摘要:

AbstractPollen and dinoflagellate cysts from marine sediments in core A180‐48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade‐wind circulation and related coastal upwelling at 15°N latitude. The sea‐surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground‐water input, this smaller temperature difference may explain the persistence of theRhizophoramangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110‐Z, from the continental shelf at t

ISSN:0267-8179    

DOI:10.1002/jqs.3390100202

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractIn a dry valley near Ventnor, Isle of Wight, thick subaerial slope deposits of Devensian Late‐glacial age overlie the Chalk. The deposits are crudely stratified chalk muds and rubble produced by frost‐shattering, and moved downslope by the release of water from melting snow‐fields and frozen ground. A laterally extensive humic horizon of a rendzina soil occurs within the sequence, clearly reflecting a period of relative slope stability. In places this horizon divides and its upper surface appears to have been disturbed, possibly by cryoturbation. Micromorphological and other analyses confirm the pedogenic origin of this humic horizon, but also demonstrate the occurrence of pedological features both above and below it. The humic horizon therefore is not a ‘buried’ soil in the strictest sense, but is part of a vertical sequence representing a single complex soil with transported, accretionary and welded components.Molluscan analyses reveal that the sequence can be divided into four local mollusc zones, showing a progressive increase in faunal diversity throughout the profile. This succession is broadly similar to other Late‐glacial sequences described from south‐east England. Minute fragments of charcoal from the lower part of the humic horizon have yielded an AMS date of 11690 ± 120 vr BP, demonstrating formation during the ‘Allerød phase’ of the Late‐glacial Interstadial. This humic horizon is correlated provisionally with the ‘Pitstone Soil’, even though existing dates from its type‐site in Buckingha

ISSN:0267-8179    

DOI:10.1002/jqs.3390100203

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe Quaternary fills of the buried valleys of southern Alberta and Saskatchewan have provided a wealth of information for the reconstruction of the glacial‐interglacial record of the western plains of Canada, and this paper reports on the previously unstudied stratigraphy of the buried Calgary Valley and its former tributaries in the lower Red Deer River area. We attempt to differentiate Empress Group sediments, which potentially relate to pre‐glacial, interglacial/ interstadial and post‐glacial lake and river deposition, using sedimentology, stratigraphy and palaeoecology. Twenty‐nine stratigraphical logs indicate that Empress Group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the Calgary Valley, located 15 km to the north of Dinosaur Provincial Park. Radiocarbon dates of 52.4 ka, 27.4 ka and>42.4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid‐Wisconsinan in age. However, outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials/interstadials and that older (even pre‐glacial) sediments could have survived. Subglacial channels, recognisable on air photographs, largely coincide with buried valley positions due to the preferential excavation of the Quaternary sediment by meltwater and are filled with post‐glacial lake sediment from which a radiocarbon date of 16 ka BP was obtained. Pre‐glacial and glacial/post‐glacial Empress Group sediments are lithologically indistinct but cover a large time span in

ISSN:0267-8179    

DOI:10.1002/jqs.3390100204

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe macrofossils, lithology and chronology of two lake basins on Disko in central West Greenland have been investigated. Both lakes were isolated from the sea in the mid‐Holocene as a result of relative land uplift. A marine‐brackish‐limnic sequence was recovered from the Qivittut Lake. The marine fauna is unusually diverse, whereas the brackish water fauna consists only of few species. Immediately after isolation the lake passed through a short‐lived eutrophic phase, after which stable, mesotrophic conditions were established. From the second lake basin, the Fortunebay Lake, only limnic sediments were recovered. This lake record demonstrates that rather stable conditions have persisted since mid‐Holocene times. Both lakes show anomalously high accumulat

ISSN:0267-8179    

DOI:10.1002/jqs.3390100205

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractPollen diagrams from organic facies overlain by glacigenic sediments at Pen‐y‐bryn, North Wales (53°7′N, 4°16′W), suggest that it is the first locality in the British Isles to provide evidence for several Devensian interstadials prior to Devensian stadial glaciation(s). The evidence is not, however, unequivocal. At least two main episodes of organic sedimentation are indicated, separated by an interval of uncertain duration. One eposide records aPinus‐Picea‐Betulaforest. A second, possibly later, event, with tree pollen less than 10% of total land pollen (TLP), suggests a cool, largely unforested environment. A third episode, with tree pollen up to 25% of TLP, may be related to the latter or be of intermediate age, whereas a fourth and later episode of organic accumulation may be of reworked material. Radiocarbon dating of organic deposits and of a wood macrofossil enclosed in basal till is inconclusive, as is preliminary uranium‐series dating. The principal biogenic episodes may correlate with Oxygen Isotope Substages 5c and 5a, but as the pollen records reflect facies floras, the correlation remains tentative; it is also possible that other temperate periods are recorded. Further resolution of the chronostratigraphy is required to help clarify the problematic correlation of interstadial and stadial events in northwest Europe and to correlate more accurately the biogenic and glacigenic facies at Pen‐y‐bryn with their Pleistocene eq

ISSN:0267-8179    

DOI:10.1002/jqs.3390100206

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA palaeotemperature record based on fossil coleopteran evidence and dated by accelerator mass spectroscopy (AMS)14C determinations on plant macrofossils has been obtained for the last glacial‐interglacial transition from the site of Gransmoor in eastern England. Calibration of the radiocarbon measurements enabled a direct comparison to be made between this palaeotemperature curve and the snow accumulation record from the GISP‐2 Greenland ice‐core. The similarity between the two data sets suggests a degree of correspondence in the pattern and timing of climatic change in Greenland and the British Isles at the end of the last cold

ISSN:0267-8179    

DOI:10.1002/jqs.3390100207

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390100208

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390100209

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390100210

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390100211

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY