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1.
The youngest ice marginal zone between the White Sea and the Ural mountains is the W-E trending belt of moraines called the Varsh-Indiga-Markhida-Harbei-Halmer-Sopkay, here called the Markhida line. Glacial elements show that it was deposited by the Kara Ice Sheet, and in the west, by the Barents Ice Sheet. The Markhida moraine overlies Eemian marine sediments, and is therefore of Weichselian age. Distal to the moraine are Eemian marine sediments and three Palaeolithic sites with many C-14 dates in the range 16-37 ka not covered by till, proving that it represents the maximum ice sheet extension during the Weichselian. The Late Weichselian ice limit of M. G. Grosswald is about 400 km (near the Urals more than 700 km) too far south. Shorelines of ice dammed Lake Komi, probably dammed by the ice sheet ending at the Markhida line, predate 37 ka. We conclude that the Markhida line is of Middle/Early Weichselian age, implying that no ice sheet reached this part of Northern Russia during the Late Weichselian. This age is supported by a series of C-14 and OSL dates inside the Markhida line all of >45 ka. Two moraine loops protrude south of the Markhida line; the Laya-Adzva and Rogavaya moraines. These moraines are covered by Lake Komi sediments, and many C-14 dates on mammoth bones inside the moraines are 26-37 ka. The morphology indicates that the moraines are of Weichselian age, but a Saalian age cannot be excluded. No post-glacial emerged marine shorelines are found along the Barents Sea coast north of the Markhida line.  相似文献   

2.
Several sections have been studied to understand the distribution and interrelation of basic genetic types of Quaternary deposits in the Uimon basin and adjacent area. The OSL date of 101 ± 10 ka from the glaciolacustrine terrace on the northeastern rim of the basin corresponds to the cool substage of MIS 5. The glaciolacustrine sediments of the northern rim are covered with widespread diamictic flows of the outburst draining of the ice-dammed lake. The diamicts are overlain by a subaerial complex of loesses and three fossil soils. From the OSL loess dates in the range of 43 to 49 ka we infer that the complex formed from the early MIS 3 through the Holocene. This is also supported by radiocarbon dates from alluvial deposits incised into the glaciolacustrine terrace and into megaflood sediments of the final draining of the last paleolake. The OSL dates in the range of 77 to 89 ka from alluvial sediments indicate that postglacial downcutting of the present-day Katun’ valley probably started just after MIS 5. The discrepancy between the beryllium dates from dropstones and Holocene TL-dates of the Katun’ valley floods ranging from 23 to 6 ka can be explained if the younger floods are related to the draining of moraine- and rock slide dammed rather than ice-dammed lakes. The younger floods, though being less voluminous than the glacial megafloods, were capable of producing giant ripple marks.  相似文献   

3.
The Late Pleistocene stratigraphy from the Severnaya Dvina‐Vychegda region of northwestern Russia is revised based on investigations of new localities, revisiting earlier localities, introduction of about 110 new OSL dates and burial depth corrections of earlier published OSL dates, in addition to six new radiocarbon dates. Most of the OSL samples studied here are from fluvial and subaquaeous sediments, which we found to be well bleached. Six chronostratigraphical units and their sedimentary environment are described, with the oldest unit consisting of pre‐Eemian glacial beds. For the first time, Early Weichselian sediments are documented from the region and a fluvial environment with some vegetation and permafrost conditions is suggested to have persisted from the end of the Eemian until at least about 92 ka ago. The period in which a Middle Weichselian White Sea Lake could have existed is constrained to 67?62 ka, but as the lake level never reached the thresholds of the drainage basin, the lake probably existed only for a short interval within this time‐span. Blocking and reversal of fluvial drainage started again around 21?20 ka ago when the Fennoscandian Ice Sheet advanced into the area, reaching its maximum 17?15 ka ago. At that time, an ice‐dammed lake reached its maximum water level, which was around 135 m above present sea level. Drainage of the lake started shortly after 15 ka ago, and the lake was emptied within 700 years. Severe periglacial conditions, with permafrost and aeolian activity, prevailed in the area until about 10.7 ka.  相似文献   

4.
The alternation of terrestrial and marine deposits is an indicator of past environmental and sea‐level changes. The age of deposition is usually dated by means of radiocarbon. However, radiocarbon dates of molluscan shells from coastal areas may be complicated by various sources of carbon, and problematic for deposits of 40–50 ka or older. Herein, we apply the Optically Stimulated Luminescence (OSL) dating method to date samples from terrestrial and marine/coastal sediments extracted from three cores in the south Bohai Sea, China. Multiple‐ and single‐aliquot regenerative‐dose procedures using OSL signals from fine‐silt (4–11 μm), coarse‐silt (38–63 μm) and fine‐sand (63–90 or 90–125 μm) quartz were employed to determine the equivalent dose (D e). The results showed that: (i) OSL ages from quartz of different grain sizes and different protocols are consistent with each other; (ii) for Holocene samples, most of the radiocarbon dates agree well with OSL ages; (iii) for pre‐Holocene samples, radiocarbon dates cluster at 40–50 14 C ka BP, whereas OSL ages are in stratigraphic order from 11 ka to 176 ka. Because of the self‐consistency of the quartz OSL ages, the stratigraphic agreement in the three cores, and the clustering of the radiocarbon dates, we suggest that the quartz OSL ages are more reliable with respect to dating the samples from the south Bohai Sea. Finally, the four marine strata identified in the south Bohai Sea are likely to have formed during the Holocene, Marine Isotopic Stage (MIS) 3–5, MIS 6 and probably MIS 7, respectively.  相似文献   

5.
The findings of BRITICE-CHRONO Transect 2 through the North Sea Basin and eastern England are reported. We define ice-sheet marginal oscillation between ~31 and 16 ka, with seven distinctive former ice-sheet limits (L1–7) constrained by Bayesian statistical analysis. The southernmost limit of the North Sea Lobe is recorded by the Bolders Bank Formation (L1; 25.8–24.6 ka). L2 represents ice-sheet oscillation and early retreat to the northern edge of the Dogger Bank (23.5–22.2 ka), with the Garret Hill Moraine in north Norfolk recording a significant regional readvance to L3 at 21.5–20.8 ka. Ice-marginal oscillations at ~26–21 ka resulted in L1, L2 and L3 being partially to totally overprinted. Ice-dammed lakes related to L1–3, including Lake Humber, are dated at 24.1–22.3 ka. Ice-sheet oscillation and retreat from L4 to L5 occurred between 19.7 and 17.3 ka, with grounding zone wedges marking an important transition from terrestrial to marine tidewater conditions, triggered by the opening of the Dogger Lake spillway between 19.9 and 17.5 ka. L6 relates to ice retreat under glacimarine conditions and final ice retreat into the Firth of Forth by 15.8 ka. L7 (~15 ka) represents an ice retreat from Bosies Bank into the Moray Firth.  相似文献   

6.
The eastern England terrestrial glacial sequences are critical to the spatial and temporal reconstruction of the last British−Irish Ice sheet (BIIS). Understanding glacial behaviour in the area of the Humber Gap is key as its blockage by ice created extensive proglacial lakes. This paper maps the glacial geomorphology of the Humber Gap region to establish for the first time the extent and thickness of the North Sea Lobe (NSL) of the BIIS. Findings establish the westerly maximal limit of the NSL. Ten new luminescence ages from across the region show the initial Skipsea Till advance to the maximal limits occurred regionally at c. 21.6 ka (Stage 1) and retreated off‐shore c. 18 ka (Stage 2). Punctuated retreat is evident in the south of the region whilst to the immediate north retreat was initially rapid before a series of near synchronous ice advances (including the Withernsea Till advance) occurred at c. 16.8 ka (Stage 3). Full withdrawal of BIIS ice occurred prior to c. 15 ka (Stage 4). Geomorphic mapping and stratigraphy confirms the existence of a proto Lake Humber prior to Stage 1, which persisted to Stage 3 expanding eastward as the NSL ice retreated. It appears that proglacial lakes formed wherever the NSL encountered low topography and reverse gradients during both phases of both advance and retreat. These lakes may in part help explain the dynamism of parts of the NSL, as they initiated ice draw down and associated streaming/surging. The above record of ice‐dammed lakes provides an analogue for now off‐shore parts of the BIIS where it advanced as a number of asynchronous lowland lobes.  相似文献   

