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Arnold, L. J., Roberts, R. G., MacPhee, R. D. E., Haile, J. S., Brock, F., Möller, P., Froese, D. G., Tikhonov, A. N., Chivas, A. R., Gilbert, M. T. P. & Willerslev, E. 2010: Paper II - Dirt, dates and DNA: OSL and radiocarbon chronologies of perennially frozen sediments in Siberia, and their implications for sedimentary ancient DNA studies. Boreas, Vol. 40, pp. 417-445. 10.1111/j.1502-3885.2010.00181.x. ISSN 0300-9483 The sedimentary ancient DNA ( sedaDNA) technique offers a potentially invaluable means of investigating species evolution and extinction dynamics in high-latitude environments. An implicit assumption of the sedaDNA approach is that the extracted DNA is autochthonous with the host deposit and that it has not been physically transported from older source deposits or reworked within the sedimentary profile by postdepositional mixing. In this paper we investigate whether these fundamental conditions are upheld at seven perennially frozen wetland sites across the Taimyr Peninsula and coastal lowlands of north-central Siberia. Optically stimulated luminescence (OSL) and radiocarbon (C) dating are used to constrain the ages of both the inorganic and organic fractions of perennially frozen deposits from which sedaDNA of extinct and extant species have been recovered. OSL and C age/depth profiles, as well as single-grain equivalent dose (D) distribution characteristics, are used to assess the stratigraphic integrity of these sedaDNA sequences by (i) identifying the presence of primary or reworked organic and inorganic material, and (ii) examining the types of depositional and postdepositional processes that have affected specific sedimentary facies. The results of this study demonstrate that even though DNA preservation and stratigraphic integrity are commonly superior in perennially frozen settings, this does not, in itself, guarantee the suitability of the sedaDNA approach. The combined OSL and C chronologies reveal that certain perennially frozen sites may be poorly suited for sedaDNA analysis, and that careful site selection is paramount to ensuring the accuracy of any sedaDNA study - particularly for 'latest appearance date' estimates of extinct taxa. [ABSTRACT FROM AUTHOR]

Simple cutting devices such as used in the printing industry allow precise and fine sectioning of frozen peats and sediments, thus enabling research with high temporal resolution. Large slices are useful in the collection of multiple synchronous subsamples for multidisciplinary research. This article describes the apparatus (called DAMOCLES) and its operation, and presents some examples from practice. These include combined microfossil, macrofossil and chemical analyses of the same sample with a sample resolution of 0.5 cm (temporal resolution c. 1 year): rapid changes occur that would have remained unnoticed with a coarser sampling distance. The final example presents a sample resolution of only 0.5 mm. These examples illustrate the possible uses of the DAMOCLES apparatus in palaeoecological research. [ABSTRACT FROM AUTHOR]

Similar to planktic foraminifers, findings of bivalves in core sediments are occasional, in this case, largely owing to the small core diameter (sample size) and the relatively large size of valves in comparison with foraminifers and ostracods. ([8]) mix the terms "total abundance" and "species diversity", as is evident from this sentence on p. 10: 'The number of species is on average 22 specimens per g of sediment, and the number of their species is on average 11 species in sample'. ([8]) that the drop in the total abundance and diversity of benthic foraminifers during I c i . 3.6 to 4.6 cal. ka BP probably corresponds to the growing discharge of glacier suspended load and the dilution of microfossils with this material. Korsun & Hald ([4]) studied modern benthic foraminifers and sediments of the northern Novaya Zemlya fjords with tidewater glaciers. [Extracted from the article]

In the lacustrine succession F4‐F5 of the Fucino Basin, central Italy, 20 visible tephra layers were identified in the time interval 250–315 ka (Marine Isotope Stages 8–9). Fifteen of them contained suitable material to explore their volcanic sources. Among these tephra some well‐known eruptions and eruptive sequences of the Roman and Roccamonfina volcanoes were identified, such as the Tufo Giallo di Sacrofano and the Lower White Trachytic Tuff, respectively. Furthermore, the sediment succession documents a more complex eruptive history of the Sabatini, Vulsini, Colli Albani and Roccamonfina volcanic complexes during the investigated period, as inferred from previously undescribed tephra deposits. Single‐crystal‐fusion 40Ar/39Ar dating of two of the inspected tephra layers combined with two already published tephra ages provided the basis for a Bayesian age‐depth model. The modelled tephra ages allow chronological constraining of so‐far undefined eruptions of the Sabatini (272.5±4.7, 281.8±4.7, 308.5±2.8, 312.8±2.1 ka), the Vulsini (311.7±2.3, 311.9±2.3 ka) and the Colli Albani (301.0±3.6 ka) volcanic districts. Two tephra layers of an undefined volcanic source from the Roman volcanoes have modelled ages of 309.5±2.7 and 310.5±2.6 ka. The new 40Ar/39Ar and modelled ages were further used for a reassessment of the timing of already known and dated eruptive units, such as the Tufo Giallo di Sacrofano (40Ar/39Ar: 289.3±4.8 ka). Tephra tentatively correlated with the Valle Santa Maria, Case Pisello and the White Trachytic Tuff Unit E3 or Unit F offer modelled ages for these eruptions of 296.6±3.9, 301.8±3.5 and 303.6±3.4 ka, respectively. The results complete the tephrostratigraphical investigations of the c. 425 ka old F4‐F5 record, extend the Mediterranean tephrostratigraphical framework and provide a significant contribution for improving knowledge on Italian volcanic explosive activity. [ABSTRACT FROM AUTHOR]

Thermokarst ponds are widespread in arctic and subarctic regions, but little is known about their temporal evolution prior to human observations. This paper presents a pioneer biostratigraphic study conducted at a subarctic site with limnologically contrasted ponds located on the eastern shore of Hudson Bay, Canada. Fossil diatom and visible near infrared ( VNIR) derivative spectral analyses were performed on short sediment cores, confirming the occurrence of three distinct stratigraphic facies as already inferred from an anterior sedimentological study: a lacustrine upper facies ( UF) and a marine lower facies ( LF), separated by an organic-rich/peat transitional zone ( TZ). Diatoms were almost absent from LF, but increased significantly in both TZ and UF. Identified diatom taxa were mainly benthic species (e.g. genera Fragilaria, Pinnularia), and their down-core distribution appeared to be related to dissolved organic carbon ( DOC) and possibly pH conditions. Diatom-inferred DOC showed a decreasing trend towards the surface (potentially associated with an increase in pH), inverse to the general trend in this region, suggesting the action of other mechanisms on DOC, such as exhaustion of external inputs from limited catchments and the role of discontinuous peat layers (former surfaces of permafrost mounds) during the initial stages of pond formation. These bryophilous substrates in aerophilic habitats probably controlled diatom community composition. The combination of diatom and VNIR data revealed similar trends between (i) opal (amorphous silica) and diatom abundances; (ii) eukaryotic/prokaryotic algae ratio and anoxia or hypoxia in bottom waters; and (iii) limonite (iron oxide) and redox conditions in surface sediments. These findings indicate that diatom community changes and pond limnological evolution in the recent past were controlled mainly by autogenic processes (e.g. local vegetation/soil development, peat accumulation and erosion), rather than by allogenic forcing mechanisms (e.g. precipitation and temperature, geochemical leaching of the surrounding glaciomarine sediments). [ABSTRACT FROM AUTHOR]

It is a scientist's mission to try to remain unbiased. However, certain factors play a role in scientific analyses that are not controlled by conscious thought. These factors are potentially very important in areas of science where interpretations are based on a scientist's ability to identify patterns or structures. One such area is the micromorphology of glacial sediments. In this paper we investigate the role of an analyst's experience in relation to pattern perception with specific reference to turbate microstructures in glacial diamictons. An experiment was conducted on 52 participants, which demonstrated that, as may be expected, more experienced (glacial) micromorphologists tend to exhibit a higher sensitivity-to-signal, but that complete novices, if given clear instructions, can reach levels of sensitivity similar to those of experts. It also showed, perhaps more surprisingly, that response bias does not decrease with experience. We discuss psychological factors, such as the drive for success and consistency, that may have contributed to these results and investigate their possible implications in the micromorphological analysis and interpretation of glacial sediments. [ABSTRACT FROM AUTHOR]

The ability of glaciers to detach and transport bedrock as glaciotectonic rafts is widely observed throughout Quaternary sections. However, the glaciological, hydrological and geological parameters controlling rafting are currently poorly constrained. There is a lack of structural and sedimentary evidence concerning rafting, and therefore the processes driving raft detachment, transport and emplacement are poorly understood. This paper contributes to our understanding by presenting a macro- and microstructural study of deformation associated with a chalk raft at West Runton, north Norfolk. Detailed thin-section analysis reveals several discrete micro-fabric orientations, representing poly-phase deformation occurring during raft transport and emplacement. A four-stage conceptual model for raft transport and emplacement is proposed, with deformation being partitioned into the relatively weaker Happisburgh Till member, the latter forming the host to the raft. Stage 1 is the main transport phase of the chalk raft, and was dominated by easterly (down-ice) directed ductile shearing. During Stage 2 a narrow ductile shear zone within the Happisburgh Till member propagated upwards through the base of the raft, leading to the detachment of an elongate block of chalk. Attenuated lenses of diamicton in this shear zone possess kinematics recording an easterly directed sense of shear. As deformation progressed, during Stage 3, the detached block impinged on the 'high-strain' zone wrapping the base of the raft, influencing the style of deformation partitioning and leading to localized, up-ice-directed kinematics. Stage 4 represents the final stages of raft emplacement, when the detachment zone at the base of the raft began to 'lock-up'. These results demonstrate the relative importance of the hydrological controls associated with raft transport and emplacement underneath an actively advancing glacier. Furthermore, the model represents an example of how micromorphological analysis can reveal detailed poly-phase deformation histories in deformed glacial sediments. [ABSTRACT FROM AUTHOR]

Tunnel valleys are common throughout the terrain of the Saginaw Lobe of the Laurentide Ice Sheet in southern Michigan. The set of valleys described in this paper is regularly spaced in a radial pattern behind the Kalamazoo Moraine, an ice-marginal position formed during retreat from the Last Glacial Maximum. These valleys are divided into proximal and distal groups lying north and south, respectively, of a major river valley that cross-cuts the tunnel valleys at right angles. Based on a series of rotasonic borings and core analysis, the proximal valleys are shallow, contain minimal sediment fill, and overlie fine-grained diamicton and glaciolacustrine sediment, whereas the distal valleys are deeply incised into the substrate and are partially filled with coarse sediment. The distal valleys terminate within a broad zone of high-relief, hummocky topography representing stagnation and collapse behind the Kalamazoo ice margin. The proximal valleys occur within a more subdued landscape located farther from the ice margin. Although some elements of existing genetic models are consistent with these valleys, none appears to be completely compatible with their stratigraphy and morphology. Initial incision of the valleys could have involved short-lived moderate- to high-discharge flows, followed by deposition during or after the events. The deep incision and thick, coarse sediment in distal valleys in the stagnant marginal zone probably involved supraglacial meltwater draining to the bed as the margin downwasted. Fining-upward eskers inset into the valleys were formed by flows of declining energy in small late-stage conduits. [ABSTRACT FROM AUTHOR]

This paper presents the first detailed sedimentological study of annual moraines formed by an alpine valley glacier. The moraines have been forming since at least AD 1980 by a subsidiary lobe of Gornergletscher, Switzerland that advances up a reverse bedrock slope. They reach heights of 0.5-1.5 m, widths of up to 6 m and lengths of up to several hundreds of metres. Sediments in these moraines are composed of proglacial outwash and debris flow units; subglacial traction till is absent entirely. Based on four representative sections, three genetic process combinations have been identified: (i) inefficient bulldozing of a gently sloping ice margin transfers proglacial sediments onto the ice, causing differential ablation and dead-ice incorporation upon retreat; (ii) terrestrial ice-contact fans are formed by the dumping of englacial and supraglacial material from point sources such as englacial conduit fills; debris flows and associated fluvial sediments are stacked against a temporarily stationary margin at the start, and deformed during glacier advance in the remainder, of the accumulation season; (iii) a steep ice margin without supraglacial input leads to efficient bulldozing and deformation of pre-existing foreland sediments by wholesale folding. Ice-surface slope appears to be a key control on the type of process responsible for moraine formation in any given place and year. The second and third modes result in stable and higher moraines that have a higher preservation potential than those containing dead ice. Analysis of the spacing and climatic records at Gornergletscher reveals that winter temperature controls marginal retreat and hence moraine formation. However, any climatic signal is complicated by other factors, most notably the presence of a reverse bedrock slope, so that the extraction of a clear climatic signal is not straightforward. This study highlights the complexity of annual moraine formation in high-mountain environments and suggests avenues for further research. [ABSTRACT FROM AUTHOR]

Livingstone, S. J., Ó Cofaigh, C., Evans, D. J. A. & Palmer, A. 2010: Sedimentary evidence for a major glacial oscillation and proglacial lake formation in the Solway Lowlands (Cumbria, UK) during Late Devensian deglaciation. Boreas, Vol. 39, pp. 505–527. 10.1111/j.1502-3885.2010.00149.x. ISSN 0300-9483. This paper is a sedimentological investigation of Late Devensian glacial deposits from the Solway Lowlands, northwest England, in the central sector of the last British–Irish Ice Sheet. In this region, laminated glaciolacustrine sediments occur, sandwiched between diamictons interpreted as subglacial tills. At one location the laminated sediments are interpreted as varves, and indicate the former presence of a proglacial lake. Correlation of these varves with other laminated sediments indicates that the glacial lake was at least 140 km2 in area and probably much larger. Extensive beds of sand, silt and gravel throughout the Solway Basin associated with the lake demonstrate ice-free conditions over a large area. Based on the number of varves, the lake was in existence for at least 261 years. The stratigraphic sequence of varves bracketed by tills implies a major glacial oscillation prior to the Scottish Re-advance (16.8 cal. ka BP). This oscillation is tentatively correlated with the Gosforth oscillation at c.19.5 cal. ka BP. Subsequent overriding of these glaciolacustrine sediments during a westward-moving re-advance demonstrates rapid ice loss and then gain within the Solway Lowlands from ice-dispersal centres in the Lake District, Pennines and Southern Uplands. It is speculated that the existence of this and other lakes along the northeastern edge of the Irish Sea Basin would have influenced ice-sheet dynamics. [ABSTRACT FROM AUTHOR]

