bluuebunny/crossref_metadata_2025 huggingface dataset:
Late‐ and post‐glacial depositional environments in the Norwegian Trench, northern North Sea
Authors: ANDERSEN ESPEN S. , ØSTMO SVEIN ROAR , FORSBERG CARL FREDRIK , LEHMAN SCOTT J.
Published: July 2010

The late Weichselian sequence in the northern part of the Norwegian Trench is composed of eight units. The two lowermost units are massive, firm to stiff diamictons, interpreted to have been deposited beneath ice‐streams that in all likelihood reached the shelf edge. They are overlain by glaciomarine and normal‐marine sediments deposited after 15000BP. The first phase of glacial retreat from the Norwegian Trench (15000–14800 BP) was very rapid and left a thin layer of proximal sediments on top of the tills. This was followed by a period with lower accumulation rates (14800–13600 BP), probably as a result of rapid source retreat and cold meltwater inhibiting dropstone fall‐out. The end of this interval marks the change from ice‐stream calving in cold water to melting on land. According to lithologic and isotopic data, the maximum rate of Fennoscan‐dian ice‐sheet disintegration took place around 12500 BP. The water temperatures declined significantly and rates of sedimentation and ice‐rafting fell in association with the Younger Dryas period. The final retreat of the ice began as early as 10 500 BP, and the transition to normal‐marine sedimentation is reflected by precipitation of iron oxide followed by pyrite, reduced sedimentation rates, and a change from terrigenous to biogenic sedimentation.
High‐resolution paleomagnetic correlation of Middle Weichselian ice‐dammed lake sediments in two coastal caves, western Norway
Authors: VALEN VIDAR , LARSEN EILIV , MANGERUD JAN
Published: July 2010

Olahola is a wavecut cave positioned well above the postglacial marine limit. The sediment sequence in the cave can be litho‐ and magnetostratigraphically correlated with the sequence in the Skjonghelleren cave, 36 km northeast of this locality. Three boulder formations in Olahola represent three ice‐free periods (including the Holocene) and two formations of laminated clay represent periods of ice‐cover. Paleomagnetic excursions in the laminated clays have been correlated with the Lake Mungo/Mono Lake excursion (28 ka), and with the Laschamp excursion (43 ka), but the resolution of these events is much better in the caves than anywhere else. The paleomagnetic records from Skjonghelleren and Olahola suggest that during the Laschamp excursion at least 0.75–1 m of sediment accumulated in Skjonghelleren before sedimentation started in Olahola, indicating also an earlier ice coverage at Skjonghelleren.
The transition from the Younger Dryas to the Preboreal: a case study from the Kattegat, Scandinavia
Authors: JIANG HUI , KLINGBERG FREDRIK
Published: July 2010

A two‐step climatic warming and oceanographic change during the Younger Dryas/Preboreal transition was registered by diatom, foraminiferal, mollusc, lithologic data and sediment accumulation rates in a high resolution sediment core from the Swedish west coast. An abrupt climatic warming in the surface water of the Kattegat occurred at c. 10 200 BP, resulting in a rapid increase in sea surface water temperatures. The attenuation of meltwater discharge into the Kattegat led to an increase in sea surface salinity. Consequently, the difference in salinity through the water column diminished. This change happened within less than 80 years. The warming of bottom water in the deeper parts of the region took place a few hundred years after the surface water warming. The climatic amelioration was recorded by increased meltwater discharge and a slight increase in abundance of relatively warm diatoms around 10 600 BP at the time of the recession of the Fennoscandian ice sheet. An increase in the number of arctic/subarctic benthic foraminifera shows that the bottom water temperature during this period was still relatively low.
A comparison of mineral magnetic, geochemical and mineralogical techniques for compositional studies of glacial diamictons
Authors: WALDEN JOHN , SMITH JOHN P. , DACKOMBE ROGER V.
Published: July 2010

Data from heavy mineral analysis, X‐ray fluorescence spectrometry (XRF) and X‐ray diffractrometry (XRD) are compared with those obtained from mineral magnetic analysis for a range of glacial diamicton samples taken from the Quaternary sequence in the Isle of Man. These data show that the mineral magnetic approach offers a useful means of characterizing glacial sediments for purposes of lithostratigraphic correlation and provenance indication and that the magnetic data are of a comparable quality to those obtained from standard applications of the more traditional techniques. The heavy mineral and XRD data indicate that little post‐depositional chemical alteration of the detrital composition of the sediments has taken place. The mineral magnetic, heavy mineral and XRF analysis suggests both similar lithostratigraphic relationships between the various diamicton units and consistent indications of their likely provenance. These are consistent with published, field‐based, stratigraphic relationships of the same sediments and ice‐flow directions in the Irish Sea Basin during the Devensian.
Reinvestigation of the interglacial pollen flora at Leveäniemi, Swedish Lapland
Authors: ROBERTSSON ANN‐MARIE
Published: July 2010

The till‐covered organic sediments at Leveäiemi, Swedish Lapland have been reinvestigated by pollen analysis in order to gather more detailed information on vegetation history and climatic conditions during the interglacial period represented at this site. A partly different picture of the vegetation succession has arisen compared to earlier studies and results. The organic sequence is still correlated with the Eemian, but the forests were probably more open during the initial and later parts of the interglaciation than suggested earlier. This is based on the higher values of Juniperus pollen noted, and a continuous curve for Populous pollen during the PAZ representing the later part of the interglaciation. Comparisons are made with other sites in northern Sweden, Finland and northern Norway, and the possibilities of separating Eeinian deposits from those formed during the Holsteinian interglaciation are discussed.
Late Glacial stable isotope record, radiocarbon stratigraphy, pollen and mollusc analyses from the Geiseltal area, Central Germany
Authors: BÖTTGER TATJANA , HILLER ACHlM , JUNGE FRANK WOLFGANG , LITT THOMAS , MANIA DIETRICH , SCHEELE NORBERT
Published: July 2010

Combined investigations of isotopes, pollen, and molliisc shells were carried out on a Latc Glacial limnic high‐resolution sediment sequence from the Geiseltal open‐cast mine in Central Gcrmany. The dala confirm thc division of the Late Glacial biozones into two colder (Older and Younger Dryas) and two warmer periods (Bølling, Allcrød), which have already bccn cstablishcd lor the Central and Northern German area. Radiocarbon data, mainly based on wood material, cover a time span between c, 10 800 BP and 12 760 BP, indicating a mean sedimentation rate of c. 2 mm/yr. The stable isotope data (δ18O, δ13C) reflect the transition periods between the climatic phases as changes in relative air humidity (transition from dry, cold to warmer. more humid conditions). The dominance of evaporation effects, however, is superimposed on any ternpcratiirc aignal throughout the profile. Repeated conversions of the hydrologic regime (silting‐up phases. lake‐level variations) characterize the specific history of the lake development.
Relative water level change in the intracoastal zone of Belgium and Northern France over the last 2500 years
Authors: LOlJWYE STEPIIEN , DCCLERCQ ERWIN
Published: July 2010

Water level positions during the Subatlantic in the coastal plain of Belgium and Northern France are assessed by means of indicators such as tidal Icvces, upper tidal fat deposits and mature salt marshes. The indicators are evaluated for the reconstruction of local mean high water and local mean spring high water levels in the intracoastal zone. No significant altitude difference is observcd between the indicators genetically related to the Dunkerque II inundation phase, i.c. before the land reclamations of the 10th century AD, and the medieval Climate Optimum (AD 1000–1350). There is no evidence for a high relative local water level or a watcr level rise during the medieval Climatc Optimiini. It is shown that a hydrological phenomenon, probably an estuary effect, caused water levcla to rise significantly in restricted areas of the former tidal flat during thc Dunkerque II phase. A comparison between the local water level record and the tide gaugc records at Oostende indicates a more marked fluctuation over the last 160 ycars than during the preceding 700 years.
A Younger Dryas (Loch Lomond Stadial) jökulhlaup deposit, Fort Augustus, Scotland
Authors: RUSSELL ANDREW J. , MARREN PHILIP M.
Published: July 2010

This study provides an insight into the impact of probably the largest flood ever to have been identified in mainland Britain by examining new sedimentary evidence from the Auchteraw terrace, Fort Augustus, Scotland. Study of three sections reveals a succession consisting of: (1) sheet gravels; (2) large trough‐shaped depressions infilled with cross‐stratified sands and gravels; (3) smaller‐scale, finer‐grained cross‐strata; and (4) sheet‐like, occasionally channelized, bimodal sand and gravel beds. This study shows that both the sedimentology and morphology of the Auchteraw terrace are consistent with jökulhlaup deposition and reveal a greater variety of lithofacies types than identified in previous studies of jökulhlaups from ice‐dammed lakes. The fine‐grained nature of the sediment discussed in this study emphasizes the importance of sediment supply for the formation of distinctive jökulhlaup successions. The sedimentary evidence recorded here provides a valuable tool for the interpretation of the magnitude and frequency of proglacial meltwater flows associated with Pleistocene ice sheets worldwide.
Pleistocene explosions and pyroclastic currents in west‐central Anatolia
Authors: NEMEC WOJCIECH , KAZANCI NIZAMETTIN , MITCHELL JOHN G.
Published: July 2010

The discovery of unexpectedly young tephra, with K‐Ar dates of 1.50 ± 0.18 and 1.38 ± 0.13 Ma BP, in the Lake Eǧirdir area sheds new light on the time‐span and magnitude of explosive volcanism in west‐central Anatolia and on the physical behaviour of pyroclastic currents. The Gölcük maar near Isparta, widely thought to have ceased its activity in Pliocene time, was apparently still erupting with strong explosions in the Early Pleistocene. The Eǧirdir tephra, 34 km NE from the volcano, indicate deposition from powerful pyroclastic surges directed by the topography. The depositing currents were fully turbulent and carried unusually large lithic clasts, up to 2–3 cm in diameter, in suspension, which is incompatible with the existing physical model for pyroclastic currents. Based on the tephra characteristics, a conceptual model of the pyroclastic current's segmentation, or lateral dynamic partition, is suggested and used further to explain the current's specific response to an encountered topographic barrier. The widely held concept of a pyroclastic current's vertical separation, or sharp rheological decoupling, is thought to describe a common secondary phenomenon.
Morphology and sedimentology of a high‐arctic esker system: Vegbreen, Svalbard
Authors: HUDDART DAVID , BENNETT MATTHEW R. , GLASSER NEIL F.
Published: July 2010

Although eskers are frequently described glaciofluvial landforms, they are poorly understood. To assist with the interpretation of Pleistocene examples, modern analogue data are required. This paper documents the morphology, sedimentology and formation of a 650 m long esker system in front of the high‐arctic glacier Vegbreen in Svalbard. The esker is located between the Neoglacial maximum and the present ice front and appears to have formed both as a supraglacial trough‐fill and as a channel/conduit‐fill along the suture formed by two confluent glacier lobes. A range of sedimentary facies is preserved within this ridge system providing evidence for braided rivers, ephemeral lakes, episodic flow regimes and sediment gravity flows. This case study provides an important analogue for glaciofluvial sedimentation between retreating ice lobes.
Biostratigraphy of Eemian sediments at Mertuanoja, Pohjanmaa (Ostrobothnia), western Finland
Authors: ERIKSSON BRITA , GRÖNLUND TUULIKKI , UUTELA ANNELI
Published: July 2010

The till‐covered clay and silt deposits at Mertuanoja, Pohjanmaa (Ostrobothnia), western Finland, have been investigated in great detail. The Eemian interglacial environment is reconstructed here on the basis of pollen, diatom and dinoflagellate analyses. The pollen stratigraphy shows an interglacial vegetational succession reflecting stable climatic conditions typical of the Eemian Stage in the Pohjanmaa area. The initial Betuta forests were followed by Pinus‐Betula forests with Quercus. The next successional phase was dominated by Betula, Pinus and Alnus; temperate deciduous trees and Corylus also grew in the area. Later, Picea advanced and temperate deciduous trees declined. Some Corylus was, however, still present and thermophilous Osmunda thrived in wet places. The diatom record indicates that the sediments were deposited first in a freshwater basin, then in the Eemian Baltic Sea, and finally in a freshwater basin once more. The presence of dinoflagellates demonstrates that the Eemian Baltic Sea, when at its maximum extent, was connected to the Atlantic Ocean, which brought northern cool‐temperate surface waters to Finland as far north as Mertuanoja. Mertuanoja is the first interglacial site at which numerous dinoflagellate cysts were encountered in Finnish Quaternary sediments.
A stage 7 marine interglacial record (the Grødeland Interglacial) on Jaeren, southwestern Norway; foraminiferal, stable isotopes and amino acid evidence
Authors: SEJRUP HANS PETTER , IVERSEN MARIANNE , LARSEN EILIV , LANDVIK JON Y. , JANOCKO JURAJ
Published: July 2010

Foraminiferal biostratigraphy, stable isotopes and amino‐acid diagenesis have been investigated in a 125 m (+ 1 to — 124 m a.s.l.) long core from Jæren, southwestern Norway. Two marine units, the 42 m thick Grødeland Sand and the 8 m thick Sunde Sand, were found between till beds. Based on the biostratigraphic data, nine foraminiferal assemblage zones are defined. The Grødeland Sand shows a development from an ice‐proximal glacial environment in the lower part, through an arctic, possibly shallow‐water, environment, into a full interglacial open‐shelf regime (the Grødeland Interglacial). The Grødeland Interglacial sediments (zone 6 Cassidulina laevigata‐Cibicides zone) were deposited at a water depth of 20 m, in an open, high‐energy shelf environment with temperature conditions similar to those prevailing in the northern North Sea today. The interglacial sediments are followed by deposits characteristic of an arctic environment which become more ice proximal upwards. Superimposed on the Grødeland Sand is a diamicton interpreted as till. Above the till is the upper marine unit (the Sunde Sand), which in the lower part yielded a shallow‐water arctic fauna replaced upwards by an ice‐proximal facies. The upper part of the Sunde Sand is barren of foraminifera and is superimposed by an upper till. The Sunde Interstadial is defined as a climatostratigraphic event resulting in deglaciation of western Norway and deposition of the Sunde Sand. Based on amino acid geochronology and inferences from the biostratigraphy, the Grødeland Interglacial is assigned to oxygen‐isotope stage 7, whereas the Sunde Interstadial is assigned to the Early Weichselian. Combined with existing data from the North Sea region and the Norwegian Sea, it is concluded that for stage 7, in addition to stages 1 and 5e, there must have been a strong influx of Atlantic water into the Norwegian Sea north of the British Isles. This circulation created a similar north‐south gradient in water masses in the North Sea to that which occurred during the Eemian and the Holocene. In the Nordic Seas, however, the stage 7 warm influx was probably restricted to the eastern part of the basin, unlike the later warm periods. This led to the development of fully interglacial conditions in the North Sea region, even though the palaeoceanographic data from the central part of the Nordic Seas suggest relatively cooler conditions for oxygen‐isotope stage 7.
Last interglacial‐glacial climatic cycle in loess‐palaeosol successions of north‐western France
Authors: ANTOINE PIERRE , ROUSSEAU DENIS‐DIDIER , LAUTRIDOU JEAN‐PIERRE , HATTé CHRISTINE
Published: July 2010

The loess series at St. Pierre‐les‐Elbeuf and St. Sauflieu are key successions for the western European Quaternary stratigraphy. The present study proposes a detailed record of the last interglacial‐glacial climatic cycle at St. Pierre and its integration into the synthetic pedosedimentary record of north‐western France using detailed correlations with the type sections of St. Sauflieu and Achenheim. Finally, comparisons with the marine isotope, Greenland GRIP chronologies and dust records are proposed. At St. Pierre, the pedostratigraphic and sedimentological analyses (total iron, organic matter, carbonate, grain size), in association with low field magnetic susceptibility measurements, demonstrate that this loess succession records the major climatic events of the Upper Pleistocene. The basal soil complex at St. Pierre is similar to those from the main successions of North (St. Sauflieu) or Northeast France (Achenheim). It shows a Bt horizon of brown leached soil, a deeply reworked grey forest soil and two isohumic steppe soils separated by a non‐calcareous loess layer. This loess level corresponds to the first aeolian event clearly observed in the succession and can be correlated with Marker II of the Central European stratigraphy located around the marine isotope stage (MIS) 5/4 boundary. The main aeolian sedimentation starts after the soil complex and ends with the top soil (brown leached soil). Finally, a good parallel is observed between the strongest peaks of the dust records of the ice cores and the main period of loess deposition in St Pierre‐lès‐Elbeuf occurring during MIS 2.
Ostracod stable isotope records from a deglacial isolation sequence in southern Sweden
Authors: HAMMARLUND DAN
Published: July 2010

A Late Weichselian sediment succession from the Kullen Peninsula, southern Sweden, was studied by means of stable carbon and oxygen isotope analyses of calcific valves of selected ostracod taxa. The lower part of the record was deposited in a slightly brackish marginal sea close to the receding inland ice, whereas the upper part is lacustrine in origin as a result of glacio‐isostatic rebound. The site was deglaciated at c. 17 200 cal BP (c. 14 500 14C BP) within the earliest ice‐free area of Sweden, and the isolation took place c. 1100 cal years later. As a result of extensive input of glacial meltwater to the near‐shore, shallow basin, the isotopic records predating the isolation give no clear indications of marine conditions. However, the isolation of the lake from the marginal sea is reflected by a distinct depletion of 18O in ostracod calcite as a response to the changing isotope hydrology of the basin. The change towards a lacustrine environment also fostered a decrease in the input of minerogenic material and a related increase in organic carbon content of the sediments, which may explain a short‐lasting depletion of 13C in dissolved inorganic carbon and ostracod calcite. During the period of c. 14 700‐13 900 cal BP a pronounced warming occurred associated with the onset of the Late Weichselian interstadial complex (Greenland Interstadial 1). Based on a distinct enrichment of 18O in ostracod calcite and applying modern spatial relations between δ18O of precipitation and temperature, this climatic shift involved an increase in mean annual air temperature in southernmost Sweden of at least 7°C.
Continental/Cordilleran ice interactions: a dominant cause of westward super‐elevation of the last glacial maximum continental ice limit in southwestern Alberta, Canada
Authors: LITTLE EDWARD C. , Jr. LIONEL E. JACKSON , JAMES THOMAS S. , HICOCK STEPHEN R. , LEBOE ELIZABETH R.
Published: July 2010

In southwestern Alberta, Canada, a westward‐rising last‐glacial‐maximum continental ice limit has been identified. This limit is defined by the upper elevation of Canadian Shield erratics deposited by last‐glacial‐maximum continental ice along the flanks of prominent ridges and buttes within the region. The interpolation between ice‐limit data points has produced two distinct slope profiles: 2.9 m/km to the east, and 4.2 m/km to the west of Mokowan Butte. Three hypotheses are proposed to explain this westward rise of the last‐glacial‐maxi ‐mum continental ice limit: (1) regional tectonic uplift, (2) glacioisostatic uplift, and (3) continental ice‐flow convergence due to topographic obstacles and interaction with montane ice. Inferred long‐term rates of tectonic uplift and glacioisostati c modelling show that these two mechanisms account for less than 25% of the observed absolute elevation increase of the limit between the Del Bonita uplands and Cloudy Ridge in southwestern Alberta. The remaining rise in elevation of the continental ice‐sheet margin in this region is thought to result from continental ice‐flow convergence due to the combined effects of the regional topography and interaction with montane glaciers to the west. The steeper rise in the former continental ice surface west of Mokowan Butte can be explained by the tographic obstruction and interaction with montane glaciers in the area of the Rocky Mountain front.
Palaeomagnetism of the Moberly formation, northern Missouri, confirms a regional magnetic datum within the pre‐Illinoian glacial sequence of the midcontinental USA
Authors: ROVEY CHARLES W. , KEAN WILLIAM F.
Published: July 2010

The Moberly formation of northern Missouri, USA includes glacigenic sediment deposited during the second major pre‐Illinoian glaciation and is overlain by three younger normal‐polarity tills. The Moberly (mostly till) preserves two different magnetic remanences. A detrital remanent magnetization has reversed polarity with shallow (‐30 to ‐40) inclinations. The shallow inclination is regionally persistent and spans different facies, including those not prone to large inclination error. A secondary overprint of normal polarity is associated with a thin oxidized zone and weakly developed paleosol in the upper portion of the till. This chemical remanent magnetization is distinguished by high coercivities typical of authigenic ferromagnetic minerals and by scattered remanence vectors upon stepwise demagnetization. The secondary normal remanence was likely acquired during a brief interglacial period between deposition of the Moberly formation and the next glaciation. The short interglacial and the shallow inclinations indicate that the glaciation which deposited the Moberly occurred shortly before a major polarity change from reverse to normal, probably the Brunhes‐Matuyama reversal.
Postglacial succession and palaeoecology of Late Quaternary macrofaunal assemblages from the central Canadian Arctic Archipelago
Authors: GORDILLO SANDRA , AITKEN ALEC E.
Published: July 2010

Temporal and spatial variations of the species composition of Late Quaternary macrofossil assemblages in the vicinity of Prince of Wales Island, central Canadian Arctic are examined in this study. A total of 2247 specimens representing 15 taxa (9 bivalves, 6 gastropods) were recovered at 32 sites. The dominant species are the bivalvesHiatella arctica, Mya truncataandAstarte borealisthat together represent 91% of the total macrofossils represented in the collections. Taphonomic analysis (i.e. ratio of opposite valves; size range; shell abrasion and overgrowth; resistance to breakage) and comparison of the species composition of Holocene macrofaunal assemblages with modern counterparts and their habitats indicate that the subfossil faunas most commonly represent para‐autochthonous assemblages which inhabited glaciomarine or nearshore marine environments. As observed previously by other authors, changes in faunal composition through time from survivor or pioneer groups (Hiatella arctica, Mya truncata, Portlandia arctica, Macoma calcarea) to more diverse faunas (e.g.Astarte borealis, Clinocardium ciliatum, Serripes groenlandicus) are noted. The succession of faunas in the study area is interpreted as the result of oceanographic changes after deglaciation due to increased summer insolation and warming of surface waters in the early Holocene.
The brackish Baltic Sea Yoldia Stage – palaeoenvironmental implications from marine benthic fauna and stable oxygen isotopes
Authors: SCHONING KRISTIAN
Published: July 2010

Eighteen sites in middle Sweden with sediments deposited during the brackish phase of the Yoldia Sea have been investigated with respect to the marine calcareous benthic fauna (i.e. foraminifera, ostracods and molluscs) and stable oxygen isotopes. At most sites the sediments consist of varved clay sequences which are correlated to the Swedish Time Scale and dated to the Early Preboreal. A marine benthic fauna has been recorded at 11 sites. The fauna occurs during c. 100 clay‐varve years and the total length of the brackish phase is estimated to be 110–190 years. Near the inlet of saline water the fauna was dominated by the foraminifera Elphidium excavatum (Terquem) and further to the east the ostracod Cytheropteron montrosiense (Brady, Crosskey and Robertson) dominated. At shallower depths the fauna occurred during a shorter period owing to the formation of a stratified water column with a low‐saline surface water. Very low δ18Oc values were recorded, i.e. between ‐9.9% and ‐4.7% because of the influence of meltwater from the ice sheet. A different isotope fractionation between the foraminifera E. excavatum and the ostracod C. montrosiense was recorded.
Estimates of effective stress beneath a modern West Antarctic ice stream from till preconsolidation and void ratio
Authors: TULACZYK SLAWEK , KAMB BARCLAY , ENGELHARDT HERMANN F.
Published: July 2010

Preconsolidation stress recorded in subglacial sediments provides important information about subglacial effective stresses. It is commonly used to reconstruct past effective stresses from sediments left after ice retreat. In this article, we use properties of sub‐ice‐stream till samples to estimate effective stresses beneath a modern West Antarctic ice stream. Two previous estimates of sub‐ice‐stream effective stress were derived for the Upstream B (UpB) area of Ice Stream B from shear wave velocities (50 ± 40 kPa, Blankenship et al 1987) and borehole water level measurements (63 ± 24 kPa, Engelhardt & Kamb 1997). However, geotechnical tests performed on samples of the UpB till have shown that if subjected to effective stress of 50–63 kPa this till would have significantly lower porosity (˜0.32–0.35) and higher strength (˜‐22–28 kPa) than it apparently has in situ (˜0.4 and ˜2kPa). We derive new estimates of sub‐ice‐stream effective stress using: (1) Casagrande's construction applied to the results of six confined uniaxial tests, and (2) a combination of void‐ratio data for 51 till samples and 3 experimentally constrained equations describing compressibility of the UpB till under normal consolidation, overconsolidation and in the critical state. Casagrande's method yields an upper bound on effective stress of 25 kPa for four till samples and values of 13, and 4.4kPa for two other samples. The void‐ratio approach gives 11.7 ± 2.6 (normal consolidation), 18.3 ± 4.4 (overconsolidation) and 2.0 ± 0.8 kPa (critical state). These new, lower estimates of effective stress are consistent with the low till strength that has been independently measured and inferred from recent theoretical ice‐stream models. Our interpretation of data on till void ratio in terms of sub‐ice‐stream effective stress means that we can qualitatively evaluate the nature of the vertical distribution of this stress in the UpB till layer. We infer that in the sampled top 3 m of till the effective‐stress distribution is non‐hydrostatic, probably close to lithostatic. The results may be useful in future modeling of ice‐stream behavior and may aid efforts to delineate paleo‐ice streams based on their geologic record.
Palaeoenvironmental interpretation of a Pleistocene alluvial succession in central Poland: sedimentary facies analysis as a tool for palaeoclimatic inferences
Authors: ZIELIńSKI TOMASZ , GOźDZIK JAN
Published: July 2010

A Pleistocene valley‐fill alluvial succession deposited in the Kleszczów Graben, central Poland, has been studied in the Belchatów openpit mine. The succession, palynologically documented to represent the Drenthe/Warthe interstadial, consists of three alluvial complexes whose component lithofacies associations indicate a fluvial system evolving from temperate‐climate meandering river to transitional‐type shallow braided network, to periglacial well‐developed braided river influenced by aeolian sand supply. The study suggests that the abundance of fine‐grained overbank deposits, occurrence of peats/palaeosols and fining‐upward cyclothems are diagnostic attributes of perennial meandering river alluvium, which may indicate temperate climatic conditions. Periglacial braided river alluvium is recognizable by an admixture of wind‐derived sand grains with aeolian surface textures and by the occurrence of ice‐wedge features, indicative of cold climatic conditions. The distinction between the two basic types of alluvium is aided by the analysis of architectural elements and palaeocurrent directional data. The study demonstrates that sedimentological facies analysis can be a useful tool for the recognition of palaeoclimatic changes in Pleistocene alluvial successions.
Climate and environment on the Karelian Isthmus, northwestern Russia, 13000‐9000 cal. yrs BP
Authors: SUBETTO DMITRY A. , WOHLFARTH BARBARA , DAVYDOVA NATALYA N. , SAPELKO TATYANA V. , BJÖRKMAN LEIF , SOLOVIEVA NADJA , WASTEGÅRD STEFAN , POSSNERT GÖRAN , KHOMUTOVA VALENTINA I.
Published: July 2010

Sediment sequences retrieved from Lake Medvedevskoye (60°13'N; 29°54'E) and Lake Pastorskoye (60°13'N; 30°02'E), Karelian Isthmus, northwestern Russia, were analysed for lithology, pollen and diatom stratigraphy, total organic carbon content and mineral magnetic parameters. Age control for both sequences was provided by AMS 14C measurements and the Vedde Ash tephra. The reconstructed climatic and environmental development shows the deglaciation of the sites and the establishment of sparse shrub and herb/grass vegetation before 12650 cal. yrs BP (‘Allerød’; GI‐1a). Steppe tundra and cold, dry conditions prevailed until about 11000 cal. yrs BP, i.e. throughout the ‘Younger Dryas’ (GS‐1) and the earliest Holocene. The establishment of open Picea‐Pinus‐Betula forest around the lakes at about 11 000 cal. yrs BP coincides with the first distinct change towards gradually warmer and more humid climatic conditions. Boreal forest with Picea, Pinus, Betula, Alnus incana and Corylus was present at the lower altitude site between c. 10700 and 10200 cal. yrs BP, while open Betula‐Pinus forest continued to dominate the vegetation around the higher altitude site. After a short, possibly colder, phase around 10200‐10000 cal. yrs BP, which is expressed by a marked reduction in vegetation cover and decreased lake productivity, climatic conditions became significantly warmer and possibly more humid. Boreal forest with Pinus, Betula, Picea, Alnus incana, Corylus and Ulmus became widespread in the region after 10000 cal. yrs BP. The delayed environmental response of the lakes and their catchment to hemispheric warming at the Pleistocene/Holocene boundary may be explained by a sustained blocking of westerly air masses due to the presence of the Scandinavian ice sheet and associated strengthened easterlies and anticy‐clonic circulation and/or extensive permafrost.
East Asian monsoon instability at the stage 5a/4 transition
Authors: XIONG SHANGFA , DING ZHONGLI , LIU TUNGSHENG , ZHANG JINGZHAO
Published: July 2010

The physics involved in the abrupt climate changes of the late Quaternary have eluded paleoclimatologists for many years. More paleoclimatic records characteristic of different elements of the global climate system are needed for better understanding of the cause‐feedback relationships in the system. The East Asian monsoon is an important part of the global climate system and the mechanical links between the East Asian monsoon and other climatic elements around the world may hold a key to our knowledge of abrupt climate changes in East Asia and probably over a larger part of the globe. Previous studies have detected millennial‐scale winter monsoon oscillations during the last glaciation and probably also during the last interglaciation in loess sequences across China. However, less attention has been paid to the abrupt summer monsoon changes and the stage 5a/4 transition, an important period for the evolution of the East Asian monsoon when the global climate shifted towards the last glaciation. Here we report on two loess sections from eastern China which were dated using a thermoluminescence (TL) technique. The pedogenic and other sediment parameters suggest that the summer monsoon experienced a two‐step abrupt retreat at the stage 5a/4 transition. The variations in the proxies for the winter monsoon are synchronized with the summer monsoon proxies during this brief interval, implying a direct and immediate link between high latitude and low latitude mechanisms. These changes may be correlated with similar climatic oscillations observed in the North Atlantic, Europe and Antarctica, raising the possibility that the forcing factors that induced these changes are global in extent.
First post‐glacial establishment of forest trees: early Holocene vegetation, mollusc settlement and climate dynamics in central Troms, North Norway
Authors: JENSEN CHRISTIN , KUIPER J. G. J. , VORREN KARL‐DAG
Published: July 2010

Sediments from two limnic basins in a sub‐continental region of northern Norway are investigated for pollen, plant macrofossils and bivalves at a high stratigraphical resolution. The basins are located at 280 and 400 m a.s.l. on the S‐SW slope of Mt. Skrubben (848 m a.s.l.). The bio‐ and lithostratigraphical records are interpreted in terms of immigration and establishment of forest tree species and climate. The mountain was deglaciated at both sites at c. 9200–9100 BP (c. 10200–10100 cal. BP). Betula pubescens forest stands established at c. 8900 BP (c. 9900 cal. BP). The first Pinus sylvestris individuals may have established at or near the lowermost investigation site at c. 8700–8600 BP (c. 9700–9600 cal. BP), while P. sylvestris forest stands were present at 400 m a.s.l. c. 7700 BP (c. 8500 cal. BP) and expanded in area and/or density from c. 7200 BP. Macrofossils of P. sylvestris occur in strata with a pine pollen influx as low as c. 200 grains cm‐2yr‐1. The immigration of P. sylvestris to the western part of northern Fennoscandia may thus have happened earlier than formerly interpreted from pollen analyses alone, where influx values as low as c. 200 grains cm‐2yr‐1 would not be considered as indicative of local presence. Alnus incana established at approximately the same time as P. sylvestris. During the period from deglaciation to c. 6600 BP (c. 7300 cal. BP), calcareous limnic sediments were deposited in the basins, with Chara species and a Sphaeriidae fauna consisting of Pisidium hibernicum, P. lilljeborgii, P. milium, P. nitidum, P. waldeni and P. casertanum. During the period c. 8800–8500 BP, P. nitidum prevailed, and almost pure CaCO3 sediments were formed. We interpret the environment as dry with a low influx of both minerogenic particles and humic substances. The period 8800–8500 BP (9800–9500 cal. yr BP) is interpreted as a period with warm and dry summers and cold and dry winters.
Seismically induced soft‐sediment microstructures (seismites) from Meikleour, western Strathmore, Scotland
Authors: MENZIES JOHN , TAYLOR JOHN
Published: July 2010

At the distal portion of a large glacial outwash fan in eastern Scotland, a suite of both macro‐ and microstructures was examined. The macrostructures reveal intense soft‐sediment deformation indicative of liquefaction, fluidization and loading processes possibly associated with neotectonic effects of seismic activity along the nearby Highland Boundary Fault. The section at Meikleour has already been examined at the macroscale and an interpretation put forward. In a follow‐up study, microstructures were examined using micromorphological techniques to attempt to establish if this technique could be successfully used, and to reconsider the macroscale interpretation. In light of micromorphological analyses, a similar interpretation of neotectonic deformations associated with seismic activity is suggested. Microstructures, never hitherto observed in fine glaciofluvial outwash, were interpreted as those possibly associated with strong seismic tremors, since no evidence existed for subsequent overriding by glacial ice, mass movement or related processes that might otherwise explain such unusual microstructures. This work further establishes the validity and reliability in using micromorphological analyses.
Quantification of the northern Italy Pliocene climate from pollen data: evidence for a very peculiar climate pattern
Authors: FAUQUETTE SÉVERINE , BERTINI ADELE
Published: July 2010

A climatic reconstruction has been carried out on the Stirone pollen sequence (northern Italy), covering the Pliocene period from the Zanclean to the early Gelasian (˜5.1 to ˜2.2 Ma). Despite the existence of a number of hiatuses, the section provides a clear picture of the vegetation and climatic evolution during this time interval, which includes the first glacial‐interglacial cycles of the Northern Hemisphere. The climate of this period has been quantified using the ‘Climatic Amplitude Method’ developed for the Neogene, and five climatic parameters have been estimated. The results show that at the beginning of the Pliocene and during the interglacial periods the climate was warm and humid (mean annual temperature from 16 to 20°C, mean annual precipitation from 1100 to 1500–1600 mm), similar to that found elsewhere in the northwestern Mediterranean area. However, during the first glacial periods the reconstructed climate differs from that found at other Mediterranean sites: the mean annual temperature, the temperature of the warmest and coldest months show lower values than those found during the lower Pliocene, but no marked reductions are observed in the annual precipitation, allowing the continuous presence of a forested environment. These results are in agreement with the hypothesis that from at least the Upper Pliocene the Po region has been a special region from the point of view of both vegetation and climate. The difference is particularly marked during the earliest glacial phases in northern Italy.
Evidence of iceberg‐ploughing in a subaqueous ice‐contact fan, glacial Lake Rinteln, NW Germany
Authors: WINSEMANN JUTTA , ASPRION ULRICH , MEYER THOMAS , SCHULTZ HARM , VICTOR PIA
Published: July 2010

The Coppenbrügge subaqueous ice‐contact fan complex of early Saalian age is about 10 km long and up to 10 km wide and is composed of offset‐stacked fan clinothems that are transgressive‐regressive sequences formed during an overall lake level rise. The individual fan bodies consist of coarse gravel in the ice‐proximal part, passing distally into sandy facies and showing large‐scale foreset bedding. The iceberg scour recognized in an open‐pit outcrop is up to 1.5m deep, up to 2m wide and cut in undisturbed mid‐fan deposits. The scour‐fill can be traced laterally for about 15m and consists of sheared sand and, in the frontal zone, of downbent overlying strata surrounded by a zone of deformed sediments. The deformed sediment produced by the iceberg keel's shearing of the trough walls is a sand mass containing angular soft‐sediment clasts that show internal folds and fractures. The basal surface of the deformed sediment is a nearly horizontal shear plane, steepening up laterally as a discrete thrust and showing a flat‐ramp‐flat geometry. The scour was formed by the iceberg keel's ploughing the substrate and pushing the sediment sideways and frontally, forming a ridge of deformed sediments at the trough end. This ridge was concurrently eroded by an accompanying meltwater underflow which apparently developed a horseshoe system of scouring vortices around the grounded iceberg. The current's scour was filled with massive, non‐stratified sand deposited rapidly from turbulent suspension. The iceberg eventually broke up and its keel part was buried. As these ice fragments gradually melted, the space was closed by normal faulting and downbending of overlying strata. The collapsing scour‐fill became partly liquified, and the resulting water‐escape structures cut the normal faults and the overlying deposits. Though produced chiefly by tangential shear strain, iceberg‐ploughing features are readily distinguishable from other glaciotectonic deformations. They can serve as a diagnostic criterion for glaciolacustrine or glaciomarine environments and the distinguishing of ice‐contact subaqueous fans from ice‐contact deltas in the stratigraphic record.
Subaqueous artesian springs and associated spring pits in a Himalayan pond
Authors: DRAGANITS ERICH , JANDA CHRISTOPH
Published: July 2010

Subaqueous, bowl‐shaped depressions found in a Himalayan pond formed in an abandoned river channel in the Lingti Valley (Spiti, NW India) are spring pits (Quirke 1930). The occurrence of the spring pits is restricted to the western end of the pond, where coarse‐grained, highly permeable alluvial fan material continues below lacustrine mud deposits. The spring pits formed by active vertical discharge of ground water from an underlying artesian alluvial fan aquifer, confined by the overlying fine‐grained lacustrine sediments. The aquifer is continuously recharged by down‐slope ground‐water flow in the alluvial fan. These small artesian springs are comparable with much larger artesian springs described in the literature and a similar mechanism of formation is proposed. Some similarities in their shapes and mechanisms of formation may indicate that spring pits represent small, nearshore examples of pockmarks. The differences of these features, formed by persistent fluidization from short‐lived seismic liquefaction processes, are discussed and the utility of the structures for palaeo‐environmental and palaeo‐ground‐water interpretation is evaluated.
Storegga tsunami sand in peat below the Tapes beach ridge at Harøy, western Norway, and its possible relation to an early Stone Age settlement
Authors: BONDEVIK STEIN
Published: July 2010

One of the early problems with the Storegga tsunami deposit was how to distinguish it from deposits of the midHolocene (Tapes) transgression. An excavation on Harøy, an island on the outermost western coast of Norway, shows a distinct, clean sand bed embedded in peat and clearly separated from the overlying Tapes beach deposits. This sand bed continues in the peat landwards of the beach ridge for at least 60 m. Radiocarbon dates of the peat show that the sand was deposited some time between 6900 and 7700 yr BP. The sedimentary structures of the bed, the 14C dates, and the fact that this is the only sand bed in the peat, suggest that the sand bed was deposited by a short‐lived event, the Storegga tsunami. On the neighbouring island, Fjørtoft, a Stone Age settlement, dated to 7500 yr BP, was discovered in the early 1970s. The settlement was found underneath a sand bed that later had been covered by the Tapes beach ridge deposits. When discovered, the sand covering the settlement was inferred as eolian sand. However, this investigation shows that the Storegga tsunami deposited a widespread sand bed on the land surface around this time with a similar grain size distribution to eolian sand. It is therefore suggested that the sand bed covering this settlement was deposited from the Storegga tsunami. Both the stratigraphy and 14C dates demonstrate that the Tapes transgression maximum was reached well after the Storegga tsunami on Harøy, between 6500 and 6100 yr BP.
Position of the palaeontological site Aven I des Abîmes de La Fage, at Noailles (Corrèze, France), in the European Pleistocene chronology
Authors: MOURER‐CHAUVIRÈ CÉCILE , PHILIPPE MICHEL , QUINIF YVES , CHALINE JEAN , DEBARD EVELYNE , GUÉRIN CLAUDE , HUGUENEY MARGUERITE
Published: July 2010

Mourer‐Chauviré, C., Philippe, M., Quinif, Y., Chaline, J., Debard, E., Guérin, C. & Hugueney, M. 2003 (September): Position of the palaeontological site Aven I des Abîmes de La Fage, at Noailles (Corrèze, France), in the European Pleistocene chronology. Boreas, Vol. 32, pp. 521–531. Oslo. ISSN 0300–9483.

The palaeontological locality of Aven I des Abîmes de La Fage, at Noailles, Corrèze, France, is a limestone swallow hole filling which includes a rich fauna of micro‐ and macromammals, and one of the most complete Pleistocene avifaunas in the Palearctic. According to the mammal fauna and to the sedimentological study, the filling was previously assigned to the penultimate, Saalian, glaciation. U/Th datings made on a stalagmitic floor deposited in a lateral gallery on top of the filling confirm this previous attribution. Revised lists of the mammal and bird faunas are provided. The comparison of the La Fage fauna with that of other European localities, radiochronologically or biostratigraphically dated, leads to the conclusion that most of the fossiliferous layers were deposited during the Marine Isotope Stage (MIS) 8 (242 to 301 ka).
Origin of black coloured laminae in speleothems from the Kraków‐Wieluń; Upland, Poland
Authors: GRADZIŃSKI MICHAŁ , GÓRNY ANDRZEJ , PAZDUR ANNA , PAZDUR MIECZYSŁAW F.
Published: July 2010

Black coloured laminae have been detected inside speleothems from nine caves situated in the Kraków‐Wieluń Upland. The black colour results from the occurrence of charcoal particles and organic compounds. These particles originated inside the caves during wood combustion caused by prehistoric human activity. The ultrastructures of charcoal particles prove that most originated in temperatures ranging from 400 up to 600°C, suggesting that the charcoal is connected with domestic fires rather than torches. Although the laminae are proof of human activity in the caves, the occurrence of one particular lamina cannot be associated with a single episode of human occupation. It is due to the fact that depositional processes and corrosion control the number and thickness of the laminae discussed. The presence of black coloured laminae within the studied Holocene speleothems indicates that the investigated caves were settled in the Neolithic, the Bronze Age and later periods. This is consistent with the former archaeological data.