7.
中国第四纪冰期划分改进建议   总被引：31，自引：5，他引：26  
施雅风 《冰川冻土》2002,24(6):687-692
由刘东生主持1位研究者提出的"以气候变化为标志的中国第四纪地层对比表"一文发表已近2a,其中由施雅风执笔第四纪冰期与海洋同位素对比部分.由于新情况的出现,需作适当改进:1)周尚哲等应用ESR测年确定祁连山北坡摆浪河源中梁赣海拔299m,高出现代河床500m处冰碛年代为42.9ka BP,天山乌鲁木齐河上游高出河床200～300m的高望峰阶地冰碛样品ESR测年为477.1ka BP和459.7ka BP,均相当于MIS 12阶段,该阶段国际上对应Kansan-Mindel冰期,与MIS 2、MIS和MIS 1都是100ka周期δ18O值特低时期;2)古里雅冰芯记录中相当于MIS3b阶段,δ18O值折算温度比现代低5℃左右,已经发现台湾雪山山庄期冰碛TL年代为(44.25±3.72)ka BP,天山乌鲁木齐河谷一处冰碛ESR年代45.9ka BP,喜马拉雅山、喀喇昆仑山和兴都库什南坡测定对应此时段冰川前进更为显著,初步检查亚、欧、北美、南美和澳洲12个地区23个地点相应于MIS 3b冷期冰川前进规模均超过MIS 2阶段,即常说LGM时,推测MIS 3b的降温值虽不及MIS 2,但降水较多,有利于冰川发展;3)MIS 3a暖期,不仅青藏高原异常暖湿,而且中国全境的降水量普遍高于现代,并有较大范围的海侵与仅低于现代海面8～10m的高海面,气候环境实际达到间冰期程度.上述3点应补充入中国冰期划分表.  相似文献   

8.
Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14C ka BP. On the shallow Måløy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c. 15 14C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15–13.3 14C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1.  相似文献   

9.
Proglacial Lake Humber is of UK national significance in terms of landscape drainage and development of the British Ice Sheet (BIS) during Marine Isotope Stage 2 (MIS 2), yet it is poorly understood in terms of its dynamics and timing. Sands and gravels exposed at Ferrybridge, West Yorkshire, UK, are interpreted as part of the Upper Littoral sands and gravels related to a high-level Lake Humber, which inundated the Humber Basin to ∼30 m OD during MIS 2. Excavations exposed well-rounded gravels of local origin extending downslope from the 27.5 m OD contour and interbedded sands and fine gravels, which are interpreted as the coarse littoral deposits and nearshore associated deposits. A sample from the distal sands returned an Optically Stimulated Luminescence age of 16.6±1.2 kyr, providing the first direct age for the high-level lake and for when North Sea Basin ice must have blocked the Humber Gap. An underlying sequence included a diamicton dated to after 23.3 ±1.5 kyr and before 20.5±1.2 kyr, indicating that the Late Devensian ice reached at least 15 km south of the Escrick Moraine prior to the high-level lake. Previous to both the high-level lake and this ice advance, loess found at the two sites investigated indicates a long period of loess deposition earlier in MIS 2. These new data for the history of Lake Humber are discussed in the context of ice-marginal oscillations in both the Vale of York and the North Sea Basin.  相似文献   

10.
藏东南波堆藏布江谷地古冰碛堰塞湖初步研究   总被引：1，自引：0，他引：1  
藏东南作为青藏高原内外动力作用最强烈的地区之一,是河流堰塞-溃决洪水链式灾害频发地区。研究该区域古堰塞湖的形成与演化,对认识、评估灾害风险具有重要意义。研究结果表明,波堆藏布江谷地保存有一套湖相沉积地层,通过地貌填图和光释光测年等手段,并结合前人研究成果,推测海因里希事件1(H1)以来波堆藏布江谷地可能发生了一期古堰塞湖事件。该古堰塞湖可能是由波堆藏布江侧蚀白玉沟沟口冰碛垄,致使冰碛物滑塌并阻江形成的,古湖的最大湖面面积约为18.8km2,库容蓄水量约为0.13km3。该古堰塞湖的形成时间可能介于H1～10ka之间,其溃决时间可能在～6ka之后,后期河流溯源侵蚀及下切作用形成了多级以湖相地层为基座的阶地。  相似文献   

11.
A large ice sheet still covered almost all of Maine and eastern New England until ca. 15 cal ka BP, reaching south of 45 °S, despite rising summer insolation intensity and major ice recession elsewhere outside the North Atlantic region. Furthermore, the well-studied moraine belt along eastern coastal Maine, including the prominent Pineo Ridge delta/moraine complex and Pond Ridge moraine, indicates repeated readvances and stillstands between ca. 16 and 15 cal ka BP. This moraine belt reflects a considerable ice sheet response over eastern North America during this time period, coeval with the latter half of the European Oldest Dryas period. Moraine deposition was concurrent with reduction or elimination of North Atlantic meridional overturning, starting with the earlier onset of peak IRD and Heinrich Event 1 (HE-1). The existing 14C chronology suggests that the coastal moraine belt and the persistence of the ice sheet until ∼ 15 cal ka BP was a response to the severe cooling of the North Atlantic region after ∼ 17 cal ka BP.  相似文献   

