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1.
B. Ahmed G. J. Alner H. Araujo J. C. Barton A. Bewick M. J. Carson D. Davidge J. V. Dawson T. Gamble S. P. Hart R. Hollingworth A. S. Howard W. G. Jones M. K. Joshi V. A. Kudryavtsev T. B. Lawson V. Lebedenko M. J. Lehner J. D. Lewin P. K. Lightfoot I. Liubarsky R. Lüscher J. E. McMillan B. Morgan G. Nicklin S. M. Paling R. M. Preece J. J. Quenby J. W. Roberts M. Robinson N. J. T. Smith P. F. Smith N. J. C. Spooner T. J. Sumner D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702
The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented. 相似文献
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Richard C. Preece Simon A. Parfitt G. Russell Coope Kirsty E. H. Penkman Philippe Ponel John E. Whittaker 《第四纪科学杂志》2009,24(6):557-580
Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north‐western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ‘Sidestrand Unio‐bed’, here defined as the Sidestrand Hall Member of the Cromer Forest‐bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio‐bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomys savini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ‘Cromerian Complex’ and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial – probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ‘new glacial stratigraphy’ during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
3.
G.R. Coope P.L. Gibbard A.R. Hall R.C. Preece J.E. Robinson A.J. Sutcliffe 《Quaternary Science Reviews》1997,16(10):1163-1195
Fossiliferous silts within the Late Pleistocene Kempton Park Gravel, of the River Thames Valley, were exposed in 1980 during foundation works for the Ismaili Centre in South Kensington, London. The results of a multidisciplinary study of the geomorphology, sediments, fossil plants, vertebrates, molluscs, ostracods and insects are reported. The silts were deposited under two distinct climatic regimes; a lower unit accumulated when the climate was arctic and an upper when the temperatures were at least as warm as those of the present day. Both these units occupy the same channel system and are separated from one another by less than a metre of sediment, implying that the climatic change was probably sudden and intense. The strongest evidence for this climatic difference comes from a study of the Coleoptera, which show an almost complete replacement of the arctic element in the fauna by a suite of temperate species. Palaeotemperature reconstructions using the Mutual Climatic Range method, based on the coleopteran assemblages from the lower unit, suggest that the mean temperature of the warmest month was 9±2 °C and that of the coldest month −22±10 °C. For the upper unit the mean temperature of the warmest month had risen to about 17 °C and that of the coldest month to about −4 °C. The episode represented by the lower unit, with its arctic climate, had not previously been recognized in the Thames Valley. The fauna from the upper, temperate, unit is very similar to that from other sites in the Kempton Park Gravel, such as that from Isleworth, 10 km upriver, which, like the upper unit at the Ismaili Centre, was characterized by the virtual absence of trees. It would appear that in such cases this treelessness does not indicate cold conditions, equivalent to those of the modern tundra, but may instead result from a combination of ecological and temporal factors. The value of multidisciplinary studies in reaching such conclusions is emphasized.The temperate episode described here is correlated with the thermal maximum at the early part of the Upton Warren Interstadial Complex. An earlier suggestion, based on amino acid epimerization ratios, that the Upton Warren Interstadial correlates with Oxygen Isotope Sub-stage 5a is not supported by the data, which show no evidence of the forested environments that characterized this period in both Britain and the adjacent Continent. It is thought that the temperate deposits at the Ismaili Centre belong to the Middle (Pleniglacial), rather than the Early, Devensian (Weichselian) and are equivalent to Oxygen Isotope Stage 3. 相似文献
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D. L. Band L. A. Ford J. L. Matteson D. M. Palmer B. J. Teegarden M. S. Briggs G. N. Pendleton R. D. Preece W. S. Paciesas 《Astrophysics and Space Science》1995,231(1-2):145-148
No absorption lines between 15 and 100 keV have been detected in burst spectra accumulated by BATSE. Almost 250 bursts have been inspected visually, and a computerized search has begun. Our simulations show that BATSE could indeed detect lines similar to those observed byGinga in strong bursts, and our tests of the detectors' actual capabilities demonstrate they function as understood. The apparent discrepancy between BATSE andGinga is not yet compelling, and therefore the BATSE nondetections do not invalidate theGinga detections. Nonetheless, the absence of BATSE line detections indicates a low line-occurrence frequency. 相似文献
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R. D. Preece M. S. Briggs G. N. Pendleton W. S. Paciesas J. L. Matteson D. L. Band L. A. Ford 《Astrophysics and Space Science》1995,231(1-2):207-210
The BATSE Spectroscopy Detectors (SDs) each have a thin beryllium window which allows detection of photons down to 5 keV. Until recently, exploitation of low-energy SD discriminator data has been held up by a lack of knowledge of its energy coverage. A recent series of in-flight changes in the instrument configuration has allowed the SD discriminators to be calibrated fairly accurately. With this in hand, we have surveyed BATSE GRBs for such features as X-ray precursors and after-glows in the roughly 5-10 keV band. For a large percentage of the BATSE bursts, no emission is observed in this energy band. In some cases where low-energy emission has been observed, ratios of flux histories indicate differential spectral evolution. In addition, we have obtained joint spectral fits between the low-energy data and the regular SD data, showing that a single spectral model is sometimes insufficient to fit the entire energy range. 相似文献
8.