Anjar, J., Larsen, N. K., Björck, S., Adrielsson, L. & Filipsson, H. L. 2010: MIS 3 marine and lacustrine sediments at Kriegers Flak, southwestern Baltic Sea. Boreas, 10.1111/j.1502-3885.2010.00139.x. ISSN 0300-9483. Sediment cores from the Kriegers Flak area in the southwestern Baltic Sea show a distinct lithological succession, starting with a lower diamict that is overlain by a c. 10 m thick clay unit that contains peat, gyttja and other organic remains. On top follows an upper diamict that is inter-layered with sorted sediments and overlain by an upward-coarsening sequence with molluscs. In this paper we focus on the clay unit, which has been subdivided into three subunits: (A) lower clay with benthic foraminifera and with diamict beds in the lower part; (B) thin beds of gyttja and peat, which have been radiocarbon-dated to 31–35 14C kyr BP ( c. 36–41 cal. kyr BP); and (C) upper clay unit. Based on the preliminary results we suggest the following depositional model: fine-grained sediments interbedded with diamict in the lower part (subunit A) were deposited in a brackish basin during a retreat of the Scandinavian Ice Sheet, probably during the Middle Weichselian. Around 40 kyr BP the area turned into a wetland with small ponds (subunit B). A transgression, possibly caused by the damming of the Baltic Basin during the Kattegat advance at 29 kyr BP, led to the deposition of massive clay (subunit C). The data presented here provide new information about the paleoenvironmental changes occurring in the Baltic Basin following the Middle Weichselian glaciation. [ABSTRACT FROM AUTHOR]

This paper describes the internal architecture of a push moraine formed by a winter-spring surge of Hagafellsjökull-Eystri (Iceland) in 1998/99. The sedimentary architecture of this push moraine consists of a multilayered slab of glaciofluvial sediments with a monoclinal structure that has been displaced laterally by the advancing ice margin. The crest and ice-distal face of the moraine consist of subhorizontal sediment sheets, while the ice-proximal face dips steeply (45??to 90?) towards the ice margin. The core of the moraine consists of frozen sediment and thin slabs of glacier ice are embedded in its proximal face. The sediment slabs are characterized by both brittle and ductile styles of deformation. We argue that the observed variation in deformation style is dependent on whether the glacial foreland was frozen or unfrozen at the time of displacement. Frozen foreland would behave in a brittle fashion, while unfrozen foreland is likely to have deformed in a more ductile manner. The associated spatial variations in the degree of foreland freezing could be explained by variation in ice-marginal snow cover. We conclude that the thermal regime of the foreland, and the timing of the ice advance, is of importance to the style of internal deformation found within ice-marginal push moraines. [ABSTRACT FROM AUTHOR]

Thirty‐two tephra layers were identified in the time‐interval 313–366 ka (Marine Isotope Stages 9–10) of the Quaternary lacustrine succession of the Fucino Basin, central Italy. Twenty‐seven of these tephra layers yielded suitable geochemical material to explore their volcanic origins. Investigations also included the acquisition of geochemical data of some relevant, chronologically compatible proximal units from Italian volcanoes. The record contains tephra from some well‐known eruptions and eruptive sequences of Roman and Roccamonfina volcanoes, such as the Magliano Romano Plinian Fall, the Orvieto–Bagnoregio Ignimbrite, the Lower White Trachytic Tuff and the Brown Leucitic Tuff. In addition, the record documents eruptions currently undescribed in proximal (i.e. near‐vent) sections, suggesting a more complex history of the major eruptions of the Colli Albani, Sabatini, Vulsini and Roccamonfina volcanoes between 313 and 366 ka. Six of the investigated tephra layers were directly dated by single‐crystal‐fusion 40Ar/39Ar dating, providing the basis for a Bayesian age–depth model and a reassessment of the chronologies for both already known and dated eruptive units and for so far undated eruptions. The results provide a significant contribution for improving knowledge on the peri‐Tyrrhenian explosive activity as well as for extending the Mediterranean tephrostratigraphical framework, which was previously based on limited proximal and distal archives for that time interval. [ABSTRACT FROM AUTHOR]

A digital database for submarine glacial landforms and sediments formed in the Arctic during and since the Last Glacial Maximum was created in order to facilitate and underpin new research on palaeo‐ice sheets and tidewater glacier dynamics. The glacimarine database (GlaciDat) documents and standardises evidence of previous glacial activity as visible on the contemporary seafloor of fjords and continental shelves around Svalbard, Greenland, Alaska, northern Russia and north of 66°30′N in Canada and Norway. An extensive literature search was conducted to create GlaciDat, which compiles nearly 60 000 individual submarine landforms, more than 1000 sediment cores and 232 radiocarbon dates. Glacial landforms included are cross‐shelf troughs, trough‐mouth fans, grounding‐zone wedges, lateral moraines, overridden moraines, (mega‐scale) glacial lineations, drumlins, crag‐and‐tails, medial moraines, terminal moraines, debris‐flow lobes (including glacier‐contact fans), recessional moraines, De Geer moraines, crevasse‐fill ridges, eskers, hill‐hole pairs, crescentic scours, and submarine channels. They were digitised as point, line and polygon features alongside a list of their individual characteristics. Sediment core locations are attributed with a description of the sampled lithofacies and sedimentation rates where available. Landforms and sediments have been standardised according to predefined nomenclatures to make the glacial evidence as consistent as possible. Marine radiocarbon dates were included when thought to be relevant for constraining the timing of large‐scale palaeo‐ice dynamics. Outlines of bathymetric data sets, which have previously been used for glacial geomorphological mapping, were also included to give an overview of already investigated research areas. GlaciDat is available for download (https://doi.pangaea.de/10.1594/PANGAEA.937782) and will aid researchers in the reconstruction of past ice dynamics and the interpretation of Arctic glacial landform–sediment assemblages. Moreover, as well as providing a comprehensive bibliography on Arctic glacial geomorphological and sedimentological research, it is intended to serve as a basis for future modelling of Arctic glacier and ice‐sheet dynamics. [ABSTRACT FROM AUTHOR]

The physical, sedimentological, mineralogical and elemental geochemical properties of sediment cores AMD1803‐02BC and 01PC from the Cape Norton Shaw Inlet were investigated to reconstruct glacial sediment discharges from southeastern Manson Icefield and document the impact of ice–ocean interactions on the sediment dynamics and opening of the North Water Polynya (NOW) in northwestern Baffin Bay since the last deglaciation. Laminated glaciomarine sediments rich in quartz and feldspar are observed prior to 11 cal. ka BP and were probably deposited by hyperpycnal currents triggered by the local retreat of the southern margin of the Innuitian Ice. Detrital proxies suggest that Early Holocene sediment dynamics were mainly influenced by sea ice and iceberg rafting and meltwater discharges related to the deglaciation of eastern Smith (~11 to 10.65 cal. ka BP) and Jones (~10.7 cal. ka BP) sounds. This also provides an upper limit to the timing of formation of the NOW. The high detrital carbonate contents during 8.8 to 6.6 cal. ka BP confirm that enhanced carbonate‐rich sediment export from Nares Strait to northern Baffin Bay occurred during and after the deglaciation of Kennedy Channel (8.8 to 8.2 cal. ka BP). Canadian Shield sediment inputs have dominated since 6.6 cal. ka BP, indicating that sedimentation is mainly influenced by Cape Norton Shaw glacier discharges. The lower level of sedimentation recorded in core 01PC during the Middle to Late Holocene suggests an accelerated landward retreat of the Cape Norton Shaw glaciers in response to warmer marine conditions. During the Neoglacial period, higher sedimentation rates and detrital proxies in the cores suggest increased glacial erosional processes, probably associated with the long‐term declines in boreal summer insolation and glacier growth. Finally, mineralogical and grain‐size data in core 02BC support the idea that increased Arctic atmospheric temperatures have had an important influence on the glacial dynamics during the industrial period. [ABSTRACT FROM AUTHOR]

In this study, we analysed a ~54‐m sediment core consisting of Quaternary sediments overlying the Neoproterozoic Muhos Formation in central western Finland, adjacent to the Gulf of Bothnia. The sediments recovered were logged, and their sedimentological characteristics defined. Two fine‐grained sediment units were subjected to biostratigraphical studies using pollen and diatom analyses. In addition, two sand‐rich units and a wooden stick were dated by the optically stimulated luminescence (OSL) and 14C‐AMS methods. The core sediments were divided into six units, where several diamicton, sand and gravel, and silt‐and‐clay‐dominated beds were studied. The results indicate that the sediment succession of the core beneath the Holocene Litorina Sea and the Ancylus Lake sediments of the Baltic Basin were deposited in glacial and lacustrine environments that existed in the Oulu River valley during the time period between the Saalian glaciation (MIS 6) and the Holocene. The stratigraphical evidence, supported by the OSL ages, suggests that the Scandinavian Ice Sheet (SIS) entered the Muhos area during the Saalian glaciation, and at least during three separate time intervals in the Weichselian stage. Stratigraphically controlled and age‐bracketed evidence shows that the first Weichselian SIS advance extended further south in the eastern part of Fennoscandia than previously estimated, and that this ice growth phase occurred during the Early Weichselian Herning Stadial (MIS 5d). The subsequent ice growth phases occurred during the Middle (MIS 4) and Late (MIS 2) Weichselian substages. The lacustrine and littoral sediments of the Muhos core were correlated with the late Eemian interglacial (MIS 5e) and two Weichselian interstadials (MIS 5c and MIS 3). [ABSTRACT FROM AUTHOR]

On the east coast of Ireland, glacigenic sediments and landforms reflect both phases of late Devensian ice retreat, and postglacial slope readjustment under a paraglacial process regime. These different phases of landscape development are commonly difficult to identify in the absence of geomorphological, sedimentary and dating evidence for the style, magnitude and timing of postglacial landscape change. Here, sediments and radiocarbon dates on raised coastal sediments adjacent to a prominent retreat moraine of the late Devensian Irish ice sheet provide evidence for one such extended phase of paraglacial sediment reworking, in the 8th and 10th centuries CE. The timing of this phase of sediment reworking provides evidence for climatic deterioration during the European late Dark Ages/early Medieval Warm Period, and is consistent with evidence across northwest Europe for enhanced landscape geomorphic change at this time. From this evidence it is inferred that landscape morphological change dominantly reflects climatic rather than anthropogenic forcing, although the latter cannot be wholly discounted. Further, this evidence highlights the sensitivity to Holocene climate forcing of coastal paraglacial systems that contain abundant glacigenic sediment supply. [ABSTRACT FROM AUTHOR]

Recent catastrophic sinkhole collapse caused by regional water table lowering induced by quarrying has led to the partial exhumation and reactivation of a buried karst cave system in the floor of the Railton Valley in the lowlands of northern Tasmania, Australia, and widespread sinkhole development. Extensive silty sediments exposed in sinkholes, OSL dated to approximately 237 ka, are interpreted to be lacustrine deposits derived from rapidly deposited glacial outwash. The silty sediments have mineralogy consistent with derivation from a source in the upper Mersey catchment rather than locally and are interpreted to be the product of rapid melting of the Mersey Valley glacier during the MIS 8/7e transition. Thick Last Glacial alluvial fan and Holocene flood‐plain deposits mantle the lacustrine sediments. Exposures of glacial erratics and weathered till in streambeds provide further evidence that the valley was impacted by earlier Pleistocene glaciations. [ABSTRACT FROM AUTHOR]

Helmens, K. F. & Engels, S. 2010: Ice-free conditions in eastern Fennoscandia during early Marine Isotope Stage 3: lacustrine records. Boreas, 10.1111/j.1502-3885.2010.00142.x. ISSN 0300-9483. The traditional notion that Fennoscandia was glaciated throughout Marine Isotope Stages (MIS) 4–2, from c. 70 kyr BP to the deglaciation 15–10 kyr BP ago, has been challenged during the last decade. Recent studies have shown that climate and environmental settings during MIS 3 were more dynamic than previously assumed, and lacustrine sediment bodies indicate open-water conditions for several sites in eastern Fennoscandia. In this study, three sediment sequences from western, eastern and northeast Finland are compared in detail with respect to their chronology, vegetation reconstruction and climatic inferences. OSL-dating places the sediments in early MIS 3. Pollen evidence suggests the presence of isolated birch trees and open birch forest close to the retreating ice margin, in contrast to vegetation reconstructions from central Europe, which indicate tree-less vegetation. Furthermore, reconstructions of climate using transfer functions have yielded surprising results, indicating present-day summer temperatures in northeast Finland. The combined results suggest ice-free and warm conditions in major parts of eastern Fennoscandia in early MIS 3, possibly during Greenland Interstadial (GIS) 14 around 53 kyr BP ago. [ABSTRACT FROM AUTHOR]

Glaciotectonic structures in subglacial till and substrate, as well as stone fabric, provenance and surface features in till, indicate that complex interactions of late Wisconsinan glacial lobes occurred along a mountain front in the western Fraser Lowland of southwestern British Columbia. Tills of this study represent subglacial deposition through the maxima of two stades in the Fraser Glaciation, the Coquitlam and the Vashon. Through each stadial maximum, temperate glacial ice was grounded and commonly overrode proglacial outwash while superimposing deformations in subglacial till during three phases: (1) pre-maximum glacier flow down valleys and into lowland piedmont ice, (2) coalescent piedmont ice during stadial maxima when flow was westward along the mountain front and across valley mouths, and (3) post-maximum glacier flow down valleys into lowland piedmont ice but prior to general deglaciation. Valley glaciers appear to have shifted flow directions during phases 1 and 3. During stadial maxima (phase 2), Fraser Lowland piedmont ice may have been part of an outlet glacier-ice stream complex that terminated in salt water over the continental shelf. [ABSTRACT FROM AUTHOR]

The submarine landforms and shallow sediment record are presented from Hambergbukta, southeastern Spitsbergen using swath‐bathymetric, subbottom acoustic, and sediment core data. The mapped landforms include large terminal and end‐moraines with associated debrisflow aprons on their distal flanks, drumlinized till surface, glacial lineations, medial and retreat moraines, crevasse squeeze ridge networks, eskers, as well as iceberg‐produced terraces and plough‐marks. Analysis of the landforms and landform assemblages in combination with the sediment core data and aerial imagery studies reveal a complex and dynamic glacial history of Hambergbukta. We present a detailed history of Hambergbreen glacier indicating two previously unknown surges as well as new details on the nature of the subsequent ice‐margin retreat. The results from two gravity cores combined with the shallow acoustic stratigraphy and high‐resolution bathymetry suggest that the c. AD 1900 surge was less extensive than previously thought and the retreat was most likely rapid after the c. AD 1900 and 1957 surges of the Hambergbreen. Mixed benthic foraminifera collected from the outer fjord basin date to 2456 cal. a BP, suggesting older sediments were re‐worked by the c. AD 1900 surge. This highlights the importance of exercising caution when using foraminifers for dating surge events in fjord basins enclosed by prominent end‐moraines. [ABSTRACT FROM AUTHOR]

Recent studies have revealed that areas with sediments pre‐dating the Last Glacial Maximum (LGM) are more common in southern Scandinavia than previously thought. To describe and date these sediments, four deep core drillings were made in the province of Småland and one in the province of Skåne, southern Sweden, and an existing sediment core drilled in the 1960s from western Skåne was re‐examined and re‐dated, all resulting in a total of 22 AMS14C ages and 19 OSL ages. With some variation, the Småland cores revealed a stratigraphy consisting of two tills separated by proglacial glacifluvial and glaciolacustrine sediments, dated to between 46 and 25 ka BP (Marine Isotope Stage (MIS) 3 to 2). We suggest that these sediments were deposited during the ice retreat of the MIS 3 Ristinge glaciation over southern Scandinavia and the subsequent re‐advance over the area in late MIS 3 and the transition to MIS 2, when the Fennoscandian Ice Sheet advanced towards its LGM marginal positions. This contrasts with the glacial history of southernmost Skåne, where an additional MIS 3 glacial advance through the Baltic Basin is suggested by the occurrence of a till named Allarp Till. New ages from sediments under‐ and overlying this till suggest that it was deposited by the same Baltic ice advance that deposited the Klintholm till in Denmark (Klintholm Advance, c. 34–30 ka). [ABSTRACT FROM AUTHOR]

Rock‐Eval pyrolysis provides a quick, relatively inexpensive means of characterizing organic‐rich strata, and has been used for decades to understand global petroleum systems. Although designed to characterize ancient kerogens, pyrolysis is increasingly being used to understand Holocene systems as well. The ability of this technique to distinguish between types of preserved organic matter is useful in characterizing climatic evolution, particularly in systems sensitive to climatic fluctuation such as isolated fens and bogs. Cores collected from the Tokewanna and Garden Basin Cattail fens in central/eastern Utah exhibit variability of organic source, with the mixture of terrestrial and algal sources varying through time, as shown through the hydrogen index (HI) and oxygen index pyrolysis parameters. A sediment core was collected at each fen, and 176 samples were taken from the cores at 6‐cm intervals. Total organic carbon (TOC) for all samples ranges from 1.3 to 44.2%, with an average of 18.2% TOC. Samples range from 84 to 687 HI, equivalent to Type I (lacustrine algal) to Type III (terrestrial) organic material (OM). Variability in HI response represents mixing of the two OM sources, and the relative amount of aqueous organic input can be estimated through time based on age‐calibrated HI curves at the two sites. The balance of organic input serves as an accurate, high‐resolution proxy for climate, and calibration with palynological data near both sites confirms patterns shown by pyrolysis, showing the utility of this method in quickly, affordably and accurately characterizing Holocene sediments for use in understanding palaeoclimate. [ABSTRACT FROM AUTHOR]

Lake Ladoga hosts preglacial sediments, although the Eurasian ice sheet overrode the area during the LGM. These sediments were first discovered by a seismic survey and are investigated using a 22.75‐m‐long core. Its upper 13.30 m comprise Holocene and Lateglacial sediments separated from the lower 11.45 m of preglacial sediments by a hiatus. They consist of highly terrigenous lacustrine sediments, which according to OSL dating, were deposited during an early stage of the last ice age (MIS 5). The palynological data allow a first reconstruction of the Early Weichselian environmental history for northwestern Russia. Birch and alder forests with broad‐leaved taxa dominated during MIS 5d (c. 118–113 ka), suggesting a climate more favourable than in the Holocene. A high content of well‐sorted sands and poorly preserved palynomorphs indicates a shallow‐water environment at least temporarily. More fine‐grained sediments and better preserved organic remains suggest deeper water environments at the core location during MIS 5c (c. 113–88 ka). Pine and spruce became dominant, while broad‐leaved taxa started to disappear, especially after c. 90 ka, pointing to a gradual climate cooling. An increase in open herb‐dominated habitats at the beginning of MIS 5b (c. 88–86 ka) reflects a colder and dryer climate. However, later (c. 86–82 ka) pine and spruce again became more common. Birch and alder forests dominated in the area c. 82–80 ka (beginning of MIS 5a). Although open treeless habitats also became more common at this time, a slight increase in hazel may point to somewhat warmer climate conditions coinciding with the beginning of MIS 5a. The studied sediments also contain numerous remains of freshwater algae and cysts of marine and brackish‐water dinoflagellates and acritarchs documenting that the present lake basin was part of a brackish‐water basin during the Early Weichselian, probably as a gulf of the Pre‐Baltic Sea. [ABSTRACT FROM AUTHOR]

Lake Ladoga in northwestern Russia is Europe's largest lake. The postglacial history of the Ladoga basin is for the first time documented continuously with high temporal resolution in the upper 13.3 m of a sediment core (Co1309) from the northwestern part of the lake. We applied a multiproxy approach including radiographic imaging, (bio‐)geochemical and granulometric analyses. Age control was established combining radiocarbon dating with varve chronology, the latter anchored to a correlated radiocarbon age from a lake close by. The age‐depth model reveals the onset of glacial varve sedimentation at 13 910±140 cal. a BP, when Lake Ladoga was part of the Baltic Ice Lake. Linear extrapolation of published retreat rates of the Scandinavian Ice Sheet provides a formation age of the Luga moraine close to Lake Ladoga's southern shore of 14.5–15.9 cal. ka BP, older than previously assumed. Varve sedimentation covers the Bølling/Allerød interstadial, the Younger Dryas stadial and the Early Holocene. Varve‐thickness variations, conjoined with grain‐size and geochemical variations, inform about the relative position of the Scandinavian Ice Sheet and the climate during the deglaciation phase. The upper limit of the varved succession marks the change from glaciolacustrine to normal lacustrine sedimentation and post‐dates the drainage of the Baltic Ice Lake as well as the formation of the Salpausselkä II moraine north of Lake Ladoga, by c. 250 years. The Holocene sediment record is divided into three periods in the following order: (i) a lower transition zone between the Holocene boundary and c. 9.5 cal. ka BP, characterized by mostly massive sediments with low organic content, (ii) a phase with increased organic content from c. 9.5 to 4.5 cal. ka BP corresponding to the Holocene Thermal Maximum, and (iii) a phase with relatively stable sedimentation in a lacustrine environment from c. 4.5 cal. ka BP until present. [ABSTRACT FROM AUTHOR]

A prominent thrust‐moraine system formed in the inner van Mijenfjorden, Svalbard, during a surge event in a tributary fjord, creating a large temporary lake. Based on geomorphological, sedimentological, stratigraphical and chronological data, the lake began to form shortly after 648–551 cal. a BP. At its maximum, the lake covered an estimated area of 77 km2 with a water volume of 1.2 km3. Lake sediment up to 80 cm thick was rapidly deposited on top of terrestrial and marine sediments. At its maximum extent, the short‐lived lake was the largest of any known Holocene lake in Svalbard. Modern river discharge would fill the lake to its highest shoreline at 23 m a.s.l. in only one season. Drainage was stepwise, as evidenced by four shorelines and abandoned drainage channels. This study has taken advantage of a unique suite of data available for such an ice‐dammed lake. The results demonstrate the power of a multidisciplinary approach for recognizing lake events in the geological record, which is essential given the low preservation potential of such sediments. [ABSTRACT FROM AUTHOR]

New information is presented on the configuration of the northern Barents Sea Ice Sheet ( BSIS) during the last glacial and deglaciation (21-11.5 ka). The glacial dynamics of the BSIS that we discuss are based on clay-mineral compositions of subglacial tills and a distinct kaolinite source in the central Barents Sea where previous workers have placed a large, single ice dome for the last glacial BSIS. Our results, which appear to show that subglacial sediments were sourced locally, suggest that the BSIS consisted at least temporarily of multiple domes and may have been more dynamic than previously thought. New radiocarbon dates are presented along with new ice-extent reconstructions for 16.5-15, 14, 13.5 and 11.5 ka. Our reconstructions add information to previous regional and continental-scale efforts in areas east of Svalbard. Ice retreat in the northern Barents Sea progressed as follows. (i) 19-16.5 ka. Major calving led to dynamic thinning in shelf troughs and was accompanied by significant ice-sheet thinning inland as a result of ice drawdown. (ii) 16.5-15 ka. Rapid ice-margin retreat of between 75-100 km occurred, via lift-off and iceberg calving, in Hinlopen and Kvitøya troughs, as well as major retreat (>300 km) in Franz Victoria Trough ( FVT) further east. (iii) 15-13.5 ka. Retreat progressed westwards from the FVT towards Svalbard with troughs east of Svalbard (Kvitøya, Olga, and Erik Eriksen) mostly ice-free by 13.5 ka. (iv) 13.5-11.5 ka. Ice retreated gradually towards residual ice masses on Svalbard, Kong Karls Land and possibly Storbanken. Our data require a modification of earlier views of the BSIS because they point toward a more dynamic ice sheet and decay that, once initiated at the shelf break, was dominated by the withdrawal of ice from the FVT that progressed westwards towards the Svalbard archipelago. [ABSTRACT FROM AUTHOR]

Physical properties, grain size, bulk mineralogy, elemental geochemistry and magnetic parameters of three sediment piston cores recovered in the Laurentian Channel from its head to its mouth were investigated to reconstruct changes in detrital sediment provenance and transport related to climate variability since the last deglaciation. The comparison of the detrital proxies indicates the succession of two sedimentary regimes in the Estuary and Gulf of St. Lawrence ( EGSL) during the Holocene, which are associated with the melting history of the Laurentide Ice Sheet ( LIS) and relative sea-level changes. During the early Holocene (10-8.5 cal. ka BP), high sedimentation rates together with mineralogical, geochemical and magnetic signatures indicate that sedimentation in the EGSL was mainly controlled by meltwater discharges from the local retreat of the southeastern margin of the LIS on the Canadian Shield. At this time, sediment-laden meltwater plumes caused the accumulation of fine-grained sediments in the ice-distal zones. Since the mid-Holocene, postglacial movements of the continental crust, related to the withdrawal of the LIS ( c. 6 cal. ka BP), have triggered significant variations in relative sea level ( RSL) in the EGSL. The significant correlation between the RSL curves and the mineralogical, geochemical, magnetic and grain-size data suggest that the RSL was the dominant force acting on the sedimentary dynamics of the EGSL during the mid-to-late Holocene. Beyond 6 cal. ka BP, characteristic mineralogical, geochemical, magnetic signatures and diffuse spectral reflectance data suggest that the Canadian Maritime Provinces and western Newfoundland coast are the primary sources for detrital sediments in the Gulf of St. Lawrence, with the Canadian Shield acting as a secondary source. Conversely, in the lower St. Lawrence Estuary, detrital sediments are mainly supplied by the Canadian Shield province. Finally, our results suggest that the modern sedimentation regime in the EGSL was established during the mid-Holocene. [ABSTRACT FROM AUTHOR]

Younger Dryas to earliest Holocene mega-landslides (>10 km2) in the eastern Fish Lake Plateau of central Utah required unusually wet conditions to drive movement. The sediment from abundant small lakes, ponds and especially fens that formed in swales between hummocks on the landslide surfaces are excellent archives of past climate. An integrated geophysical, geochemical and micro-palaeontological investigation characterized fen deposits, determining the timing of mass movement and establishing the subsequent climate history of the region. High-resolution P-(compressional) wave surveys of fen deposits were conducted to image fen-landslide contacts. Past climate states were assessed through loss on ignition, pollen and diatom abundances. Diatoms, in particular, record large variations in precipitation as the present-day wetland switched from fen (intermittent standing water) to pond states in response to variable precipitation. One core was analysed for detailed climate proxies. A wet episode (pond) prevailed from 11.5 to 10 ka after which the climate became much drier (fen) until 6 ka due to weakening of the North American Monsoon. After 2.5-2.0 ka, reduced insolation produced cooler summers and wet winters (pond). Only recently (<500 years) has a fen re-emerged based on direct observation and the disappearance of diatoms that require standing water. 14C ages of basal sediment from four cores show two episodes of movement: 12.8-12.5 and 10.5 ka. The earlier ages indicate that Younger Dryas high effective precipitation caused mass wasting. Later, during early Holocene times, colder winters followed by warmer summers and vigorous monsoons drove movement as rapid spring snow-melt was followed by wet summers. In broad terms, this work highlights variable climate conditions that can drive mass movement, as well as the sensitivity of diatom records in fens to effective precipitation. [ABSTRACT FROM AUTHOR]

Optical Stimulated Luminescence ( OSL) is a technique that can be used for dating geological materials deposited within the last half-million years, including sediments transported by air, water or gravity, as well as rocks heated at high temperatures. Recently, several studies have shown that OSL can also provide information on sediment transport. The pulsed photon-stimulated luminescence ( PPSL) unit (also known as a portable OSL reader) developed by the Scottish Universities Environmental Research Centre is an instrument designed to read luminescence signals from bulk (untreated) sediment samples comprising poly-mineral and poly-grain fractions. In this contribution, we evaluate the potential of the PPSL unit to assess the degree of OSL signal resetting in 27 young deposits (<2 ka) transported by different geomorphic agents in volcanic, coastal and fluvial depositional settings located in Mexico. Our results are in agreement with previous findings that used the Risø TL/ OSL reader, confirming that sediments transported by debrisflows contain the highest inherited luminesce signals. Infrared stimulation ( IRSL) values in volcanic ash, lavas, and sand beach and dune deposits exhibit low scatter. However, with blue stimulation ( BLSL) these samples reveal a large degree of scattering, attributed to charge transfer in the case of the coastal deposits and to the low sensitivity of quartz in the case of volcanic material. The luminescence signals of fluvial sediments exhibit a highly scattered distribution in both IRSL and BLSL. We conclude that the use of a PPSL unit is a simple approach to assess the degree of OSL signal resetting in deposits sourced from different geological environments. This research contributes to previous studies that have investigated new applications of the PPSL unit to assist in OSL dating of geological materials. [ABSTRACT FROM AUTHOR]

Reconstructions of environmental changes at sub-decadal to decadal resolution based on central Baltic Sea sediments rely on accurate and precise high-resolution sediment depth/age relationships. A model chronology for Baltic Sea sediments is presented here based on established historical records of anthropogenic radionuclides (137Cs/241Am/bomb14C), polychlorinated biphenyls ( PCBs), lead (Pb) and stable lead isotope (206/207Pb ratios), and radionuclide 210Pb and 14C decay dating methods. Marker horizons consisting of chemical precipitates formed by documented Major Baltic Inflow ( MBIs) events and an extended diatom bloom period were also integrated into the model. The main time markers in Baltic Sea sediments that formed during the last 120 years were the following: (i) the deepest observation of 210Pbunsupp. (marking the 210Pb dating horizon) and departure of Hg from natural background levels at c. AD 1900; (ii) first detectable presence of PCBs at AD 1935; (iii) radionuclide production (i.e. 241Am) due to nuclear weapons testing between AD 1954 and AD 1975, with a peak in AD 1963; (iv) maximum heavy metal and PCB concentrations in the AD 1960s/1970s; (v) the Chernobyl nuclear accident in AD 1986 as a sharp 137Cs increase; (vi) exceptionally strong diatom blooms with a massive diatom layer found in the Eastern Gotland Basin in AD 1988-1990; and (vii) characteristic manganese-carbonate layers in the deeper central basins formed by MBIs in AD 1993 and AD 2003. A precise and accurate sediment depth/age relationship can only be achieved in restricted areas of the Baltic Sea where continuous sedimentation has prevailed and there has been limited postdepositional disturbance. We demonstrate that parallel Hg and 137Cs measurements can be used to assess the quality of sediment sequences for high-resolution environmental reconstructions. We show examples of sediment profiles that conform to the historical record, and examples from Western Baltic Sea areas where it appears to be impossible to establish accurate geochronologies. [ABSTRACT FROM AUTHOR]

In this study, we report standard quartz SAR OSL and post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR290) measurements made on sand-sized quartz and K-feldspar extracts from the loess-palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ∼15 and ∼80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ~800 Gy. Otherwise, the dose recovery ratio deviates from unity. The De values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR290 results are compared with multiple elevated temperature-pIRIR (MET-pIRIR) data. It appears that the low temperature MET-pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR290 results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ∼10% signal loss occurs in pIRIR signals. Long-term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR290 signal is reached after ∼300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol. [ABSTRACT FROM AUTHOR]

At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up-ice of the Marine Isotope Stage ( MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non-glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared-stimulated luminescence ( IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid- MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a−1 along the Denali Fault since MIS 7. The non-glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30-36 14C ka BP, making Silver Creek one of the few well-constrained MIS 3-aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow-tundra to steppe-tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon. [ABSTRACT FROM AUTHOR]

A palaeolimnological study of the annually laminated sediment sequence of Lake Xiaolongwan, a small maar lake in northeastern China, revealed distinct diatom responses to Lateglacial and early Holocene climate change between c. 19 700 and c. 10 700 a BP. In addition to analyses of diatom assemblage composition and of the bio-volume accumulation rate of planktonic diatoms, geochemical (total nitrogen, total organic carbon) and physical (varve type and thickness) indicators were used to assess past environmental change. The diatom assemblages reveal a complex interplay between direct climate effects on the seasonal lake conditions (timing of ice cover break-up, water column mixing and thermal stratification), catchment-mediated effects on the concentrations of nutrients and dissolved organic carbon and, possibly, biotic interactions between the different algal groups present in the phytoplankton of Lake Xiaolongwan (diatoms, Chrysophyceae and Dinophyceae). The most remarkable changes in the aquatic system were: (i) a sharp increase in Asterionella formosa and the collapse of Handmannia balatonis at c. 14 780 a BP, corresponding with the onset of the Bølling -- Allerød interstadial; (ii) a sharp rise in Stephanodiscus minutulus at c. 12 840 a BP, marking the start of the Younger Dryas event and (iii) when the lake phytoplankton became dominated by Dinophyceae instead of diatoms at c. 11 170 a BP, after the Pre-Boreal oscillation. Two diatom assemblage zones characterize the Younger Dryas at Lake Xiaolongwan, suggesting a bipartite division of this stadial event as in several records from eastern Asia and Europe. The quasi-synchronicity of these events with the oscillations described in the North Atlantic realm demonstrates that during the Lateglacial, North Atlantic dynamics at centennial and millennial time scales had a strong control upon the climate in northeastern China. [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]

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]

Increasing interest in global climate change has led to attempts to understand and quantify the relationship between chemical weathering processes and environmental conditions, especially climate. This interest necessitates the identification of new climate proxies for the reconstruction of two important Earth surface processes: physical erosion and chemical weathering. In this study, an AMS 14 C-dated 2.8-m-long sediment core, GH09 B1, from Lake Gonghai in north-central China was subjected to detailed geochemical analyses to evaluate the intensity of chemical weathering conditions in the catchment. Multivariate statistical analysis of major and trace elemental data of 139 subsamples revealed that the first principal component axis PCA1 explained ∼53% of the variance in the assemblage of elements/oxides with significant positive correlations between PCA1 scores and the separation of mobile and soluble elements/oxides from the immobile and resistant elements/oxides, which is thus able to indicate the chemical weathering in the catchment. These results are supported by the down-core trends of other major and trace elemental ratios of chemical weathering intensity as well as by pollen data from the same core. Variations in PCA1, chemical index of alteration ( CIA), Rb/ Sr ratio and other oxides ratios indicate stronger chemical weathering due to a wet climate during the Medieval Warm Period ( MWP). However, the MWP was interrupted by an interval of relatively weaker chemical weathering conditions from AD 940-1070. Weak chemical weathering under a dry climate occurred during the Little Ice Age ( LIA), and increased chemical weathering intensity during the Current Warm Period ( CWP). Our proxy records of chemical weathering over the last millennium correlate well with the available proxy records of precipitation from Gonghai Lake as well as with the speleothem oxygen isotope record from Wanxiang Cave, but do not show a significant correlation with the temperature record in N China, suggesting that the chemical weathering intensity in the study area was mainly controlled by the amount of rainfall rather than by temperature. We conclude that high resolution lacustrine sediment geochemical parameters can be used as reliable proxies for climate variations at centennial-decadal time scales. [ABSTRACT FROM AUTHOR]

Despite extensive study and debate regarding the significance of turbate (also known as 'rotational') microstructures in glacially deformed sediments, characteristics regarding the dimensions of these features remain unresolved. This study presents the first explicitly quantitative measurement and analysis of turbate microstructure dimensions, and their relation to till texture through thin section analysis. Samples were taken from coarse-resolution horizontal and vertical transects of a macroscopically homogenous subglacial till, with subset areas of each thin section (30 mm2) analysed. The frequency and apparent a-axes and b-axes of both coreless and cored turbate structures (and their corestones) were measured, and simple univariate statistical methods used to establish the (in-)variability of these dimensions through the till profile. Summarizing findings, (i) the dimensions of both cored and coreless turbate populations display log-normal distributions when all measurements are analysed together, although not all individual sample populations possess these same distributions; (ii) turbate dimension populations are inconsistent within a sample block, precluding evaluation of turbate variability through a profile from single thin sections; (iii) analysis of turbate morphology and variability provisionally indicate that the three-dimensional structure of turbates are likely to be cylindrical or flared, while weak relationships are also observed amongst till texture, turbate dimensions and frequency. [ABSTRACT FROM AUTHOR]

The Late Pleistocene and Holocene glacial and postglacial sediments of the Baltic Sea basin are conventionally classified into units according to the so-called Baltic Sea stages: Baltic Ice Lake, Yoldia Sea, Ancylus Lake and Litorina Sea. The Baltic Sea stages have been identified in offshore sediment cores by fundamentally different criteria, precluding detailed comparisons of the sediment units amongst different sea areas and studies. Here, long sediment cores and reflection seismic and pinger sub-bottom profiles were studied from an offshore area in the Gulf of Finland, northern Baltic Sea. The strata are divided on the basis of sedimentological criteria into three allostratigraphical formations with subordinate allostratigraphical members and lithostratigraphical formations, following the combined allostratigraphical and lithostratigraphical ( CUAL) approach. Sedimentological features are recommended as the primary stratigraphical classification criteria because they do not require the palaeoenvironmental inferences of salinity and water level that are inherent in the conventional classification practice. The presented stratigraphical division is proposed as a flexible template for future stratigraphical work on the Baltic Sea basin, whereby lower-rank allounits and lithounits can be included and removed locally, while the alloformations will remain at the highest hierarchical level and guarantee regional correlatability. The stratigraphical division is compatible with international guidelines, facilitating communication to the wider scientific community and comparison with other similar basins. [ABSTRACT FROM AUTHOR]

Stratigraphical exposures of both glacial and non-glacial sediments at Morgan Bluffs, a >6-km long exposure on the east coast of Banks Island, comprise a discontinuous archive of Quaternary environmental change. A detailed facies analysis of the sediments and a new stratigraphical framework is incompatible with the many climatostratigraphical units proposed previously. Instead, three distinct intervals of sedimentation are recognized. The first records the progradation of a delta, followed by fluvial aggradation of a braided river valley perhaps ∼1 Ma. The second documents glacigenic sedimentation, including fluctuations of a tidewater glacier margin, in a marine basin more than 0.78 Ma. The third records till deposition by the NW Laurentide Ice Sheet during the Late Wisconsinan, followed by the progradation of a deglacial, ice-contact delta into an ice-dammed lake ∼12.8 cal. ka BP. The revised stratigraphical framework adds important new terrestrial observations to a sparse and fragmentary data set of Quaternary environmental change in the Canadian Arctic. This study challenges former references and correlations to the previously proposed climatostratigraphical framework and nomenclature. [ABSTRACT FROM AUTHOR]

A new geochemical record from the paaleolake Santiaguillo documents the hydrological variability of sub-tropical northern Mexico over the last ∼14 cal. ka. Summer-season runoff, lake water salinity and deposition of sediments by aeolian activity were reconstructed from concentrations of K, Ca and Zr/ K in bulk sediments. More-than-average runoff during c. 12.3 -9.3 cal. ka BP represented an interval of enhanced summer precipitation. Arid intervals of c. 14 -12.3 cal. ka BP and c. 6-4.3 cal. ka BP were characterized by average and more-than-average aeolian activity. Comparison with proxy records of summer as well as winter precipitation from tropical and sub-tropical North America and sea surface temperatures from the Atlantic and Pacific provides insight into the source of moisture and possible forcing. The wet Pleistocene− Holocene transition and early Holocene was contemporary with warmer conditions in the Gulf of California. We suggest that the Atlantic had minimal influence on the summer precipitation of the western part of sub-tropical northern Mexico and that the source of moisture was dominantly Pacific. [ABSTRACT FROM AUTHOR]

The grain size of the loess-like sediment in the Jinsha River Valley is essentially similar to that of typical loess, and it differs from that of the fluvial sediment in the Jinsha River area. We conclude that the loess-like sediment is of aeolian origin, as is the loess of the Chinese Loess Plateau. The geochemical characteristics of the loess-like sediment are similar to those of dammed lake and fluvial sediments in the same area, which is significantly different from those of the typical loess in NW China. The geochemical characteristics show that the loess-like sediment originated from proximal materials. Combined with the grain-size distribution pattern of the aeolian deposits, we suggest that the loess-like sediment of the Jinsha River Valley originated from the dammed lake and fluvial sediments that accumulated in the valley. The local mountain-valley wind circulation (especially the valley wind in winter and spring) provided the transport force for the loess-like sediment. The presentation of the loess-like sediment may indicate the appearance of the grassland and forest steppe and the beginning of the dry-hot valley phenomenon. [ABSTRACT FROM AUTHOR]

Two fluvial sediment cores taken from a floodplain of the Hawkesbury- Nepean River system in the Sydney region, eastern Australia are dated using Optically Stimulated Luminescence ( OSL) to provide a reliable chronology essential for the management and planning of water resources. Nine charcoal 14 C ( AMS) dates constrain these OSL ages. Quartz extracted from seven OSL samples from each of the cores was measured using both single-grain and multi-grain OSL techniques. Three of the single-grain natural dose distributions appear to be well bleached, but the others appear to be incompletely bleached to various degrees. Three minimum-age models ( MAM, MAMUL and IEU) are applied to the single-grain dose distributions. We conclude that these models give consistent age estimates. For one of the cores it appears to be necessary to use a minimum-age model to obtain accurate ages, but in the other core incomplete bleaching is probably less important than postdepositional mixing and mixing during sampling. As a result, the burial age is probably best estimated using the weighted average of the individual single-grain dose estimates. The application of multi-grain OSL techniques to these samples results in an average apparent age overestimation of ∼200 years, which is significant for these samples, but negligible for sediments older than a few thousand years. The intention is that the chronology obtained in this study will be used in conjunction with a proxy flood record, derived from floodplain sediments, to gain an understanding of the long-term variability in periods of high and low rainfall in eastern Australia. [ABSTRACT FROM AUTHOR]

The Cueva del Camino site ( Pinilla del Valle, Madrid, Spain) is located in the upper valley of the Lozoya River in the Sierra de Guadarrama, a mountain range extending NE−SW within the Central Range System. Due to its location within a mountain range on the central Iberian Peninsula at an altitude of 1114 m a.s.l. and the numerical dating of its sediments, the palaeontological site of Cueva del Camino has proved a highly relevant location for studying the ecological changes linked to the climatic fluctuations at the end of Marine Isotope Stage ( MIS) 5 and the beginning of MIS 4. Environmental reconstructions suggest a rather open, patchy landscape throughout the succession, with abundant evidence of dry meadows, scrublands and rocky habitats. The climate can be considered as generally warm, reaching mean annual temperatures ( MATs) of up to 13.8° C (i.e. higher than today's by up to 2.9° C). Three cooler events can be seen throughout the succession as reflected by the presence of Rana iberica, Anguis fragilis and Coronella austriaca. The first of these events may correlate with MIS 5b; the second in the Central sector may correlate with the Stadial I pollen event occurring at the end of MIS 5a; and the third event, corresponding to the coldest MAT of the entire succession with MATs 0.9° C lower than today's, may correspond to the transition from MIS 5a to MIS 4. The evolution of mean annual precipitation ( MAP) is characterized by warm periods, drier and cold periods, as well as wetter periods (up to +356 mm compared to today's MAP values), similar to what occurs today in the high-elevation areas of the neighbouring mountains. Our study gives new quantitative estimations for the climatic fluctuations in mountain environments of central Spain at the MIS 5/4 transition and their associated ecological changes. [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]

Glacier thermal regime is shown to have a significant influence on the formation of ice-marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up-glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast-form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin (<10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge-shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ∼40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the Little Ice Age and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze-on, which requires stable glacier geometry. While the annual moraines on the eastern side of Midtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice-stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold-based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought. [ABSTRACT FROM AUTHOR]

Analyses of fossil mollusc successions have rarely been used to study the development of floodplain forests during the Holocene. The Ohře River, located in a prehistorically settled chernozem area in the Czech Republic, is partly situated in Cretaceous marlstones, yielding sediments suitable for fossilization directly in floodplain deposits. We analysed five fossil mollusc successions situated in the lower stretch of the Ohře River and compared the results with recent mollusc assemblages studied along the entire 256 km of the river. Fossil samples were composed mostly of open-country species throughout the Holocene or the whole preserved succession. Only some samples also contained woodland assemblages, but these were always greatly impoverished, with a very low frequency of strictly woodland species. Although the natural-looking appearance of the present-day floodplain forests of the lower river stretch has resulted in its being declared a nature reserve, modern floodplain forest mollusc assemblages there are also impoverished. This reduction in the distribution of strictly woodland species compared with modern assemblages in the upper stretch of the river seems to be the result of an ancient human settlement and continuous disturbances of the floodplain forest development since the Neolithic. Thus, fully developed floodplain forest assemblages occur recently only in the upper non-impacted stretch of the river. Based on the studied fossil successions we can conclude that the lower Ohře River floodplain was probably a mosaic of open and disturbed forest habitats throughout the Holocene. This area is part of a central European landscape island, where forests probably never fully developed and open patches from the early Holocene continually developed into an agricultural landscape. [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]