Late Glacial Age Research Articles

Climate information from C, N and O stable isotope analyses of mammoth bones from northern Siberia

Nineteen Late Pleistocene samples of fossil mammoth and four of horse and bison from the Leptev Sea area were studied for their C, N and O stable isotope composition. The majority of the samples have interstadial (MIS 3) ages and only two have late-glacial ages. The carbon and nitrogen isotope values are in good agreement with those previously measured on other mammoths from the same area. They seem to indicate, for the interstadial period, a stability of the climate conditions characterised by low and constant rainfall with only few oscillations. Only after the LGM are more humid conditions apparent. The calculated oxygen isotope composition of water are several per mill more positive than those of modern meteoric water in the area. They do not seem to correlate with well-established Late Pleistocene temperature changes but rather with aridity. The temporal pattern indicates a rapid increase of dry conditions after around 34 ka BP. Only the two samples dated after the LGM might indicate an effective increase in temperature.

Environmental changes in Lebanon during the Holocene: Man vs. climate impacts

Pollen and archaeological studies were undertaken in the Southern Bekaa Valley (Lebanon, Mediterranean region). Two Holocene records retrieved in the Aammiq and Chamsine/Anjar wetlands, respectively located at the foothills of Mount Lebanon and Anti-Lebanon Mountain, in the Southern Bekaa Valley, were analyzed to highlight climatic vs. anthropogenic influence on landscape patterns. Our data records support hypothesis on climatically driven modification during the Late Glacial Age and the early Holocene. Human disturbances in the study area are only depicted after c. 8 ky cal. BP, with different patterns in eastern and western parts of the Southern Bekaa Valley. These modifications are in line with major landscape changes in the Eastern Mediterranean region. Since c. 8 ky cal. BP, major deforestation events on Mount Lebanon are recorded in the Aammiq area depicting human interference, while in Chamsine/Anjar, no sign of such activities can be interpolated since strong deciduous oak development is recorded. Archaeological records from the same region confirm human impact on the forest during the Neolithic period. Numerous bifacial flint tools, such as axes, adzes, and chisels, manufactured in the prehistoric workshops of the Southern Bekaa Valley, attest to the beginning of the deforestation during this period. From c. 3.5 to c. 2 ky cal. BP, deforestation seems reduced on Mount Lebanon while in the Chamsine/Anjar area oak forest expansion is still recorded. During the same period, grazing activities were performed in the Bekaa Valley. Between c. 2 and c. 1 ky cal. BP, and on both sites, deforestation and grazing practices are inferred from pollen records. No cultivated plants are recorded in this region. In this view, these Holocene data illustrate important differences in patterns of human activity in comparison with other areas located in the Eastern Mediterranean, where cultivated olive trees and forests decline are well identified. From c. 1 ky cal. BP into the modern period, increasing human perturbations affected the pollen record on both sites.

New evidence from the western Canadian Arctic Archipelago for the resubmergence of Bering Strait

Widespread molluscan samples were collected from raised marine sediments to date the last retreat of the NW Laurentide Ice Sheet from the western Canadian Arctic Archipelago. At the head of Mercy Bay, northern Banks Island, deglacial mud at the modern coast contains Hiatella arctica and Portlandia arctica bivalves, as well as Cyrtodaria kurriana, previously unreported for this area. Multiple H. arctica and C. kurriana valves from this site yield a mean age of 11.5 14C ka BP (with 740 yr marine reservoir correction). The occurrence of C. kurriana, a low Arctic taxon, raises questions concerning its origin, because evidence is currently lacking for a molluscan refugium in the Arctic Ocean during the last glacial maximum. Elsewhere, the oldest late glacial age available on C. kurriana comes from the Laptev Sea where it is < 10.3 14C ka BP and attributed to a North Atlantic source. This is 2000 cal yr younger than the Mercy Bay samples reported here, making the Laptev Sea, ~ 3000 km to the west, an unlikely source. An alternate route from the North Atlantic into the Canadian Arctic Archipelago was precluded by coalescent Laurentide, Innuitian and Greenland ice east of Banks Island until ~ 10 14C ka BP. We conclude that the presence of C. kurriana on northern Banks Island records migration from the North Pacific. This requires the resubmergence of Bering Strait by 11.5 14C ka BP, extending previous age determinations on the reconnection of the Pacific and Arctic oceans by up to 1000 yr. This renewed ingress of Pacific water likely played an important role in re-establishing Arctic Ocean surface currents, including the evacuation of thick multi-year sea ice into the North Atlantic prior to the Younger Dryas geochron.

Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550–10,250 cal yr BP (9230 ± 50 14C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.

Evidence for a Younger Dryas glacial advance in the Andes of northwestern Venezuela

Deposits of push moraine, outwash and glaciolacustrine sediments, recovered from two areas in the northwestern Venezuelan Andes document the latest Pleistocene advance of Mérida ice. Underlying peats provide maximum ages on till and outwash evidently emplaced during the Younger Dryas (YD) climatic event. One example recovered from the Humboldt Massif, where the farthest extent of YD ice buried peat in the surface of Late Glacial till, provides a within-glacier advance age of 12.4 ka cal BP. The peat lies on moraine deposited during a stillstand event when the Humboldt Glacier retreated to the area of Lago Verde at ∼ 4000 m a.s.l. Approximately 0.5 km upvalley, toward Lago Suero, YD till buries peat deposited in glaciolacustrine sediments of presumed Late Glacial age. Farther north, in the Mucuñuque–Mucubají Catchment of the eastern cordillera, a push moraine of possible YD age buries older till of Late Glacial age; ∼ 0.2 km upvalley, outwash of YD age buries glaciolacustrine peat and organic-rich alluvial sediment dated to 13.7 and 13.3 ka cal BP. The latest Mérida advance documented here is approximately synchronous with the YD cold event of Europe and the North Atlantic Region (ca. 11.6–12.7 ka cal BP). The YD event in both areas of the northwestern Venezuelan Andes nearly reestablished earlier Late Glacial ice positions, and termination appears to have been abrupt; the valleys in both areas were evacuated of YD ice without emplacement of recessional moraines as during the main deglaciation. At the Humboldt site, equilibrium line altitudes (ELA's) for the Late Glacial were about 50 m lower than during the inferred YD; in the Mucuñuque–Mucubají catchment, ELA's for the Late Glacial (~ 3900 m a.s.l.) are difficult to establish given the absence of lateral moraines.

Radiocarbon age of late glacial deep water from the equatorial Pacific

Radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2.8 km in the western equatorial Pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater. This places a lower limit on the depth of the interface for the hypothetical radiocarbon‐depleted glacial age seawater reservoir required to explain the 190‰ drop in the 14C/C for atmospheric CO2, which occurred during the mystery interval (17.5 to 14.5 calendar years ago). These measurements restrict the volume of this reservoir to be no more than 35% that of the ocean. Further, 14C measurements on a single Last Glacial Maximum age sample from a central equatorial Pacific core from a depth of 4.4 km water fail to reveal evidence for the required 5‐ to 7‐kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean. Nor does the 13C record for benthic forams from this abyssal core yield any evidence for the excess respiration CO2 expected to be produced during thousands of years of isolation. Nor, as indicated by the presence of benthic foraminifera, was the dissolved oxygen used up in this abyssal water.

Fluvial responses to tectonics and climate change during the Late Weichselian in the eastern part of the Pannonian Basin (Hungary)

Fine-grained sandy–silty channel–belt and floodplain deposits of the Berettyó–Körös Rivers, a main eastern transverse tributary system of the modern Tisza River in the eastern part of the Pannonian Basin, were deposited during the Late Pleistocene under net subsiding conditions. The palaeo-drainage network pattern of a 2500 km 2 large part of the alluvial plain was reconstructed based on interpretation of airborne photographs and analysis of 18th century topographic maps, which show the natural river patterns that predate the introduction of river regulation schemes. The investigation showed that a large meandering river system, with two main channel belts surrounding a floodbasin, entered the alluvial plain from the northeast, and a braided river entered the alluvial plain from the southeast. Detailed sedimentary logs of seven continuous corings and several sand and clay-pit sections were used to characterize different alluvial units. Optical luminescence dating (OSL) of 25 quartz samples and four 14C datings showed that the sediments are of Late Pleniglacial to Late Glacial age. Transport directions inferred from heavy mineral analyses combined with the OSL ages strongly suggest that the large meandering system represents the palaeo-Tisza River, which supposedly flowed along the northeast–southwest striking Érmellék depression during the Late Pleniglacial. The braided river can be regarded as a precursor to the Fekete and Fehér–Körös Rivers, which entered the alluvial plain from the southeast during the Late Glacial. The interpretation of seismic profiles, field measurements of neotectonic activity, and variations in thickness of sediments along the studied profile revealed that river development was largely controlled by subsidence along the Érmellék depression until 14 to 16 ky, and by uplift of the southeastern part of the catchment area. The studied fluvial successions also document the response of the palaeo-Tisza and Körös system to the climate changes of the Weichselian Late Pleniglacial–Late Glacial period. Much of the sand from the meandering zones was deposited during the Bølling–Allerød and Ságvár–Lascaux interstadials, whereas some dated sand units from the braided zone represent the Older and Younger Dryas. The error ranges of OSL dates, which often exceed the duration of Weichselian substages and subdivisions, prevented an unambiguous correlation of the studied sections with the millennial-scale climate changes of the last 25 ky. Meandering and braided river activity coexisted under different climate conditions, whereas locations of the main channel belts are related to subsidence anomalies. The results of our study thus clearly indicate that tectonics was the primary control on river development.

Assessment of δ13C and C/N ratios in bulk organic matter as palaeosalinity indicators in Holocene and Lateglacial isolation basin sediments, northwest Scotland

AbstractCarbon isotopes (δ13C) and C/N ratios from bulk organic matter have recently been used as alternative proxies for relative sea‐level (RSL) reconstruction where there are problems associated with conventional biological indictors. A previous study on a single isolation basin (Upper Loch nan Eala) in northwest Scotland has shown a clear relationship between δ13C, C/N ratios and palaeosalinity from Younger Dryas and Holocene aged sediments. In this paper we present results of δ13C and C/N ratio analyses from other isolation basins in northwest Scotland over the Holocene and the Lateglacial period in order to validate this technique. The results from the Holocene sequences support the earlier findings that this technique can be used to identify RSL change from isolation basins over the Holocene in this region. The relationship between δ13C, C/N ratios and RSL change is not apparent in sediments of Lateglacial age. Other environmental variables such as atmospheric CO2 concentration, poor vegetation development and temperature influence δ13C values during this period. Copyright © 2007 John Wiley &amp; Sons, Ltd.

The Plant Species Composition and Phytogeographical Significance on Algific Talus Slope in Korea

Algific talus slopes are lacal cold micro-environmental habits where cool air escapes through vents and fissures of talus layer, and ice forms in summer. To access the phytogeographical significance and to develop the conservation strategy on vegetation of the algific talus, plant species composition on seven algific talus in South Korea was investigated. As a results, phytogeographically significant northern elements such as Cystopteris fragilis (L.) Bernh., Diplazium sibiricum (Turcz. ex Kunze) Sa.Kurata, Polypodium virginianum L., Vaccinium vitis-idaea L. and Hackelia deflexa (Wahlenb.) Opiz were distributed in these algific talus slopes (below N37˚43'). In addition, subalpine species such as Woodsia subcordata Turcz, Rosa suavis willd., Clematis fusca var. coreana (H.Lev. & Vaniot) Nakai, Calamagrostis langsdorfii (Link) Trin. and Carex vaginata var. petersii (C.A.Mey.) Akiyama were also distributed as typical relictual species of these algific talus (less than alt. 400m). The algific talus slopes in Korean peninsular can be regarded as the insular refugia that northern plant species advanced southward during the latest glacial age have been isolated and adapted in some local microhabitats. Because the algific talus slopes as paleorefugia are very important in terms of phytogeography as well as meteorology ans geology, developments of strategies for in situ and ex situ conservation on these small isolated and threatened populations associated with the algific talus urgently needed.

The lateglacial vegetation and radiocarbon dating of Lake Trilistnika, Rila Mountains (Bulgaria)

Pollen analysis, supplemented by 5 14C dates, was carried out on the lateglacial section (160 cm) of a core retrieved from the glacial Lake Trilistnika (2216 m) in the northwestern Rila Mountains (Bulgaria). The reconstruction of the lateglacial vegetation history is linked for the first time to a chronological framework for the time window 13000–10000 b.p. The delimitation of an interstadial/stadial cycle, analogous with the Bolling/Allerod-Younger Dryas from Western Europe, is based on important changes in the pollen stratigraphy. Mountain-steppe vegetation composed of Artemisia, Chenopodiaceae, Poaceae and other cold-resistant herbs, with isolated stands of Pinus and Juniperus-Ephedra shrubland, dominated the landscape after the ice-retreat. Interstadial conditions were established before 12815±130 b.p. The spread of tree vegetation at lower elevation as a response to the climate improvement was confined to the time interval 12110±95–11140±75 b.p. The Younger Dryas stadial is characterised by a re-advance of the mountain-steppe vegetation. The results are compared with other sites of lateglacial age from the high mountains (Rila, northern Pirin, western Rhodopes) in southern Bulgaria.

Eolian Additions to Late Quaternary Alpine Soils, Indian Peaks Wilderness Area, Colorado Front Range

Surface horizons of many alpine soils on Quaternary deposits in high-mountain settings are enriched in silt. The origin of these particles has been debated, particularly in the Rocky Mountain region of North America. The most common explanations are frost shattering of coarser particles and eolian additions from distant sources. We studied soil A horizons on alpine moraines of late-glacial (Satanta Peak) age in the Colorado Front Range. Surface horizons of soils on these moraines are enriched in silt and have a particle size distribution that resembles loess and dust deposits found elsewhere. The compositions of sand and silt fractions of the soils were compared to possible local source rocks, using immobile trace elements Ti, Nb, Zr, Ce, and Y. The sand fractions of soils have a wide range of trace element ratios, similar to the range of values in the local biotite gneiss bedrock. In contrast, silt fractions have narrower ranges of trace element ratios that do not overlap the range of these ratios in biotite gneiss. The particle size and geochemical results support an interpretation that silts in these soils are derived from airborne dust. Eolian silts were most likely derived from distant sources, such as the semiarid North Park and Middle Park basins to the west. We hypothesize that much of the eolian influx to soils of the Front Range occurred during an early to mid-Holocene warm period, when sediment availability in semiarid source basins was at a maximum.

A high-resolution climatic change since the Late Glacial Age inferred from multi-proxy of sediments in Qinghai Lake

Based on multi-proxy analysis of pollen, carbonate, TOC, TN and d 13 C of organic matters, a high-resolution climatic evolution of Qinghai Lake since the Late Glacial Age is reconstructed. The results indicate that the boundary between the Last Glacial Maximum and the Late Glacial Age is at about 18.2 cal.ka BP. The warm and wet period, which began at about 15.4 cal.ka BP, culminated at 7.4 cal.ka BP and came to its end at about 4.5 cal.ka BP. After that, the climate gradually became cold and dry. The multi-proxy analysis indicates that the climate fluctuated greatly during the transitional period from the Late glacial Age to the Holocene, and this is in good accordance with that reflected by deep sea cores of North Atlantic, ice cores of Greenland, lake sediments in Europe, loess sequences and Guliya ice core in China. The climatic evolutional characteristic of the Qinghai Lake since the Late Glacial Age shows that the driving force of the East-Asia Monsoon correlates with solar radiation on the ten-thousand-year scale.

Pleistocene palynology of Nepal

As part of the Himalayas, Nepal has undergone numerous changes in the past 50 Ma. Folding was responsible for the creation of the Kathmandu Basin. It is here that the most complete sequence of Pleistocene sediments in Nepal is to be found. In this paper, the palynology and palynofacies of the Gokarna, Thimi and Patan Formations is discussed. It is shown that a scanning electron microscope is essential in order to identify the sporomorphs accurately. Without this detailed information, it would prove impossible to pinpoint the climatic signal. It is also necessary to take the sedimentological regime into consideration before a climatic interpretation can be made. The pollen assemblages show that all three formations were deposited during cool conditions with a mean annual temperature 6–7°C lower that at present. Based on the radiocarbon dates, the Patan Formation would appear to be of Late Glacial age. While the Gokarna and Thimi Formations were deposited during the Würm, their exact age is still uncertain as some of the radiocarbon dates are at or beyond the limit of this method. It is hoped that optically stimulated luminescence will be able to resolve this problem.

Late glacial and Holocene vegetation, climate and fire history inferred from Lagoa Nova in the southeastern Brazilian lowland

The pollen and charcoal record of a 1,500-cm-long lake sediment core from Lagoa Nova allows a reconstruction of vegetation, climate and fire history in the Atlantic lowland of southeastern Brazil. Today the potential vegetation of the study region would be dense and tall semi-deciduous forest, related to a dry season of 4 months and 1,250 mm precipitation per year. The lowermost core section of Lagoa Nova is probably of late Glacial age and contains only few, poorly preserved pollen grains, indicating dry environmental conditions. Pollen preservation was good above 1,005-cm core depth. Extrapolating from four radiocarbon dates, this interval represents about the last 10,000 years. During the early Holocene (until about 8,500 b.p.), the landscape was dominated by savanna of the campo cerrado type (open shrub woodland), with frequent trees of Curatella americana and small areas of gallery forests along the drainage system. Savanna fires, probably natural, were frequent at that time. The palaeovegetation pattern is consistent with a long dry season of about 6 months and annual precipitation lower than today. Then, up to about 7,560 b.p., gallery forests expanded in the valleys, reflecting a shorter dry season of about 5 months and somewhat higher annual rainfall. Fire was less frequent during this wetter period. Between about 7,560 and 6,060 b.p., savanna expanded and gallery forests retreated, indicating a return to drier climatic conditions of probably between 5 and 6 months dry season and lower precipitation. Fire was again frequent, but not as frequent as during the early Holocene. During the mid to late Holocene period between about 6,060 and 2,180 b.p., the valleys were covered by semi-deciduous forest, but on the hills cerrado vegetation continued to grow. The dry season was probably around 5 months and rainfall was higher than in the preceding period. During the following period between about 2,810 and 600 b.p., the open cerrado on the hills changed to closed cerrado, reflecting wetter conditions with a shorter dry season than in the previous period. It was only after about 600 b.p. that dense semi-deciduous forests expanded throughout the study region, indicating the start of modern, wet climatic conditions with an annual dry season of about 4 months. Fire was nearly absent during this period. The reconstructed palaeoenvironment from the Lagoa Nova record is similar to that of Lago do Pires, indicating that changes in past vegetation, climate and fire frequency are regionally consistent in southeastern Brazil.

Foraminifera as indicators of methane-rich environments: A study of modern methane seeps in Santa Barbara Channel, California

Methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late Quaternary, via the release of methane from marine reservoirs. Carbon isotopic excursions of foraminifera observed in high-resolution sediment records from Santa Barbara Basin (ODP Site 893) have been interpreted as evidence of episodes of methane release during the late Quaternary. However, the potential relationship between methane in the modern environment and its effect on the stable isotopic composition of benthic and planktonic foraminifera is not well understood. Short cores taken inside a ∼500-m-diameter pockmark with active methane seeps in Santa Barbara Channel, CA, USA, yield information on the effect of high concentrations of environmental methane on foraminiferal assemblages and their stable isotopic composition. These seeps reside at ∼120 m water depth in the eastern portion of the channel, associated with faults and fractures in the Miocene Monterey Formation. Planktonic foraminiferal assemblages and radiocarbon ages show that surface sediments are of late Glacial age (∼25 300 calendar years). This finding suggests an absence of Holocene and deglacial sedimentation in the seep area, likely due the formation of the pockmarks and subsequent winnowing or lack of sedimentation. Benthic foraminiferal assemblages are marked by high abundance of Bolivina tumida, a species previously observed during interstadial episodes and the early Holocene in Santa Barbara Basin, interpreted to include episodes of high methane flux from the basin. While oxygen isotopic values of both benthic and planktonic foraminifera appear normal for cool, glacial conditions, negative carbon isotopic values are seen in benthic foraminifera, primarily in the near-surface intervals. In one interval (1–2 cm below surface), both benthic and planktonic species record highly negative carbon isotopic values, implying that isotopically light methane influenced the entire water column. This spike is of similar or larger magnitude than several earlier observed spikes in the late Quaternary record from ODP Site 893. Single specimen isotopic analyses give an indication of the total range of carbon isotopic values recorded (−0.01 to −25.23‰ for benthics, −0.07 to −22.22‰ for planktonics) in the spike interval. Since modern methane seeps are commonly associated with authigenic carbonate precipitation, scanning electron microscopy was used to assess the possibility that post-depositional alteration may have affected the isotopic composition of the test. These experiments indicate that authigenic carbonate is absent and therefore unable to account for the highly negative carbon isotopic signatures. These data improve our understanding of methane-associated environments by showing that foraminiferal isotopic composition and assemblages may be used to discern the flux of methane from the oceanic reservoir in the geologic record.

GPR images of periglacial slope deposits beneath peat bogs in the Central European Highlands, Germany

Abstract This research investigates the use of ground penetrating radar (GPR) to determine the continuity of periglacial slope deposits under peat bogs. In the Central European Highlands, periglacial slope deposits are a common parent material for soils and play a critical role in determining the nature of chemical and physical processes in soil development. There is a common agreement on the general distribution of these slope deposits, but there is an ongoing debate in German literature concerning the actual age of these deposits. In particular, the youngest head can usually be found under peat bogs of Late Glacial age ( 14 C and pollen stratigraphy) and has lead to a minimum age determination of pre-Alleröd. Stratigraphic investigations were made using drill cores, and GPR was used to define the continuity of the head under the bog. Several examples from southeastern Bavaria are given.

Radiocarbon Dates from the Oxford Ams System: Archaeometry Datelist 31

Radiocarbon Dates from the Oxford Ams System: <i>Archaeometry</i> Datelist 31

The paleogeographic implications of loess mounds: Laizhou Bay plain

The loess mounds are a newly discovered type of landforms on the Laizhou Bay plain south of the Bohai Sea. Research shows that they were formed in the late period of the late Pleistocene when the Bohai Sea was exposed in the period of late Wumu glacial age and changed into plain. As the exposed area is not protected by vegetation, the sediments at the sea bottom are blown and transported southward by strong north winds, and deposit on the coastal plains. As thick loess is accumulated, the loess mound landforms are formed in the direction of down wind.

Investigations regarding Alpine talus slopes using ground‐penetrating radar (GPR) in the Bavarian Alps, Germany

AbstractThe applicability of ground‐penetrating radar (GPR) for the investigation of loose debris was tested at two sites (Viererkar and Zugspitzplatt). A pulseEKKO 100 GPR system equipped with 25 MHz antennae was utilized. The aim of the investigation was to record the base of the debris layer, and thereby acquire an estimation of the backweathering rates of the adjacent rockwalls. The study areas are situated in the Northern Alps near the German–Austrian border. The sites are characterized by steep limestone rockwalls and extensive talus accumulations. A total of six profiles was surveyed.The method is suitable and effective for a quick survey in this dry, high‐ohmic substrate. The GPR system was able to deliver information about the subsurface stratigraphy to c. 70 m depth. The boundary line to the bedrock was discovered – depending upon the profile surveyed −5 to 25 m below the surface. The base of the debris material sometimes shows no distinct reflection. Buried features (V‐shaped furrows, zones overdeepened by ice action, geological structures) could be detected. Arched structures well below the talus–bedrock interface can be interpreted as drainage systems in the karstic bedrock. A thick scree layer of Late Glacial age was separated from a thinner layer on the talus surface, which was related to the Holocene.The backweathering rates were fixed by a calculation of talus volume to c. 100 mm/103 a during the Holocene (Viererkar) and 150–300 mm/103 a (Zugspitzplatt). The detrital formation in north‐exposed sites is twice as intense as in south‐exposed sites. These results match the rates of recent rockfall in the same area of investigation. The calculated backweathering for the late glacial period is 150–730 mm/103 a.The magnitude of the calculated rockwall retreat lies well within the range of previous measurements. The discrepancy between some weathering rates highlights the fact that recent and past relief formation must be differentiated. Otherwise recent removal rates may be overestimated. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Identification and significance of a visible, basalt‐rich Vedde Ash layer in a Late‐glacial sequence on the Isle of Skye, Inner Hebrides, Scotland

AbstractThis paper reports the discovery of a visible, tephra horizon of Late‐glacial age from the site of Loch Ashik in the Isle of Skye, the Inner Hebrides, Scotland. Although the tephra shards have a bimodal geochemical composition identical to that of the Vedde Ash (a well known marker horizon within Late‐glacial sequences. The horizon at Ashik is dominated by basaltic shards and devitrified tephra shards, giving the layer its characteristic black colour. Only rhyolitic shards have previously been reported from Vedde Ash horizons in the British Isles. This new evidence raises some important questions about the factors that govern the distribution and accumulation of basaltic tephra, and about the methods used to detect ash shards in basins distal to centres of volcanic activity. Copyright © 2001 John Wiley &amp; Sons, Ltd.