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Arnold, L. J. & Roberts, R. G. 2011: Paper I - Optically stimulated luminescence (OSL) dating of perennially frozen deposits in north−central Siberia: OSL characteristics of quartz grains and methodological considerations regarding their suitability for dating. Boreas, Vol. 40, pp. 389-416. 10.1111/j.1502-3885.2011.00209.x. ISSN 0300−9483. Optically stimulated luminescence (OSL) dating of coarse-grained quartz is increasingly being used as the main chronological tool in late Quaternary palaeoenvironmental reconstructions of Siberia. However, relatively little information has been published on the suitability of OSL dating for the various types of perennially frozen sediments found in this region. Here we provide a systematic examination of the quartz luminescence characteristics of 21 perennially frozen samples from the Taimyr Peninsula and adjacent coastal lowlands of north-central Siberia, and discuss their implications for the reliability of single-grain and multi-grain OSL chronologies in such contexts. The results of this study suggest that the quartz luminescence characteristics of these samples are, in principle, favourable for OSL dating but, in practice, require that a series of validation checks are made of the chosen experimental conditions. If these tests are satisfied, then reliable OSL chronologies should be obtained for sedimentary deposits in this region. Importantly, however, the single-grain and multi-grain aliquot equivalent dose (D) distribution characteristics for our samples reveal that there are advantages in targeting certain types of depositional settings for OSL dating studies of Siberian sediments. We also show that samples from the same depositional settings, and even from the same sites, do not necessarily display similar D distribution characteristics. The latter complication favours the use of single-grain analysis to unravel the bleaching and burial histories of young (mid- to late Holocene) sediments in these Arctic environments. [ABSTRACT FROM AUTHOR]

This paper presents a reconstruction of the marginal zone of the Anglian (Elsterian, 480–420 ka BP) age ice sheet in the Danbury‐Tiptree area, East Anglia, UK. The research area is a unique locality where the ice front abutted against a 30‐km‐long and 100‐m‐tall ridge in an otherwise lowland area. Observations from three main field localities (Danbury quarry, Royal Oak pit and Tiptree quarry) are complemented with ground penetrating radar survey data, borehole data analysis, laboratory analyses and geological map interpretation. A four‐stage model of the evolution of the landscape in the Danbury‐Tiptree area is presented. The results are of broader importance, in that the sedimentary record sheds light on the processes operating at a constrained ice‐sheet margin. The paper identifies the most important characteristics of the depositional environments at an ice front terminating within this type of setting: (i) high temporal and spatial variability of energetic depositional conditions, resulting in the presence of a vast array of distinct depositional sub‐environments; (ii) mechanisms promoting differential erosion leading to enhanced topography, and (iii) unusually high overburden pressure in the topographically constrained ice margin within the otherwise lowland area influencing the ice‐sheet–bedrock interaction in this particular research area, inducing postglacial seismicity. [ABSTRACT FROM AUTHOR]

This paper presents the results of high‐resolution sedimentological analyses of sediment cores from the eastern Gulf of Finland (Baltic Sea). Sampling sites in the periphery of sedimentary basins were selected on the basis of acoustic profiling analyses. The research allowed tracing of the transition from the freshwater Ancylus Lake to the Littorina Sea. A specific transitional layer of 'blue clays', indicating the first stage of brackish water inflow into the Gulf of Finland, was dated to 9.1 ka BP. The date of first appearance of Littorina silty clay sedimentation was as follows: from 8.0 ka BP near Gogland Island, from 7.0 ka BP near Moshchny Island and from 5.9 ka BP near the Berezovye Islands. Holocene cycles of hypoxia, associated with periods of warming, were identified and cycles of 'warming – transgression – anoxic conditions' and 'cooling – regression – oxygen‐rich conditions' were revealed. During the first stage of Littorina transgression (8.0–7.0 ka BP), the near‐bottom environment in the deepest sedimentary basin of the eastern Gulf of Finland was characterized by oxygen deficiency. In contrast, 7.0–6.0 ka BP was dominated by oxygen‐rich conditions and active processes of bioturbation. Anoxic conditions occurred again from 6.0–4.8 ka BP (Holocene Climatic Optimum), resulting in the accumulation of undisturbed silty clays with subhorizontal lamination. The interval from 4.8–2.0 ka was then characterized by oxygen‐rich near‐bottom conditions favourable for benthic organisms. The grain‐size distributions throughout the sediment cores from the easternmost sedimentary basins suggest a relative lowering of the sea level from 3.5–1.8 ka and a rise after 1.8 ka BP. [ABSTRACT FROM AUTHOR]

Despite numerous palaeoenvironmental investigations of loess–palaeosol sequences across the Carpathian Basin, well‐dated high‐resolution records are scarce. This paper presents a new high‐resolution chronology for the loess‐palaeosol sequence at Surduk (Serbia), based on optically stimulated luminescence (quartz) and post‐infrared infrared stimulated luminescence (polymineral) dating. The presented record spans 53–19 ka, with primary loess deposition occurring after 52±2 ka, and differs from previously published chronologies that relied on less precise and now superseded dating protocols. Based on the new chronology, mass accumulation rates (MARs) for Surduk were constructed and compared with sites in the Carpathian Basin. The results demonstrate that accumulation periods across this area are not consistent in timing or rates. The high‐resolution dating strategy identifies a disturbance in sediment deposition that occurred after 45±2 ka and implies that site contains a hiatus. Finally, we show samples that failed routine dose recovery and preheat plateau tests, and had low fast ratios. Supported by bulk sample geochemical analysis it is proposed that a potential abrupt source shift, during the Last Glacial Maximum, may be the cause of the anomalous luminescence behaviour. [ABSTRACT FROM AUTHOR]

The Bristol Channel, including onshore areas, is critical for reconstructing Pleistocene glacial limits in southwest Britain. Debate about the precise regional southern limits of Devensian (Oxygen Isotope Stage (OIS) 2) and Anglian (OIS 12) glaciations has recently been rekindled. The Paviland Moraine (Llanddewi Formation), Gower, south Wales is conventionally regarded as Anglian in age. Its ‘old’ age has been based on reported highly weathered clasts, a subdued morphology and ‘field relationships’ to fossil beach sediments of now disputed age(s). Relatively little about its sedimentary characteristics has been previously published. This paper: (i) presents new sedimentological evidence including lithofacies analysis, XRF analysis and electrical resistivity tomography (ERT) of sediment cores and electrical resistivity of a tied 3D field grid; (ii) re‐assesses the proposed ‘old’ age; (iii) suggests a likely depositional origin; and (iv) discusses implications for regional glacial dynamics and future research priorities. The sediments comprise mostly dipping glacigenic diamict units containing mainly Welsh Coalfield erratics. The location and subdued moraine morphology are attributed to the hydrological influence of the underlying limestone, the local topography and ice‐sheet behaviour rather than to long‐term degradation. Moraine formation is attributed mainly to sediment gravity flows that coalesced to produce an ice‐frontal apron. Neither geochemical data nor clasts indicate prolonged subaerial weathering and in‐situ moraine sediments are restricted to a limestone plateau above and inland of fossil beach sediments. We recommend rejecting the view that the moraine represents the only recognized OIS 12 deposit in Wales and conclude that instead it marks the limit of relatively thin Last Glacial Maximum (LGM) ice in west Gower. This requires revision of the accepted view of a more restricted LGM limit in the area. We suggest that substrate hydrological conditions may be a more influential factor in moraine location and form than is currently acknowledged. [ABSTRACT FROM AUTHOR]

It is uncommon in the North Sea basin and northwestern Europe for the ice-marginal glacial successions of the Middle Pleistocene, Anglian (Elsterian) age to be well preserved and not overridden by subsequent glaciations. The existence of extensive and thick ( ˜20 m) Middle Pleistocene sand and gravel successions in East Anglia, England, provide a unique opportunity to reconstruct and understand the palaeoenvironmental conditions in the Anglian ice-marginal zone, and further across the North Sea basin. This paper uses data from 80 sections in two sand and gravel quarries in East Anglia to provide the first evidence concerning: (i) the character of the ice-marginal processes in the unique, transitional zone between the topographically constrained and unconstrained Anglian ice-sheet margin; (ii) the role of meltwater in the re-shaping of topographically driven preglacial drainage; and (iii) the position and the number of oscillations of the Anglian ice-sheet margin in the form of a sediment-landform assemblage. Moreover the current research adds to the discussion on the presence and extent of the proglacial lake in the North Sea Basin during the Anglian glaciation. The sand and gravel successions in the Anglian ice-marginal zone are primarily reworked proto-Thames sediments deposited by meltwater. At the beginning of the glaciation, the meltwater followed the preglacial (proto-Thames) river course. However, as the ice sheet advanced, it was re-routed, overwhelming and abandoning the old river course and depositing an extensive ice-marginal subaqueous fan. The succession includes evidence for at least two enhanced meltwater release events, as well as indications of glaciolacustrine sedimentation. The character of the described sedimentary settings is discussed in the wider context of the presence of the North Sea Lake. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive palaeoenvironmental data set from Lake Skrzynka, northern Poland. A sediment core from the lake was investigated to reconstruct Lateglacial and Holocene environmental changes in northern Poland using a combination of palynology and stable carbon and oxygen isotope studies of carbonates and sediment geochemistry. The undisturbed sedimentation in Lake Skrzynka continues from the Allerød to the present. Our data suggest the persistence of dead ice in the Lake Skrzynka basin up to the Allerød. The sedimentary record of the lake reflects a considerable difference between the Lateglacial/early Holocene and the middle/late Holocene in terms of environmental conditions. The Lateglacial was characterized by rapid environmental changes, while climatic conditions throughout the Holocene were relatively stable. The trophic state of the lake was strictly dependent on climatically controlled vegetation changes and erosion tendencies in the vicinity of Lake Skrzynka. During the Lateglacial and early Holocene, as a result of predominantly open plant communities and enhanced nutrient export from the watershed, Lake Skrzynka experienced an increased trophy. The stabilization of forest cover and reduced input of nutrients resulted in the establishment of oligotrophic conditions in the lake in the early Boreal. During the late Subatlantic, the lake became eutrophic as a result of human disturbance of the local hydrological balance. The postglacial history of Lake Skrzynka can be regarded as representative of small, alkaline, through-flow lakes in temperate climates. [ABSTRACT FROM AUTHOR]

The Mount Cook area in the Southern Alps of New Zealand is heavily glacierized with numerous peaks over 3000 m a.s.l. feeding several large valley glaciers. The region is subject to rapid tectonic uplift and heavy precipitation (up to 15 m per year). This paper describes the clast roundness, clast shape and textural characteristics associated with five glaciers (Fox, Franz Josef, Hooker, Mueller and Tasman) in terms of inputs to the glacier system, transport by the glaciers and reworking following glacial deposition. Inputs include rockfall, alluvial fan and avalanche material delivered to the surface of valley glaciers. Basal debris, where observed at the terminus of two glaciers, consists mainly of incorporated fluvial material. Following deposition, reworking is mainly by subglacial and proglacial streams. The dominant facies are (i) boulder gravel with mainly angular clasts on the steep slopes above the glaciers, (ii) sandy boulder gravel, with mainly angular and subangular clasts, forming lateral and end moraines, and (iii) sandy boulder/cobble gravel with mainly subrounded clasts, and sand, which represent glacially transported sediment reworked by braided rivers. Diamicton is rare in the contemporary glacial environment. Since most sediment associated with glaciers in the Southern Alps lacks unambiguous indications of glacial transport, interpretation of similar sediments in the geological record should not necessarily exclude the involvement of glacial processes. [ABSTRACT FROM AUTHOR]

The continuing development of analytical methods for investigating sedimentary records calls for iterative re‐examination of existing data sets obtained on loess‐palaeosol sequences (LPS) as archives of palaeoenvironmental change. Here, we re‐investigate two LPS (Hecklingen, Zilly) in the northern Harz foreland, Germany, being of interest due to their proximity to the Scandinavian Ice Sheet (SIS) and the position between oceanic climatic influence further west and continental influence towards the east. First, we established new quartz OSL and polymineral IRSL chronologies. Both methods show concordant ages in the upper part of the Hecklingen profile (~20–40 ka), but in the lower part IRSL underestimates OSL ages by up to ~15 ka for the period 40–60 ka. Interpretations hence refer to the OSL data set. Second, we applied Bayesian age‐depth modelling to data sets from Hecklingen to resolve inversions in the original ages, also reducing averaged 1σ uncertainty by ~19% (OSL) and ~12% (IRSL). Modelled chronologies point out phases of increased (MIS 2, early MIS 3) and reduced (middle and late MIS 3) sedimentation, but interpretation of numerical rates is problematic because of intense erosion and slope wash particularly during MIS 3. Finally, previously obtained grain‐size data were re‐investigated by end member modelling analyses. Three fundamental grain‐size distributions (loadings) explain the measured data sets and offer information on intensity and – combined with modelled OSL ages – timing of geomorphic processes. We interpret the loadings to represent (i) primary loess accumulation, (ii) postdepositional pedogenesis and/or input of aeolian fine fractions, and (iii) input of coarse aeolian material and/or slope wash. The applied modelling tools facilitate detailed understanding of site‐formation through time, allowing us to correlate a strong peak in mean grain size at ~26–24 ka to the maximum extent of the SIS and increased influence of easterly winds. [ABSTRACT FROM AUTHOR]

The Swedish Varve Chronology is an unparalleled tool for linking the deglacial history of Sweden with associated palaeo‐environmental change at an annual time scale, and it forms part of Sweden's cultural heritage. A full deglacial chronology connected to the present day does not yet exist; a notable gap is in southeasternmost Sweden, where few varved records are successfully connected to reconstruct ice‐margin retreat. Deglaciation in southern Sweden covers both the climate transition to the Bølling warm period (~14.7 ka BP) and the ice‐margin transition from a subaqueous to terrestrial terminus. To facilitate investigations into the links between ice‐margin dynamics and abrupt climate change, we revisited the varve chronologies of southern Sweden. We digitized unpublished records, reanalysed existing varve thickness records, and obtained and analysed new varve series both on land and offshore. This combined approach has enabled us to refine and extend the existing south coast chronology east and 78 km northwards. Our new Skåne‐Småland chronology records 725 years of deglaciation, in addition to a younger floating chronology in parts. This chronology suggests that the glacial‐lake terminating Fennoscandian Ice Sheet in southern Sweden initially retreated northwards at ~110–160 m a−1 slowing to 60–70 m a−1 near the palaeo‐shoreline. Between today's mainland and the (now) island of Öland the retreat rates increase three‐ to fivefold. Ice‐margin retreat was initially oriented towards the north (as along the south coast), but later pivoted towards the northwest, signifying a landward retreat of terrestrial 'Swedish' ice that became divorced from the Baltic Sea ice‐sheet catchment. Our new 725‐year‐long varve thickness series reveals repeated multidecadal scale episodes of increased sedimentation. These likely signify phases of enhanced ice‐sheet melting that repeat and persist throughout the deglaciation of Skåne‐Småland. [ABSTRACT FROM AUTHOR]

In the Middle Danube Basin, Quaternary deposits are widely distributed in the Vojvodina region where they cover about 95% of the area. Major research during the last two decades has been focused on loess deposits in the Vojvodina region. During this period, loess in the Vojvodina region has become one of the most important Pleistocene European continental climatic and environmental records. Here we present the dating results of 15 samples taken from the Nosak loess‐palaeosol sequence in northeastern Serbia in order to establish a chronology over the last three glacial–interglacial cycles. We use the pIRIR290 signal of the 4–11 μm polymineral grains. The calculated ages are within the error limits partially consistent with the proposed multi‐millennial chronostratigraphy for Serbian loess. The average mass accumulation rate for the last three glacial–interglacial cycles is 265 g m−2 a−1, which is in agreement with the values of most sites in the Carpathian Basin. Our results indicate a highly variable deposition rate of loess, especially during the MIS 3 and MIS 6 stages, which is contrary to most studies conducted in Serbia where linear sedimentation rates were assumed. [ABSTRACT FROM AUTHOR]

Large and complete glaciotectonic sequences formed by marine‐terminating glaciers are rarely observed on land, hampering our understanding of the behaviour of such glaciers and the processes operating at their margins. During the Late Weichselian in western Iceland, an actively retreating marine‐terminating glacier resulted in the large‐scale deformation of a sequence of glaciomarine sediments. Due to isostatic rebound since the deglaciation, these formations are now exposed in the coastal cliffs of Belgsholt and Melabakkar‐Ásbakkar in the Melasveit district, and provide a detailed record of past glacier dynamics and the inter‐relationships between glaciotectonic and sedimentary processes at the margin of this marine‐terminating glacier. A comprehensive study of the sedimentology and glaciotectonic architecture of the coastal cliffs reveals a series of subaquatic moraines formed by a glacier advancing from Borgarfjörður to the north of the study area. Analyses of the style of deformation within each of the moraines demonstrate that they were primarily built up by ice‐marginal/proglacial thrusting and folding of marine sediments, as well as deposition and subsequent deformation of ice‐marginal subaquatic fans. The largest of the moraines exposed in the Melabakkar‐Ásbakkar section is over 1.5 km wide and 30 m high and indicates the maximum extent of the Borgarfjörður glacier. Generally, the other moraines in the series become progressively younger towards the north, each designating an advance or stillstand position as the glacier oscillated during its overall northward retreat. During this active retreat, glaciomarine sediments rapidly accumulated in front of the glacier providing material for new moraines. As the glacier finally receded from the area, the depressions between the moraines were infilled by continued glaciomarine sedimentation. This study highlights the dynamics of marine‐terminating glaciers and may have implications for the interpretation of their sedimentological and geomorphological records. [ABSTRACT FROM AUTHOR]

This study offers new insights into the origin and depositional history of the mixture of sediments infilling one of the largest offshore, northward‐orientated, clinoform‐structured, tunnel valleys (TVs) of Elsterian age in the southern North Sea (SNS). Specifically, the study sheds light on the provenance of TV deposits based on K‐Ar dating of illite, QEMSCAN® heavy mineral assemblage study, and U‐Pb and fission track dating on single grains of apatite. Early Pleistocene substrate and the TV infill demonstrate provenance from the Scandinavian and Baltic realms as well as from Renish central Europe and the Alps. Prior to Elsterian glaciation fluvial transport to the SNS increasingly switched from Baltic sources to a more central European influence. However, based on similar provenance of both the substrate and TV infill, the episode of subglacial tunnel valley formation interrupted this central European influence. Glacial erosional processes associated with the expansion of the Elsterian ice sheet to the SNS reworked a large amount of sediment from the Early Pleistocene deposits of the SNS. The sediment was eventually deposited as the tunnel valley infill. Taking into account a high uncertainty related to the facies of TV sedimentary infill, which thus far has been inferred from seismic reflection surveys only, this study offers the first comprehensive set of data on the composition and provenance of the offshore Elsterian TV sediment. [ABSTRACT FROM AUTHOR]

Here, we present new sedimentary data of the amber bearing layer from the Holocene coastal plain on the SW Saaremaa Island where amber is not known in sedimentary successions but is common in Stone Age and Bronze Age archaeological sites. A layer of buried organic matter ( BOM), sandwiched between sandy coastal deposits and containing pieces of natural amber, was discovered during fieldwork and analysed in detail. Results show that the BOM layer is buried under approximately 90-cm-thick sandy coastal deposits and consists of the remains of different coastal plants. Palaeogeographical reconstructions and sediment compositions indicate that the layer was deposited in the coastal zone and buried quickly by sandy marine sediments. According to AMS radiocarbon dating of knotgrass seeds ( Polygonum lapathifolium), deposition of the BOM layer took place in the Late Bronze Age; about 2.7-2.5 cal. ka BP. Infrared spectra and isotopic composition of the analysed amber from the BOM layer indicate Baltic amber, also known as succinite. The stable isotope ratio indicates the origin of the amber to be south of Estonia. Therefore, it is proposed that the amber was probably transported to Saaremaa within organic matter (along the main SW- NE orientated current flows) from the SE coast of the Baltic Sea where secondary Baltic amber deposits are known to exist widely. Amber items are common in Late Bronze Age settlement sites and burials in Saaremaa and are considered to originate from present-day Latvia, Lithuania, Kaliningrad district (Russia) and Poland. The current study shows that during the Late Bronze Age natural amber accumulated in the coastal zone of Saaremaa Island and that the islanders could collect it. Therefore, the possibility exists that some Bronze Age archaeological amber objects could be made of local material as opposed to being a result of trade with southern neighbours, as formerly thought. [ABSTRACT FROM AUTHOR]

The Bornholm Basin has experienced a complex history linked closely to the structural development of the Tornquist Zone strike-slip fault system. The latest major tectonic development was late Cretaceous and early Tertiary Rønne Graben inversion caused by dextral transpressional strike-slip movements focused around rigid blocks such as Bornholm. By applying the strike-slip concept, it is possible to show that the Rønne Graben inversion push-up structure was created by restraining left step-over. The fault system continues northwest and north of Bornholm where the strike-slip movement resulted in right step-over and the formation of a pull-apart basin: the northern part of the Bornholm Basin. Detailed seismo-acoustic and sediment core studies show that, despite a rather uniform present bathymetry in the central part of the Bornholm Basin, the Quaternary deposits mirror the pull-apart basin synsedimentary depositional pattern with depocentres close to the major normal faults, bounding the Christiansø Ridge. IODP Site M0065 penetrated a secondary fault zone and provided detailed information on neotectonic events and on environmental changes during the Holocene. The generally rather homogeneous sediments in the cores indicate a dominance of oxic conditions in the Bornholm Basin during the Holocene. However, strong internal seismic reflectors, indirectly reflecting variations in the sediment density and the reflection coefficient, were caused by a shift to stronger laminated, organic-rich sediments that were deposited during the Medieval Warm Period (MwP). The variable depth positions of the MwP-related strong reflectors indicate large differences in the spatial and temporal sedimentation pattern in the Bornholm Basin. These differences in the depositional environment may have been caused by local neotectonic events in the basin. [ABSTRACT FROM AUTHOR]

The piedmont aeolian sediment in Central Asia is has been widely used for Quaternary palaeoclimatic reconstructions. Here we present detailed sedimentological and rock magnetic investigations on 188 samples from the ~9.4-m-thick Urumqi River section ( URS) in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland. Optically stimulated luminescence ( OSL) dating constrains the time-span of the URS loess sedimentation from c. 28 to c. 6.8 ka. This chronology implies that the onset of the URS loess sedimentation is approximately synchronous with the Shangwangfeng Glaciation ( MIS 2) in the headwaters of the Urumqi River. Analyses of sediment grain size and rock magnetic parameters indicate that sediment grain-size composition controls magnetic properties of the URS loess, i.e. the wind intensity model, distinct from the pedogenic model interpreting the variations in magnetic properties of the loess in the Chinese Loess Plateau ( CLP). Overall, the variations in sediment grain size and magnetic properties throughout the URS indicate that the present study area was dominated by a climate of strengthened wind associated with gradually intensified aridity during the latest Pleistocene. In contrast, the intensity of aridity and coldness during the early Holocene gradually became relatively weakened. [ABSTRACT FROM AUTHOR]

During the Middle Pleistocene late Saalian glaciation of northern central Europe numerous pro-glacial lakes formed along the southwestern margin of the Scandinavian Ice Sheet. Little is known about the drainage history of these lakes, the pathways of glacial lake outburst floods and their impacts on erosion, sedimentation and landscape evolution. This study investigated the impact of the late Saalian Weser and Münsterland Lake (Germany) outburst floods. In particular, we reconstructed the routing and flow dynamics of the lake outburst flood and analysed the flood related sediments. We employed one-dimensional hydraulic modelling to calculate glacial lake outburst flood hydrographs. We modelled the flow pathway and local flow conditions along the pathway based on the boundary conditions of two different hydrographs and two different ice-margin positions. The modelling results were compared with geomorphological and sedimentological field data in order to estimate the magnitude and impact of the flood on erosion and sedimentation. Two major lake drainage events are reconstructed for the study area, during which approximately 90-50 km3 of water was released. Modelling results indicate that the lake outburst floods created a high-energy flood wave with a height of 35-50 m in confined valley areas that rapidly spread out into the Lower Rhine Embayment eventually flowing into the North Sea basin. The sedimentary record of the outburst floods comprises poorly sorted coarse-grained gravel bars, long-wavelength bedforms and sandy bedforms deposited by supercritical and subcritical flows. Some parts of the sandy flood deposits are rich in reworked mammoth bones or mammoth and horse teeth, pointing to reworking of older fluvial sediments, hydraulic concentration and subsequent re-sedimentation of vertebrate remains. These deposits are preserved in sheltered areas or at high elevations, well above the influence of postglacial fluvial erosion. The flood-related erosional features include up to 80-m-deep scour pools, alluvial channels and streamlined hills. [ABSTRACT FROM AUTHOR]

Physical evidence for the drainage of glacial lakes remains relatively rare in depositional records, giving rise to much debate on the location of outlets and discharge pathways, as well as on the climate impact of the attendant meltwater forcing. Lake Ojibway developed following the withdrawal of the Laurentide Ice Sheet in northern Ontario and Quebec, Canada. The late-stage evolution of this large ice-dammed lake was influenced by the complex dynamics of the retreating ice margin, which highly complicates the identification of the termination of Lake Ojibway in glaciolacustrine sediment records. Here, we document the composition of sections of rhythmites that contain in their upper part an anomalously thick and whitish bed (10-15 cm) that is in turn overlain by ~1 m of faintly bedded rhythmites. Grain-size analyses showed that the thick whitish bed consists primarily of fine to coarse silt (2-63 µm), contrasting with the lower and upper rhythmites that are largely dominated by clay (<2 µm). The detrital carbonate content of the thick silt bed is characterized by consistently high values (2.5 to 2.8%), whereas the bounding rhythmites show lower and highly variable values. Oxygen isotope measurements further show a marked change going from typical glacial meltwater values (- -29.6 to -27.7‰; VSMOW) for the lower rhythmites and the silt bed to modern-like meteoric values (-18.4 to -14.6‰) for the uppermost rhythmites. These data suggest that this marker bed may be associated with a major drawdown event that possibly corresponds to the final drainage of Lake Ojibway. AMS radiocarbon dating of ostracods extracted from the drainage bed also documents an important hardwater effect within the Ojibway basin. [ABSTRACT FROM AUTHOR]

The Late Pleistocene stratigraphy from the Severnaya Dvina- Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre- Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67−62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time-span. Blocking and reversal of fluvial drainage started again around 21−20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17−15 ka ago. At that time, an ice-dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka. [ABSTRACT FROM AUTHOR]

Analysis of a high-resolution suite of modern glacial sediments from Jostedalen, southern Norway, using a portable optically stimulated luminescence ( OSL) reader, provides insights into the processes of sediment bleaching in glacial environments at the catchment scale. High-magnitude, low-frequency processes result in the least effective sediment bleaching, whereas low-magnitude, high-frequency events provide greater bleaching opportunities. Changes in sediment bleaching can also be identified at the scale of individual bar features: tails of braid-bars and side-attached bar deposits have the lowest portable reader signal intensities, as well as the smallest conventional OSL residual doses. In addition to improving our understanding of the processes of sediment bleaching, portable reader investigations can also facilitate more rapid and comprehensive modern analogue investigations, which are commonly used to confirm that the OSL signals of modern glacial sediments are well bleached. [ABSTRACT FROM AUTHOR]

The nature of permafrost and related environmental conditions in the Weichselian Late Pleniglacial and Lateglacial are reconstructed based on the assessment of frost structures that are best documented in the Loess Belt and in plateau areas composed of glacial till. Investigations were conducted in the central-eastern part of the European Sand Belt ( SE Poland and NW Ukraine) on a fluvio-aeolian sedimentary succession and took into account its chronological context given by luminescence dating. Various generations of periglacial structures found in these deposits indicate not only the development of permafrost (ice-wedge pseudomorphs) and decreased humidity (composite wedge casts) but also the degradation of permafrost (large-scale involutions) and, finally, the establishment of deep seasonal frost (frost cracks). The diversity of structures in the study region appears to result from local conditions rather than increasing continentality of climate towards the east. [ABSTRACT FROM AUTHOR]