12.
冰蚀湖中的沉积物不仅记录了湖泊演化及气候变化的历史,还间接地反映冰川发育过程。年保玉则山(果洛山)下的希门错是在冰川强烈退缩后形成的一个典型冰蚀湖。从地域分布上讲,该区冰川发育遗迹分为4个部分,即上希门错以上、上希门错和希门错之间、希门错出口附近和希门错以北6～10km处。前人依据冰碛物的暴露年龄和上覆黄土的热释光年代将上述4组冰碛物划分为4次冰进,包括形成于MIS3阶段的尼格曲冰期、形成于末次盛冰期的希门错冰期、以上希门错和希门错之间的冰碛物作为标志的末次冰消期和形成于全新世的新冰期。通过对采自希门错长达12.8m的岩芯研究发现,希门错自约38kaB.P.以来有连续的湖泊沉积,这一地质证据说明在湖泊存在的这段时间内,冰川规模都没有超过现在湖泊所在位置。希门错冰期的形成时代应该至少老于湖泊沉积物底界的年龄,即大于38kaB.P.,而并非末次冰盛期的产物;尼格曲冰期的形成时代则应该更老。文章还初步分析了湖泊沉积物与冰碛物测年结果代表的不同意义和差别及其造成不一致的原因,认为冰碛物的暴露年代和热释光年代均可能代表了冰川退缩后的年代,而不能代表冰川的形成和发育年龄,冰川存在的时间要比通过冰碛物所测的年代更老。进一步深入研究青藏高原典型冰蚀湖的形成时代、演化过程不仅有利于对湖泊气候环境记录的全面认识,也将为冰川形成与演化历史、特别是冰川形成年代和其他测年资料的科学解释提供可靠的依据。  相似文献   

13.
We report new ages on glaciofluvial (outwash) sediment from a large upland in northern Lower Michigan—the Grayling Fingers. The Fingers are cored with > 150 m of outwash, which is often overlain by the (informal) Blue Lake till of marine isotope stage (MIS) 2. They are part of an even larger, interlobate upland comprised of sandy drift, known locally as the High Plains. The ages, determined using optically stimulated luminescence (OSL) methods, indicate that subaerial deposition of this outwash occurred between 25.7 and 29.0 ka, probably associated with a stable MIS 2 ice margin, with mean ages of ca. 27 ka. These dates establish a maximum-limiting age of ca. 27 ka for the MIS 2 (late Wisconsin) advance into central northern Lower Michigan. We suggest that widespread ice sheet stabilization at the margins of the northern Lower Peninsula, during this advance and later during its episodic retreat, partly explains the thick assemblages of coarse-textured drift there. Our work also supports the general assumption of a highly lobate ice margin during the MIS 2 advance in the Great Lakes region, with the Fingers, an interlobate upland, remaining ice-free until ca. 27 ka.  相似文献   

14.
A 30 m-deep drill core from a glacially overdeepened trough in Northern Switzerland recovered a ~180 ka old sedimentary succession that provides new insights into the timing and nature of erosion–sedimentation processes in the Swiss lowlands. The luminescence-dated stratigraphic succession starts at the bottom of the core with laminated carbonate-rich lake sediments reflecting deposition in a proglacial lake between ~180 and 130 ka ago (Marine Isotope Stage MIS 6). Anomalies in geotechnical properties and the occurrence of deformation structures suggest temporary ice contact around 140 ka. Up-core, organic content increases in the lake deposits indicating a warming of climate. These sediments are overlain by a peat deposit characterised by pollen assemblages typical of the late Eemian (MIS 5e). An abrupt transition following this interglacial encompasses a likely hiatus and probably marks a sudden lowering of the water level. The peat unit is overlain by deposits of a cold unproductive lake dated to late MIS 5 and MIS 4, which do not show any direct influence from glaciers. An upper peat unit, the so-called «Mammoth peat», previously encountered in construction pits, interrupts this cold lacustrine phase and marks more temperate climatic conditions between 60 and 45 ka (MIS 3). In the upper part of the core, a succession of fluvial and alluvial deposits documents the Late Glacial and Holocene sedimentation in the basin. The sedimentary succession at Wehntal confirms that the glaciation during MIS 6 did not apparently cause the overdeepening of the valley, as the lacustrine basin fill covering most of MIS 6 is still preserved. Consequently, erosion of the basin is most likely linked to an older glaciation. This study shows that new dating techniques combined with palaeoenvironmental interpretations of sediments from such overdeepened troughs provide valuable insights into the past glacial history.  相似文献   

