摘要:

AbstractStudies on distal airfall tephra layers preserved in lake sediments and peats in northern New Zealand have documented the stratigraphic, chronologic, and compositional relationships of 46 eruptives, aged c. 17000–700yr BP, which originated from six North Island volcanic centres: Taupo (9 tephras), Okataina (8), Maroa (1) (rhyolitic); Mayor Island (2) (peralkaline); Tongariro (11), Egmont (15) (andesitic). Sources were distinguished by mineralogy and composition, field relations, and14C chronology. All known rhyolitic tephra‐producing eruptions from Taupo, Okataina, and Maroa volcanoes since c. 17000yr BP are represented, but only a small proportion of the known tephras erupted from Tongariro, Egmont, or Mayor Island volcanoes is recorded. The distal tephras from these latter volcanic centres may thus reflect atypically powerful (or oblique) eruptions, or dispersal by strong winds. An improved record of volcanism for the Tongariro, Egmont, and Mayor Island centres might be obtainable from suitable lakes or bogs more proximal to t

ISSN:0267-8179    

DOI:10.1002/jqs.3390030202

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractGreigite has been identified in the sediments of Loch Lomond using X‐ray diffraction. Greigite is the dominant magnetic mineral in the oldest sediments recovered, while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies. A layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations, probably as a consequence of magnetite dissolution associated with sulphide rich pore‐waters produced at the time of a marine incursion.The greigite largely oxidises once the sediment is exposed to air, but if freeze dried the greigite becomes surprisingly stable. Following freeze drying the greigite can be heated to 280°C in air before it alters and loses its strong ferrimagnetic proper

ISSN:0267-8179    

DOI:10.1002/jqs.3390030203

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractMammalian fossils recently discovered near Fulbeck in Lincolnshire, include abundant hippopotamus, suggesting an Ipswichian date for the Fulbeck Sand and Gravel (new name). These deposits mark a former course of the River Witham; clasts indicate derivation from outcrops of Jurassic rocks and chalky till to the south and south‐east. The relationship of the Fulbeck Sand and Gravel to the terrace deposits of the River Trent necessitates a revised chronology. The Balderton Sand and Gravel (new name), laid down by the Trent along its former course to the Lincoln Gap, is shown to be older than the Ipswichian Fulbeck Sand and Gravel, and was probably deposited during the Wolstonian Stage. The Eagle Moor Sand and Gravel (new name), probably glaciofluvial outwash from the chalky tills of the region, is considerably older than the Balderton Sand and Gravel and, together with the tills, is assigned to the early part of the Wolstonian, or the Anglian glacial Stage. It is suggested that the Balderton and Eagle Moor terraces equate with the lower and upper facets of the composite Hilton Terrace of the Middle Tren

ISSN:0267-8179    

DOI:10.1002/jqs.3390030204

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper presents a major revision of the Late Devensian Lateglacial environmental history of the Isle of Skye, Scotland, based upon a combination of geomorphological, biostratigraphical and radiocarbon evidence. The distribution of glacial and periglacial landforms, and of raised shorelines, suggests that there was only one extensive readvance of local glaciers in southern Skye following the wastage of the Late Devensian ice sheet. Pollen‐stratigraphic evidence from 10 sites inside and 4 sites outside the mapped ice limits indicates that this readvance occurred during the Loch Lomond Stadial. At that time over 180km2of the uplands of south‐central Skye were covered by glacier ice, a much more extensive glaciation than previously envisaged. Palynological evidence from four Lateglacial profiles implies that degree of exposure to strong westerly winds was the principal factor determing vegetational contrasts on the island, and that regional differences in vegetational type were less pronounced than has hitherto been suggested. The glacial and palaeobotanical reconstructions reported here are more compatible with Lateglacial data from the Scottish mainland and Hebridean islands than were the previously‐published accounts for the Isle of

ISSN:0267-8179    

DOI:10.1002/jqs.3390030205

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractIn 1985, a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western Europe was initiated jointly by laboratories in Leicester, Meudon, Caen, Milan, Cardiff and Southampton, involving a limited amount of comparative work on the loess from types sites in the Loess Plateau of central China. Preliminary results include the following: (1) Experimental procedures in particle size analysis, clay sample preparation and microscopy have been standardised in all cooperating groups; distinctive fabrics indicative of depositional mechanisms have been recognised. (2) Comparison of aeolian, colluvial and alluvial silt by laser‐scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re‐deposited by slope processes and flowing water. (3) The variability in the anisotropy of thelimon à doubletfacies has been assessed by image analysis of scanning electron microscopy (SEM) and optical microscopy. Strong anisotropy has also been measured in thin section imagery of loess from Normandy and Poland as the product of freezing and thawing. This is confirmed by scanning electron microscopy and by experimental freezing of some silts. (4) The clay fabric and mineralogy in western European loess differ from those in Chinese loess, especially in the case of semi‐arid deposits. (5) Distribution of CaCO3, using thin sections and SEM analysis, has been determined for loess from Normandy and the Rhǒne valley in France and for some Chinese loess, At Saint Vallier, zones of CaCO3concentration occur masking much of the original (loess) sedimentary skeleton which is a locally reworked loessic silt with some laminations. Despite considerable scatter, the palaeomagnetic results indicate a reversed polarity throughout, placing the whole Saint Vallier sequence in the Matuyama chron.These preliminary results suggest the existence of two different palaeoenvironments: one typified by central China, with arid glacials and humid interglacials; and the other represented by western Europe, with generally high humidities. There was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern Italy than in western littoral

ISSN:0267-8179    

DOI:10.1002/jqs.3390030206

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractRecent publications have presented palynological data from the early postglacial period in the British Isles, which have been interpreted as reflecting sequential glacial retreat following the Loch Lomond Stadial, The methodologies and results of these studies were examined and were concluded to be insufficient to demonstrate glacial retreat. A more cautious methodology was adopted and tested at several pollen sites in the Awe valley, Scotland. The results differed from previous studies in not demonstrating the sequence of palynological changes predicted from the hypothesis. These results need to be replicated at other localities, however, before the deglacial chronology hypothesis can be dismissed. Proposals to test the hypothesis further are suggested.

ISSN:0267-8179    

DOI:10.1002/jqs.3390030207

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390030208

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390030209

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390030210

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390030211

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY