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1.
Clarification of the temporal relationships amongst records of environmental change is dependent on accurate timescales. Event markers such as tephra layers are extremely important for constraining chronologies and providing tie points. In this report we present evidence of a previously unknown early Holocene Icelandic cryptotephra from a lake in northern Scotland—the ‘An Druim Tephra’. The calibrated radiocarbon age of 9560 cal. yr BP for this new cryptotephra makes it an important addition to the suite of cryptotephras now recorded from the last glacial termination and early Holocene in northwest Europe. In addition we report evidence in support of a ‘Younger Borrobol Tephra’ from Lateglacial sediments of Allerød age. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

2.
The last British-Irish Ice Sheet (BIIS) created a landscape with many sedimentary basins that preserve archives of paleoenvironmental and paleoclimatic change during the Last Glacial-Interglacial Transition (LGIT; ~ 18-8 ka BP). The typical lithostratigraphic succession of these archives is composed of minerogenic/allogenic sediments formed during cold climatic conditions and organic-rich/authigenic sediments during warmer climates. This paper presents a multi-core lithostratigraphy compiled from the extant lake and surrounding basin at Llangorse Lake, south Wales, a basin lying within the southernmost limits of the last BIIS. This lake contains one of the longest continuous terrestrial sediment successions in the UK. Uncertainty previously existed concerning the presence and distribution of sediments at the site related to the Windermere Interstadial (~ 14.7 to ~ 12.9 ka BP) and Loch Lomond Stadial (~ 12.9 to 11.7 ka BP). A new borehole survey demonstrates that LGIT-age sediments are present at the site with nekron mud (gyttja), corresponding to the Lateglacial Interstadial, deposited in the deeper part of the lake waters and that these deposits are equivalent in age to marl deposits found at shallower depths at the margins of the basin. These deposits are associated with warmer conditions experienced during the Windermere Interstadial and Holocene, whilst minerogenic-rich sediments were deposited during the colder climatic conditions of the Dimlington Stadial and the Loch Lomond Stadial with rangefinder radiocarbon dates confirming this attribution. A model of lake level changes shows that drainage of the Dimlington Stadial glacial lake caused the largest fall, but there was also a further, smaller lake level fall at the end of the Windermere Interstadial and/or the start of the Loch Lomond Stadial, before the level rose in the early Holocene. The lithostratigraphic results presented here form the framework for further paleoenvironmental and paleoclimatic research at Llangorse Lake.  相似文献   

3.
Gough's Cave is still Britain's most significant Later Upper Palaeolithic site. New ultrafiltered radiocarbon determinations on bone change our understanding of its occupation, by demonstrating that this lasted for only a very short span of time, at the beginning of the Lateglacial Interstadial (Greenland Interstadial 1 (GI-1: Bølling and Allerød)). The application of Bayesian modelling to the radiocarbon dates from this, and other sites from the period in southwest England, suggests that re-colonization after the Last Glacial Maximum took place only after 14,700 cal BP, and is, therefore, more recent than that of the Paris Basin and the Belgian Ardennes. On their own, the radiocarbon determinations cannot tell us whether re-colonization was synchronous with, just prior to, or after, Lateglacial warming. Isotopic studies of humanly-modified mammalian tooth enamel may be one way forward.  相似文献   

4.
Radiocarbon dates are described from a section through Lateglacial and early Flandrian sediments at Llanilid, Mid-Glamorgan, South Wales. Comparisons between age determinations on the alkali soluble (humic) and alkali insoluble (humin) organic fractions from 12 biostratigraphic horizons reveal the extent of contamination by both older and younger carbon residues. The Llanilid time-scale suggests that for the Lateglacial, the earliest organic sediments date from around 13 200 yr BP, the early Interstadial Juniperus maximum occurred at ca. 12 400-12 500 yr BP with a marked decline some 200 years later, the main Betula phase lasted only from ca. 11 700 to 11 400 yr BP and the end of the Interstadial occurred around 11 100 yr BP. The beginning of the Flandrian dates from ca. 10 000 yr BP, the Juniperus maximum occurred approximately 200 years later, the expansion of birch woodland began around 9600 yr BP, while the first hazel arrived in the area at ca. 9300 yr BP. These age determinations are discussed in the context of radiocarbon dates from comparable biostratigraphic horizons in western Britain and the dating of Lateglacial events in the ocean core records from the North Atlantic.  相似文献   

5.
Changes in chironomid midge larval assemblages in Lateglacial (c. 13.5–10 ka yr BP) lake sediments from Whitrig Bog are used to infer climatic (temperature) change. The earliest sediments contain few, predominantly cold stenothermic taxa. This fauna is replaced by an assemblage dominated by thermophilic taxa, indicating rising temperatures. The relatively warm Interstadial is punctuated by at least two brief cold oscillations which are characterized by the return of certain cold-water taxa and the demise of some elements of the thermophilic fauna. The earlier of the two oscillations was apparently shorter and colder than the second. The highest Lateglacial Interstadial temperatures were attained either shortly before or after the first cold oscillation. This timing of the Lateglacial thermal maximum is apparently later than has been previously inferred from fossil beetle data. The Lateglacial Interstadial is terminated by the Loch Lomond (Young Dryas) Stadial, which is indicated in this monolith by an abrupt return of cold stenothermic Chironomidae and the virtual elimination of thermophilic taxa. Temperatures during the Younger Dryas appear to have been colder than during either of the previous minor cold oscillations. Climatic inferences from chironomid analysis broadly support and augment conclusions drawn from sediment chemistry and palynological evidence derived from the same monolith, although there is evidence that the vegetation and chironomid responses to early postglacial warming were out of phase.  相似文献   

6.
Magnetostratigraphical results from various historical, Holocene, Lateglacial and Glacial deposits from Central Jutland, Vendsyssel, the Baltic Sea and Schleswig-Holstein are illustrated and discussed. Although only a few archaeomagnetic case studies have yet been made in Denmark, magnetic datings with accuracies of about ±50 years have been obtained on mediaeval kilns by comparing with a dipole transformed modification of the British archaeomagnetic master curve. Furthermore, a study of the expected east–west orientation of some 330 Romanesque churches in Denmark seem to indicate that about 25% of these churches were magnetically orientated; thus some kind of a magnetic compass may have been in common use in the twelfth century in Denmark. Radiocarbon-dated Holocene lake sediments from lake Skanderborg reveal a distinct pattern of magnetic secular variation with fairly short time constants, which may be useful in magnetostratigraphical correlations of other lake sediments. Also Lateglacial and Early Postglacial sediments from the southern Baltic Sea show systematical magnetic patterns, whereas glacial boulder clay at the bottom shows disturbed directions, obviously moulded by the moving ice. Lateglacial Younger Yoldia clay from North Jutland shows well-developed short periodic swings as well as an extreme declination variation of some 80° to 90°, the so-called 'Nørre Lyngby declination excursion' around 14,000 B.P. A sequence of Older Yoldia clay at the same site furthermore shows significantly low inclination values, the so-called 'Rubjerg low inclination excursion' of an age between 23,000 B.P. and 40,000 B.P. Finally, a well-clustering palaeomagnetic direction from a Weichselian glacial boulder clay from Timmerhorn north of Hamburg is discussed from a hierarchical, statistical point of view.  相似文献   

7.
Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site‐specific palaeo‐records are needed. Here we present a multi‐proxy study of a 350‐cm‐long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain‐size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, δ13Corg) and stable water isotopes (δ18O, δD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre‐lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post‐drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core‐based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice‐rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst‐affected regions of the Arctic.  相似文献   

8.
Pollen-stratigraphic evidence is presented from a site in the Grampian Highlands of Scotland in which a detailed record is preserved of early Postglacial plant succession in an area previously occupied by glacier ice. Following an initial period of open habitat conditions during which sedge-moss communities were interspersed with large areas of bare, disturbed ground, the area around the site was colonised first by Empetrum heath, and then successively by juniper scrub, birch, and then birch-hazel woodland. On a local scale, the biostratigraphic record implies a rapid shallowing of lake waters during the early Postglacial, due possibly to relatively dry climatic conditions which prevailed in the area after ca. 9000 B.P. Radiocarbon dates were obtained from the basal sediments in the site, but these are regarded as aberrant due to groundwater contamination. In view of the poor resolution associated with the radiocarbon-dating of Lateglacial and early Flandrian events in Britain, a method is proposed here whereby pollen stratigraphic evidence at widely separated sites can be employed to gauge the extent to which deglaciation at the end of the Loch Lomond (Younger Dryas) Stadial was time-transgressive across the Highlands of Scotland  相似文献   

9.
《Quaternary Science Reviews》2007,26(3-4):517-535
A pollen profile from Okarito Pakihi Bog in south Westland, New Zealand extending from near present back to Marine Isotope Stage (MIS) 6 provides a continuous record of vegetation and climate change for the past two glacial cycles. Independent chronological control was obtained by AMS radiocarbon dating of organic sediments in the upper part of the sequence and OSL dating of inorganic silts in the lower part, with a unique tie point provided by the ca 26.5 cal ka Kawakawa Tephra. As was probably a common occurrence in this region, the basin developed as a moraine-dammed proglacial lake and remained lacustrine until the early Holocene, when a peat bog developed. Survival of the depositional site through subsequent multiple ice advances, unusual in a glaciated landscape, was probably assisted by lateral displacement of the basin relative to its source area, across the Alpine Fault.There is good correspondence between inferred periods of substantial treeline depression in the pollen profile and the record for ice advance in this region. More cooling events are evident in the pollen record, however, presumably due to the fragmentary nature of glacial geomorphology. The pollen record also shows broad consistency with the MIS record and hence with the Milankovitch orbital forcing model, but with some departures, including an early onset to the last glacial maximum (LGM). Several sub-Milankovitch scale events are also evident, including a mid-LGM warming and Lateglacial reversals during both the last and the penultimate deglaciation.  相似文献   

10.
Recently, the sediment stratigraphy and geochronology of the well‐known Palaeolithic site Byzovaya in northern Russia were investigated. New technological analyses of the artefacts suggest a Middle Palaeolithic Mousterian culture, and occupation by Neanderthals, not Modern humans as previously thought. We present here a new and detailed documentation of the stratigraphy, including the geological context of the artefacts and faunal remains. From sedimentological criteria we confidently interpret the find‐bearing strata as debris‐flow deposits, covered by aeolian sediments. The chronology is based on radiocarbon and luminescence (OSL) dates from the find‐bearing and overlying strata. The results are utilized to reconstruct the geological history at the excavation area. The stratigraphy varies considerably across the excavation area. The most intact and undisturbed part of the sequence was found inside the most recent Excavation II. In this part the artefacts and bones appear to have been permanently sealed and protected by aeolian sand. The older Excavation I shows a more complicated stratigraphy, as the finds may have been temporarily exposed during the early Holocene owing to ravine incision and slumping activity. The individual radiocarbon dates that were collected from different parts of the site and from various stratigraphic positions are re‐investigated in this study. By using Bayesian statistics the conclusion is that the site was occupied during a restricted period around 30.6–34.7 ka. A series of partly unpublished OSL dates of coversand from different sites demonstrates a regional aeolian signal during the Lateglacial in northern Russia, 15–14 ka.  相似文献   

11.
Six new radiocarbon ages and a pollen sequence are provided for Laguna Stibnite, a small lake on the Taitao Peninsula, Chile (latitude 46°25'S, longitude 74°24'W). The sediments record a late-glacial to present sequence, with a basal age of 14 335 ± 145 yr BP (Q-2840). The radiocarbon ages provide the basis for a sound chronology in a region of Chile where few palynological studies have been made and where previous radiocarbon ages are ambiguous. The chronology from Laguna Stibnite supports the acceptance of a radiocarbon chronology based on wood fragments (rather than bulk analysis) at a site near Puerto Edén further south in the Chilean Channels (49°08'S). These data from Laguna Stibnite provide evidence for an early deglaciation (before 14 000 yr BP) in this region of southern Chile. The sequence provides no evidence for a climatic reversal between 11 000 yr BP and 10 000 yr BP, the so-called Younger Dryas chron.  相似文献   

12.
《Quaternary Research》2014,81(3):445-451
Some scholars have argued that the formation and outburst of an ancient dammed lake in the Jishi Gorge at ca. 3700 cal yr BP resulted in the destruction of Lajia, the site of a famous prehistoric disaster in the Guanting Basin, upper Yellow River valley, China. However, the cause of the dammed lake and the exact age of the dam breaching are still debated. We investigated ancient landslides and evidence for the dammed lake in the Jishi Gorge, including dating of soil from the shear zone of an ancient landslide, sediments of the ancient dammed lake, and loess above lacustrine sediments using radiocarbon and optically stimulated luminescence (OSL) dating methods. Six radiocarbon dates and two OSL dates suggested that the ancient landslides and dammed lake events in the Jishi Gorge probably occurred around 8100 cal yr BP, and the ancient dammed lake was breached between 6780 cal yr BP and 5750 cal yr BP. Hence, the outburst of the ancient dammed lake in the Jishi Gorge was unrelated to the ruin of the Lajia site, but likely resulted in flood disasters in the Guanting Basin around 6500 cal yr BP.  相似文献   

13.
The results of eight radiocarbon datings of Lake Chapala sediments (site T46) are presented, the age inversions (AI) observed and their age progression discussed. As deduced from some AIs and the 210Pb activity (site CHP4), the bioturbation zone in the lake varies over a depth of 5–25 cm. The linear sedimentation rates (LSRs) calculated from 14C ages do not match the LSR calculated from unsupported 210Pb activity for the upper sediments. This demonstrates the usefulness of dating sediments with complementary radiometric techniques such as short-lived isotope counting (SLIC), i.e., 210Pb and 137Cs. This approach leads to the following conclusions: (1) The incorporation of detrital particles with ancient carbon into the sedimentary column of the lake occurred by a combination of: (a) the presence of outcrops of hydrothermal petroleum with ages >40 ka (ka = thousands of years) in the lake, and (b) mass transport due to the presence of two elongated gyre circulation patterns integrated by cyclonic circulation (counterclockwise) in the north portion of the lake and anticyclonic circulation in the southern part. (2) Consequently, the 14C ages of shallow lake sediments have geologic ages one order of magnitude greater compared to their ages determined by the 210Pb method. (3) A bioturbation mechanism is not necessary to explain the 14C AI in the top 70 cm and from 110 to 150 cm depth of the sediments. (4) According to the biological proxies data for the last 600 years B.P., the paleoclimate at Lake Chapala has changed from sub-humid to dry environmental conditions, and eutrophication has increased over the past 100 years due to local input from ongoing agricultural activities.  相似文献   

14.
Recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived 10Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
《Quaternary Science Reviews》1999,18(8-9):1075-1125
Holywell Coombe is a valley cut into the scarp-face of the North Downs Chalk cuesta, near Folkestone, Kent. Its geological importance stems from a highly fossiliferous sequence of Lateglacial and Holocene deposits that line the valley floor. These have yielded a molluscan succession of particular importance, providing a record of environmental change throughout the past 13,000 radiocarbon years. Waterlogging of the basal deposits has prevented oxidation, leading to the preservation of a range of organic fossils, such as plant and insect remains, that normally do not survive in calcareous environments. This enables linkage between faunal and vegetational records, allowing the differential rates of response of particular groups to be critically compared. The importance of the site was revealed in 1968 in trial pits connected with an aborted Channel Tunnel project. Resurrection of plans to build a tunnel led in 1987 to major ‘rescue’ excavations and multidisciplinary investigations, the results of which are reviewed here. A three-dimensional picture of the valley infill was established from a network of 180 boreholes. Critical parts of the sequence were investigated in specially excavated trenches and sections exposed during construction of the tunnel. Systematic sampling at a number of locations within the valley provided a palaeontological record from the full stratigraphical succession. A number of Lateglacial and Holocene soils were found to be represented in the sequence, including that formed during the Allerød phase of the Lateglacial interstadial. The molluscan zonation scheme previously defined at Holywell Coombe, and applicable over large areas of southern Britain and possibly further afield, has been refined and dated with greater precision. The Lateglacial sequence has been extended back to the early part of the Lateglacial interstadial by this study and the site chronology is now underpinned by over 35 new radiocarbon dates. Quantitative palaeoclimatic reconstructions from beetle remains, using the Mutual Climatic Range method, cover the period between 13,000 and 9000 yr BP. The earliest sediments, marsh deposits with thermophilous insect taxa and a species-poor molluscan assemblage, date from around 13,000–12,000 yr BP. Just before the end of this period, changes in beetle faunas record climatic cooling, heralding slope instability and the accumulation of thick colluvial deposits. By 11,500 yr BP the climate had stabilized and slope movement had ceased, allowing the formation of the ‘Allerød soil’. There followed a major deterioration to the arctic climate of the Younger Dryas, during which renewed erosion from the valley sides brought further material onto its floor, burying and sealing the earlier sediments. The beginning of the Holocene saw the onset of tufa formation around two dominant springs in the upper valley. There was progressive development of forest, hazel-dominated woodland being established by 9500 yr BP. There is some evidence for thinning of the forest canopy during the late Mesolithic and Neolithic, but the major clearance occurred during the Early Bronze Age, causing renewed instability on slopes and consequent hillwash accumulation. This final depositional phase continued, with pauses marked by soil formation in the Early Bronze Age and the Iron Age, to the present day. The hillwash seals structures relating to prehistoric human activity, including plough-marks, and contains an extensive sequence of artefacts.  相似文献   

16.
With accelerated melting of alpine glaciers, understanding the future state of the cryosphere is critical. Because the observational record of glacier response to climate change is short, palaeo‐records of glacier change are needed. Using proglacial lake sediments, which contain continuous and datable records of past glacier activity, we investigate Holocene glacier fluctuations on northeastern Baffin Island. Basal radiocarbon ages from three lakes constrain Laurentide Ice Sheet retreat by ca. 10.5 ka. High sedimentation rates (0.03 cm a?1) and continuous minerogenic sedimentation throughout the Holocene in proglacial lakes, in contrast to organic‐rich sediments and low sedimentation rates (0.005 cm a?1) in neighbouring non‐glacial lakes, suggest that glaciers may have persisted in proglacial lake catchments since regional deglaciation. The presence of varves and relatively high magnetic susceptibility from 10 to 6 ka and since 2 ka in one proglacial lake suggest minimum Holocene glacier extent ca. 6–2 ka. Moraine evidence and proglacial and threshold lake sediments indicate that the maximum Holocene glacier extent occurred during the Little Ice Age. The finding that glaciers likely persisted through the Holocene is surprising, given that regional proxy records reveal summer temperatures several degrees warmer than today, and may be due to shorter ablation seasons and greater accumulation‐season precipitation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

17.
Investigations of Lateglacial to Early Holocene lake sediments from the Nahe palaeolake (northern Germany) provided a high-resolution palynological record. To increase the temporal resolution of the record a targeted search for cryptotephra was carried out on the basis of pollen stratigraphy. Three cryptotephra horizons were detected and geochemically identified as G10ka series tephra (a Saksunarvatn Ash), Vedde Ash and Laacher See Tephra. Here we present the first geochemically confirmed finding of the ash from the Laacher See Eruption in Schleswig-Holstein—extending the so far detected fallout fan of the eruption further to the north-west. These finds enable direct stratigraphical correlations and underline the potential of the site for further investigations.  相似文献   

18.
Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 14C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes (Limnocythere ceriotuberosa) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.  相似文献   

19.
《Quaternary Science Reviews》1999,18(10-11):1247-1314
Gravel quarries at Somersham, Cambridgeshire, have yielded evidence for a Pleistocene channel of the R. Great Ouse, containing temperate stage sediments between cold stage sediments. In the earlier cold stage, fluviatile gravels and floodplain loessic sediment accumulated. In the later cold stage a further series of gravel units and floodplain sediments were deposited, together with lake sediments. The lake sediments are associated with Lake Sparks, dammed by Late Devensian ice in the Wash at ca. 18.5 ka BP. The lake sediments overlie gravels with a radiocarbon date from an organic horizon indicating a Middle Devensian age. Clast lithological analyses from the earlier and later gravels suggest that reworking of gravels has occurred within a relatively stable catchment. The petrography of the earlier cold stage loessic sediment and temperate stage fine sediment indicates an Anglian affinity, which conflicts with the biostratigraphic interpretation. Pollen and macroscopic plant remains from sediments of both cold stages and from the temperate stage indicate, respectively, assemblages with a typical full-glacial aspect with a rich flora of shrubs and open ground herbs(including an assemblage at ca. 18 ka), and temperate freshwater and marine-influenced organic sediments. On the basis of pollen analysis these are ascribed to substages Ip II and III of the Ipswichian Stage(O.I.S. 5e), with a Pinus-Quercus-Corylus biozone in the former and a biozone with Carpinus in the latter. Marine-influenced sediments, at −3.7 to −0.3 m OD, indicate transgression in Ip II and regression in Ip III.Molluscan assemblages from the temperate stage and the later cold stage are described; two are from the Late Devensian, at a time near the maximum extension of ice into the Wash. Foraminifer and ostracod faunas are described from post-Ipswichian sediments and may be reworked. Radiocarbon dates confirm the age of the later gravel suite as Devensian and a calibration of the measurements is given. Amino acid ratios from Corbicula fluminalis valves from temperate stage sediments are reported, with measurements from different parts of the valve; the results tend to support an Ipswichian age. TL measurements of the earlier cold stage loessic sediment and associated sand indicate a pre-Ipswichian age for the sediments. The earlier cold stage is correlated with the pre-Ipswichian cold stage, the Wolstonian of Mitchell et al.(1973); problems with this correlation are discussed.Various periglacial phenomena, including thermal contraction networks and cracks, diapirs, involutions and coversand are associated with the Devensian sequence. The complex environmental history, based on stratigraphy and palaeontology, is described, and related to other nearby sites in southern Fenland.  相似文献   

20.
We present a database of late-Quaternary plant macrofossil records for northern Eurasia (from 23° to 180°E and 46° to 76°N) comprising 281 localities, over 2300 samples and over 13,000 individual records. Samples are individually radiocarbon dated or are assigned ages via age models fitted to sequences of calibrated radiocarbon dates within a section. Tree species characteristic of modern northern forests (e.g. Picea, Larix, tree-Betula) are recorded at least intermittently from prior to the last glacial maximum (LGM), through the LGM and Lateglacial, to the Holocene, and some records locate trees close to the limits of the Scandinavian ice sheet, supporting the hypothesis that some taxa persisted in northern refugia during the last glacial cycle. Northern trees show differing spatio-temporal patterns across Siberia: deciduous trees were widespread in the Lateglacial, with individuals occurring across much of their contemporary ranges, while evergreen conifers expanded northwards to their range limits in the Holocene.  相似文献   

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