possibly Saalian, and Eemian age. The Early Weichselian seems to be missing, while most of the Middle and Late Weichselian foraminiferal zones known from Vendsyssel occur. The foraminiferal zones and the corresponding macrofossil zones are correlated with the oxygen isotope stratigraphy. A cross-section through deposits from the Saalian-Eemian-Weichselian marine basin in North Jutland and the Kattegat illustrates the development of the basin through this period of time. The centre of basin subsidence shifted from the southwest in the pre-Eemian to the northeast in the Eemian, and remained there throughout the Weichselian.     

塔里木盆地西南部叶城凹陷下白垩统克孜勒苏群扇三角洲沉积特征及模式

以野外露头、岩心观察为基础,结合录井、测井及粒度分析,认为叶城凹陷下白垩统克孜勒苏群发育进积型扇三角洲,划分出扇三角洲平原与扇三角洲前缘水下分流河道、分流间湾与河口坝。扇三角洲平原受重力流作用明显;扇三角洲前缘主要受牵引流作用,在盆地的短轴方向延伸范围较小,而在长轴方向延伸范围较大,与相邻扇三角洲前缘朵叶叠置连片。扇三角洲由山前向断陷湖盆进积,在盆地的短轴方向构成一侧为陡坡、另一侧为宽缓斜坡的单断式断陷盆地充填模式。这种沉积模式不仅控制了扇三角洲各亚相单元的发育特征,而且对微相类型与砂体分布有控制作用。     

Supposed area-wasting of the Weichselian ice sheet in Denmark

The deglaciation at the end of the Weichselian in the Danish area has previously been considered to occur as a frontal wastage. Since the glacier ice was assumed to be debris-free, the wasting should be characterized by outwash plains and successions of end-moraines. The almost complete lack of sandur plains in the eastern part of the area and indications from recent investigations of widespread occurrence of flow till justify a re-evaluation of the mentioned deglaciation model.
Two morphological features have a general occurrence: the plains and the 'tunnel' valleys. The plains appear stepwise in the landscapes, and are frequently limited by steep slopes. Topmost is a subcircular kame-like hill. Sedimentologically, the plains mainly consist of melt water deposits, and the scattered occurrences of till are interpreted as flow till. The plains continue from the open landscape into the 'tunnel' valleys where they appear as terraces.
These features are considered to have been formed during the deglaciation. The almost horizontal surface of the ice sheet over large areas caused a sensitivity to changes in the climate. The wasting of the ice may therefore be expected to affect large areas almost simultaneously. On the assumption that the ice contained debris, an increasing amount of clastic matter was released on the ice surface. This material was concentrated in the depressions. If such a depression perforated the ice, the content of sediments settled on the substratum and a plain was established. During continued wasting the thickness of the ice decreased and the depressions were enlarged. They assumed the character of sandur plains. As still larger areas of these supraglacial sandurs rested on the basement the successive lower situated plains were formed. The latest ice was preserved where the 'tunnel' valleys are situated to-day.     

Lithology and palynology of Weichselian alluvial fan deposits near Eerbeek, The Netherlands

In a sandpit in an alluvial fan in the central Netherlands, four interstadials could be recognized. The upper two are ¹⁴C-dated and assigned to Hengelo and Moershoofd, while the lower two belong to either Odderade or Brorup. Lithological evidence suggested the existence of two zones indicative of permafrost separated by a zone in which running water was more important. The lower permafrost zone was found to be situated between the Moershoofd and Odderade interstadials, the younger zone to belong to the Upper Pleniglacial.     

Lithostratigraphy of the Late Saalian to Middle Weichselian Skærumhede Group in Vendsyssel, northern Denmark

The Quaternary sedimentary succession in Vendsyssel, northern Denmark, contains a unique, high‐resolution record of the last interglacial and glacial periods. There is still much debate, however, about the timing and ice extent in this southwestern part of the Scandinavian Ice Sheet, particularly during the Middle Weichselian. In this study, a detailed lithostratigraphical subdivision is established for the Late Saalian to Middle Weichselian Skærumhede Group on the basis of numerous, up to 250 m deep, boreholes in Vendsyssel. The sediments mainly consist of marine clays, glaciolacustrine sediments and tills, and the total thickness of the Skærumhede Group is up to 140 m. Marine intervals have been used as stratigraphical marker units to separate the formations indicative of ice‐sheet activity in Vendsyssel, and the timing of the events has been constrained by a large number of optically stimulated luminescence (OSL) and radiocarbon ages. The Skærumhede Group is subdivided into seven formations and two members, reflecting shifts between marine and terrestrial sedimentation caused by fluctuations of the Scandinavian Ice Sheet and changes in sea level. The lowermost Skærumhede Till Formation was deposited directly on top of the bedrock during the Warthe advance c. 160–140 kyr BP. Above, there are fine‐grained marine sediments, subdivided into the Lower, Middle and Upper Skærumhede Clay Formations. The marine formations are separated by the Brønderslev Formation related to the Sundsøre ice advance from the north c. 65–60 kyr BP, and the Åsted Formation, deposited during the Ristinge advance from an east–southeastern direction c. 55–50 kyr BP. The uppermost formation in the group is the Lønstrup Klint Formation, which is an upwards‐coarsening sequence of mainly glaciolacustrine sediments deposited prior to the Kattegat advance c. 30–29 kyr BP. The new evidence from Vendsyssel has shown that the Skærumhede Group covers a large area, and that it can be used as a regional stratigraphical marker horizon. Furthermore, it contributes to a better understanding of the timing and extent of glacial events during the Late Saalian to Middle Weichselian in southwest Scandinavia.     