Hafnium ( Hf) and zirconium ( Zr) concentrations measured in over 4100 agricultural soil samples from Europe were assessed with the focus on their relationship to the distribution of aeolian deposits, such as loess and coversands. Comparison of extractable ( aqua regia; ICP-MS) and total ( XRFS) concentrations shows that only 1.0 to 1.7% of the total Hf and Zr is chemically extractable because of the resistant nature of their host minerals. Resistate minerals, such as zircon, are commonly found in the predominantly silty fraction of loess deposits. In this study a statistical analysis of total Hf and Zr soil data from areas with and without loess was carried out to derive threshold values of 10 mg kg−1 ( Hf) and 318 mg kg−1 ( Zr). These values were subsequently applied across the project area in an attempt to indicate the presence of aeolian deposits. The spatial distribution of above-threshold concentrations suggests a more extensive and coherent loess belt across central and eastern Europe, providing additional evidence of loess across Brittany, Aquitaine and near the Vosges mountains in France as well as in the basins of central and northern Spain. Above-threshold concentrations were also detected in loess regardless of its thickness, emphasising the importance of the abundance of zircon in the upper part of the soil profile rather than the actual thickness of the deposit. Soil data however, failed to indicate various loess facies within most of the Pannonian Basin, suggesting that this approach only works where deposits contain a sufficient amount of zircon. This may also explain why the extensive coversands across northern Germany and Poland were largely undetected. This study demonstrates that continental-scale soil geochemical data can help identify and map the distribution of zircon-rich loess and coversand, and subsequently enhance and improve current knowledge of the extent of these deposits. [ABSTRACT FROM AUTHOR]

The lithostratigraphy of pre- Late Weichselian sediments and OSL-dating results from four localities in the Suupohja area of western Finland, adjacent to the centre of the former Scandinavian glaciations, are presented. The studied sections expose glacifluvial, quiet-water, littoral and aeolian deposits overlain by Middle and/or Late Weichselian tills. Litho- and biostratigraphical results together with seven OSL age determinations on buried glacifluvial sediment at Rävåsen (94±15 ka) and on till-covered littoral and aeolian sediments at Risåsen, Rävåsen, Jätinmäki and Kiviharju (79±10 to 54±8 ka), accompanied by previous datings and interpretations, suggest that the glacifluvial sediments at Risåsen were deposited at the end of the Saalian Stage ( MIS 6) and those at Risåsen were deposited possibly in the Early Weichselian Substage (MIS 5d?). Palaeosol horizons and ice-wedge casts together with the dated littoral and aeolian sediments between the Harrinkangas Formation ( Saalian) and the overlying till(s) indicate that western Finland was ice-free during most of the Weichselian time. Littoral deposits, dated to the Middle Weichselian ( MIS 4-3), occur at altitudes of 50-90 m a.s.l., which indicates significant glacio-isostatic depression. The depression resulted from expansion of the ice sheet in the west of Finland at that time. [ABSTRACT FROM AUTHOR]

We provide evidence for the subglacial to ice-marginal successive deposition of the Lohtaja− Kivijärvi ice lobe margin esker influenced by the changes in the meltwater delivery and proglacial water depth within the Finnish Lake District lobe trunk during the last deglaciation in Finland. The study is mostly based on the sedimentological data from the 100 km long esker chain with 15 logged sites. The long breaks in the lobe margin esker and the re-emerged deposition along the stable position of the subglacial meltwater route were related to the discontinuities and reappearances of the neighbouring eskers. This considerable variability in the meltwater discharge and debris transport under the described deglacial conditions cannot be explained by markedly decreased meltwater production due to palaeoclimatic factors or lack of debris within the trunk region. The primary control on the changes in meltwater availability and related esker deposition was thus due to the spatial and temporal changes in ice mass properties and shifting of the meltwater flow paths within the trunk. These changes were initiated by the topographically higher and partly supra-aquatic Suomenselkä watershed area with subsequent deepening of the proglacial water during the deglaciation. The understanding of the long-lived esker deposition along the former ice-stream trunk margin adds to the evaluation of palaeoglaciological reconstructions and geomorphologically based spatial models for ice-stream landscapes. [ABSTRACT FROM AUTHOR]

We document the Lateglacial to Holocene sedimentation and vegetation history of a small, infilled crater landform in the West- Eifel Volcanic Field ( WEVF; western Germany). We analysed geomorphological landform change, sedimentological and geochronological data, pollen, and plant macrofossils of a 16-m-long sediment core from the Eichholz Maar ( EHM). The EHM erupted between ∼20 and 15 ka ago ( MIS 2). Lacustrine siliclastic infilling was completed about 7500 years ago. Lateglacial rates of sedimentation are generally 2 to 5 times higher than in other maar lakes of the WEVF. Local factors, therefore, overprint the relative efficacy of the climate-controlled variance of sedimentation rates at the Lateglacial/ Holocene transition. The predominance of local factors relates to inherent geomorphological process-response mechanisms that were triggered by the EHM eruption. Rapid crater infilling and its completion by the mid- Holocene are attributed to a combination of small storage capacity and geomorphological activity. A late Boreal interval of significant lake-level fall can, however, be attributed to a period of continental-scale climate change as recorded in other European lacustrine settings. Our findings highlight the importance of utilizing geomorphological information to reveal the relative significance of local controls as opposed to climate control when investigating small-sized lake settings with active sediment supply systems. [ABSTRACT FROM AUTHOR]

In the present investigation, an age model of carbonate-rich cores from a seamount top in the Central Indian Basin ( CIB) was constructed using both isotopic (230 Thexcess, AMS 14 C, oxygen isotopes) and biostratigraphic methods. The chronologies using the two methods are in good agreement, yielding a record of the late Middle Pleistocene to the Pleistocene-Holocene transition (550 to 11.5 ka). The first appearance datum ( FAD) of the radiolarian Buccinosphaera invaginata (180 ka) and coccolith Emiliania huxleyi (268 ka) and the last appearance datum ( LAD) of the radiolarian Stylatractus universus (425 ka) were used. A monsoon-induced productivity increase was inferred from carbonate, organic carbon and δ13C records in response to the Mid- Brunhes Climatic Shift ( MBCS), consistent with an increased global productivity. While the coccolith diversity increased, a decrease in coccolith productivity was found during the MBCS. At nearly the same time period, earlier records from the equatorial Indian Ocean, western Indian Ocean and eastern Africa have shown an increased productivity in response to the influence of westerlies and increased monsoon. The influence of easterlies from Australia and the intensification of aridity are evidenced by increased kaolinite content and clay-sized sediments in response to the MBCS. An increased abundance of Globorotalia menardii and other resistant species beginning from marine isotope stage ( MIS) 11 and the proliferation of coccolith Gephyrocapsa spp. indicate increased dissolution, which is consistent with the widespread global carbonate dissolution during this period. The relatively high carbonate dissolution during the transition period of MIS 3/2 and glacial to interglacial periods ( MIS 6, 7 and 8) may be due to the enhanced flow of corrosive Antarctic Bottom Water ( AABW) into the CIB. [ABSTRACT FROM AUTHOR]

In unconsolidated sediments subject to strain, clays and silts are realigned into particular optical birefringent arrangements (plasmic fabrics), which provide information on the style and intensity of sediment deformation. A relatively new, non-destructive, optical microscopy technique for automatically recording and quantifying birefringence (previously commercialized under the name ' Metripol') is pioneered in this study as a valuable and innovative micromorphological tool with which to examine deformation in unconsolidated sediments. Metripol is applied to unistrial plasmic fabric in glaciotectonized and ice keel scoured sediment from the Netherlands and former Glacial Lake Agassiz ( Manitoba, Canada) respectively. Colour-coded images are produced in which colour represents relative optical retardation and thus optical anisotropy through the quantity |sinδ| and optical orientation of anisotropy through the angle Ø (also indicated by linear azimuths). In this study Metripol typically demonstrates that the better developed the unistrial plasmic fabric is, the higher the |sinδ| values, the larger the areas of high |sinδ| values, and the longer and more densely populated the azimuths. In addition, some unistrial plasmic fabrics under Metripol demonstrate lower |sinδ| than previous examples and the surrounding sediment, despite being 'perceived' as demonstrating higher birefringence under a standard petrographic microscope. This is particularly true in clay-rich sediments and has implications for the way we currently describe and interpret unistrial plasmic fabrics in unconsolidated sediment. Finally, the identification and quantification of additional structures that would otherwise have gone undetected using a standard petrographic microscope (e.g. linear and circular structures that are likely to represent discrete shears and skelsepic plasmic fabric, respectively) highlight the potential for Metripol to gather information on the deformation history of unconsolidated sediments that is unavailable to standard techniques. [ABSTRACT FROM AUTHOR]

Hydrofracture systems are being increasingly recognized within subglacial to ice-marginal settings and represent a visible expression of the passage of pressurized meltwater through these glacial environments. Such structures provide a clear record of the fluctuating hydrostatic pressure and of the resulting brittle fracturing of the host sediment/bedrock and the pene-contemporaneous liquefaction and introduction of sediment-fill. A detailed macro- and microstructural study of a hydrofracture system cutting Devonian sandstone bedrock exposed at the Meads of St John, near Inverness ( NE Scotland), has revealed that this complex multiphase system was active over a prolonged period and accommodated several phases of fluid flow. The main conduits that fed the hydrofracture system are located along bedding within the sandstone, with the site of the wider, steeply inclined to subvertical, transgressive linking sections being controlled by the contemporaneous development of high-angle fractures and normal faults, the latter occurring in response to localized extension within the bedrock. A comparison with published engineering hydraulic fracturing data indicates that the various stages of sediment-fill deposited during a flow event can be directly related to the fluctuation in overpressure during hydrofracturing. A model is proposed linking the evolution of this hydrofracture system to the retreat of the overlying Findhorn glacier. The results of this study also indicate that the development and repeated reactivation of subglacial hydrofracture systems can have a dramatic effect on the permeability of the bed, influencing the potential for overpressure build-up within the subglacial hydrogeological system, and facilitating the migration of meltwater beneath glaciers and ice sheets. [ABSTRACT FROM AUTHOR]

The Provo shoreline of Lake Bonneville formed following the Bonneville flood, and, based on previous dating, was formed during a period of overflow from about 17.5 to 15.0 cal. ka. In many places the Provo shoreline consists of a pair of distinct shorelines, one ∼3 m higher than the other. We present data from two cuts through double beaches to show that the upper beach is younger and represents sedimentation after a lake-level rise. In addition, the lower beach deposits are internally stratified by beds that suggest three more lake-level rises during its development. The Provo beach complex thus appears to have been built during rising lake levels, which can be explained by rises in the overflow threshold by sequential landslide deposition. Evaluation of beach altitudes demonstrates that the two beach crests throughout the Bonneville basin experienced equivalent rebound from removal of the lake load, and therefore they formed after the rebound associated with the Bonneville flood occurred in early Provo time. However, radiocarbon ages on gastropods collected within the beach deposits suggest both that the sequence of five beach deposits formed from c.18.1 to c. 17.0 cal. ka, and that the Bonneville flood occurred before 18 cal. ka. These ages are discordant with previous dates on shells within offshore sands, and raise questions about the validity of radiocarbon ages for shells in Lake Bonneville as well as about the age of the Bonneville flood and Provo shoreline. The timing for maximum Provo lake depths and its association with climate stages during deglaciation remain unresolved. [ABSTRACT FROM AUTHOR]

Flakket on the island of Anholt in Denmark is a cuspate foreland facing the microtidal Kattegat sea. It is composed of a number of beach ridges typically covered by dune sand and separated by swales and wetlands. OSL dating indicates that the evolution of Flakket began c. AD 1000. Foreland growth was punctuated by a major episode of coastal reorganization leading to coastal retreat c. AD 1800. Coastal retreat led to the formation of an erosion surface that separates older and higher-lying beach-ridge and swale deposits from younger and lower-lying deposits. The palaeo-sea level is deduced from the architecture of the deposits, and interpretation of ground-penetrating radar data and geomophological observations indicates that relative sea level was about 1.90±0.25 m above present sea level c. AD 1000, but about 0.00±0.25 m relative to present sea level c. AD 1830 and c. AD 1870. Anholt is situated at the margin of the uplifted Fennoscandian area; assuming uplift to be about 1.2 mm a−1 it follows that absolute sea level was about +0.70±0.25 m at AD 1000, but around −0.22±0.25 m at AD 1830 and around −0.17±0.25 m at AD 1870. Within the uncertainties of the age control, the sea-level indicators mapped by ground-penetrating radar reflections and the variability of estimates of uplift found in the literature, the result obtained for AD 1000 is consistent with findings from the Stockholm area in Sweden and with a recently published global sea-level curve. [ABSTRACT FROM AUTHOR]

Core 86027-144 (74°15.56′ N, 91°14.21′ W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal δ18O and δ13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8 cal. ka BP) records deglaciation, ice-sheet destabilization, float-off and subsequent break-up. Zone II ( c. 10.8-10.4 cal. ka BP) shows ice-proximal to ice-distal glaciomarine conditions, interrupted by pervasive land-fast sea-ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4-9.9 cal. ka BP), where planktonic foraminifera ( N eogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW-SE; however, the deep-water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open-water season greater than present) in Zone IV (9.9-7.8 cal. ka BP) perhaps corresponds to the regional 'Holocene Thermal Maximum' previously proposed. A transitional period (Zone V; 7.8-6.7 cal. ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea-ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio-isostatic shallowing of inter-island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea-ice and modern microfossil assemblages, commence at c. 6.7 cal. ka BP (zones VI- VII). Although climate ultimately forces long-term environmental trends, core 86027-144 data imply that regional dynamics, especially changes in sea-level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago. [ABSTRACT FROM AUTHOR]

