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The cosmogenic nuclide exposure history method is undergoing major developments in analytical, theoretical, and applied areas. The capability to routinely measure low concentrations of stable and radioactive cosmogenic nuclides ha...
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The cosmogenic nuclide exposure history method is undergoing major developments in analytical, theoretical, and applied areas. The capability to routinely measure low concentrations of stable and radioactive cosmogenic nuclides has led to new methods for addressing long-standing geologic questions and has provided insights into rates and styles of surficial processes. The different physical and chemical properties of the six most widely used nuclides: He-3, Be-10, C-14, Ne-21, Al-26, and Cl-36, make it possible to apply the surface exposure dating methods on rock surfaces of virtually any lithology at any latitude and altitude, for exposures ranging from 10(2) to 10(7) years. The terrestrial in situ cosmogenic nuclide method is beginning to revolutionize the manner in which we study landscape evolution. Single or multiple nuclides can be measured in a single rock surface to obtain erosion rates on boulder and bedrock surfaces, fluvial incision rates, denudation rates of individual landforms or entire drainage basins, burial histories of rock surfaces and sediment, scarp retreat, fault slip rates, paleoseismology, and paleoaltimetry. Ages of climatic variations recorded by moraine and alluvium sediments are being directly determined. Advances in our understanding of how cosmic radiation interacts with the geomagnetic field and atmosphere will improve numerical simulations of cosmic-ray interactions over any exposure duration and complement additional empirical measurements of nuclide production rates. The total uncertainty in the exposure ages is continually improving. This article presents the theory necessary for interpreting cosmogenic nuclide data, reviews estimates of parameters, describes strategies and practical considerations in field applications, and assesses sources of error in interpreting cosmogenic nuclide measurements. (C) 2001 Elsevier Science Ltd. All rights reserved. [References: 371]
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Paraglacial geomorphology is the study of earth-surface processes, sediments, landforms, landsystems and landscapes that are directly conditioned by former glaciation and deglaciation. The withdrawal of glacier ice exposes landsca...
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Paraglacial geomorphology is the study of earth-surface processes, sediments, landforms, landsystems and landscapes that are directly conditioned by former glaciation and deglaciation. The withdrawal of glacier ice exposes landscapes that are in an unstable or metastable state, and consequently liable to modification, erosion and sediment release at rates greatly exceeding background denudation rates. This paper (1) reviews research on paraglacial processes, landforms and landscape change in a range of geomorphological settings (2) explores the importance of paraglacial landscape modification and sediment recycling as a component of alternating glacial/nonglacial landscape evolution; (3) assesses the nature and significance of paraglacial facies in Quaternary stratigraphic sequences; and (4) develops a general model of the sequence of paraglacial landscape modification and the changing nature of paraglacial landsystems. Six paraglacial landsystems are identified: rock slopes, drift-mantled slopes, glacier forelands, and alluvial, lacustrine and coastal systems. Each contains a wide range of paraglacial landforms and sediment facies. Collectively these landforms and sediments (e.g. talus accumulations, debris cones, alluvial fans, valley fills, deltas and coastal barrier structures) can be conceptualised Lis storage components of an interrupted sediment cascade with four primary sources (rockwalls, drift-mantled slopes, valley-floor glacigenic deposits and coastal glacigenic deposits) and four terminal sediment sinks (alluvial valley-fill deposits, lacustrine deposits, coastal/ nearshore deposits and shelf/offshore deposits). Paraglacial sediment stores and sinks may form major sources of readily erodible sediment during the early stages of glacial cycles, leading to high rates of sediment transport during periods of glacier or ice-sheet expansion. Probably because of the limited preservation potential of paraglacial sediments that were subsequently over-run by glacier ice, identification of paraglacial facies in both terrestrial and marine settings has been almost exclusively limited to sequences that post-date the Last Glacial Maximum. The unifying concept of paraglacial geomorphology is that of glacially conditioned sediment availability. Relaxation of landscape elements to nonglacial conditions operates over timescales of 10(1)-> 104 years, and is conditioned by both process and spatial scale. ate of sediment reworking can be described by an exhaustion model. In the case of primary reworking of glacigenic sediment, the rate of reworking declines approximately exponentially through time, though extrinsic perturbation may rejuvenate paraglacial sediment flux long after termination of the initial period of paraglacial adjustment. Landscape-scale (particularly alluvial and coastal) systems may exhibit intrinsically complex responses due to reworking of secondary paraglacial sediment stores. The long relaxation time of such systems implies that many areas deglaciated in the Late Pleistocene or Early Holocene have still not fully adjusted (in terms of sediment supply) to nonglacial conditions. (C) 2002 Elsevier Science Ltd. All rights reserved. [References: 354]
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Salt marshes, most now embanked, together with genetically related wetlands and high intertidal flats, make a major environmental contribution to the lowland coasts of Northwest Europe. They occur in many different contexts, but c...
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Salt marshes, most now embanked, together with genetically related wetlands and high intertidal flats, make a major environmental contribution to the lowland coasts of Northwest Europe. They occur in many different contexts, but chiefly on open and barrier coasts and in estuaries and embayments, and range greatly in scale, from a modest total that measure hundreds of square kilometres in individual extent, to an enormous number each of an area no greater than tens to a few hundred hectares. These marshes and associated environments are under complex natural controls and experienced from the mid-Holocene onward human exploitation and, increasingly, interference. The main external controls are the sea-level, tidal and sediment-supply regimes. Intrinsic infuences are provided by the halophytic vegetation and sediment autocompaction. Upward sea-level movements and autocompaction combine to provide accomodation space within which marshes build upward. Field data and simulation modelling show that youthful mineralogenic marshes grow up rapidly and can mature within a few hundred years of inception. They consist of a vegetated platform dissected typically by extensive networks of blind-ended, branching tidal creeks and gullies. The how-resistant surface vegetation, shaping the combined wave-tide boundary layer on the platforms, both traps and binds tidally introduced mineral sediment, but also contributes an organic component of indigenous origin to the deposit. When sea-level becomes stable or falls, however, in response to century-millennial scale fluctuations, the organic sediment component becomes dominant and mineralogenic marshes are transformed into organogenic ones. Organogenic marshes normally display a considerable range of sub-environments which create much spatial variation in the peat facies which accumulate. At an advanced stage, domed raised bogs, rising significantly above the general landscape, may appear on the marshes. Because peat is such a porous and permeable sediment, and there is little or no tidal inundation, organogenic marshes in Northwest Europe typically lack surface channels for internal drainage. The stratigraphic sequences accumulated during the Holocene beneath coastal marshes and high tidal flats typically present an alternation on a vertical scale of decimetres to metres of silts (mineralogenic marshes, high intertidal mudflats) and peats (organogenic highest intertidal-supratidal marshes). Coastal barriers and some channels are represented by local accumulations of sand and/or gravel. The silts and peats form couplets which are generally considered to be related to fluctuations of sea-level about the general upward trend. Field investigations and modelling show that, in areas where marshes are mature, the upward change from an organogenic to a sequence of mineralogenic marshes (transgressive overlaps) is accompanied by the initiation and invasive development of a branching network of tidal creeks. These decay and infill during the reversal of the environmental sequence and the approach, expressed as a series of repressive overlaps, of the next set of peat-forming conditions. The operation of the continuous, progressive, irreversible and asymptotic process of sediment autocompaction exerts a major, secondary control on depositional regimes and marsh behaviour. A variety of local responses are consequently possible in an extensive marsh, even though the marsh may be everywhere in dynamic equilibrium with environmental factors. Autocompaction also strongly shapes the character of Holocene coastal sequences as now perceived, introducing significant stratigraphic distortions and displacements which, for the time being, limit the accuracy of sea-level curves and rates of sea-lever change based on dated intercalated peats. Prehistoric humans benefitted from the resources of coastal salt marshes, especially at the times when peat marshes begin to be transgressed. Feat domes not yet fully collapsed may have
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The characteristic feature of the Quaternary geology of eastern Germany (location map, Fig. 1) is a sequence of more than 50 horizons and complexes of glacial (laminated clays, tills, glaciofluvial sediments) and periglacial (rive...
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The characteristic feature of the Quaternary geology of eastern Germany (location map, Fig. 1) is a sequence of more than 50 horizons and complexes of glacial (laminated clays, tills, glaciofluvial sediments) and periglacial (river gravels, gelifluction sheets, alluvium, loess) facies. In the period between the younger Tertiary and the first Elsterian continental glaciation, at least four gravel terraces were built up under cold climate conditions. The youngest of these gravel bodies lacks Scandinavian rocks and is interbedded with Elsterian glaciolacustrine deposits. Pre-Elsterian temperate periods have been recorded at a number of places (i.e. Zeuchfeld, Untermassfeld, Voigtstedt, Sussenborn). Two major ice advances with additional minor oscillations have been identified, of Elsterian and Saalian ages. Complete Eemian and Holsteinian sequences are represented showing vegetational development through each interglacial cycle (cool, temperate-warm, cool). The Weichselian glacial Stage in eastern Germany is represented by thick periglacial sedimentation, including gravels, gelifluction sheets, alluvium, debris covers and loess. Within these sediments is a wide variety of glaciotectonic structures and periglacial soil structures, including classical involutions and ice-wedge casts. An outline of the present state of knowledge of the Quaternary of eastern Germany is given in Tables 1-3 while Table 4 presents a stratigraphical comparison with the neighbouring regions and countries. The palaeogeography of the region during the periods of the European continental glaciation is depicted in Fig. 2. (C) 2002 Published by Elsevier Science Ltd. [References: 160]
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We present a new time-slice reconstruction of the Eurasian ice sheets (British-Irish, Svalbard-Barents-Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10...
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We present a new time-slice reconstruction of the Eurasian ice sheets (British-Irish, Svalbard-Barents-Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British-Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 2726 ka) than the eastern limit on the Russian Plain (at c. 20-19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm(2)) and volume (similar to 24 m Sea Level Equivalent) at c. 21 ka. Our continental-scale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA (www.bcdc.no; http://doi.pangaea.de/10.1594/PANGAEA.848117).
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Multidisciplinary investigations of the sequence at Beeches Pit, West Stow (Suffolk, UK), have a direct bearing the age of the Hoxnian Interglacial and its correlation with the continental Holsteinian and with the global marine re...
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Multidisciplinary investigations of the sequence at Beeches Pit, West Stow (Suffolk, UK), have a direct bearing the age of the Hoxnian Interglacial and its correlation with the continental Holsteinian and with the global marine record. At this site, glacial deposits (till and outwash gravels) referable to the Anglian Lowestoft Formation fill a subglacial channel cut in Chalk bedrock. Above these glacial deposits a series of interglacial sediments occurs, consisting of limnic, tufaceous and colluvial silts, lacking pollen but rich in shells, ostracods and vertebrates. Lower Palaeolithic flint artefacts of Acheulian character have also been recovered, including refitting examples. Charred material is abundant at certain horizons and many of the bones have been burned. Several discrete areas of burnt sediment are interpreted as hearths. The molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance. The land snail assemblage from the tufa consists of woodland taxa with no modern analogue, including species that are either extinct (e.g. Zonitoides sepultus) or which no longer live in Britain (e.g. Platyla polita, P. sitnilis, Neniatlantapauli). This is also the type locality of Retinella (Lyrodiscus) skertchlyi, which belongs to a subgenus of zonitid land snail now living only on the Canary Islands. There are indications from this fauna ('the Lyrodiscus biome') that the climate was wetter and perhaps warmer than the present day. The vertebrate fauna is also noteworthy with species of open habitats, such as rabbit (Oryctolagus cf. cuniculus), and of closed forest, such as squirrel (Sciurus sp.) and garden dormouse (Eliornys quercinus) present at different times. The occurrence of southern thermophiles, such as Aesculapian snake (Zamenis longissimus), indicates temperatures warmer than those of eastern England today. The upper levels include much material reworked from the interglacial sediments, although there is clear faunal evidence for climatic deterioration. Both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the Hoxnian. Uranium series dates from the tufa (similar to 455 ka BP), TL dates from burnt flints (414 +/- 30 ka BP) and a range of amino acid racentization data all support correlation of this interglacial with MIS 11. However, four OSL dates from sand beneath the interglacial sequence yield a mean age of 261 +/- 31 ka BP, far younger than all other age determinations and far younger than implied by the biostratigraphy. Archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a Lower Palaeolithic context. Biostratigraphical correlations with other Lower Palaeolithic sites support the suggestion that Acheulian and Clactonian industries both occurred in southern Britain during the same substage of the Hoxnian, although not necessarily at precisely the same time. The characteristics of the MIS I I interglacial in Britain are discussed in the light of evidence from Beeches Pit and elsewhere. (c) 2006 Elsevier Ltd. All rights reserved.
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To date, research on neotectonics and related continental topography development has mostly focused on active plate boundaries characterized by generally high deformation rates. The intraplate sedimentary basins and rifts of the N...
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To date, research on neotectonics and related continental topography development has mostly focused on active plate boundaries characterized by generally high deformation rates. The intraplate sedimentary basins and rifts of the Northern Alpine foreland are associated with a much higher level of neotectonic activity than hitherto assumed. Seismicity and stress indicator data, combined with geodetic and geomorphologic observations, demonstrate that Europe's intraplate lithosphere is being actively deformed. This has major implications for the assessment of its natural hazards and environmental degradation. The lithosphere of the Northern Alpine foreland has undergone a polyphase evolution with an intense interplay between upper mantle thermal perturbations and stress-induced intraplate deformation that points to the importance of lithospheric folding of the thermally weakened lithosphere. In this paper, we address relationships between deeper lithospheric processes, neotectonics and surface processes in the Northern Alpine foreland with special emphasis on tectonically induced topography. The objectives are to quantify the effects of ongoing Alpine collision and Atlantic ridge-push on the intraplate deformation in Europe and its impact on topography evolution and related natural hazards.This paper reviews the four-dimensional topographic evolution of the European lithosphere through a multi-disciplinary approach linking geology, geophysics and geotechnology. Until now, research on neotectonics and related topography development of intraplate regions has received little attention. Our study examines a number of selected natural laboratories in continental Europe. From orogen through platform to continental margin, these natural laboratories include the Carpathians-Pannonian system, the Northwest European Platform, Iberia and the Atlantic continental margin.We focus on lithosphere memory and neotectonics with special attention to the thermo-mechanical structure of the lithosphere, mechanisms of large-scale intraplate deformation, Late-Neogene anomalies in subsidence and uplift, and links with surface processes and topography evolution. (C) 2004 Elsevier Ltd. All rights reserved.
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Whether during past climate stages or into a progressively warming world, changes in precipitation constitute a key component of climatic change. Quantitative proxies for palaeo-precipitation are relatively rare. The magnetic prop...
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Whether during past climate stages or into a progressively warming world, changes in precipitation constitute a key component of climatic change. Quantitative proxies for palaeo-precipitation are relatively rare. The magnetic properties of the windblown loess units and interbedded palaeosols of the famous Chinese Loess Plateau provide key palaeo-precipitation data for this populous, monsoon dominated region. The loess/palaeosol sediments record rainfall totals, directly complementing the oxygen isotope records of Chinese speleothems. These isotopic records predominantly reflect moisture source, and hence large-scale atmospheric circulation changes. The two major Asian monsoon systems appear to display antiphase behaviour. Dominance of the Indian summer monsoon system seems associated with minimum precession/maximum northern hemisphere summer heating; dominance of the East Asian summer monsoons with maximum precession. At similar to 2.8 Ma, more intense development of the East Asian winter monsoon initiated major increases in dust deposition rates, and formation of relatively unweathered loess layers. Glacial-stage loess units then interleaved with interglacial/interstadial-stage palaeosols throughout the Quaternary period. Decoupling of the loess/palaeosol rainfall records from the Chinese cave records of moisture source shows that the Indian and East Asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool, glacial stages. The timing of these East Asian climatic transitions, the subsequent intensification of northern hemisphere glaciations, and the association between monsoon circulation changes and North Atlantic temperatures, indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture. (C) 2016 Elsevier Ltd. All rights reserved.
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Fossil corals provide valuable data for reconstructing past sea levels, as they are often well preserved in the fossil record and can be dated with U-series methods. Here we present a global and internally consistent database of U...
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Fossil corals provide valuable data for reconstructing past sea levels, as they are often well preserved in the fossil record and can be dated with U-series methods. Here we present a global and internally consistent database of U-Th dated fossil coral sea-level indicators, including full consideration of all (known) associated uncertainties (both vertical and chronological). We include carefully determined taxon-specific depth distributions, rather than blanket depth uncertainty terms as used in most previous work. This is based on a synthesis of extensive modern ecological information on depth ranges. These ranges are found to be spatially variable (between ocean basins, between regions, and on sub-regional scales) because depth itself is not limiting instead, depth distributions arise from complex physical, chemical, and biological interactions with coral-reef growth, distribution, and composition. One of the main causes for recognition of the greater depth-variability of coral taxa has been the routine inclusion of deep-diving and ROV surveys in coral ecological studies over the past few decades, which has broken through the "shallow-water" bias of early surveys by adding frequent observations on deeper occurrences (although more are needed). It is also clear from our assessment that coral habitat-depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels, and that application to sea-level studies then requires these studies also to identify fossil corals to the species level. Samples identified only to the genus level give rise to wide uncertainties in habitat depth and, hence, sea level. Our database contains extensive metadata to assist evaluations of dating quality, as well as geomorphic and stratigraphic metadata. We demonstrate with examples how such metadata can help to evaluate sea-level reconstructions, for example by identifying outlier points. One example discusses the Last Interglacial (LIG), where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present, which yields a mean age of 124.6 ka with 95% probability bounds at 118.5 and 129.5 ka. We conclude with identification of key outstanding issues relating to: (i) current incomplete understanding of tectonic setting (including the current lack of independent verification of uplift/subsidence rates and reliance of somewhat unsatisfactory, and circular, use of the elevation of Last Interglacial deposits); (ii) the depth-distributions of coral taxa and; (iii) the complete documentation of stratigraphic, geomorphological and other contextual information, with suggestions for strategies to address these issues. (C) 2016 Elsevier Ltd. All rights reserved.
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High-resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at Ribains maar (French Massif Central) during the Late Pleistocene (similar to 131-similar to 105 ka BP), with a focu...
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High-resolution diatom analysis was carried out to assess the limnological and climatic changes that took place at Ribains maar (French Massif Central) during the Late Pleistocene (similar to 131-similar to 105 ka BP), with a focus on the Eemian interglacial in particular. Numerical analyses were used to show that most of the variability in the fossil diatom assemblages was due to climate independently from the changes in the lake catchment vegetation (as represented by pollen data). Diatom-based quantitative reconstructions of the past limnological conditions, as well as a comprehensive literature review on the auto-ecological requirements for the principal diatom taxa, were used to interpret the record. An absolute time-scale for the sequence was derived by matching the major pollen shifts with the radiometrically dated changes in oxygen isotopes observed in Italian stalagmites. This study shows that at Ribains maar, the transition from the Riss (= Saalian) Glacial to the Eemian interglacial was marked by a gradual increase in the contribution of spring-blooming diatom species, indicating a longer growing season and milder winter/spring conditions Lit that time. A short cooling event interrupts this trend and may correspond to a stadial. At the start of the Eemian a peak in benthic taxa and the suppression of spring-blooming flora probably reflects the effects of deglaciation on the catchment. During the Eemian interglacial itself three main phases were distinguished within the diatom record. The first phase (similar to 8000 years in duration) was dominated by Stephanodiscus minutulus, which suggests that intense mixing in the water-column took place during spring. The pollen record was simultaneously dominated by Quercus and Corylus that typify this phase as the climatic optimum of the Eemian. The second phase, almost equal in duration to the first phase (similar to 7000 years), is generally dominated by Cyclotella taxa and suggests a less productive lake and much reduced period of spring mixing compared with the first phase. In the pollen diagram this corresponds to an interval dominated by Carpinus-Picea-Abies that indicates a cooler and wetter climate. The third and last phase of the Eemian, similar to 2000 year long, saw the return to Stephanodiscus-dominated assemblages, indicating a warming that may correspond to the Dansgaard-Oeschger event 25 identified in the Greenland ice-core record. In the early stage of the Wurm Glacial (= Weichselian), assemblages in the Melisey I stadial (similar to 3000 year long) were dominated by either Aulacoseira subarctica or Asterionella formosa, which Suggest colder spring conditions than during the late Eemian, but not as cold as the ones indicated by the pollen record. Stephanodiscus spp. again dominate during the Saint-Germain Ia interstadial (similar to 5000 year long) suggesting a return to the conditions that prevailed before the Melisey stadial, in agreement with the pollen record. The record ends with the Montaigu cold event, which is characterised by a. Pinus peak in the pollen record, and corresponds to a large abundance of A. subarctica in the diatom sequence. Throughout the Eemian the abundance of Stephanodiscus spp., which is thought to be driven by winter conditions, show cyclic fluctuations that most likely match the cooling events identified in a pollen record from Germany. Variation in insolation throughout the Eemian may have been the driving factor behind the species succession observed in the diatom sequence. While this study demonstrates that diatom analysis of lake sediment can provide very detailed information n long-term climate change, a review of the few other diatom investigations published on European Eemian deposits shows that this technique has been so far seldom used to its full potential in this context in central and southern Europe. (C)2007 Elsevier Ltd. All rights reserved.
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