ISSN:0267-8179    

DOI:10.1002/jqs.3390010101

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractDuring the Holocene the volcano Hekla explosively emitted highly silicic tephra on four occasions. The ash was widely dispersed by the wind. Distinctive light‐coloured ash layers are now to be seen in the peats of Northern Iceland. Ash from the 1104 AD eruption was carried as far as Scandinavia. The most recent three tephra are preserved in the top 6 m of sediment in Lake Svinavatn. Chemical data from the sediment of Lake Svinavatn, which lies near the north coast of Iceland 170 km from Hekla, reveal the presence of silicic ash above the tephra visible to the naked eye. Unlike the vertical spread of ash in ocean sediment cores which results from biological mixing effects, the upwards spread of ash in the Svinavatn lake sediment cores appears to have been produced by erosion of ash from the lake catchment in the decades following the eruptions. The variations in concentrations of 11 elements, as determined by neutron activation analysis, can be explained by an exponentially decreasing input from catchment erosion. The additional input to each of the three Hekla ash layers was in the region of 3% of the ash which fell on the Svinavatn catchmen

ISSN:0267-8179    

DOI:10.1002/jqs.3390010102

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractVertical or inclined planar fissures that may for the most part be classified as joints are commonly seen in exposures of both the Coralline and Red Crag in East Anglia. Measurements of fissure orientation reveal orthogonal patterns of alignment in both formations. The field relations of the fissures to the host Crag sediment suggest a tectonic rather than periglacial origin. It is proposed that the fissure system is the product of early Pleistocene tectonic flexuring in the area, on the western margin of the subsiding southern North Sea basin.

ISSN:0267-8179    

DOI:10.1002/jqs.3390010103

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe legacy of repeated Pleistocene glaciations has endowed many Welsh river valleys with locally thick successions of glacial and alluvial sediments. Investigations of a well‐preserved flight of terraced sediments with good exposures at Capel Bangor, on the Afon Rheidol, mid‐Wales, has allowed its Quaternary valley fill stratigraphy to be examined in detail. Study has revealed five terraced fills consisting of seven distinct sedimentary units. These range from Late Devensian ice‐contact and ice‐marginal deposits, to Holocene high‐sinuosity stream sediments with episodes of man‐induced accelerated deposition of fine‐grained alluvium, and to aggradation and subsequent incision associated with historic metal mining. Examination of general sedimentary properties (e.g., granulometry, sedimentary structures, terrace surface morphology) show both differences in the pattern and controls of deposition and also progressive changes over Late Devensian and Holocene times. The sediments of the Rheidol Valley record the response and subsequent recovery of a drainage basin to glaciation, and the increasing influence of man on sediment yields, channel processes, and sed

ISSN:0267-8179    

DOI:10.1002/jqs.3390010104

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractPollen diagrams traditionally are read as if pollen percentages were linearly related to relative tree abundances, although the slopes and intercepts of these relationships are accepted to differ among taxa. Corresponding map patterns of modern pollen and tree percentages support this assumption of linearity, which also underlies the use of linear regression on percentage data for pollen‐tree calibration. Fagerlind, however, showed that the theoretical relationship need not be linear and may be confounded by interdependencies among taxa. Regressions and scatter plots of modern pollen and tree percentages are here compared with results of extended R‐value (ERV) models, which correct for the ‘Fagerlind effect’. Three data sets from Wisconsin and Michigan, USA illustrate that regression coefficients provide a first approximation to their ERV equivalents, but scatter plots derived from the ERV analyses showreducedscatter aboutlinearisedrelati

ISSN:0267-8179    

DOI:10.1002/jqs.3390010105

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Quaternary glacial sequence proposed for the Ecuadorian Andes by Walter Sauer is critically reviewed. Examination of his field evidence at sections exposing Quaternary sediments east of Quito has led to a fundamental reinterpretation. Deposits which Sauer considered as glacial, glacio‐fluvial, glacio‐lacustrine and pluvio‐glacial in origin appear to have been formed mainly by volcanic, volcano‐loessic, laharic, fluvial, colluvial and pedogenic pr

ISSN:0267-8179    

DOI:10.1002/jqs.3390010106

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe 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 conclusio

ISSN:0267-8179    

DOI:10.1002/jqs.3390010107

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

Abstract230Th/234U dates are presented for 26 speleothems from three areas in Britain: Assynt, N.W. Scotland; N.W. Yorkshire; Mendip Hills, Somerset. These dates suggest that speleothem growth was widespread but rare in the period from 40 to 26 Ka, absent from 26 to 15 Ka, and abundant from 15 Ka to the present. The absence of speleothems between 26 and 15 Ka is attributed to glaciation in Yorkshire and Assynt and, tentatively, to continuous permafrost development in the Mendip Hills. The occurrence of speleothems before 26 Ka places restrictions on the extent of any ice sheet which may have been present in Scotland, and indicates that N.W. Scotland was not subjected to continuous permafrost at that time.

ISSN:0267-8179    

DOI:10.1002/jqs.3390010108

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractLate‐Pleistocene deposits in north County Mayo were deposited in three main glacigenic environments. 1. Drumlins and basal tills were formed when ice moved from the Irish lowlands and local mountain catchments into Donegal Bay. 2. Gilbert‐type deltas accumulated up to 80m I.O.D. on the lowlands and subaqueous moraines formed across minor valleys when marine‐based ice grounded inland. 3. A thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice‐rafting immediately outside of these ice limits. The muds contain anElphidium clavatum‐dominated, low‐diversity microfauna which is characteristic of cold‐water conditions adjacent to glacier termini. Valves ofMacoma calcareafrom the mud have been14C dated at 16940 ± 120 and 17300 ± 100 BP.The high‐level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north County Mayo. Although the field evidence cannot be used to determine former sea level history with any accuracy, it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of Ireland. Raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in Ireland and represent marine transgressions prior to glacial unloading. It is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in Ireland than

ISSN:0267-8179    

DOI:10.1002/jqs.3390010109

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390010110

出版商:John Wiley&Sons, Ltd    

年代:1986

数据来源: WILEY