bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Late Weichselian stable isotope stratigraphy compared with biostratigraphical data: A case study from southern Sweden
Authors: Hammarlund Dan , Lemdahl Geoffrey 
Published: February 2007

AbstractLate Weichselian lake sediments from a site in southern Sweden, were analysed for stable carbon and oxygen isotopes, as well as plant macrofossils and insect remains. By comparison of independent data sets, general climatic changes were demonstrated. Lithological, chemical and stable isotope data reveal two significant climatic oscillations at ca. 12 200–12 000 and ca. 11 000–10 200 yr BP respectively. Continental climatic conditions, indicated by evaporative enrichment of 18O in lake marl, characterise parts of the early lake history, including the Older Dryas Stadial. Distinct variations of δ13C in organic material is discussed in terms of climatically induced changes in lake‐water chemistry. Different types of photosynthetic assimilation of dissolved inorganic carbon is proposed as a contributing factor influencing lake marl δ13C. The universal application of a positive correlation between lake marl δ18O and mean annual air temperature is questioned.Quantifications of mean summer and winter temperatures based on beetle analysis show a climatic optimum around 12 000 yr BP, a marked cooling around 11 000 yr BP and a strong amelioration at ca. 10 200 yr BP. These climatic events were accompanied by distinct changes in aquatic vegetation. Plant macrofossil and insect analyses indicate an open vegetation during the entire period studied.Biostratigraphical data reflecting local limnic and terrestrial vegetation and regional climate facilitate the interpretation of stable isotope data.
Climatic deterioration and the end of the Gortian Interglacial in sediments from Derrynadivva and Burren Townland, near Castlebar, County Mayo, Ireland
Authors: Coxon Peter , Hannon Gina , Foss Peter 
Published: February 2007

AbstractPollen and macrofossil analyses of two sequences of organic sediment in western Ireland have allowed the recognition of the latter parts of the Gortian Interglacial, a Middle Pleistocene temperate stage. The palaeobotanical information from the two sites identifies the preservation of partial sequences from the Gortian Interglacial (believed to be the equivalent of the Hoxnian Stage of Britain and the Holsteinian of Europe). The pollen and macrofossil data from one of the sites, Derrynadivva, span the middle and latter parts of the temperate stage. The results show that fire influenced the vegetation throughout the middle part of the temperate stage, and the termination of the organic depositional sequence appears to have been due to environmental deterioration. The former is identified through the abundant occurrence of charcoal in the sediments, whereas the latter is apparent in the sediment sequence and in the reworking of thermophilous pollen types into the upper part of the deposit. The second site, Burren Townland, records only part of the later zones of the interglacial, but the ericaceous assemblages of the latter part of the Gortian Interglacial are well developed and well preserved. Macrofossil analyses and scanning electron microscopy work on the pollen at the latter site has allowed the recognition of Rhododendron ponticum, adding to previous records of this species, which now has a very disjunct European distribution.
The Würmian Late‐glacial in Iowland Switzerland
Authors: Ammann B. , Lotter A. F. , Eicher U. , Gaillard M.‐J. , Wohlfarth B. , Haeberli W. , Lister G. , Maisch M. , Niessen F. , Schlüchter Ch. 
Published: February 2007

AbstractA synthesis is provided of Late‐glacial (14‐9 ka BP) environmental changes in lowland Switzerland (the ‘Swiss Plateau’). The chronology of deglaciation and subsequent developments in vegetation cover in the area are summarised. The sequence of climatic variations experienced in the region during the Late‐glacial is then described and a curve representing the main palaeotemperature variations is presented.
Wisconsinan Late‐glacial environmental change in southern New England: A regional synthesis
Authors: Peteet D. M. , Daniels R. , Heusser L. E. , Vogel J. S. , Southon J. R. , Nelson D. E. 
Published: February 2007

AbstractA synthesis of vegetational and climatic history during the Wisconsinan Late‐glacial (13‐9 ka BP) is presented for the southern New England region. The interpretations are based on a number of pollen‐stratigraphical investigations supported by plant macrofossil data. Chronology is based partly on AMS dates of plant macrofossils. Reference is made briefly to the controversial nature of the evidence for deglaciation in the region. A curve representing mean July temperature changes in the region during the period 13‐9 ka BP is provided.
Patterned fen development in northern Scotland: developing a hypothesis from palaeoecological data
Authors: Charman Daniel J. 
Published: February 2007

AbstractThe recent discovery and description of patterned fens in Scotland has raised questions about their origins and development. A series of possible developmental models has been derived which are tested using data from a well‐developed site in Sutherland, northern Scotland. The site morphology indicates that the fen has developed over a more complex subpeat topography and that the present‐day features are unrelated to the original mineral surface. Stratigraphical information together with radiocarbon dates and pollen age estimates suggest that the mire developed initially in one, perhaps two, narrow gullies as poor fen peats from the early tenth millenium BP. The mire then spread on to surrounding slopes with the onset of ombrotrophic peat accumulation, where the most recent basal age estimate is ca. 3500 yr BP. Poor fen peats extending to the surface began growth at ca. 2850 yr BP, once this ombrotrophic peat cover was complete. A reconstruction of mire conditions based on macrofossil, pollen and other microfossils shows the nature and timing of these changes in more detail. The findings show that the existing models of patterned fen development are not applicable to the Scottish systems. Instead, the poor fen systems are recent developments, which may overlie extensive earlier peat deposits of ombrotrophic character, and are unrelated to earlier peat development. The site has probably developed as a result of localised hydrological changes within the underlying peat body and mineral base, resulting in increased volume and quality of the water supply. It is suggested that this may be by the development and emergence of sub‐peat pipes at the head of a suitable slope.
Modelling ice‐sheet sensitivity to late weichselian environments in the svalbard‐barents sea region
Authors: Siegert Martin J. , Dowdeswell Julian A. 
Published: February 2007

AbstractIce‐proximal sedimentological features from the northwestern Barents Sea suggest that this region was covered by a grounded ice sheet during the Late Weichselian. However, there is debate as to whether these sediments were deposited by the ice sheet at its maximum or a retreating ice sheet that had covered the whole Barents Sea. To examine the likelihood of total glaciation of the Late Weichselian Barents Sea, a numerical ice‐sheet model was run using a range of environmental conditions. Total glaciation of the Barents Sea, originating solely from Svalbard and the northwestern Barents Sea, was not predicted even under extreme environmental conditions. Therefore, if the Barents Sea was completely covered by a grounded Late Weichselian ice sheet, then a mechanism (not accounted for within the glaciological model) by which grounded ice could have formed rapidly within the central Barents Sea, may have been active during the last glaciation. Such mechanisms include (i) grounded ice migration from nearby ice sheets in Scandinavia and the central Barents Sea, (ii) the processes of sea‐ice‐induced ice‐shelf thickening and (iii) isostatic uplift of the central Barents Sea floor.
Pliocene—pleistocene boundary in the Kleszczów Graben at Belchatów, central Poland
Authors: Krzyszkowski D. , Szuchnik A. 
Published: February 2007

AbstractThe Pliocene‐Pleistocene boundary, defined using pollen analysis, has been recorded in sections at the Belchatów outcrop, Kleszczów Graben, central Poland. The boundary is located at the top of the green clay subunit of the Tertiary Clayey‐sandy unit. A pollen flora of Reuverian C type, dominated by pine, 10–20% of ‘Reuverian elements’ and scarce thermophilous Tertiary trees, was found directly below this subunit. Cold stage floras of Praetiglian type were, in turn, recorded in the Łekińsko Formation, lying directly on the green clays. The Pliocene—Pleistocene transition at Belchatów demonstrates the characteristic features of this boundary in western Europe, that is, the disappearance of Tertiary thermophilous tree pollen taxa, followed by a cooling to open‐forest or forest‐steppe conditions. Both pollen analysis and geological data suggest continuous sedimentation at least from the Upper Pliocene to the Prae‐Tiglian, with no change of sediment sources and no marked hiatuses. The fluvial deposits of the Praetiglian Łekińsko Formation, although Pleistocene in age, mark a final period in the Tertiary evolution of the Kleszczów Graben. Later, there is a hiatus to the deposition of the first glacigenic sediments in the region possibly of Elsterian age.
Quaternary stratigraphy of the buried valleys of the lower Red Deer River, Alberta, Canada
Authors: Evans David J. A. , Campbell Ian A. 
Published: February 2007

AbstractThe Quaternary fills of the buried valleys of southern Alberta and Saskatchewan have provided a wealth of information for the reconstruction of the glacial‐interglacial record of the western plains of Canada, and this paper reports on the previously unstudied stratigraphy of the buried Calgary Valley and its former tributaries in the lower Red Deer River area. We attempt to differentiate Empress Group sediments, which potentially relate to pre‐glacial, interglacial/ interstadial and post‐glacial lake and river deposition, using sedimentology, stratigraphy and palaeoecology. Twenty‐nine stratigraphical logs indicate that Empress Group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the Calgary Valley, located 15 km to the north of Dinosaur Provincial Park. Radiocarbon dates of 52.4 ka, 27.4 ka and > 42.4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid‐Wisconsinan in age. However, outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials/interstadials and that older (even pre‐glacial) sediments could have survived. Subglacial channels, recognisable on air photographs, largely coincide with buried valley positions due to the preferential excavation of the Quaternary sediment by meltwater and are filled with post‐glacial lake sediment from which a radiocarbon date of 16 ka BP was obtained. Pre‐glacial and glacial/post‐glacial Empress Group sediments are lithologically indistinct but cover a large time span in southern Alberta.
Direct comparison of UK temperatures and Greenland snow accumulation rates, 15000—12000 yr ago
Authors: Lowe J. J. , Coope G. R. , Sheldrick C. , Harkness D. D. , Walker M. J. C. 
Published: February 2007

AbstractA palaeotemperature record based on fossil coleopteran evidence and dated by accelerator mass spectroscopy (AMS) 14C determinations on plant macrofossils has been obtained for the last glacial‐interglacial transition from the site of Gransmoor in eastern England. Calibration of the radiocarbon measurements enabled a direct comparison to be made between this palaeotemperature curve and the snow accumulation record from the GISP‐2 Greenland ice‐core. The similarity between the two data sets suggests a degree of correspondence in the pattern and timing of climatic change in Greenland and the British Isles at the end of the last cold stage.
The vertical dimensions of Late Devensian glaciation on the mountains of Harris and southeast Lewis, Outer Hebrides, Scotland
Authors: Ballantyne Colin K. , McCarroll Danny 
Published: February 2007

AbstractOn North Harris and southeast Lewis a weathering limit separates glacially‐moulded bedrock on low ground from frost‐shattered bedrock and blockfields on high plateaux. Analysis of the depths of horizontal stress‐release joints demonstrates significant contrasts in bedrock weathering above and below this boundary, and the survival of gibbsite only in soils above the weathering limit indicates that it represents the upper limit of Late Devensian glacial erosion. The weathering limit declines regularly in altitude on either side of the former ice shed, and is therefore interpreted as a periglacial trimline defining the upper limit of a locally‐nourished ice mass at its maximum extent, rather than a former thermal boundary between protective cold‐based and erosive warm‐based ice. Calculated basal shear stress values are consistent with this interpretation. The configuration of the trimline indicates that at the last glacial maximum the area supported an ice cap that achieved a maximum altitude of ca. 700 m above present sea level and declined in altitude to the west‐northwest and east‐southeast at an average gradient of ca. 20 m km−1. Extrapolation of the dimensions of this ice cap suggests that it terminated ca. 7–10 km west of the present coast of Harris, and was confluent with mainland ice a short distance east of the present coastline.
The back‐barrier and barrier depositional history of Romney Marsh, Walland Marsh and Dungeness, Kent, England
Authors: Long Antony J. , Innes James B. 
Published: February 2007

AbstractPrevious stratigraphical investigations of Romney Marsh have tended to be local in scale, and this has hindered efforts to establish a unifying stratigraphical framework for this area. This paper addresses this problem, by describing the results of a 12‐km transect across Romney Marsh, linking previously studied back‐ and fore‐marsh sites (Horsemarsh Sewer and Broomhill respectively), and presenting additional pollen, diatom and radiocarbon data from an intermediate, mid‐marsh site (Brookland). One main organic unit is recorded across much of Romney Marsh, although its age, altitude and composition varies. Microfossil and radiocarbon data from Brookland and elsewhere on Romney Marsh show that this organic unit accumulated under a general removal and return of marine conditions that took place between ca. 5100 and 2000 yr BP.A recently proposed model of barrier development is used to investigate the history of back‐barrier sedimentation in Romney and Walland Marshes. This model suggests a three‐phase life‐history for gravel barriers, which consists of initiation, stability and breakdown. Although there are problems in relating back‐barrier deposits directly to barrier dynamics, nevertheless the Romney Marsh data do, for the most part, agree with the expected number and sequence of sea‐level tendencies predicted by this model. The back‐barrier stratigraphical data suggest that initiation, stability and breakdown of the Dungeness foreland occurred between ca. 6000 and 5000 yr BP, 5000 and 2000 yr BP and 2000 yr BP and present, respectively.
Late Pleistocene deposits at Block Fen, Cambridgeshire, England
Authors: West R. G. , Peglar S. M. , Pettit M. E. , Preece R. C. 
Published: February 2007

AbstractOrganic sediments in a gravel quarry at Block Fen, Cambridgeshire, form a sheet dividing lower from upper gravels. Analyses of pollen, macroscopic plant remains and molluscs from these organic sediments are presented. They indicate the presence of temperate freshwater and slightly brackish fine floodplain sediments, which, on the basis of the palaeobotany, are correlated with the temperate Ipswichian Stage. The freshwater sediments, ascribed to Ipswichian substage IIb, occur at ca. −3 m OD. Marine‐influenced tidal sediments, ascribed to Ipswichian substage III, occur at ca. −6 m OD. No evidence was found for the presence of more than one temperate stage in the sequence. The lower gravels are then correlated with the cold Wolstonian Stage and the upper gravels with the cold Devensian Stage. In contrast to the woodland environments indicated by the palaeobotany of the Ipswichian organic sediments, post‐Ipswichian pollen diagrams and macroscopic plant remains in the upper suite of sands and gravels indicate open tree‐less vegetation typical of the cold Devensian Stage. They also contain a typical cold‐stage mollusc fauna. The sediments containing these floras and faunas are associated with thermal contraction cracks, indicating the presence of permafrost. The final sand and gravel aggradation in the Devensian forms the Block Fen Terrace, near 0 m OD. The evidence indicates that it is younger than the lacustrine sediments resulting from the blocking of the Fenland at the Wash by Late Devensian ice at ca. 18.5 ka BP.The sequence at Block Fen is related to nearby Ipswichian and Devensian sediments at Chatteris, March, Wimblington and Mepal, and to deposits at Wretton on the east margin of Fenland. The correlation permits an outline reconstruction of the history of the valley carrying the River Great Ouse between the Isle of Ely and the Chatteris and March ‘islands’ from the time of a gravel aggradation before the Ipswichian to the Flandrian. The reconstruction shows the time and level of the Ipswichian marine incursion into the Middle Level of Fenland and the extent of aggradation and erosion in the Devensian.
Englacial and proglacial glaciotectonic processes at the snout of a thermally complex glacier in Svalbard
Authors: Hambrey Michael J. , Huddart David 
Published: February 2007

AbstractMany glaciers in Svalbard, which tend to be thermally complex with both warm and cold ice, produced complex ‘push moraines’ or ‘thrust‐moraine complexes’ at the time of their maximum neoglacial advance, and during their subsequent recession. Uvěrsbreen, which nearly reaches the coast of northwest Spitsbergen, has a push moraine 50 m high, comprising gravel and sand of fluvial origin, and diamicton derived from basal ice, as well as thrust masses of dead ice. The push moraine is almost entirely a product of the tectonic processes, especially thrusting, that occurred in the snout of the glacier and in the frozen sediments immediately in Journal of Quaternary Science front. Thrusting is probably initiated where the glacier switches from a sliding mode to a state of being frozen to the bed. Thrusting in the foreland is an extension of the same processes that occur within the ice itself, and a sole thrust probably extends from the frozen sediment that underlies the base of the glacier near its snout. Thrusting results in subglacial sediment being uplifted to a high level within the glacier or even to the surface. Subsidiary near‐horizontal thrusts parallel to the bedding plane link thrusts dipping up‐glacier, and result in local thickening of individual subglacial sedimentary units. Gravels incorporated in this way retain their integrity but sands are folded, whereas uplifted debris‐rich basal ice is intensely folded. The distinctive tectonic style of low‐dip bedding in gravels, truncated by high‐angle (30–40°) thrusts, and only localised folding in less competent material, differs from most descriptions of such ridges, but may be typical of many push moraines composed principally of fluvial material.
On the sensitivity of Holocene talus‐derived rock glaciers to climate change in the Ben Ohau Range, New Zealand
Authors: Kirkbride Martin , Brazier Vanessa 
Published: February 2007

AbstractThe morphology and surface ages of talus‐derived rock glaciers are investigated to establish the timing of rock glacier formation in the central Southern Alps. Samples of rock weathering rinds show that all rock glaciers studied were formed during the Neoglacial period, but differences exist between sites in the number of new rock glacier lobes formed by Holocene climatic fluctuations. A qualitative conceptual model is proposed to explain rock glacier formation in terms of two thresholds. An external threshold relates to the presence of a cool climate capable of allowing internal ice to form within talus slopes. An internal threshold relates to the presence of sufficiently thick talus at a site to generate a shear stress capable of overcoming internal friction within the talus/ice mass. The model produces a non‐steady‐state response to explain why unmodified talus, single‐lobed and double‐lobed rock glaciers developed at adjacent sites under the same climatic regime. Individual landforms have different sensitivities to formation, which depend partly on the previous history of talus accumulation and rock glacier activity at a site. The model demonstrates how successive cool climate periods may be fully represented by rock glacier lobes at sensitive sites but under‐represented at insensitive sites. Sensitivity (and therefore climatic representativeness) is favoured by high rates of debris supply. By implication, the timing of formation of rock glacier lobes in regions of prolonged cool climate and low debris production is less likely to correspond to the timing of climatic cooling and more likely to follow the ‘rules’ of deterministic chaos.
Mineral magnetic analysis of a ‘weathering’ surface within glacigenic sediments at Glanllynnau, North Wales
Authors: Walden John , Addison Kenneth 
Published: February 2007

AbstractA number of ‘weathering’ horizons have been identified within glacigenic sediment sequences in North Wales and have been instrumental in determining various proposed Late Quaternary event chronologies. This paper applies the techniques of mineral magnetic analysis to such a sediment sequence at Glanllynnau. The presence (or otherwise) of evidence for weathering processes on the upper surface of the Criccieth Till, which is overlain by further glacial materials, is examined. Despite a marked colour variation between the ‘weathered’ and non‐weathered components of the Criccieth Till, their mineral magnetic properties suggest little or no variation in iron oxide assemblages. The consequences of this for the environmental interpretation of the sediment sequence are discussed.
Regional differences in the Lateglacial climate of northern Europe based on coleopteran analysis
Authors: Coope G. R. , Lemdahl G. 
Published: February 2007

AbstractThe termination of the Last Glaciation, the Lateglacial period, was characterised by highly unstable climates which, in northern Europe, oscillated between warm temperate and arctic conditions. Different indicators of past climate have provided contrasting views on the timing and intensity of these climatic changes. Here we present preliminary reconstructions of the thermal climate interpreted from subfossil coleopteran assemblages from Britain, Norway, Sweden and Poland, in which regional differences can be ascribed to the varying influence of, (a) the North Atlantic surface water temperatures, (b) the proximity of the Fennoscandian ice sheet and (c) the ice free continent. Quantification of the thermal climate enables these local differences to be resolved.