Lacustrine sedimentation and tectonics: an example from the Weichselian at Lønstrup Klint, Denmark

Sedimentological analysis of the Weichselian deposits exposed in the coastal cliff section at Lønstrup Klint, northern Jutland, Denmark, demonstrates the presence of four sedimentary units comprising fine-grained lacustrine and fluvial deposits of the latest Middle Wcichselian. The Lønstrup Klint section also shows an interplay between glaciotectonics and sedimentation. The two lower sedimentary units are separated by an erosional unconformity of pretectonic origin, whereas the upper two units are syntectonic. The glaciotectonic processes reflect the Late Weichselian expansion of the Scandinavian ice cap into northern Jutland. The sedimentary structures indicate high rates of deposition. The area underwent dramatic palaeogeographic changes from deep lake to proglacial fluvial plain in a time-span of a few thousand years.     

A Middle Weichselian interstadial lake deposit on Sejerø, Denmark: macrofossil studies and dating

Studies of lake sediments on Sejerø in southern Kattegat indicate a treeless arctic environment with the dwarf shrub Salix polaris, herbs and wetland mosses. The mean July temperature was around 8 to 10°C. An AMS radiocarbon age determination of a Salix twig yielded an age of around 36 000 ¹⁴C yr BP, which is in accordance with previous conventional dating of bulk sediment samples. Copyright © 2006 John Wiley & Sons, Ltd.     

Rapid tunnel-valley formation beneath the receding Late Weichselian ice sheet in Vendsyssel, Denmark

Interpretation of Transient ElectroMagnetic (TEM) data and wire-line logs has led to the delineation of an intricate pattern of buried tunnel valleys, along with new evidence of glaciotectonically dislocated layers in recessional moraines in the central part of Vendsyssel, Denmark. The TEM data have been compared with recent results of stratigraphical investigations based on lithological and biostratigraphical analyses of borehole samples and dating with Optically Stimulated Luminescence (OSL) and radiocarbon. This has provided an overview of the spatial distribution of the late Quaternary lithostratigraphical formations, and the age of the tunnel valleys has been estimated. The tunnel valleys are typically 5–10 km long, 1 km wide and are locally eroded to depths of more than 180 m b.s.l. The valleys are interpreted to have been formed by subglacial meltwater erosion beneath the outermost part of the ice sheet during temporary standstills and minor re-advances during the overall Late Weichselian recession of the Scandinavian Ice Sheet. The formation of the tunnel valleys occurred after the retreat of the Main ice advance c . 20 kyr BP and before the Lateglacial marine inundation c . 18 kyr BP. Based on the occurrence of the tunnel valleys and the topography, four ice-marginal positions related to the recession of the northeastern Main advance and seven ice-marginal positions related to the recession from the following eastern re-advance across Vendsyssel are delineated. All the tunnel valleys were formed within a time interval of a few thousand years, giving only a few hundred years or less for the formation of the tunnel valleys at each ice-marginal position.     

Signature of the Baltic Ice Stream on Funen Island, Denmark during the Weichselian glaciation

Ice streams are major dynamic elements of modern ice sheets, and are believed to have significantly influenced the behaviour of past ice sheets. Funen Island exhibits a number of geomorphological and geological features indicative of a Late Weichselian ice stream, a land-based, terminal branch of the major Baltic Ice Stream that drained the Scandinavian Ice Sheet along the Baltic Sea depression. The ice stream in the study area operated during the Young Baltic Advance. Its track on Funen is characterized by a prominent drumlin field with long, attenuated drumlins consisting of till. The field has an arcuate shape indicating ice-flow deflection around the island's interior. Beneath the drumlin-forming till is a major erosional surface with a boulder pavement, the stones of which have heavily faceted and striated upper surfaces. Ploughing marks are found around the boulders. Exact correspondence of striations, till fabric and drumlin orientation indicates a remarkably consistent flow direction during ice streaming. We infer that fast ice flow was facilitated by basal water pressure elevated to the vicinity of the flotation point. The ice movement was by basal sliding and bed deformation under water pressure at the flotation level or slightly below it, respectively. Subglacial channels and eskers post-dating the drumlins mark a drainage phase that terminated the ice-stream activity close to the deglaciation. Identification of other ice streams in the Peribaltic area is essential for better understanding the dynamics of the land-based part of the Scandinavian Ice Sheet during the last glaciation.     

