摘要:

AbstractGeomorphological mapping of southern Skye indicates evidence for a single readvance of locally‐nourished glaciers. These comprised a major icefield that occupied c. 155 km2of the main mountain area, a small icefield c. 10 km2in extent in the Kyleakin hills and ten corrie glaciers with a total area of c. 16 km2. The absence of Lateglacial pollen sites, shorelines and periglacial features within the limits of local glaciation implies a Loch Lomond Readvance age for this glacial event. The area‐weighted mean equilibrium line altitude (ELA) of the reconstructed Loch Lomond Readvance glaciers (319 m) conforms with a regional eastwards rise in ELAs that indicates dominant westerly airstreams during the Loch Lomond Stadial. An easterly decline in ELAs across the former icefields is interpreted in terms of easterly transfer of snow across ice‐sheds by westerly winds, though the altitudes of corrie glacier ELAs suggest that the dominant snow‐bearing winds were southerlies. Calculations based on the area‐weighted mean ELA for the major icefield (308 m) indicate a stadial mean July sea‐level temperature of c. 6 °C. The anomalously low gradients of certain former icefield outlet glaciers are attributed to deformation of subglacial sediment, an effect that may vitiate the assumption of linear ablation/accumulation gradients in the calculation of former ELAs for reconstruc

ISSN:0267-8179    

DOI:10.1002/jqs.3390040201

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractFour major ash zones recorded in piston cores raised from the Iceland Plateau north of Iceland are shown to be coincident with the last four interglacial isotopic stages. Their geochemical composition links the ashes to volcanic events on Iceland. The occurrence of these ash layers, which record events orders of magnitude larger than the ‘normal’ Holocene volcanic eruptions, can not be explained by changes in sea ice cover and atmospheric circulation alone. It is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the Icelandic Ice

ISSN:0267-8179    

DOI:10.1002/jqs.3390040202

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractBedrock surfaces exposed around Llyn Llydaw, North Wales demonstrate contrasting styles of erosion beneath a Late Devensian ice sheet and a Loch Lomond Stadial (LLS) valley glacier. Ice sheet erosion involved lee‐side fracturing, surface fracture wear and abrasive wear, while LLS erosion was primarily by abrasive wear. Preservation of ice sheet erosional features indicates limited rates of erosion during the LLS. Analysis of the geometry and distribution of erosional markings suggests that the low erosional capacity of the LLS glacier was due to a low basal sliding velocity. This prevented the formation of lee‐side cavities, reduced the debris flux over the bed and minimised particle‐bed contact loads. Reconstructions of the mass balance and geometry of the LLS glacier indicate that most of its balance velocity could be achieved by internal deformation alone. A combination of low subglacial water pressures and an unusually rough substrate explain the low sliding velocities. High bed roughness is due to the absence of leeside cavities and a change in flow orientation between ice sheet and LLS times, which meant that the LLS glacier was in contact with roughness elements which were generated in cavities beneath the ice

ISSN:0267-8179    

DOI:10.1002/jqs.3390040203

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe Chalbi flat, located 60 km outside the rift to the east, forms a moist, salt‐clay encrusted playa which also functions as an inland sink for alluvial fans. Residual lacustrine beds, including freshwater carbonates and travertines, crop out along its higher periphery. Mammalian bones of lacustrine and terrestrial elements, and K/Ar dating of the capping lava suggest a lake or a swamp environment 2–2.5 million years ago. Radiocarbon dating ofMelanoides tuberculataandPlanorbisand a sediment assemblage composed of clotted micrite, calcareous molds, root marks and stromatolites point to an additional early Holocene Chalbi lake or swamps 11000‐9500 yr BP. The data suggest wet environmental conditions outside the rift, which is consistent with the occurrence of a wet period in the early to middle Holocene in intertropical Africa, but out of phase with the climatic conditions in Sinai and Israel and with the high‐latitude maximum lake levels and glacier advance. These relations have probably been caused by migration of climati

ISSN:0267-8179    

DOI:10.1002/jqs.3390040204

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe distributions of seven woodland types, plus unforested areas, are mapped for the British Isles at 5000 BP. The map was compiled using data of modern soil distribution, present‐day ecological preferences of the tree taxa present, and the pollen recor

ISSN:0267-8179    

DOI:10.1002/jqs.3390040205

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractLubbock Lake (Southern High Plains of Texas) contains a cultural, faunal, and floral record within a virtually complete geological record spanning the past 11 100+ years. More than 88 archaeological occurrences have been excavated from five major stratigraphic units. The Paleoindian record (11 500–6500yr BP) begins with Clovis‐age occupation (ca. 11 100yr BP) found within fluvial deposits (stratum 1). Subsequent Paleoindian occupations are found in lake and marsh sediments (stratum 2). Archaic occupations (8500‐2000yr BP) are contained within aeolian and marsh deposits (strata 3 and 4). Ceramic occupations (2000‐500yr BP) are found on a soil developed in stratum 4, in marsh sediments (strata 4 and 5), and in slopewash and aeolian sediments (stratum 5). The Protohistoric (500‐300yr BP) and Historic (300‐100yr BP) remains are in slopewash, aeolian, and marsh sediments (stratum 5) and associated soils. The Southern High Plains remained a grasslands throughout the last 11 500 years and neither man nor bison abandoned the region. The successive local faunas reflect changing ecosystems under pluvial to arid to more mesic to semiarid conditions. The occupation of Lubbock Lake through time appears to have been by small groups of people for both economic and short‐term residential uses. These hunter‐gatherer peoples underwent adaptive change brought about by climatic stress and alterations to

ISSN:0267-8179    

DOI:10.1002/jqs.3390040206

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe glacial succession in the western part of the Cheshire‐Shropshire lowland records the advance, coalescence and subsequent uncoupling of Irish Sea and Welsh ice‐sheets during the Late Devensian stage. During advance a discontinuous sheet of basal till was emplaced across the floor of the region by subglacial lodgement. On retreat, compression of the Irish Sea ice sheet against bedrock obstruction generated a zone of supraglacial sedimentation resulting in the creation of the Wrexham‐Ellesmere‐Wem‐Whitchurch moraine system, and the formation of a wide range of sedimentary environments, including ice‐marginal sandur troughs, ice‐front alluvial fans, proglacial ribbon sandur, and subglacial, ice‐contact and proglacial lakes. The geometry of sedimentary units, and their lithologic and geomorphic characteristics, display spatially ordered patterns of sediment‐landform assemblage which show that the statigraphic succession is a response to rapidly changing depositional conditions at a retreating supraglacial ice‐margin punctuated by minor still‐stands and i

ISSN:0267-8179    

DOI:10.1002/jqs.3390040207

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390040208

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390040209

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390040210

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY