摘要:

AbstractDetailed descriptions are given of sediments exposed in the ‘Loch Don Sand Moraine’, Isle of Mull, Scotland. Two distinct sediment‐landform associations occur within the ‘moraine’: (i) a Gilbert‐type glaciomarine delta complex graded to ca. 34 m Ordnance Datum; and (ii) thrust moraines consisting of deformed sands and silts. Whereas previous studies have attributed the ‘moraine’ to a single glacial readvance, this paper shows that the delta and the thrust moraines formed during ice‐sheet deglaciation and the Loch Lomond Readvance, respectively. Depositional conditions and the palaeoenvironment for each stage of ‘moraine’ formation are reconstructed. During the Loch Lomond Readvance, till deposition and thrust moraine formation appear to have been controlled by drainage conditions in the margina

ISSN:0267-8179    

DOI:10.1002/jqs.3390080402

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA complex of channels underlying the Baginton‐Lillington Gravel (Baginton Formation) at Waverley Wood Quarry, Warwickshire is described. Fossil pollen and plant macrofossils, Coleoptera, Ostracoda, Mollusca and Mammalia are described from the channel‐fill deposits. Consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate. At the top of Channel 2 evidence for a cold, continental climatic episode can be recognised, suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage. At two levels in the channels human artefacts were recovered confirming the presence of Palaeolithic people in Warwickshire during the deposition of the sediments. Amino‐acid geochronology suggests an age within the ‘Cromerian Complex’ Stage for the channels. The small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the ‘Cromerian Complex’ Stage of East Anglia. The regional stratigraphic significance of the Waverley Wood successio

ISSN:0267-8179    

DOI:10.1002/jqs.3390080403

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA large interior basin in west‐central Newfoundland (covering the area of modern Deer Lake, Grand Lake, Sandy Lake and Birchy Lake) is connected to the sea by a narrow breach of a coastal mountain range. During retreat of Late Wisconsinan glaciers, this basin was occupied by a short‐lived glacial lake impounded by remnant ice in coastal fjords, and drained by a spillway at the western end of the lake. Evidence for this lake is fragmentary, and consists of strandline features that fall on a plane of elevation consistent with the post‐glacial isostatic tilt. Following collapse of the ice dams and subsequent lake drainage at some time prior to 12 220 yr BP, the Deer Lake basin was inundated by the sea to an elevation of about 45 m a.s.l. Deltas were formed at the basin edges, and thick successions of fine‐grained rhythmites blanketed the basin floor. Isostatic rebound resulted in falling relative sea levels, and, following a stillstand marked by a period of deltaic deposition at 33 m a.s.l., isolation of the Deer Lake basin from marine influence in the early Holocene.This style of deglaciation differs from previously accepted models for this part of eastern Canada, which showed progressive retreat from the coast to remnant centres on topographic highs. In the model proposed here, a large, low‐elevation basin was deglaciated early, at a similar time to ice retreat to coastal positions from offshore. This pattern of deglaciation may be found in other areas with similar topographic

ISSN:0267-8179    

DOI:10.1002/jqs.3390080404

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractGeochemical and mineral magnetic studies of lake sediments from the Kårsa valley in north Sweden demonstrate that down‐core variations in magnetic properties have been determined by post‐depositional magnetite dissolution rather than by sediment source changes. A low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss. An increase in the sedimentation rate and a reduction in the organic carbon content, primarily due to glacier reformation, allowed magnetite preservation. Thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change. This new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial (stadial) and interglacial (interstadial) episodes during the Quaternary pe

ISSN:0267-8179    

DOI:10.1002/jqs.3390080405

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTill is of common occurrence in the marine environment and can be both subglacial and proglacial in origin. Former glacial margins are often represented by till tongues, that are interbedded with stratified glaciomarine sediment, and the relationship is readily mappable using seismic reflection techniques. It is inferred that within individual till tongues, sediment‐gravity flow deposits form transitional contacts with till of subglacial origin, but these contacts cannot be distinguished on seismic profiles. These unstratified, gravity‐induced deposits formed in close proximity to the glacial source at the grounding line are considered to be secondary tills (flow‐till complex) in terms of the INQUA classification of tills.Till‐tongue successions and till deltas are large, ice‐marginal depocentres associated with floating front ice‐margins, and appear to be closely related in origin.Tabular and hummocky moraines of the mid‐Norwegian Shelf also are considered to be products of floating‐front margins and represent a large proportion of the retreat tills formed during ice recession.Seismostratigraphic evidence for channelisation in ice‐marginal deposits appears to provide a means of distinguishing between former tidewater and float

ISSN:0267-8179    

DOI:10.1002/jqs.3390080406

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract‘Calibrating’ amino acid ratios with uranium‐series dates requires an accurate knowledge of current mean annual temperatures (CMATs) over the region studied. To measure these, test‐tube sized ‘diffusion sensors’ were emplaced for 1 year (in 1984, 1985 and 1986), both outside and inside Minchin Hole sea‐cave in South Wales and Belle Hougue sea‐cave in Jersey, both of which have yielded Oxygen Isotope Substage 5e uranium‐series ages on speleothems. Our outside temperatures agreed with meteorological ones. Our inside temperatures were over 1°C lower. To allow for this, a mean of ‘empirical’, ‘linear’ and ‘parabolic’ epimerisation calculations suggests that ratios from molluscs inside the caves should be multiplied by over 1.1 for comparison with outside ratios. This raises Bowenet al.'s ‘Pennard’ stage ratios from inside Minchin (and Bacon) Hole up towards the ‘Unnamed’ stage ratios outside, and suggests that the Unnamed sites are also from Oxygen Isotope Substage 5e, as proposed by Proctor and Smart. The same conclusion is reached more strongly by comparisons with the ratios and temperatures inside Belle Hougue to the south, and at Eemian (assumed 5e) sites in The Netherlands, Germany and Denmark to the east. The Pennard ratios from outside sites may provide further evidence for global sea stands close to the present

ISSN:0267-8179    

DOI:10.1002/jqs.3390080407

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390080401

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY