Late Quaternary glaciation in the Hebrides sector of the continental shelf: was St Kilda overrun by the British‐Irish Ice Sheet?

Until recently, the British‐Irish Ice Sheet (BIIS) was thought to have reached no farther than a mid‐continental shelf position in the Hebrides Sector, NW Britain, during the last glaciation (traditional model). However, recent discovery of widespread shelf‐edge moraines in this sector has led to a suggestion of much more extensive ice (Atlantic Shelf model). The position of the St Kilda archipelago, approximately mid‐way between the Outer Hebrides and the continental shelf edge, makes it ideal as an onshore location to test which of the two competing models is more viable. To this end, we (i) reassessed the characteristics, stratigraphy and morphology of the Quaternary sediments exposed on the largest island (Hirta), and (ii) applied time‐dependent 2D numerical modelling of possible glacier formation on Hirta. Instead of three glaciations (as previously suggested), we identified evidence of only two, including one of entirely local derivation. The numerical model supports the view that this glaciation was in the form of two short glaciers occupying the two valleys that dominate Hirta. The good state of preservation of the glacial sediments and associated moraine of this local glaciation indicate relatively recent formation. In view of the low inferred equilibrium line altitude of the glacier associated with the best morphological evidence (～120 m), considerable thickness of slope deposits outside the glacial limits and evidence of only one rather than two tills, a Late Devensian rather than Younger Dryas age is preferred for this glaciation. Re‐examination of the submarine moraine pattern from available bathymetry suggests that the ice sheet was forced to flow around St Kilda, implying that the ice was of insufficient thickness to overrun the islands. Accepting this leaves open the possibility that a St Kilda nunatak supported local ice while the ice sheet extended to the continental shelf edge.     

Late Devensian and Flandrian palaeoenvironmental changes on the Scottish continental shelf west of the Outer Hebrides

Examination of two radiocarbon-dated vibrocores taken from south of St Kilda at a water depth of about 155 m, a short distance within the maximum position of the Late Devensian (Dimlington Stadial) ice sheet, suggests that the St Kilda Basin became free of glacier ice after 15250 yr BP. Sedimentation in a shallow, low energy, high arctic, muddy environment continued until after 13500 yr BP. There followed a higher energy temperate episode during which water depths were roughly about 40 m: this is correlated with the latter part of the Windermere Interstadial and with the warmer interval known in shallow Scottish seas about or a little before 11 000 yr BP. The Loch Lomond (Younger Dryas) Stadial is marked in the vibrocores by the return of muddy sediments and a cold-water fauna. Relatively shallow water conditions seem to have persisted into the earliest Flandrian, when the water depth was still roughly 60 m, corresponding to a sea-level in the area 90–100 m below present. It is suggested that pack ice was widespread in the northeast Atlantic before the Windermere Interstadial and also during the Loch Lomond Stadial, when it transported shards of Icelandic volcanic ash into the St Kilda basin. Estimates of sea-surface temperature for the last part of the Windermere Interstadial are close to those derived from the deep-sea record for the same period.     

天山夏特河流域晚第四纪冰川沉积序列与地貌演化

夏特河源于天山最大现代冰川作用中心托木尔一汗腾格里峰的东北坡,流域内保存有形态较为清晰的四套冰川沉积.这些地形记录了夏特河流域的古冰川变化,对它们进行研究可获得该地晚第四纪以来的冰川时空演化规律.在第三套冰碛夹层中的砂质透镜体里采集了 5个OSL年代学样品,应用单片再生(SAR)测年技术测得它们的年龄为(13.3±0....     

东天山黑沟流域冰川沉积序列及OSL测年研究

黑沟源于东天山最大现代冰川作用中心博格达峰的南坡. 在第四纪冰期与间冰期旋回中,该流域的冰川均发生过多次规模较大的进退,在谷中留下了较为完整的冰川沉积序列. 这些冰川地形包含有重要的古气候变化信息,对其研究可重建黑沟流域的冰川演化史. 应用OSL对该流域的冰川沉积物进行定年,测定结果表明冰水沉积物（沙质透镜体）比冰碛物更适宜应用单片再生剂量（SAR）测年技术进行测定. 基于测得的年龄并结合地貌地层学原理可初步得出：晚第四纪期间,黑沟流域共发生了5次规模较大的冰川作用,分别为全新世期间的小冰期（16世纪以来冷期的冰进）与新冰期（距今3~4 ka的冰进）,末次冰期晚冰阶（MIS 2）与早冰阶（MIS 4）以及倒数第二次冰期（MIS 6）.     

Strandflat development and Quaternary shorelines on Tiree and Coll,Scottish Hebrides

The islands of Tiree and Coll in the Scottish Inner Hebrides are dominated by staircases of glaciated rock-platform surfaces in Lewisian gneiss that are interpreted here as areas of strandflat. The rock platform surfaces exhibit differential glacio-isostatic uplift from east to west and are considered to indicate at least four separate periods of strandflat formation during prolonged intervals of Quaternary cold climate. It is suggested that many of the well-known areas of high rock platform located farther east in the Scottish Inner Hebrides represent eroded remnants of the strandflat surfaces described here. The existence of the Tiree and Coll strandflat surfaces in conjunction with their formation during periods of Quaternary glaciation implies that they were produced during periods when mainland Scotland was ice-covered yet when the western margin of the ice sheet was normally located east of these islands. A prominent Late-glacial raised shoreline also occurs on both islands and declines in altitude to the west, from 22 m in northeastern Coll to 9 m in western Tiree. It is believed that this shoreline, whose regional gradient is 0.39 m km^?1, may represent part of the Main Wester Ross Shoreline that was formed in the Northwest Highlands of Scotland during a period of glacial advance that interrupted the decay of the last (Late Devensian) ice sheet. The general similarity in altitude between the Late-glacial shoreline features and rock platform surfaces implies that during each period of Quaternary strandflat formation, relative sea-level returned to the same approximate position. This would appear to indicate that the glacio-isostatic and glacio-eustatic components affecting the positions of relative sea level in Scotland have remained in approximate equilibrium throughout the duration of the Quaternary.     

Weichselian stratigraphy and palaeoenvironments at Bellsund, western Svalbard

A coastal cliff facing the ocean at the west coast of Spitsbergen has been studied, and seven formations of Weichselian and Holocene age have been identified. A reconstruction of the palaeoenvironment and glacial history shows that most of the sediments cover isotope stage 5. From the base of the section, the formation 1 and 2 tills show a regional glaciation that reached the continental shelf shortly after the Eemian. Formation 3 consists of glacimarine to marine sediments dated to 105,000–90,000 BP. Amino acid diagenesis indicates that they were deposited during a c . 10,000-year period of continuous isostatic depression, which indicates contemporaneous glacial loading in the Barents Sea. Foraminifera and molluscs show influx of Atlantic water masses along the west coast of Svalbard at the same time. Local glaciers advanced during the latter part of this period, probably due to the penetration of moist air masses, and deposited formation 4. A widespread weathering horizon shows that the glacial retreat was succeeded by subaerial conditions during the Middle Weichselian. Formation 5 is a till deposited during the Late Weichselian glacial maximum in this area. The glaciation was dominated by ice streams from a dome over southern Spitsbergen, and the last deglaciation of the outer coast is dated to 13,000 BP. A correlation of the events with other areas on Svalbard is discussed, and at least two periods of glaciation in the Barents Sea during the Weichselian are suggested.     

The high-level marine shell beds of Scotland and the build-up of the last Scottish ice sheet

It is argued that high-level shell beds buried by till at various localities around the Scottish coast are in situ and represent a marine transgression immediately prior to and consequent upon loading of the earth's crust by the build-up of the last Scottish ice sheet. The high-level rock platforms of the Hebrides may also have been eroded at this time. A relationship between the build-up of the last Scottish ice sheet and world sea-level is suggested and it is further argued that the Scottish ice sheet was a more sensitive indicator of the onset (and termination) of a period of northern hemispheric glaciation than either the Laurentide or Scandinavian ice sheets. It is suggested that the build-up of the last Scottish ice sheet took place in the Early Devensian and a tentative correlation is proposed between the Scottish evidence and the deep-sea evidence for glacier build-up at ca. 75,000 years B.P     

Thermal belt and cold air drainage on the mountain slope and cold air lake in the basin at quiet, clear night

This paper reviews results of recent observations on the thermal belt, cold air drainage and cold air lake, which are striking in local climatic phenomena in mountain areas.The height (A) of the warmer part, the thermal belt, of the mountain slopes changes with time from early evening, midnight to early morning and also seasonally and differs according to the velocity of the upper general wind and cloudiness, but is generalized by the height difference (H) between the bottom of the basin and the surrounding mountain ridges. Roughly speaking, A = (0.25–0.30) H.On the mountain slopes, cold air flows down intermittently. The air temperature shows positive correlation to the wind speed of cold air drainage in the source region of cold air drainage. On the other hand, however, there is a negative correlation between the wind speed and air temperature in the drainage region at the lower part of the slope. Above the downslope cold air drainage, there is an anti-down-slope wind. The relatively large drainages are formed at frequencies corresponding to periods of oscillation of 1–2 hours and the smaller ones are of several minutes.In the basin or valley bottom, cold air lakes are formed. They are well defined by a strong inversion in air temperature. In most cases, the stagnant air in the cold air lake flows down slowly in accordance with inclination of the basin or valley floor. Above the cold air lake, we find the neutral or weak inversion layer. In some periods the drained cold air flows into this layer from the side slopes of the mountains. However, the radiation cooling of the basin or valley floor seems to be more effective for the formation of the cold air lake. Above the neutral or weak inversion layer, there is a layer of the general wind caused by the synoptic scale circulation systems. Their effects are controlled by the surrounding topography as well as the basin or the valley itself.In short, the structure of thermal belt, cold air drainage and cold air lake is a good example of the small-scale climatic processes under the influence of the synoptic scale phenomena and the one-order-greater scale topography.     

Thermal belt and cold air drainage on the mountain slope and cold air lake in the basin at quiet,clear night

This paper reviews results of recent observations on the thermal belt, cold air drainage and cold air lake, which are striking in local climatic phenomena in mountain areas. The height (A) of the warmer part, the thermal belt, of the mountain slopes changes with time from early evening, midnight to early morning and also seasonally and differs according to the velocity of the upper general wind and cloudiness, but is generalized by the height difference (H) between the bottom of the basin and the surrounding mountain ridges. Roughly speaking, A = (0.25–0.30) H. On the mountain slopes, cold air flows down intermittently. The air temperature shows positive correlation to the wind speed of cold air drainage in the source region of cold air drainage. On the other hand, however, there is a negative correlation between the wind speed and air temperature in the drainage region at the lower part of the slope. Above the downslope cold air drainage, there is an anti-down-slope wind. The relatively large drainages are formed at frequencies corresponding to periods of oscillation of 1–2 hours and the smaller ones are of several minutes. In the basin or valley bottom, cold air lakes are formed. They are well defined by a strong inversion in air temperature. In most cases, the stagnant air in the cold air lake flows down slowly in accordance with inclination of the basin or valley floor. Above the cold air lake, we find the neutral or weak inversion layer. In some periods the drained cold air flows into this layer from the side slopes of the mountains. However, the radiation cooling of the basin or valley floor seems to be more effective for the formation of the cold air lake. Above the neutral or weak inversion layer, there is a layer of the general wind caused by the synoptic scale circulation systems. Their effects are controlled by the surrounding topography as well as the basin or the valley itself. In short, the structure of thermal belt, cold air drainage and cold air lake is a good example of the small-scale climatic processes under the influence of the synoptic scale phenomena and the one-order-greater scale topography.     

Aragonite depositional facies in a Late Ordovician calcite sea,Eastern Laurentia

The Black River (Upper Ordovician – Sandbian) and Trenton (Upper Ordovician – Katian) groups are traditionally interpreted as a deepening-upward succession deposited in a progressively subsiding Appalachian Basin margin that contained warm-water, marine, photozoan deposits that pass upward into cool-water, marine, heterozoan carbonates. This succession is customarily interpreted to reflect an incursion of cold, high-latitude ocean waters into the area. This view is herein confirmed for coeval carbonates in the northern part of the basin, particularly the St. Lawrence Platform. They are now well explained in this study on the basis of recent studies of cool-water carbonates and calcite–aragonite seas. Overall the succession is one of Sandbian photozoan ramp deposits succeeded by Katian heterozoan ramp carbonates that changed back to photozoan ramp deposits prior to the Hirnantian glaciation. The current interpretation, that deposition took place throughout a calcite sea time, seems at odds with this series of strata. Instead it is herein proposed that deposition took place during an aragonite sea time wherein calcite sea-like sediments accumulated under cold ocean-water temperatures. Such an interpretation is supported by recent experimental data that supports the importance of seawater temperature on CaCO₃ polymorph precipitation. If correct, this means that some of the evidence for calcite sea deposition through time brought about by global tectonics, should be re-evaluated to make sure it was not simply cool-water carbonate production.     

First cosmogenic 10Be age constraint on the timing of Younger Dryas glaciation and ice cap thickness,western Scottish Highlands

We use cosmogenic ¹⁰Be surface exposure age techniques at a locality close to Rannoch Moor, western Scottish Highlands, in order to establish the age and chronology of its most recent glaciation. Glacial erratics and an in situ bedrock quartz vein sampled from this site—the summit of Beinn Inverveigh—have yielded zero‐erosion exposure ages of 12.9 ± 1.5 ka to 11.6 ± 1.0 ka, implying complete ice cover of the mountain during the Younger Dryas, or Loch Lomond Stadial. These results fit closely with published ¹⁴C dates that bracket the maximum (lateral) extent of ice cap outlet glaciers, and are the first internally consistent ages to specifically address this period of glaciation in Scotland. Furthermore, the dates imply that previous palaeoglaciological reconstructions for this area may have underestimated both the thickness of the former ice cap and, by implication, its volume. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

The quaternary glacial history of the Lahul Himalaya,northern India

This paper presents the first glacial chronology for the Lahul Himalaya, Northern India. The oldest glaciation, the Chandra Glacial Stage, is represented by glacially eroded benches at altitudes greater than 4300 m above sea-level. This glaciation was probably of a broad valley type. The second glaciation, the Batal Glacial Stage, is represented by highly weathered and dissected lateral moraines, which are present along the Chandra valley and some of its tributaries. This was an extensive valley glaciation. The third major glaciation, the Kulti Glacial Stage, is represented by well-preserved moraines in the main tributary valleys of the Chandra valley. This represents a less extensive valley glaciation. Two minor glacial advances, the Sonapani I and II, are represented by small sharp-crested moraines, which are within a few hundred metres or few kilometres of the present-day glaciers. The change in style and extent of glaciation is attributed to an increase in aridity throughout the Quaternary, due either to global climatic change or uplift of the Pir Panjal mountains to the south of Lahul, which restricted the northward penetration of the south Asian summer monsoon. © 1996 John Wiley & Sons, Ltd.     

The post to late glacial valley reconstruction on the Haramosh north side (Mani, Baska and Phuparash valleys)

The post to late glacial valley reconstruction is focused on the Mani- Baska and Phuparash valleys on the Rakaposhi- Haramosh Muztagh in the south Karakoram. The recently glaciated valleys join the Indus valley near Sassi at 1500 m. The knowledge of the tributary valley reconstruction can be seen in the context of the scientific discussion about the extent of glaciation along the main Indus valley. Today, the recent avalanche fed glaciers come down from high lying catchment areas with an average altitude of 6700–6800 m and terminate at 2700 m. Snow line runs at 4700–4800 m in the steep flanks which is common in the Karakoram Mountains. The postglacial extent is marked by the great lateral moraine (GLM) and reached down not more than 2.5–5 km away from the recent glaciers with a calculated snow line depression of 300 m in maximum. It can be shown that the valleys were already glaciated during the lastest Late Glacial down to the valley outlet at 1500 m. The snow line was depressed 600–700 m during that period. A high glacial ice filling of the Haramosh valley and glacial erosion of the flat top of the Darchan ridge as an intermediate valley head is strongly probable.     

山东蒙山第四纪冰川组合遗迹的发现及初步研究

本文介绍了山东蒙山地区南坡保存的丰富而清晰的第四纪冰川遗迹,重点展示了兰溪山谷的冰石河、侧碛堤组合,并对相伴产出的擦痕、磨光面、颤痕等冰川遗迹进行了调查与测量。同时对冰石河、侧碛堤的分布、规模、物质组成、岩石特征进行了介绍。根据侧碛堤的排列位置及砾石的风化程度,初步确定为末次冰期的冰碛遗迹;对山谷两侧磨光面上的擦痕进行了测量统计,显示谷壁磨光面上擦痕的长宽比具有10:1左右的比例规律;根据侧碛最大高度法(MELM),结合对于蒙山侧碛的调查,对蒙山雪线的高度进行了估算,初步估算蒙山南坡末次冰期时的雪线高度约为700 m左右。蒙山地区这些组合冰川遗迹的发现,为中国东部第四纪冰川的研究提供了直接的证据。     

Water balance of Britain, 50,000 yr B.P. to the present day

Estimates made of lowland precipitation and evaporation in Britain during the last (Devensian) glaciation suggest that during the cold periods of the Devensian precipitation was probably low, between 260 and 370 mm/year, with winter precipitation between 80 and 120 mm, whereas at the thermal maximum of the Upton Warren Interstadial lowland precipitation was probably in the range 450 to 650 mm/year. Two summer precipitation regimes are identified during the cold periods, one with high values and the other with low. The high summer precipitation variant leads to moist conditions with July and August precipitation values similar to those at the present day, and global circulation models suggest that the moist regime may have existed at the time of the maximum advance of the ice sheets. On the other hand, the low summer precipitation variant leads to a dry summer with wind action creating aeolian deposits, and this variant probably existed at earlier times in the glacial period. About 6500 yr B.P., in the Atlantic period, forest conditions probably caused increased evaporation which more than compensated for the increased precipitation of the time, causing low runoff conditions. The clearance of British forests by man since 6500 yr B.P. has probably led to an absolute increase in runoff values even though precipitation values have fallen.     

Middle Pleistocene lacustrine deposits in eastern Essex,England and their palaeogeographical implications

Investigations in quarry exposures in the Asheldham Gravel and related deposits of southeast Essex are described. Section logging, mapping and borehole investigations are supported by clast lithological, heavy and clay mineralogical determinations. The sediments are derived from reworking of local Thames basin materials, fine sediment being predominantly from the London Clay. The sequence is shown to represent an aggradation that began as the fluvial infilling of the River Medway valley. The River Thames, diverted into this valley by glaciation further west, overwhelmed the Medway, reworking the deposits. The valley was subsequently drowned and fine laminated lake sediment was initially deposited. This was during a period when the valley was drowned by the glacial lake ponded in the southern North Sea basin by the Anglian/Elsterian ice sheet. Progradation by a braid-delta complex advanced along the valley and subsequently fluvial deposition returned. Valley widening and straightening accompanied the delta progradation. The deposits were dissected by deep fluvial valleys infilled by Hoxnian interglacial sediments. The Asheldham Gravel is therefore placed in the Anglian/Elsterian Stage.     

Late Quaternary glaciation of the Cordillera Real,Bolivia

Glacial geological studies in tropical mountain areas of the Southern Hemisphere can be used to address two issues of late Pleistocene climate change: the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics. Radiocarbon dates from the Cordillera Real and from other areas in Perú and Bolivia suggest that late Pleistocene glaciation culminated between 14 000 and 12 000 yr BP, followed by rapid deglaciation. Because deglaciation was apparently synchronous with that in Northern Hemisphere regions, insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time. Late Pleistocene glaciation in the Cordillera Real culminated when precipitation was 200 mm yr^?1 higher and temperatures were 3.5° ±1.6°C lower than today; this produced an equilibrium-line altitude depression of about 300 ± 100 m on the western side of the cordillera. Prior to this, conditions were drier and probably at least as cold. However, the lack of moraines in the Cordillera Real dated to the Last Glacial Maximum (ca. 18000 yr BP) precludes using the equilibrium-line altitude method to quantitatively evaluate the discrepancy between warm sea-surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period.     

贵州丹寨地区南华系地层地球化学特征及其对古气候、古环境的意义

南华系是地球历史上最重要的成冰时期,为了示踪冰期前后的气候与环境的变化,本文通过对南华系细屑岩的化学成分分析,重塑南华系古气候、古环境的演化过程。分析结果显示铁丝坳组具有明显低的CIA指数以及低Ti/Al比值,说明该时期主要以寒冷干燥气候为主,化学风化程度低,物源供应和沉积速率相对较低,为冰期特征,隆里组和大塘坡组具有高的CIA指数以及相对较高的Ti/Al比值,表明该时期主要以温暖湿润气候为主,化学风化程度相对较高,物源供应和沉积速率相对较高,为间冰期特征。南沱组的CIA指数以及Ti/Al比值具有交替变化特征,说明南沱组沉积时期气候存在冷暖交替变化,反映了冰期与间冰期的相互转换特征。另外,在铁丝坳组顶部和大塘坡组的下部以及南沱组中上部,具有一定程度的正Eu异常,说明在南华系沉积时期,存在热液活动,而这种热液活动可能与冰期的消亡存在着成因联系。