Late Devensian raised shorelines and ice limits in the inner Moray Firth area, northern Scotland

Marine, fluvial and fluvioglacial landforms and the deposits associated with them, have been mapped in the inner Moray Firth area. The landforms identified indicate a close association between the decay of the Late Devensian Scottish ice sheet and the formation of raised marine features. Analysis of the altitudes of the marine terraces has identified ten glacio-isostatically tilted raised shorelines of Late Devensian age, sloping down towards N25°E, at progressively lower gradients between 0.57 and 0.15 m/km. The shorelines were formed in close association with a westward- and southward-receding ice margin and the shoreline sequence suggests that rates of ice margin retreat were most rapid where the ice terminated in the sea.     

A re-evaluation of Late Devensian glacial Lake Humber levels in the Vale of York,UK

Proglacial Lake Humber formed in the Vale of York and Ancholme Valley during the Late Devensian (Weichselian) glaciation, but its lake levels and their precise ages are uncertain. Three-dimensional geological modelling, based on 193 borehole sediment logs from the eastern part of the Vale of York, indicates that glaciolacustrine sediments extend no higher than 10?m O.D. By contrast, recent palaeoenvironmental reconstructions for the region that suggest Lake Humber had eight recessional shorelines, extending from 42?m to 5?m O.D. Above 10?m O.D., the sediments become more discontinuous, and comprise clay with occasional chalk and flint gravel, and matrix-rich diamicton interdigitated with sands and gravels. Sedimentary and geochemical analyses of sands and gravels from one of the putative shorelines, at 25?m O.D., indicate an easterly provenance for these sediments. They are interpreted here as colluvial deposits, sourced largely by periglacial weathering of Jurassic and chalk bedrock. Collectively, the geological evidence suggests that the highest level of Lake Humber during the Late Devensian did not exceed 10?m O.D., and therefore reconstructions invoking higher lake levels are thought to be unlikely.     

Dimensions and deglacial chronology of the Outer Hebrides Ice Cap,northwest Scotland: implications of cosmic ray exposure dating

Cosmic ray exposure ages of frost-weathered bedrock from mountain summits in the Outer Hebrides exceed the age of Late Devensian glaciation. Exposure ages of most glacially-abraded bedrock surfaces at low and intermediate elevations are younger than the age of maximum Late Devensian glaciation. These results confirm that previously mapped periglacial trimlines in the Outer Hebrides define the upper limit of bedrock erosion by Late Devensian ice. They are consistent with the interpretation, based on geomorphological evidence, that the trimlines mark the approximate upper limit of a Late Devensian Outer Hebrides Ice Cap. A postglacial exposure age from the summit of Oreval (662 m) suggests that this mountain was overrun during the last glaciation, indicating thicker ice cover and a lower surface gradient west of the ice-cap divide than previously inferred. Although bedrock surfaces below the trimlines are strongly ice-moulded, some show evidence of prior cosmic ray exposure, which we attribute to limited erosion during Late Devensian glaciation. If this interpretation is correct, the youngest apparent ages from these surfaces give the most reliable dates for deglaciation, at ca. 14.5–14 ka. This implies that ice persisted at favourable sites through the warm opening phase of the Windermere Interstade. Comparison with radiocarbon-dated evidence from offshore cores suggests net ice margin retreat of ∼74 km eastwards across the adjacent shelf in > 2.3 ± 1.0 ka. The dating evidence is consistent with relatively rapid retreat of calving margins to the coast, then slower withdrawal of ice margins to high ground. Copyright © 2005 John Wiley & Sons, Ltd.     

A revised seismic stratigraphy for Quaternary deposits on the inner continental shelf west of Scotland between 55°30'N and 57°30'N

A stratigraphy for Quaternary deposits on the western Scottish shelf has been erected using seismic and borehole data. Eight new formations are defined and described with evidence presented for the environ-ment of deposition of each formation. Most of the Quaternary sediments preserved on the shelf arc shown to have accumulated under stadial or glacial conditions. The possible age of each formation is discussed within the context of evidence provided from the mainland, shelf and deep-sea cores. Two are thought to be pre-Devensian, one is possibly pre-Devcnsian. one is possibly Early and/or Middle Devensian, two are probably Late Devensian, one is Late Devensian to Holocenc and one Present day in age. It is suggested that the Late Devensian ice reached the shelf margin south of the Outer Hebridcan Platform.     

Late Quaternary marine terraces in the Mediterranean coastal area of Syria: Geochronology and neotectonics

In order to provide new data on the neotectonics and geodynamic properties of western Syria, studies of marine terraces have been carried out. The most attention was paid to the lower terraces in the range of 3–5 to 30–35 m above sea level, because they have more complete distributions along the shore. The lower terraces were examined along the coastal area from Tartus to Latakia, and along the carbonate cliff on Arwad Island. Seven ²³⁰Th/U dates for these terraces are in the range of 85–130 ka, suggesting the age interval of the last interglacial (MIS 5). New dates on the lower terraces provide a basis for stratigraphical and geomorphological interpretation as well as neotectonic reconstruction. According to the geomorphological data and lithological composition of those terraces, two main uplifted blocks can be established. One coincides with the Latakia block, and another corresponds to the western margin of the Banias volcanic plateau. These blocks are divided by a subsided structure corresponding to the Nahr el Kebir graben. The amplitude of neotectonic uplifting in the Latakia and Banias blocks reaches 15–20 m for the Late Pleistocene.     

Periglacial trimlines,former nunataks and the altitude of the last ice sheet in Wester Ross,northwest Scotland

High-level weathering limits separating ice-scoured topography from frost-weathered detritus were identified on 28 mountains in Wester Ross at altitudes of 700–960 m, and a further 22 peaks support evidence of ice scouring to summit level. Weathering limits are defined most clearly on sandstone and gneiss, which have resisted frost shattering during the Late Devensian Lateglacial, but can also be distinguished on schists and quartzite. Schmidt hammer measurements and analyses of clay mineral assemblages indicate significantly more advanced rock and soil weathering above the weathering limits. The persistence of gibbsite above weathering limits indicates that they represent the upper limit of Late Devensian glacial erosion. The regular decline of weathering-limit altitudes along former flowlines eliminates the possibility that the weathering limits represent former thermal boundaries between protective cold-based and erosive warm-based ice. The weathering limits are therefore interpreted as periglacial trimlines that define the maximum surface altitude of the last ice sheet. Calculated basal shear stresses of 50–95 kPa are consistent with this interpretation. Reconstruction of ice-sheet configuration indicates that the former ice-shed lay above 900 m along the present watershed, and that the ice surface descended northwestwards, with broad depressions along major troughs and localised domes around independent centres of ice dispersal. Extrapolation of the ice surface gradient and altitude suggests that the ice sheet did not overrun the Outer Hebrides, but was confluent with the independent Outer Hebrides ice-cap in the North Minch basin. Erratics located up to 140 m above the reconstructed ice surface are inferred to have been emplaced by a pre-Late Devensian ice sheet (or ice sheets) of unknown age. © 1997 John Wiley & Sons, Ltd.     

Glacial meltwater erosion of the Mid-Cheshire Ridge: implications for ice dynamics during the Late Devensian glaciation of northwest England

Mapping of glacial meltwater channels along the length of the 25-km Mid-Cheshire Ridge reveals evidence for four distinctive channel morphologies, which are used to establish the pattern of meltwater flow during the Late Devensian glaciation. A key characteristic of all channels is an abrupt change in morphology between inception on the Mid-Cheshire Ridge and the downstream continuation on the surrounding Cheshire Plain, with large reductions in channel cross-sectional area at this point. The interpretation of this evidence is that meltwater flowing off the bedrock ridge was absorbed into a layer of permeable sediment beneath the Late Devensian ice sheet. This permeable sediment is significant because it would have acted as a deforming layer beneath the former ice sheet in this area. Reconstruction of the Late Devensian ice sheet based on information from the meltwater channels and using values of shear stresses typical of ice sheets resting on deformable beds (ca. 20 kPa) suggests an ice surface elevation over the Irish Sea of ca. 700 m. This value is considerably less than previous estimates of the vertical extent of the ice sheet of ca. 1000–1200 m and has important implications for the rapidity and mode of deglaciation during the Late Devensian. Copyright © 1999 John Wiley & Sons, Ltd.     

Late Weichselian and Holocene shoreline displacement in the Trondheimsfjord area, central Norway

Shoreline displacement data from the Trondheimsfjord area have been collected and a synthesis of the Late Weichselian and Holocene relative uplift is presented. The isobase direction is N 30–35°E during the whole period. The gradients of the shorelines are 1.7? m/km at 11,800 years B.P., 1.3 m/km at 10,000 years B.P., gradually decreasing towards the present with a value of 0.2 m/km at 5,000 years B.P. Some irregularities in the shoreline gradient curve in the Late Weichselian and Preboreal chronozones may be ascribed to crustal readjustments by faults. An interpolation of the 9,500 years B.P. shoreline to the Ångermanland and Baltic area shows a relative uplift at 11,800 years B.P. of 400–450 m in the central area of glaciation. The island of Hitra was probably deglaciated at about 12,000 years B.P. and Ørlandet/Bjugn somewhat later. The Younger Dryas ice marginal deposits at Tautra have been deposited early in this chronozone, and deposits proximal to this at Hoklingen and Levanger were probably deposited in the late part of the same chronozone.     

Anomalously high uplift rates along the Ventura—Santa Barbara Coast, California—tectonic implications

The NW—SE trending segments of the California coastline from Point Arena to Point Conception (500 km) and from Los Angeles to San Diego (200 km) generally parallel major right-lateral strike-slip fault systems. Minor vertical crustal movements associated with the dominant horizontal displacements along these fault systems are recorded in local sedimentary basins and slightly deformed marine terraces. Typical maximum uplift rates during Late Quaternary time are about 0.3 m/ka, based on U-series ages of corals and amino-acid age estimates of fossil mollusks from the lowest emergent terraces.In contrast, the E–W-trending segments of the California coastline between Point Conception and Los Angeles (200 km) parallel predominantly northward-dipping thrust and high-angle reverse faults of the western Transverse Ranges. Along this coast, marine terraces display significantly greater vertical deformation. Amino-acid age estimates of mollusks from elevated marine terraces along the Ventura—Santa Barbara coast imply anomalously high uplift rates of between 1 and 6 m/ka over the past 40 to 100 ka. The deduced rate of terrace uplift decreases from Ventura to Los Angeles, conforming with a similar trend observed by others in contemporary geodetic data.The more rapid rates of terrace uplift in the western Transverse Ranges reflect N—S crustal shortening that is probably a local accommodation of the dominant right-lateral shear strain along coastal California.     

Evidence for the recurrence of large-magnitude earthquakes along the Makran coast of Iran and Pakistan

The presence of raised beaches and marine terraces along the Makran coast indicates episodic uplift of the continental margin resulting from large-magnitude earthquakes. The uplift occurs as incremental steps similar in height to the 1–3 m of measured uplift resulting from the November 28, 1945 (M 8.3) earthquake at Pasni and Ormara, Pakistan. The data support an E—W-trending, active subduction zone off the Makran coast.The raised beaches and wave-cut terraces along the Makran coast are extensive with some terraces 1–2 km wide, 10–15 m long and up to 500 m in elevation. The terraces are generally capped with shelly sandstones 0.5–5 m thick. Wave-cut cliffs, notches, and associated boulder breccia and swash troughs are locally preserved. Raised Holocene accretion beaches, lagoonal deposits, and tombolos are found up to 10 m in elevation. The number and elevation of raised wave-cut terraces along the Makran coast increase eastward from one at Jask, the entrance to the Persian Gulf, at a few meters elevation, to nine at Konarak, 250 km to the east. Multiple terraces are found on the prominent headlands as far east as Karachi. The wave-cut terraces are locally tilted and cut by faults with a few meters of displacement.Long-term, average rates of uplift were calculated from present elevation, estimated elevation at time of deposition, and ¹⁴C and U–Th dates obtained on shells. Uplift rates in centimeters per year at various locations from west to east are as follows: Jask, 0 (post-Sangamon); Konarak, 0.031–0.2 (Holocene), 0.01 (post-Sangamon); Ormara 0.2 (Holocene).     

Depositional history of the Tyne valley associated with retreat and stagnation of Late Devensian Ice Streams

This paper provides sedimentological and morphological data from an investigation of the Late Devensian glacigenic deposits along the Tyne valley, northeast England. The area lies in the central sector of the British-Irish Ice Sheet, with the lowlands influenced by both the Tyne Gap and Tweed-Cheviot ice streams. The sequences here provide insights into the existence of complex, multi-phase activity within the British-Irish Ice Sheet. Field mapping of the area reveals kamiform topography in the Tyne lowlands and lower South Tyne valley, whilst the mid Tyne is characterised by high-level sandur terraces. Inset below the glacial features are river terraces. The sedimentary sequence comprises diamicton overlain by gravel and sandy gravels; sands, muddy sands and gravels; laminated silty sands and muds; and well sorted sands and gravel. The depositional environments indicate ice-contact, subaqueous and terrestrial sedimentation, with supraglacial, proglacial, subaquatic and paraglacial landsystems. Following the onset of deglaciation, westward retreat of Tyne Gap ice resulted in land to the east and southeast of its margin becoming ice-free. Continued/renewed southward flow of ice along the North Sea coast formed a persistent barrier to sediment-charged meltwaters draining the Tyne Gap ice margin. The separation of these two ice masses allowed a glacial lake to develop in the lower Tyne fed by a large proglacial sandur system, which with ice marginal retreat subsequently merged with Glacial Lake Wear. The sediment sequences record the final waning of the Tyne Gap ice stream, and are contiguous with sediments that extend west through the Tyne Gap and into the Cumbrian lowlands.     

内蒙古狼山山前台地成因及其新构造运动意义

内蒙古狼山地处阴山造山带西段、河套断陷带的西北缘,晚新生代以来狼山山前断裂广泛发育、构造抬升强烈。研究晚更新世以来狼山的构造隆升对深入了解河套断陷带的形成演化机制及其隆升过程对河套盆地古地理格局的影响具有重要的意义。狼山山前翁格勒其格和乌兰敖包台地的沉积学、地貌学和年代学研究表明,T1台地形成于47.4 kaB.P.,其沉积物为晚更新世河套古大湖沉积;T2台地形成于69 kaB.P.,其沉积物可能为黄河流经狼山山前的冲积物。台地特征的分析显示,狼山山前台地主要由构造抬升形成,两级台地记录了狼山晚更新世晚期(Qp^3-2)以来的构造隆升过程。69 kaB.P.到47.4 kaB.P.翁格勒其格和乌兰敖包地区的隆升速率分别为1.34 m/ka和1.25 m/ka,47.4 kaB.P.以来分别为0.81 m/ka和1.18 m/ka,狼山南段(翁格勒其格地区)构造抬升有减小的趋势。晚更新世晚期(Qp^3-2)以来由于狼山的快速隆升,导致黄河河道不断东迁,河套平原的古河道是其迁移的证据。狼山山前湖岸阶地的研究进一步证实晚更新世晚期河套地区发育统一古大湖。     

Pattern and chronology of glacial Lake Peace shorelines and implications for isostacy and ice‐sheet configuration in northeastern British Columbia,Canada

Recognition of positions of glacial lakes along the margin of continental ice sheets is critical in reconstructing ice configuration during deglaciation. Advances in remote sensing technology (e.g. LiDAR) have enabled the generation of accurate digital‐elevation models (DEMs) that reveal unprecedented geomorphic detail. Combined with geographical information systems, these tools have considerably advanced the mapping and correlation of geomorphic features such as relict shorelines. Shorelines of glacial Lake Peace (GLP) developed between the Laurentide and Cordilleran ice sheets in northeastern British Columbia and northwestern Alberta. Shoreline mapping from high resolution DEMs produced more than 55 500 elevation data points from 3231 shorelines, enabling the identification of four major phases of GLP: Phase I (altitude 960–990 m a.s.l.); Phase II (890–915 m a.s.l.); Phase III (810–865 m a.s.l.); and Phase IV (724–733 m a.s.l.). The timing of Phase II of GLP is estimated by two optical ages of <16.0±2.5 and 14.2±0.5 ka BP. Extensive mapping of the shorelines allows for measuring of glacial isostatic adjustment as ice retreated. Shorelines currently dip to the northeast at around 0.4–0.5 m km^?1. This slope reflects the asynchronous retreat of the Cordilleran (CIS) and Laurentide (LIS) ice sheets. The relative uplift in the southwest of the study area within the Rocky Mountains and foothills suggests that the Late Wisconsinan (MIS 2) CIS persisted in the foothill after the LIS lost mass and retreated, or that the Late Wisconsinan CIS was very thick and caused deep crustal loading, which resulted in more uplift in the southwest before reaching equilibrium during, or shortly after deglaciation.     

Influence of Southern Upland ice on glacio-isostatic rebound in Scotland: the Main Rock Platform in the Firth of Clyde

This paper identifies an anomaly between the currently acccpted isobasc pattern for raised shorelines in Scotland. which is a simple ellipsoid centred over the Western Highlands, and current models for the morphology of the Late Devensian ice-sheet. which show a primary dome in the Western Highlands but a prominent secondary dome over the Southern Uplands. One explanation of this anomaly is that it is an artefact of inadequate shoreline data for south-west Scotland. To test this hypothesis, altitude data on the Main Rock Platform in the Firth of Clyde area have been collected and analysed. and demonstrate patterns that probably result from the influence of Southern Upland ice. The ice-sheet models in this area are therefore supported.     

西藏错那-拿日雍错地堑的第四纪正断层作用及其形成机制探讨

青藏高原内部的近东西向伸展变形在藏南地区形成了一系列近南北向裂谷带,对其中最东端的错那-沃卡裂谷带南段错那-拿日雍错地堑调查结果表明,它是第四纪活动明显的半地堑式断陷盆地。控制该盆地发育的主边界断裂带是近南北走向、倾向东侧和长80～110km左右的盆地西缘正断层,是区域内N90°～92°E方向伸展变形的产物。断裂活动速率的多种估算结果表明,该断裂带百万年时间尺度的平均垂直活动速率介于0.2～0.9mm/a之间;MIS 8和MIS 6以来的断裂平均活动速率的合理估计值是0.6±0.2mm/a;但末次冰期盛冰阶以来的断裂平均活动速率明显增加,介于1.0～2.1mm/a之间,合理的估计值为1.3±0.3mm/a,末次冰盛期以来断裂垂直活动速率的增加极可能是该断裂带进入地震丛集期的反映。该地堑近于严格的南北走向及其与当雄-羊八井地堑相似的活动强度,指示了下地壳物质侧向流动所产生的纵向拉张作用最有利于该区近南北向裂谷带的形成。     

A reinterpretation of the Lateglacial environmental history of the Isle of Skye,Inner Hebrides,Scotland

This 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 180km² of 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 Skye.     

Evidence of Late Pleistocene ice-dammed lakes in West Siberia

The article discusses geological data on proglacial lakes and spillways in the West Siberian Plain, data on crucial features of the Late Pleistocene reorganization of the drainage pattern of northern Eurasia. The discussion focuses on Late Pleistocene sediments along the margin of the last ice sheet and south of it, including new data recently obtained by the Russian-Norwegian project PECHORA in Trans-Uralia. Based on these data, the margin of the last ice sheet in the western and central parts of West Siberia is localized well above the Arctic Circle, i.e. 150-250 km north of the previously suggested ice limit. The available geochronological evidence indicates that the last ice dam across West Siberia, which diverted the great Siberian rivers to the south, appeared at early stages of the last, Weichselian ice age. The normal, northbound, drainage was restored later, within the time-span accessible to radiocarbon dating, when two pre-Holocene river terraces with mammal fauna were formed. The Late Weichselian was the driest period with ubiquitous aeolian activity and an absence of large water bodies. Preceding ice-dammed lakes of West Siberia could only drain through the Turgai valley which leads southward into the Aral and Caspian seas. The sedimentary sequence of this passage consists of lacustrine clay, diamictic gravity flows and aeolian sediments younger than 29 kyr which infilled the former spillway mainly in the Late Weichselian. The basal sand and gravel mantling the bedrock floor, which descends from 55 m a.s.l. at 55°N to 30-40 m a.s.l. in the south, is the only signature of a southward drainage. This fluvial episode probably reflects overflow of a Siberian proglacial lake whose water level could reach 60 m a.s.l. prior to 29 kyr BP.     

天山北麓塔西河河流阶地的变形特征及成因探讨

通过对穿过吐谷鲁背斜的塔西河变形阶地测量和年代学分析，计算出该背斜处地壳抬升速率在75～130ka间为1．70～3．24mm／a．12～13ka间增至12．25～8．16mm／a．全新世时则为2．25—2．57mm／a,明显具有脉动性的特点，其平均隆升速率为2．06～3．57mm／a．第四纪以来．构造活动及气候变化控制着河流下切和侧蚀作用的进行．因此塔西河阶地的形成和发育明显受第四纪以来构造活动和气候变化等因素的影响，具有多成因性和多层次性．是构造气候相互耦合作用的结果．     

Late Quaternary evolution of the Tees-Swale interfluve east of the Pennines: the role of glaciation in the development of river systems in northern England

Detailed mapping of the interfluve between the lower Tees and Swale valleys has allowed improved understanding of the sequence of Late Quaternary evolution of this watershed area, which encompasses the Devensian glaciation, glacial retreat and reoccupation of the landscape by post-glacial drainage systems. This evidence is described in the context of earlier research, including ideas of inter-relations between the Tees and Swale river systems. Although there is good evidence of meltwater transfer across the interfluve at more than one location there is no clear indication of a fluvial connection. Deglaciation left behind a disrupted and somewhat chaotic surface, with scattered depositional landforms and basins, in some of which have accumulated post-glacial sedimentary sequences from which palaeoecological records can be reconstructed. Since deglaciation the rivers have incised their valleys, typically by ∼30 m, into the glaciated landscape. Progressive stages in this incision are marked by terraces between the former 30 m landscape level and the modern floodplains.     

祁连山东南缘基于RGMAP的数字化地貌研究

在RGMAP平台下, 以数字高程模型DEM为基础, 结合野外路线调查、图切构造地貌剖面, 较系统地研究了青藏高原东北缘祁连山东南麓(达坂山—拉脊山) 地区典型层状地貌分布发育特征, 初步识别出了调查区的两级夷平面(一级夷平面海拔3000m、二级夷平面4000m左右)、多级山足剥蚀面(1~ 11级) 及主要入海水系如黄河及其支流, 如湟水河、大通河发育的河流阶地系列, 其中湟水河发育7级河流阶地, 黄河5级河流阶地, 黄河干流于盐锅峡段贯通之前, 湟水河一度为黄河上游源头.结合野外调查和室内分析, 本文详细描述了各级层状地貌分布特征、沉积学、形成时代及其与新构造运动的关联, 说明典型层状地貌的发育是青藏高原晚新生代以来间歇性构造抬升的结果.