Ole Bennike Lars Hedens Kirsty High Joakim S. Korshj Geoffrey Lemdahl Kirsty Penkman Richard C. Preece Knud Rosenlund Finn A. Viehberg 《Boreas: An International Journal of Quaternary Research》2019,48(1):107-118
During a pre‐site survey and construction of a new metro route and station in Copenhagen, fossiliferous organic‐rich sediments were encountered. This paper reports on multidisciplinary investigations of these organic sediments, which occurred beneath a sediment succession with a lower till, glacifluvial sand and gravel, an upper till and glacifluvial sand. The organic sediments were underlain by glacifluvial sand and gravel. The organic‐rich sediments, which were up to 0.5 m thick, accumulated in a low‐energy environment, possibly an oxbow lake. They were rich in plant fossils, which included warmth‐demanding trees and other species, such as Najas minor, indicating slightly higher summer temperatures than at present. Freshwater shells were also frequent. Bithynia opercula allowed the sediments to be put into an aminostratigraphical framework. The amino acid racemization (AAR) ratios indicate that the organic sediments formed during Marine Isotope Stage 7 (MIS 7), which is consistent with optically stimulated luminescence dating that gave ages of 206 and 248 ka from the underlying minerogenic deposit. The assemblages from Trianglen are similar to interglacial deposits from the former Free Port (1.4 km away) in Copenhagen, except that Corbicula and Pisidium clessini were not found at Trianglen. The presence of these bivalves at the Free Port and the ostracod Scottia tumida at Trianglen indicates a pre‐Eemian age. AAR data from archived Bithynia opercula from the Free Port were almost identical to those from Trianglen, indicating that the two sites are contemporary. We suggest the Trianglen interglacial be used as a local name for the MIS 7 interglacial deposits in Copenhagen. MIS 7 deposits have rarely been documented from the region, but MIS 7 deposits may have been mistaken for other ages. The use of AAR ratios in Bithynia opercula has a great potential for correlation of interglacial non‐marine deposits in mainland northern Europe. 相似文献
9.
The Condat tufa is a localised deposit, reaching 8.2m in thickness, composed of freshwater carbonates deposited in a complex series of environments which include marsh, spring and stream facies. Five radiocarbon determinations had previously been obtained from different stratigraphic levels within the tufa and had given a consistent series, ranging from 12320 ± 175 BP to 31050 ± 1500BP. Although the youngest two dates, from near the surface of the tufa, had been rejected as being anomalously young, the older dates were regarded as indicating tufa formation during the last cold stage. Biostratigraphic analyses of the molluscan and ostracod faunas, presented here, demonstrate that the tufa formed under fully temperate conditions throughout. The occurrence of certain snails that are either locally extinct (e.g. Belgrandia marginata) or unknown living in western France (e.g. Daudebardia brevipes), together with the geomorphological setting, suggest that the tufa is of interglacial age. New radiocarbon determinations of the Condat tufa all proved to be >33 Ka BP and support this conclusion. 相似文献
10.
Organic sediments in a gravel quarry at Block Fen, Cambridgeshire, form a sheet dividing lower from upper gravels. Analyses of pollen, macroscopic plant remains and molluscs from these organic sediments are presented. They indicate the presence of temperate freshwater and slightly brackish fine floodplain sediments, which, on the basis of the palaeobotany, are correlated with the temperate Ipswichian Stage. The freshwater sediments, ascribed to Ipswichian substage IIb, occur at ca. ?3 m OD. Marine-influenced tidal sediments, ascribed to Ipswichian substage III, occur at ca. ?6 m OD. No evidence was found for the presence of more than one temperate stage in the sequence. The lower gravels are then correlated with the cold Wolstonian Stage and the upper gravels with the cold Devensian Stage. In contrast to the woodland environments indicated by the palaeobotany of the Ipswichian organic sediments, post-Ipswichian pollen diagrams and macroscopic plant remains in the upper suite of sands and gravels indicate open tree-less vegetation typical of the cold Devensian Stage. They also contain a typical cold-stage mollusc fauna. The sediments containing these floras and faunas are associated with thermal contraction cracks, indicating the presence of permafrost. The final sand and gravel aggradation in the Devensian forms the Block Fen Terrace, near 0 m OD. The evidence indicates that it is younger than the lacustrine sediments resulting from the blocking of the Fenland at the Wash by Late Devensian ice at ca. 18.5 ka BP. The sequence at Block Fen is related to nearby Ipswichian and Devensian sediments at Chatteris, March, Wimblington and Mepal, and to deposits at Wretton on the east margin of Fenland. The correlation permits an outline reconstruction of the history of the valley carrying the River Great Ouse between the Isle of Ely and the Chatteris and March ‘islands’ from the time of a gravel aggradation before the Ipswichian to the Flandrian. The reconstruction shows the time and level of the Ipswichian marine incursion into the Middle Level of Fenland and the extent of aggradation and erosion in the Devensian. 相似文献