摘要:

AbstractScanning electron microscopy combined with pollen, spore, rhizopod and fungal analyses of two peat profiles at Claggan Mountain, Co. Mayo, sheds new light on the Holocene history ofErica erigenain western Ireland. This heather is referred to the Mediterranean‐Atlantic group in the Irish flora, and is remarkable for its disjunct distribution in Europe, where it occurs in Ireland, Bordeaux in France, and in Spain and Portugal.Scanning electron microscopy has proved a powerful tool, allowing the unambiguous identification of ericoid pollens to species level and it is used to identify the first occurrence ofErica erigenapollen in the peat profiles. Radiocarbon dating of the profiles shows thatErica erigenais a relatively recent arrival at Claggan Mountain, appearing for the first time in the historic period at 1431 AD. The details of vegetational changes associated with the expansion ofE. erigenahave been explored by conventional pollen, spore, rhizopod and fungal analyses. Drying of the peat surface and replacement of bog vegetation by ericaceous heathland during a period of marked agricultural activity in the region was associated with its spread.The relatively recent arrival ofE. erigenaat Claggan Mountain, suggests that introduction might explain its presence here, and its disjunct distribution in Europe. Documented trade and pilgrimage routes between Ireland and those areas in Europe where the heather occurs may have allowed its recent introduction into Ireland. Further pollen analysis work, using SEM techniques, will be required if an earlier occurrence for the heather in Ireland is to be proved. The combination of techniques described here may prove useful in the study of the history of other plants with pollen that is difficult to identify using conventional light microscop

ISSN:0267-8179    

DOI:10.1002/jqs.3390050102

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractMapping, analysis and interpretation of glacigenic sediments in the King Valley, Tasmania has led to a revision of the Pleistocene stratigraphy of Tasmania. The sediments provide evidence of a glaciation that occurred between the Middle Pleistocene Henty Glaciation and the Early Pleistocene Linda Glaciation. TheMoore Glaciationis estimated, on the basis of weathering rinds, amino‐acid dating and palaeomagnetism to have occurred between 400000 and 550000 yrs BP. At Baxter Rivulet, sediments of the Moore Glaciation rest unconformably on highly weathered till and weathered Ordovician limestone and are overlain by outwash gravel of the Henty Glaciation. The Moore Glaciation sediments can be divided into four formations on the basis of lithology, organic content and degree of chemical weathering. The Huxley Formation (oldest) was deposited by an ice advance of the Mt. Jukes Glacier and is overlain by the Baxter Formation. The Baxter Formation consists of a bed of organic silty sand which records a cool non‐forested flora of an interstadial period. The overlying Pyramid and Moore formations are outwash gravels from the Mt. Jukes and King Valley glaciers respectively. Though deposited during the same general ice advance, these two gravels were deposited at different times and show that the glaciers of the West Coast Range had spatially differentiated responses to climatic cha

ISSN:0267-8179    

DOI:10.1002/jqs.3390050103

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractActivity ratios of234U/238U,230Th/234U, and230Th/232Th have been determined for calcite, gypsum and halite speleothems from caves of the Nullarbor Plain, mostly in the area N and NW of Mundrabilla Station, for the purpose of U‐series dating. All calcite speleothems contain adequate amounts of uranium for dating, but some show an excess of230Th. Stratigraphic relationships indicate that there were at least three phases of calcium carbonate deposition in the Nullarbor caves. The calcite samples, with one possible exception, have ages in excess of ca. 400000 yrs BP. This suggests that no significant amounts of calcium carbonate deposition have taken place during the last 400ka.At present, active deposition of speleothems is restricted almost entirely to gypsum and halite. The only gypsum speleothem dated was found to have a finite age of ca. 185 ka. Six dates on a small halite speleothem containing insect and arachnid remains indicate that it formed rapidly during Holocene tim

ISSN:0267-8179    

DOI:10.1002/jqs.3390050104

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper attempts to explain downstream variations in the rates and processes of Holocene floodplain formation in a small to medium‐sized, lowland catchment in Central England. Four macro‐reaches were identified and horizons from at least one stratigraphic cross‐section from each were radiocarbon dated. Considerable diachronism was revealed with the basal age and hence minimum residence time of the top two metres varying from 1000‐9000yrs. The trend, adecreasein minimum residence time downstream, is explained by the basin‐and‐gorge bedrock long‐profile inherited from the Devensian glaciation of the area. This is illustrated by a positive relationship between the mean floodplain accumulation rate and the SL index (slope‐stream length product). Pollen analysis of the organic sediments shows that floodplain clearance took place around 1 300 BP, but probably locally, pre‐dated and post‐dated accelerated alluviation associated with agricultural expansion in the catchment. This study concludes that (a) different macro‐reaches in this small to medium‐sized catchment have adjusted in different ways to long‐term catchment changes as part of autogenic floodplain evolution, (b) this has involved a change in the catchment's sediment conveyance characteristics during the Holocene, and (c) an important control on channel behaviour and floodplain sedimentation throughout the Holocene (as well as at present) has been the valley slopes inherited from the Quaterna

ISSN:0267-8179    

DOI:10.1002/jqs.3390050105

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe relative ages of Neogfacial deposits above 2900m near Cloudveil Dome, Middle Teton, and Teepe glaciers, central Teton Range, western Wyoming, were determined using topographic position, weathering features, lichenometry, vegetation characteristics, and soils. A three‐fold deposit sequence is identified and correlated with the Gannett Peak, Audubon and Indian Basin Neoglacial advances described elsewhere in the Teton and nearby Wind River ranges. While soil profile morphology proved very useful in distinguishing deposits of different age, other age indicators such as clay mineralogy and soil chemistry, proved of only marginal value in age discrimination. This chronosequence, emplaced over the last ∼5000yr, provides an excellent setting upon which to test changes in plant species composition and its use as a relative dating method.Vascular plant species composition cannot be used to discriminate deposits of the different advances, possibly because of random colonisation and establishment combined with extensive mass wasting during the Neoglacial. However, certain vegetation features, such as total cover and species densities, appear useful as relative dating meth

ISSN:0267-8179    

DOI:10.1002/jqs.3390050106

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPhilips Inlet and Wootton Peninsula are located at 82°N and 85°W on the northwest coast of Ellesmere Island and are composed of three bedrock controlled zones: (1) 900 m undulating plateau dissected by fiords; (2) a deeply fretted cirque terrain>1200m; (3) a 300m plateau bounded by coastal cliffs. Each zone contains different glacier morphologies and these control glacigenic sediment and landform assemblages. The extent of the last glaciation is mapped using the distribution of moraines, kames, meltwater channels and glacimarine sediments. Glaciers advanced on average<10 km from their present margins and many piedmont lobes coalesced and floated in the sea. Morainal banks were deposited at the grounding lines of floating glaciers, and where debris‐charged basal ice occurred, subaqueous fans were deposited upon deglaciation. Marine shells dating 20.2 ka BP (<2km from present ice margin) and 14.9ka BP (from a morainal bank) document full glacial marine fauna. Thirty‐three radiocarbon dates document glacier retreat patterns and are used to reconstruct the postglacial sea level history (glacioisostatic rebound pattern). An equidistant shoreline diagram is constructed using the 8.5ka BP shoreline as a guide. Tilts from 0.73‐0.85m/km are calculated for this shoreline. Using two firm control points and tilts from elsewhere on northern Ellesmere Island, the 10.1 ka BP (full glacial) marine limit descends from 117m as at the fiord heads to 63 m asl at the north coast. Deglaciation started with a pronounced calving phase throughout the field area between 10.1 and 7.8ka BP. This chronology is similar to that from northeast Ellesmere Island and attests to an early Holocene warming trend recorded in high arctic ice cores. A maximum lag of 2.1 ka exists between the field area and locations to the south of the Grant Land Mountains suggesting differences in glacioclimatic regimes on either side of the mountain range. Persistent reconstructions of all‐pervasive ice sheets for the last glaciation of the area are obsolete and should be

ISSN:0267-8179    

DOI:10.1002/jqs.3390050107

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPeriglacial landforms and deposits of Devensian age are commonly observed on the higher hill slopes of North Derbyshire but to date very few glacial features or sediments have been recognised. At Seal Edge, the escarpment slope has been sculptured by both frost and nivational processes but at Middle Seal Clough there are lobate ridges located beyond the talus foot that are probably moraines, formed during the Dimlington Stadial of the Late Devensian, by a small corrie glacier. The history of the ‘coombe’ has been interpreted from a study of both the inorganic and organic sediments and although the results are not conclusive, they indicate that ice and snow were important in the development of the coombe and that the peat formations in the basin also provide the earliest record to date for events in the vegetation history of the southern Pennine moorla

ISSN:0267-8179    

DOI:10.1002/jqs.3390050108

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390050101

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY