Late Quaternary fluvial terraces near the Daocheng Ice Cap,eastern Tibetan Plateau

The timing of terrace formation relative to the glacial–interglacial cycle and what factors control that timing, such as changes in climate and/or uplift, are controversial. Here we present a study of the terraces along the Yazheku River using electron spin resonance (ESR) dating and analysis of the sedimentary characteristics in order to establish the timing of terrace formation and to assess the forcing mechanisms that have been proposed. The Yazheku River flows in glacial trough leading from the Haizi Shan, on the eastern Tibetan Plateau. The range was uplifted during the Quaternary and repeatedly glaciated by ice caps. The four highest major terraces (T5, T4, T3, and T2) are the result of both climatic and tectonic influences. Strath terraces T5–T2 were created during Haizi Shan glacial expansions during MIS 16, 12, 6 and 3–4, respectively. The major aggradation phases of the four terraces occurred during the deglaciations at the ends of MIS 16, 12, 6, and 2. Down-cutting, which led to the generation of the four terraces, immediately followed the deposition of the T5–T2 gravel units. These incisions occurred during the transitions between MIS 16–15, MIS 12–11, MIS 6–5, and MIS 2–1.     

Evidence from the Trent terrace archive, Lincolnshire, UK, for lowland glaciation of Britain during the Middle and Late Pleistocene

The late Middle Pleistocene fluvial terrace sequence of the lower Trent system, Lincolnshire (eastern England), provides an excellent record of environmental change, including evidence for the last two interglacial episodes. It also provides important stratigraphical evidence for the timing and extent of three separate glaciations. Two of these, the Anglian and Devensian, are well-established correlatives of Marine Isotope Stages (MIS) 12 and 2 respectively; the third is a hitherto un-named post-Anglian-pre-Devensian glaciation in eastern England that has been the subject of much previous speculation, but can now be attributed with some confidence to MIS 8. Crucially, the recognition of MIS 7 interglacial deposits within the Balderton-Southrey terrace of the proto-Trent indicates that the underlying Wragby Till, which is ascribed to this additional glaciation, was emplaced no later than MIS 8. The oldest terrace preserved within the lower Trent staircase, the Eagle Moor-Martin Terrace, is considered to be a complex glacial outwash terrace related to the Wragby Till glaciation. It is suggested that deposits representing MIS 11-9, which are conspicuously absent throughout the Trent system, were removed by this glaciation. This is a departure from previous interpretations, which have suggested MIS 10 or MIS 6 as the most likely stages in which an extensive post-Anglian-pre-Devensian lowland glaciation might have occurred in Britain. However, the widespread preservation of undisrupted post-MIS 8 fluvial sequences throughout the Trent valley and in neighbouring systems, within which MIS 7 interglacial deposits have now been recognized at a number of localities, indicates that ice sheets are unlikely to have advanced further into this catchment during MIS 6 than during the Devensian (MIS 2). Recognition of a British glaciation during MIS 8 corresponds with widespread evidence in Europe, which suggests that glacial deposits classified as ‘Saalian’ represent both MIS 8 and MIS 6; in many areas, distinguishing these remains controversial, as confident correlation with either stage is often only possible where glacial sediments interdigitate with well-constrained fluvial records.     

Timing and style of Late Pleistocene glaciation in the Queer Shan,northern Hengduan Mountains in the eastern Tibetan Plateau

Glacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd.     

Remotely sensed observations of the turbidity maximum in the highly turbid Humber Estuary, UK

The Humber Estuary, UK, divides into the Ouse and Trent estuaries at the so-called Apex within its upper reaches. Remotely sensed Compact Airborne Spectrographic Imager (CASI) images and boat measurements were used to observe a strong turbidity maximum in the upper Humber and Ouse during a spring tide in November 1995. Surface suspended particulate matter (SPM) concentrations during the late ebb, as estimated from the CASI data, increased from approximately 6 to 13 g I⁻¹ moving up-estuary into the Ouse. Greater SPM concentrations (∼10 g I⁻¹) were evident in the deeper channels of the Ouse, compared with shallower areas, possibly due to faster ebb currents there and differential down-estuary advection of the turbidity maximum. Ribbons, or streaks, of lower SPM and slightly cooler waters were observed. It appears that slightly cooler and lower turbidity waters from the confluent Trent estuary remained fairly distinct for distances of approximately 2 km down-stream of its confluence with the upper Humber and Ouse. These waters eventually broke into ribbon-like or streak-like structures within the higher SPM-laden and slightly warmer waters of the Humber. They were discernible for more than 5 km down-estuary of the confluence of the Humber, Ouse, and Trent. Boat measurements showed that the turbidity maximum occurred over a fairly restricted region of the upper Humber, between about 20 to 50 km from the tidal limit at high water. The turbidity maximum’s sediment load was largely suspended in the water column during stronger currents. SPM rapidly settled close to the bed during high water and low water slack periods. At these times, SPM concentrations in a thin, near-bed layer were >60 g I⁻¹ in the turbidity maximum region of the Ouse and >30 g 1⁻¹ in the upper Humber (where channel volumes were much greater). SPM within the turbidity maximum comprised very fine-grained material and its low organic content demonstrated that the SPM was essentially mineral, clastic sediment derived originally from erosion and decay of crustal rocks.     

Tectonic and climatic controls on Holocene channel migration,incision and terrace formation by the Rio Grande in the Palomas half graben,southern Rio Grande rift,USA

In order to evaluate potential effects of tectonics and climate change on the behaviour of the axial Rio Grande in the Rio Grande rift, a 16·5 km stretch of modern floodplain and Holocene terraces were mapped in the tectonically active Palomas half graben, south‐central New Mexico, USA. In addition, 51 cores and natural exposures were logged and 20 radiocarbon dates were obtained from charcoal, bulk organic matter, mollusc shells and pedogenic calcite. The Holocene alluvium comprises four terraces above the modern floodplain, each of which formed by a period of river incision followed by stability and renewed floodplain construction to a level below that of the previous terraces. Estimated times of incision between Terraces I and II, II and III, and III and IV are after 12 400, 8040 to 5310, and 760 to 550 yr bp , respectively, whereas the incision between Terrace IV and the modern floodplain occurred within the last 260 years. Although there is some evidence for tectonic control on river behaviour in the southern part of the basin, terrace formation is interpreted as being related to climate change, with periods of incision corresponding to times of increased aridity and low sediment/water discharge ratio in the Rio Grande. This process may have resulted from a reduction in intensity and magnitude of summer storms which supply sediment to the axial river, coupled with an increase in spring discharge peak caused by snowmelt in upstream mountain catchments.     

The Quaternary history of the Wash fluvial network, UK

This paper appraises and compares the Middle-Upper Pleistocene sedimentary sequences preserved in the fluvial systems draining into the Fenland Basin and the Wash estuary. Of the main Fenland rivers the longest records, which extend back to the initial Anglian (glacial) formation of the basin, are found in the Great Ouse and its tributaries, particularly the Cam and the Nar. These sequences preserve sediments representing all four post-Anglian interglacials. The Nene also has an extensive post-Anglian history, with evidence for a Hoxnian estuary that is presumed to have been the precursor of the Wash. North of the Nene, however, the Welland and Witham (proto-Trent) have relatively short sequences, which are thought to commence with a later (post-Anglian-pre-Devensian) glaciation that affected Lincolnshire and fed the previously-recognized Tottenhill outwash delta south of Kings Lynn. Prior to Devensian deglaciation the Witham valley was occupied by the Trent, which was the trunk river of the late Middle Pleistocene Wash system. During periods of low sea level the river would have extended north-eastwards across what is now the floor of the North Sea, possibly via the Inner Silver Pit. Several of the central Fenland sequences show evidence of infrequent terrace formation during the late Quaternary, although this might in part be due to poor vertical separation between terraces, so that differentiating them has been difficult; this has been exacerbated by mixed biostratigraphical signals due to the preservation of sediments representing more than one interglacial beneath a single terrace surface. In several of the systems there is evidence for valley rejuvenation to the lowest terrace or valley-floor level during the MIS 4-3 transition. The observed differences within what, during the predominant periods of lower sea level, would have been a single Wash river system are difficult to explain.     

Ipswichian (Eemian) floodplain deposits and terrace stratigraphy in the lower Great Ouse and Cam valleys,southern England,UK

Gao, C. & Boreham, S. 2010: Ipswichian (Eemian) floodplain deposits and terrace stratigraphy in the lower Great Ouse and Cam valleys, southern England, UK. Boreas, 10.1111/j.1502‐3885.2010.00191.x. ISSN 0300‐9483. Thick argillaceous deposits named the Mannings Farm Beds recently uncovered in the third terrace at Mannings Farm near Willingham, Cambridgeshire contain a pollen sequence covering the transitions from Ipswichian/Eemian substages I to II and II to III, when oak and hornbeam expanded, respectively. This is the longest record hitherto obtained in Britain, providing important insight into the major forest successions in this temperate stage. The frequent occurrence of Ipswichian deposits in the third terrace suggests the development of an extensive floodplain on the valley bottom, similar to the case for the present‐day lower Great Ouse and Cam. The Mannings Farm Beds testify to a complete interglacial sequence emplaced between cold‐climate gravels that was directly associated with the terrace development. The third terrace developed during the Ipswichian and the preceding and succeeding cold stages. Major river downcutting, which shaped the third terrace, occurred during the Early Devensian/Weichselian. Previously reported interglacial fossils from this terrace that are inconsistent with an Ipswichian affinity are probably reworked material derived from pre‐Ipswichian interglacial deposits, or their significance as biostratigraphical indicators needs to be confirmed. The second and first terraces developed from the late Early Devensian onwards. Ipswichian deposits filling flood‐scoured deep channels in bedrock are preserved locally below these low terraces.     

Weichselian geology and palaeoenvironmental history of the central Taymyr Peninsula, Siberia, indicating no glaciation during the last global glacial maximum

The Taymyr Peninsula constitutes the eastern delimitation of a possible Kara Sea basin ice sheet. The existence of such an ice sheet during the last global glacial maximum (LGM), i.e. during the Late Weichselian/Upper Zyryansk, is favoured by some Russian scientists. However, a growing number of studies point towards a more minimalistic view concerning the areal extent of Late Weichselian/Upper Zyryansk Siberian glaciation. Investigations carried out by us along the central Byrranga Mountains and in the Taymyr Lake basin south thereof, reject the possibility of a Late Weichselian/Upper Zyryansk glaciation of this area. Our conclusion is based on the following: Dating of a continuous lacustrine sediment sequence at Cape Sabler on the Taymyr Lake shows that it spans at least the period 39-17 ka BP. Even younger ages have been reported, suggesting that this lacustrine environment prevailed until shortly before the Holocene. The distribution of these sediments indicates the existence of a paleo-Taymyr lake reaching c. 60 m above present sea level. A reconnaissance of the central part of the Byrranga Mountains gave no evidence of any more recent glacial coverage. The only evidence of glaciation - an indirect one - is deltaic sequences around 100-120 m a.s.l., suggesting glacio-isostatic depression and a large input of glacial meltwater from the north. However, ¹⁴C and ESR datings of these marine sediments suggest that they are of Early Weichselian/Lower Zyryansk or older age. As they are not covered by till and show no glaciotectonic disturbances, they support our opinion that there was no Late Weichselian/Lower Zyryansk glaciation in this area. We thus suggest that the Taymyr Peninsula was most probably glaciated during the early part of the last glacial cycle (when there was only small- to medium-scale glaciation in Scandinavia), but not glaciated during the later part of that cycle (which had the maximum ice-sheet coverage over north-western Europe). This fits a climatic scenario suggesting that the Taymyr area, like most of Siberia, would come into precipitation shadow during times with large-scale ice-sheet coverage of Scandinavia and the rest of north-western Europe.     

Late Quaternary river terrace sequences in the eastern Kunlun Range,northern Tibet: A combined record of climatic change and surface uplift

The Kunlun Range, a reactivated orogenic belt, constitutes the northern margin of the Tibetan Plateau. The extreme relief and major landforms of the Kunlun Range are a product of late Cenozoic tectonics and erosion. However, well-developed late Quaternary terraces that occur along the northern slope of the Kunlun Range probably resulted from climatic change rather than surface uplift. The terrace sequences formed in thick Quaternary valley fills and have total incision depths of 50–60 m. Optically stimulated luminescence dating was employed to place time controls on the valley fills and associated terraces. Dating results suggest that periods of significant aggradation were synchronous between different rivers and correspond to the last glacial stage. The abrupt change from aggradation to incision occurred between 21.9 ± 2.7 and 16 ± 2.2 ka, coincident with the last glacial–interglacial transition. Additional terraces developed during the late glacial period and early to middle Holocene. Based on a broader set of chronological data in northern Tibet, at least four regional incision periods can be recognized. Chronological data, terrace elevation profiles, and climate proxy records suggest that these terracing periods were triggered by cool and/or wet climatic conditions. A geometric survey of the riverbed longitudinal profile suggests that surface uplift serves as a potential dynamic forcing for long-term incision. A model is proposed for terrace formation as a response to climatic perturbation in an uplifted mountain range.     

A terrestrial palynological record for the last two glacial cycles from southwestern New Zealand

A pollen profile from Okarito Pakihi Bog in south Westland, New Zealand extending from near present back to Marine Isotope Stage (MIS) 6 provides a continuous record of vegetation and climate change for the past two glacial cycles. Independent chronological control was obtained by AMS radiocarbon dating of organic sediments in the upper part of the sequence and OSL dating of inorganic silts in the lower part, with a unique tie point provided by the ca 26.5 cal ka Kawakawa Tephra. As was probably a common occurrence in this region, the basin developed as a moraine-dammed proglacial lake and remained lacustrine until the early Holocene, when a peat bog developed. Survival of the depositional site through subsequent multiple ice advances, unusual in a glaciated landscape, was probably assisted by lateral displacement of the basin relative to its source area, across the Alpine Fault.There is good correspondence between inferred periods of substantial treeline depression in the pollen profile and the record for ice advance in this region. More cooling events are evident in the pollen record, however, presumably due to the fragmentary nature of glacial geomorphology. The pollen record also shows broad consistency with the MIS record and hence with the Milankovitch orbital forcing model, but with some departures, including an early onset to the last glacial maximum (LGM). Several sub-Milankovitch scale events are also evident, including a mid-LGM warming and Lateglacial reversals during both the last and the penultimate deglaciation.     

白令海北部陆坡100ka来的古海洋学记录及海冰的扩张历史

白令海北部陆坡B2-9柱状样中生源组分的研究显示, 自MIS5.3期以来表层生产力指标的粗组分和蛋白石含量呈阶梯状增加, 反映表层生产力阶段式的增长.全新世表层生产力达到最高, 并且MIS3.2~2期高, 比MIS5.3~3.3期最低.高有机碳含量对应于高C/N比值, 显示有机碳混合来源, 不能作为表层生产力的指标.MIS5.1, 3.3~3.2期和全新世高的有机碳含量和C/N比值反映间冰期陆源有机物质输入量的增加.MIS5.3期至中全新世, 不断增加的陆源砂级和粉砂级颗粒组分说明随着气候的逐渐变冷, 陆架海冰在不断扩张.伐冰碎屑和碳屑颗粒冰期、间冰段和末次冰消期升高, 而间冰期降低, 反映冰期白令海陆架海冰扩张和间冰期海冰消融的过程.冰期海冰扩张与北美大陆气候的相互关联, 揭示了晚第四纪冰期旋回中白令海海冰扩张及其对全球气候变化的响应.      

A contribution to Pleistocene chronology in southeast Essex,England

Parallel to the Essex coast north of the mouth of the Thames, a series of gravel spreads ranging in altitude from near sea level westward to more than 200 ft O.D. (mean sea level) proved to be the remnants of an abandoned Thames/Medway terrace system, rather than a series of “raised” beaches, as their location had suggested. The seaward side of the ancient river valley has subsequently been “captured” by subsidence.Evidence is given for five terraces, with surface levels between 5 and 75 ft O.D. Because of subsidence of the Essex coast, the terrace levels are not easily correlatable with either the Thames or Medway terrace levels. Temporal placement is attempted on the basis of one site in the 25 ft Barling terrace, which yielded a Middle Acheulian archaeological assemblage associated with a cool temperate fauna including an early form of mammoth. An ice wedge cast in the Barling terrace was filled with floodloam which weathered to a parabraunerde soil during an interglacial climate warmer than now. For these reasons man is thought to have lived on the floodplain of the Barling terrace either at the onset of the Wolstonian (Riss) glacial or during an interstadial of that stage. The question of possible linkages between Swanscombe and Clacton terraces is discussed.     

Sedimentology and luminescence ages of Glacial Lake Humber deposits in the central Vale of York

The sedimentary sequence through the Hemingbrough Formation exposed at two sites in the central part of the Vale of York, south of the Escrick moraine ridge, is described and used to reconstruct the palaeoenvironmental history of Glacial Lake Humber. Interbedded wave ripples and laminated silts and clays at both sites indicate that Lake Humber was characterised by fluctuating water levels, often no deeper than wave base. Optically stimulated luminescence ages of 21.0 ± 1.9, 21.9 ± 2.0, and 24.1 ± 2.2 kyr returned from two wave-rippled sandy beds within the glaciolacustrine sequence at Hemingbrough, c. 10 km south of the Escrick moraine ridge, provide the first direct chronological determination for the low-level phase of Lake Humber. As these beds are principally attributed to glacial meltwater emanating from the Vale of York ice lobe of the British Ice Sheet, when its margin was at or near the Escrick moraine ridge, this corroborates the interpretation that this ridge marks the LGM ice limit.     

Late Quaternary glaciation of the Tianshan, Central Asia, using cosmogenic Be surface exposure dating

Glacial deposits are present at the head of the Ürümqi River valley, Tianshan, Central Asia. ¹⁰Be surface exposure ages of 15 boulders from three sites along a 12 km valley transect range from 9 to 21 ka suggesting emplacement by glacial retreat and advance commencing at the global last glacial maximum (LGM) and most likely abating in the early Holocene. Although the age spread for a given locality is not small, perhaps indicating post-depositional reworking, maximum ages per site are either coeval with or are post-LGM and inconsistent with previous pre-LGM electron spin resonance ages.     

The Scandinavian Ice Sheet: from MIS 4 to the end of the Last Glacial Maximum

Lambeck, K., Purcell, A., Zhao, J. & Svensson, N‐O. 2010 (April): The Scandinavian Ice Sheet: from MIS 4 to the end of the Last Glacial Maximum. Boreas, Vol. 39, pp. 410–435. 10.1111/j.1502‐3885.2010.00140.x. ISSN 0300‐9483. Glacial rebound modelling, to establish constraints on past ice sheets from the observational evidence of palaeo‐shoreline elevations, is well established for the post‐ Last Glacial Maximum (post‐LGM) period, for which the observational evidence is relatively abundant and well distributed spatially and in time. This is particularly the case for Scandinavia. For the earlier part of the glacial cycle this evidence becomes increasingly sparse and uncertain such that, with the exception of the Eemian period, there are very few, if any, direct sea‐level indicators that constrain any part of the Scandinavian Ice Sheet evolution before the LGM. Instead, we assume that ice‐sheet basal conditions during Marine Isotope Stage 3 (MIS 3) are the same as those for the LGM, focus on establishing these conditions from the rebound analysis for the LGM and Lateglacial period, and then extrapolate to the earlier period using observationally constrained locations of the ice margins. The glacial rebound modelling and inversion follow previously established formulations, with the exception that the effects of water loading from proglacial lakes that form within the Baltic Basin and elsewhere have been included. The data set for the inversion of the sea‐ and lake‐level data has been extended to include marine‐limit data in order to extend the observational record further back in time. The result is a sequence of time slices for the Scandinavian Ice Sheet from the time of MIS 4 to the Lateglacial that are characterized by frozen basal conditions until late in the LGM interval when rapid thinning occurred in the eastern and southern sectors of the ice sheet. The primary function of these models is as an interpolator between the fragmentary observational constraints and to produce quantitative models for the glaciation history with predictive capabilities, for example regarding the evolution of the Baltic Basin.     

Glacio-isostasy and Glacial Ice Load at Law Dome, Wilkes Land, East Antarctica

The Holocene sea-level high stand or “marine limit” in Wilkes Land, East Antarctica, reached 30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 ¹⁴C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 ¹⁴C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105°–160° E) suggests that a similar ice load of up to 1000 m existed along the EAIS margin between Wilkes Land and Oates Land.     

Complex fluvial response to Lateglacial and Holocene allogenic forcing in the Lower Rhine Valley (Germany)

The Rhine catchment experienced strong changes in upstream allogenic forcing during the last 20,000 years. Climatic changes of the glacial–interglacial transition and steadily growing human impact during the second half of the Holocene forced the Rhine to adapt, resulting in changes in the fluvial morphology. The lower Rhine left two late Weichselian terraces and many Holocene palaeo-meanders in the Lower Rhine Valley (western Germany). This well-preserved terrace sequence is used to investigate the exact course of events of the lower Rhine response to changes in allogenic forcing. Five detailed cross-sections that integrate new and existing borehole data were constructed, and the deposits were analysed with regards to abandonment of terraces, changes in number of active channels, fluvial style, terrace gradients, and overbank sedimentation during the Lateglacial and Holocene. We improved and expanded the chronology of the Lower Rhine Valley deposits by dating new samples (¹⁴C, OSL), and integrated these with existing dating evidence (archaeological and historical data, cross-cutting relationships). Twice during the glacial–interglacial transition, the lower Rhine changed from braided to meandering fluvial style. During both transitional episodes (meandering) secondary channels existed alongside the main channel, with a life span up to 2500 years. The findings imply that the lower Rhine was inherently slow to complete the full morphological transition to a single thread meandering system. On specific aspects of response, the morphological response (point bar/terrace formation, contraction to a single thread) extended over relatively long periods of time, whereas discharge-related response (e.g. fluvial style change, abandonment of braidplains, channel bed lowering/incision) seems to have been near instantaneous. Reach-specific conditions determine the degree to which the geomorphic response is delayed and the complexity of the resultant morphology. Increased human-induced sediment delivery (last 2000–3000 years) is expressed as relative thicker and coarser overbank deposits in the entire study area. In the downstream part of the Lower Rhine Valley it accelerated high-stand deltaic backfilling and decreased incision. The response to human activities occurred relatively quickly in contrast to the long-term fluvial response to the glacial–interglacial transition, because the human impact mainly involved change in delivery of the suspended load.     

黄河中游响应气候变化和地表相对抬升发育阶地研究

揭示河流系统响应气候变化和地表抬升的机制是理解流域地貌演化以及水系发育过程的基础,其核心难题是如何充分认识它们在阶地发育中扮演的角色.以往的研究倾向于分开讨论气候变化和地表抬升在河流阶地发育中的作用,认为河流堆积/侧蚀和下切行为分别与冰期和间冰期气候对应,或者将阶地作为地表抬升的直接证据.首先,从上下游河段对比的视角初...     

OSL‐based chronostratigraphy of river terraces in mountainous areas,Dunajec basin,West Carpathians: a revision of the climatostratigraphical approach

The technique of optically stimulated luminescence (OSL) dating applied to fluvial sediments provided a geochronological framework of river terrace formation in the middle part of the Dunajec River basin – a reference area for studies of evolution of river valleys in the northern part of the Carpathians (West Carpathians). Fluvial sediments at 18–90 m above valley bottoms were dated in the valleys of the Dunajec River and one of its tributaries. The resulting ages range from 158.9±8.3 to 12.2±1.3 ka. This indicates that some of the terrace sediments were deposited much later than previously assumed on the grounds of a combined morphostratigraphical and climatostratigraphical approach. The OSL‐based chronostratigraphy of terrace formation consists of seven separate phases of fluvial aggradation, separated by periods of incision and lateral erosion. Some of the ages determined correspond to warm stages of the Pleistocene – Marine Isotope Stage 3 (MIS 3) and MIS 5 – demonstrating that some terraces were formed during interstadial or interglacial periods. The results provide a key for evaluating rates of neotectonic uplift, allowing us to decipher the response of a fluvial system to climate change within the context of the glacial–interglacial scheme.