Horsák, M. 2010: Mollusc assemblages in palaeoecological reconstructions: an investigation of their predictive power using transfer function models. Boreas, Vol. 40, pp. 459-467. 10.1111/j.1502-3885.2010.00195.x. ISSN 0300-9483. Fossil mollusc assemblages are commonly used to reconstruct past environments, as their shells are abundant in various types of calcium-rich deposits. However, it is impossible to exactly evaluate estimates derived from fossil data using directly measured factors. To assess the accuracy of environmental variables derived from mollusc species composition, two modern data sets (training and test), each consisting of 73 samples of treeless fen communities, were constructed along with known local and climatic variables. The main predictors of species composition were isolated using canonical correspondence analysis and forward selection with the Monte Carlo permutation test. The accuracy of prediction for those factors that were significant in the forward selection was studied via four commonly used transfer function models. Three independent gradients of species composition driven by calcium content, moisture and temperature were detected. The best predictions were found for variables that correlated with the main changes in species composition. The strongest correlation between the predicted and measured values of the test data set was observed for water conductivity ( r=0.86), a good proxy of calcium content. The locally weighted-weighted averaging transfer function model performed best out of all the models for the majority of variables tested. Mollusc assemblages were found to be useful for estimating local environmental variables based on a given species composition. Along with the specific advantages of mollusc fossil material, there is much potential for the use of their fossil assemblages to reconstruct palaeoenvironmental variables using transfer function models calibrated from recent compositional data and directly measured factors. [ABSTRACT FROM AUTHOR]

Ó Cofaigh, C., Evans, D. J. A. & Hiemstra, J. F. 2010: Formation of a stratified subglacial 'till' assemblage by ice-marginal thrusting and glacier overriding. Boreas, 10.1111/j.1502-3885.2010.00177.x. ISSN 0300-9483. A thick sequence of glaciotectonically stacked till and outwash is preserved in a coastal embayment at Feohanagh, southwest Ireland. The sequence contains a variety of diamicton lithofacies, including laminated, stratified and massive components, but stratified diamictons dominate. Stratification/lamination is imparted by the presence of numerous closely spaced subhorizontal and anastomosing partings, which give a fissile appearance to the diamictons. Many partings are the result of sandy or thin gravelly layers within the diamictons. Some diamictons contain interbeds and lenses of sand, mud and gravel, which still preserve the original stratification. The sequence at Feohanagh is the product of a two-stage depositional process in which initial glaciolacustrine sedimentation in an ice-dammed lake was followed by glaciotectonic thrusting and overriding, during which the lake sediments were reworked and variably deformed. Similar late Quaternary sequences of glaciotectonically stacked stratified sediments and till have been described from around the coastal margins of Ireland and Britain, where they constitute glaciotectonite-subglacial traction till continuums rather than true lodgement tills as traditionally implied. Thick stratified diamicton assemblages are likely to occur in areas where steep topography provides pinning points for the glacier margin to stabilize and deliver large volumes of sediment into a glaciolacustrine or glaciomarine setting before proglacial and subglacial reworking of the sediment pile. The resulting geological-climatic unit, often defined as 'till', will contain a large amount of stratified and variably deformed material (laminated and stratified diamictons will be common), including intact sediment rafts, reflecting low strain rates and short sediment transport distances. [ABSTRACT FROM AUTHOR]

The morpho-sedimentary anisotropy of a field of moraine ridges, classified previously as ribbed moraine, was studied by means of ASTER satellite data, airborne radiometric (AR) data, digital elevation models (DEMs) and azimuthal measurement of electrical conductivity (σa) in Kivitaipale, south-central Finnish Lapland. The 20 km long corridor of moraine ridges is diagonally oriented to the youngest (Late Weichselian) active-ice streamlined features and presumably dates back to post-Younger Dryas. The maximum σa anisotropy of sediments is parallel to the orientation of the ridge crests. Crudely to well stratified gravels and sands of glaciofluvial open channel origin and moderately sorted sediments attributed to glaciofluvial sliding bed facies are exposed in the cores of the ridges, whereas signs of (basal) till cover or glaciodynamic deformations are absent. On the basis of morpho-sedimentary anisotropy, we contend that the origin of the studied corridor of ridges is linked to subglacial outburst event(s) rather than a transverse-to-ice-flow origin of ribbed moraine. The triggering mechanism for the outburst(s) remains unresolved, yet the timing of outburst(s), concurrent with the maximum post-Younger Dryas fault instability, may imply that earthquake(s) contributed to subglacial drainage. [ABSTRACT FROM AUTHOR]

Two new long sediment cores (EC1 and EC3), recovered from different locations within the infilled basin at Les Echets, France, provide a new high-resolution record of terrestrial and lacustrine responses to climatic changes during Marine Isotope Stages (MIS) 3 and 2. The lithologies of the cores are described in detail and correlated with each other by stratigraphic marker horizons, fluctuations in organic matter and AMS radiocarbon ages. The tentative correlation of the new cores to those described and analysed by de Beaulieu et al. (1980) and de Beaulieu & Reille (1984a) provides a preliminary chronostratigraphic framework. Sedimentation during MIS3 started with accumulation of sands and silts and was followed by alternating gyttja and clayey gyttja silts. Exceptionally high sedimentation rates during MIS2 led to the infilling of the basin. Alternating organic-rich and minerogenic-rich sediments appear to coincide with changes in pollen assemblages (de Beaulieu & Reille 1984a) and suggest that millennial-scale climatic changes controlled lake productivity and catchment stability during most of MIS3. [ABSTRACT FROM AUTHOR]

Boulders resting on meltwater-sculpted and striated-granite bedrock near the head of the southern outlet spillway of glacial Lake Agassiz are used to generate paleodischarge calculations. The rounded nature of many boulders suggests fluvial transport and a corestone origin. The distribution of boulders in clusters and linear trains records the interaction of clasts during transport and deposition. The geomorphology of the spillway with streamlined erosional remnant hills is characteristic of other large flood spillways. Using the Manning equation and a variety of empirical equations to determine paleovelocity, preferred discharges between 0.364 and 0.102 Sv are calculated. These discharges agree well with flood discharges using modeling methodologies, and most likely represent ephemeral and catastrophic flood events linked to either episodic incision at the outlet or the result of rapid inputs of meltwater to Lake Agassiz. [ABSTRACT FROM AUTHOR]

Bracketing ages on marine-freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about -15 m from 14 000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 m a -1 , similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a -1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet. [ABSTRACT FROM AUTHOR]

Interpretation of indicator dispersal trains preserved in till sheets is widely used to investigate past glacial processes and to explore for buried bedrock mineralization. We present a conceptual model of erosion and entrainment and transport of indicator material in a glacial system. Indicator concentration in an individual size fraction of till is controlled by dilution and comminution. Dilution is the result of incorporation of additional material to the glacier's debris load down-ice of the indicator source, and is described in terms of erosivity and erosion length scale. Erosivity describes the amount of bed material eroded along a flowline, and is a function of both bed properties and the erosive power of the glacier. Erosion length scale describes the persistence of an indicator dispersal signal during transport, and controls both the maximum total indicator concentration and the eventual length of apparent dispersal. We adapt a modified batch grinding particle comminution model to describe breakdown of indicator material during transport and modification of the indicator particle size distribution. Indicator dispersal concentrations are the product of dilution and comminution processes. [ABSTRACT FROM AUTHOR]

The occurrence of sandy clay deposited in a warm marine environment just below the till of the last glaciation has created controversy about its age and stratigraphic position in the sedimentary basin of the Kola Peninsula. Data on marine microfauna, diatoms, malacofauna and pollen composition indicate that during the period when the sandy clay was deposited the climate was similar or even warmer than at present. According to 14C dates, sedimentation of the sandy clay occurred around 40 ka BP. Based on these data, some researchers have attributed these marine deposits to the third Late Pleistocene Belomorian (sensu Lavrova 1960) interglacial transgression. At the same time there are geological indications suggesting re-deposition of these subtill sediments. To solve this problem we have reinvestigated the subtill interglacial marine deposits from the Varzuga section (∼66.4°?N and 36.6??E). Four different marine shell species and enclosing sandy clay sediments taken from the subtill marine unit of the section were dated by the electron spin resonance (ESR) and optically-stimulated luminescence (OSL) methods at about 103 and 104 ka, respectively. The results indicate that the subtill marine deposits belong to the first Late Pleistocene Boreal transgression that, according to our previous studies of the marginal areas of the Eurasian North, has occurred in the time interval from approximately 145 to 70 ka BP. [ABSTRACT FROM AUTHOR]

Macroscopic observation, thin-section analysis and electron microscope study were used in a detailed examination of till exposed in a valley escarpment. The till displays two kinds of bedding: (1) beds of different colour (lithology) that are not separated from one another by distinct boundaries, and (2) beds that are separated by distinct subhorizontal planes of discontinuity, commonly consisting of several beds of the first type. Beds showing no clear separation are interpreted as having been deposited through continuous lodgement, while the distinct discontinuities most probably record sliding planes of the glacier sole during breaks in till deposition. These features, along with the qualitative and quantitative microscopic evidence, indicate that the lower and middle parts of the till were deposited by hard lodgement. The process of deposition was interrupted several times by episodes of non-deposition, some of them accompanied by glacial erosion. The upper part of the till was deposited by continuous lodgement that was transitional between hard and soft lodgement processes. Such a succession indicates the prevalence of a cooler subglacial thermal regime which changed upwards into a milder one. The till examined displays mainly brittle deformation — namely Riedel shears that are primarily concentrated between the subhorizontal discontinuities characteristic of the lower and middle parts of the section. A dense set of Riedel shears also cuts thicker portions of the upper part of the till and, in some places, such shears combine along additional subhorizontal (discrete) shear planes. The direction of the fractures, as well as the strong fabric orientation of stone a-axes within the till, indicate an ice flow in the studied area from NW to SE. [ABSTRACT FROM AUTHOR]

The present study examines sedimentation rates in the eastern Gotland Basin using a variety of methods that reveal considerable heterogeneity in the rates, both spatially and temporally. High-resolution seismic recordings and correlation with long sediment cores indicate increased thickness of strata and higher sedimentation rates (0.75 mm a[sup -1]) in the eastern part of the basin than in the western part (0.23 mm a[sup -1]) since the Littorina transgression some 8000 [sup 14]C years BP. This difference is apparently a consequence of a counterclockwise near-bottom circulation in the basin with periodically high current speeds that cause winnowing on the steep SE slope of the basin and differential settling of sediments in areas of low current speeds. On shorter time scales, recent sediment accumulation rates based on radiometric dating ([sup 210]Pb) are in general twice as high as those observed 25 years ago using the same method. The higher modern rates, compared to those of the 1970s, may partly be due to increased eutrophication, as more carbon is buried in the sediment, and partly due to increased erosion in shallow water areas. However, strong lateral variations are evident. The average sediment accumulation rates vary between 119 and 340 g m[sup -2] a[sup -1] (corresponding to sedimentation rates of 2.1-2.5 mm a[sup -1]) in the deepest part of the basin. Very high rates (6100 g m[sup -2] a[sup -1], corresponding to sedimentation rates of 30 mm a[sup -1]) are observed on an intraslope basin site (offshore Latvia) at a water depth of only 70 m. The radiometrically determined sediment accumulation rates are up to three times higher than those estimated from average water column concentrations of suspended matter and from sediment trap flux rates. The discrepancy suggests that sedimentation in the deep basin may have a substantial contribution from near-bottom lateral transport. [ABSTRACT FROM AUTHOR]

Glacial deposits and landforms, interpreted from the continuous seismic reflection data, have been used to reconstruct the Late Weichselian ice-sheet dynamics and the sedimentary environments in the northeastern Baltic Sea. The bedrock geology and topography played an important role in the glacial dynamics and subglacial meltwater drainage in the area. Drumlins suggest a south–southeasterly flow direction of the last ice sheet on the Ordovician Plateau. Eskers demonstrate that subglacial meltwater flow was focused mostly within bedrock valleys. The eskers have locally been overlain by a thin layer of till. Thick proximal outwash deposits occupy elongated depressions in the substratum, which often occur along the sides of esker ridges. Ice-marginal grounding-line deposit in the southern part of the area has a continuation on the adjacent Island of Saaremaa. Therefore, we assume that its formation took place during Palivere Stadial of the last deglaciation, whereas the moraine bank extending southwestward from the Sõrve Peninsula is tentatively correlated with the Pandivere Stadial. The wedge-shaped ice-marginal grounding-line deposit was locally fed by subglacial meltwater streams during a standstill or slight readvance of the ice margin. The thickness of the glacier at the groundingline was estimated to reach approximately 180 m. In the western part of the area, terrace-like morphology of the ice-marginal deposit and series of small retreat moraines 10–20 km north of it suggest stepwise retreat of the ice margin. Therefore, a rather thin and mobile ice stream was probably covering the northeastern Baltic Sea during the last deglaciation. [ABSTRACT FROM AUTHOR]

Shallow seismic profiling indicated the presence of a drowned lagoon-barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island-lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths. [ABSTRACT FROM AUTHOR]

The Holocene depositional setting of the Laptev Sea was studied using three marine sediment cores from water depths between 77 and 46 m. Based on sedimentary parameters (TOC content, δ[sup 13]C[sub org], sedimentation rates) controlled by radiocarbon age models the palaeoenvironment of a strongly coupled river-shelf system was reconstructed since ∼11 ka BP. Caused by a transgressing sea after the last glaciation, all cores reveal progressive decreases in sedimentation rates. Using the sedimentary records of a core from the Khatanga-Anabar river channel in the western Laptev Sea, several phases of change are recognized: (1) an early period lasted until ∼10 ka BP characterized by an increased deposition of plant debris due to shelf erosion and fluvial runoff; (2) a transitional phase with consistently increasing marine conditions until 6 ka BP, which was marked at its beginning near 10 ka BP by the first occurrence of marine bivalves, high TOC content and an increase in δ[sup 13]C[sub org]; (3) a time of extremely slow deposition of sediments, commencing at ∼6 ka BP and interpreted as Holocene sea-level highstand, which caused a southward retreat of the depositional centres within the now submerged river channels on the shelf; (4) a final phase with the establishment of modern conditions after ∼2 ka BP. [ABSTRACT FROM AUTHOR]

The laminated sediments at Pudozh in eastern Karelia are generally assumed to have been deposited between 13 000 and 16 000 [sup 14] C yr BP and have been used to date the recession of the active ice margin. However, 17 AMS [sup 14] C measurements performed on terrestrial plant macrofossils contained in these sediments show that deposition began during the late Allerød, when the ice margin had already receded to the northern part of Lake Onega. Based on an age model, we assume that the 1933-year-long varved sequence covers the time period between c. 12 900 and 11 000 calendar years BP. During this period, which comprises the later part of the Late Weichselian and the early Holocene, the local vegetation consisted of open, tree-less dwarf shrub heaths. Increased soil erosion may have occurred before 12 550 calendar years BP. [ABSTRACT FROM AUTHOR]