Stratigraphy and age of a Neoglacial sedimentary succession of proglacial outwash and an alluvial fan in Langedalen,Veitastrond, western Norway

This study presents the sedimentary succession of an outwash plain and an alluvial fan located along the valley Langedalen at the south-eastern side of the Jostedalsbreen ice cap in inner Sogn, western Norway. A newly exposed ~2.8-m-high section along the southern riverbank of Langedøla river shows alternating layers of minerogenic sediments and peat layers with tree logs, identified as Salix sp. The section is situated in the distal part of an alluvial fan built out from the southern slope of Langedalen. Six AMS radiocarbon dates of tree fragments indicate that the accumulation of the fine-grained sediments in the lower part of the section was initiated earlier than the basal radiocarbon date of 914–976 calibrated years CE (1σ age range). These basal, fine-grained sediments are interpreted as proglacial outwash deposited in a floodplain depression or abandoned river channel in a low-energy glaciofluvial environment. Periods of low glacier cover, low river discharge or low-water stands over the floodplain allowed peat formation and the growth of trees and shrubs in the valley. The radiocarbon dates further indicate relatively rapid sediment accretion (~2.7–3 cm a⁻¹) between 190 and 125 cm below the sediment surface, equivalent to approximately 1220 to 1250 cal. a CE (1σ age range). At ~60 cm depth below the surface, dated to approximately 1590 to 1620 cal. a CE (1σ age range), a transition to more coarse-grained, sandy and gravelly sediments indicates increased sediment supply and distal expansion of the alluvial fan. This occurred most likely as a consequence of increased sediment yield from expanding glaciers along the southern valley side of Langedalen as a response to the initial Little Ice Age glacier growth. Based on these results, the accretion and progradation of glacier-fed alluvial fans mainly occur during periods of glacier advance rather than during glacier recession.     

Coleoptera from the Late Weichselian deposits at Nørre Lyngby, Denmark and their bearing on palaeoecology, biogeography and palaeoclimate

The freshwater sediments exposed on the cliffs at Nørre Lyngby northern Jutland has long been a classical locality for the study of Danish Quaternary geology, palaeontology and archaeology. These deposits date from the latter part of the Allerød period (i.e. G I-1). Samples for insect analysis have been taken from both the northern and southern exposures of these deposits. Ninety-five- taxa of Coleoptera (beetles) were obtained, of which 69 could be named to species. Of the latter, 23 are not found living in Denmark today. Most of these are still living in northern Fennoscandia but one species is now confined to Mongolia. These assemblages have enabled a detailed picture of the local environment to be reconstructed, showing that the basin-like profile of the deposits represents a section through a channel with slowly moving water. It has been possible to quantify the thermal climate of the time using the Mutual Climatic Range method indicating that mean July temperatures were about 10°C and mean January temperatures were about – 12°C. These figures are considered in the context of Lateglacial climatic reconstructions obtained from coleopteran assemblages elsewhere in northwestern Europe.     

Composite stable isotope records from a Late Weichselian lacustrine sequence at Grrenge, Lolland, Denmark: evidence of Allerød and Younger Dryas environments

Stable oxygen and carbon isotope data from a lacustrine sequence at Grænge, southeast Denmark, revealed distinct cnvironmental changes related to Late Weichselian climatic development in the region. Comparison of isotopic records obtained from sedimentary carbonates and freshwater molluscs enabled reconstruction of changes in the lacustrine environment. The degree of thermal and chemical stratification of the lake was evaluated and supported by pollen data from an earlier study of the site. During the Allerød interstadial, dimictic and stagnant conditions characterized the lake, whereas the stratification was disturbed during thc Younger Dryas stadial probably as a result of deforestation and increased wind impact. The origin of sedimentary carbonates was examined by mineralogic and morphologic studies. A considerable input of clastics and detrital carbonates, associated with pronounced enrichment of ¹⁸O and ¹³C. wds recorded in the Younger Dryas sediments indicating soil degradation and increased erosion. A climatic warming preceding the Pleis-tocene/Holocene boundary is clearly reflected in the different stable isotope records and in the lithostratigraphy.