15.
冰碛的形态特征是气候变化的标记.以往的野外考察发现末次冰期的冰碛具有近乎统一的发育模式.选取藏东南帕隆藏布江流域的10条冰川, 研究其前方末次冰期冰川堆积特征, 以揭示其所反映的气候变化过程. 结果表明: 末次冰期MIS2形成最高大的冰碛垄, 我们称之为主冰碛垄, 这套冰碛垄示意当时冰期气候持续稳定时间最长.为主冰碛垄所部分覆盖而由其底部延伸出来的, 尚有至少两套范围更大、 但规模较小的冰碛垄, 表明MIS2之前冰期气候可能曾更加严酷, 但持续时间相对要短, 可能反映MIS4和/或MIS3的冰期气候特点.主冰碛垄内侧一直到现代冰川相当长的河谷段, 通常呈现多道冰碛垄, 规模均较主冰碛小, 它们有的不排除作为后退冰碛(recessional moraine)的可能性, 但晚冰期(YD)、 抑或H1事件应当是值得注意的.临近现代冰川末端, 一般能够辨别新冰期和小冰期冰碛垄. 因此, 藏东南这样一系列的冰川堆积, 以其形态、 范围和规模特征, 辅之以高精度的系统测年, 几乎可恢复出气候变化曲线来, 了解与全球氧同位素曲线之间的齿合关系.  相似文献   

16.
天山乌鲁木齐河源末次冰期冰川沉积光释光测年   总被引：6，自引：5，他引：1  
乌鲁木齐河源地区是中国冰川遗迹保存最丰富、地貌最典型的区域之一,是根据冰川遗迹重建第四纪冰川历史的理想地区。大量的研究工作以及技术测年结果也使其成为试验冰川沉积光释光（optically stimulated luminescence,OSL）测年可行性的理想地点。共采集了6个冰碛及上覆黄土样品用于光释光测年。提取38~63 μm的石英颗粒,运用SAR-SGC法测试等效剂量。各种检验表明测试程序是适用的。通过地貌地层关系、重复样品、已有年代的对比等方法,检验该地冰川沉积OSL测年的可行性。结果表明,OSL年代结果与地貌地层新老关系非常吻合,与已有的其他测年技术的年代结果也具可比性,表明这些样品的OSL信号在沉积之前晒退较好,OSL年代是可信的。冰川观测站侧碛垄的OSL年代为14.8±1.2 ka;9号冰川支谷口附近冰碛的OSL年代为13.5±1.1 ka和17.2±1.3 ka;上望峰冰碛的OSL年代为20.1±1.6 ka。综合OSL年代结果与此前其他测年结果,这几套冰碛垄形成于深海氧同位素MIS 2阶段应该是比较统一的认识。上望峰冰碛上覆黄土的OSL年代（10.5±0.8 ka）也印证了该结论。OSL年代指示上望峰冰碛对应于末次冰期最盛期,冰川观测站和9号冰川支谷谷口冰碛对应于晚冰期。下望峰冰碛的OSL年代为36.3±2.8 ka,对应于MIS 3阶段。下望峰冰碛的形成时代,仍有待更多沉积学以及测年工作进一步确定。  相似文献   

17.
《第四纪科学杂志》2017,32(1):48-62
The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British–Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 ± 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 ± 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at ∼26 ka around the time of increased ice‐rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at ∼24 ka. OSL dating (19.6 ± 1.5 ka) of the post‐glacial Hell Bay Gravel at Battery suggests there was then an ∼5‐ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, ∼390 km to the north. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.
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18.
The deglacial history of the central sector of the last British–Irish Ice Sheet is poorly constrained, particularly along major ice‐stream flow paths. The Tyne Gap Palaeo‐Ice Stream (TGIS) was a major fast‐flow conduit of the British–Irish Ice Sheet during the last glaciation. We reconstruct the pattern and constrain the timing of retreat of this ice stream using cosmogenic radionuclide (10Be) dating of exposed bedrock surfaces, radiocarbon dating of lake cores and geomorphological mapping of deglacial features. Four of the five 10Be samples produced minimum ages between 17.8 and 16.5 ka. These were supplemented by a basal radiocarbon date of 15.7 ± 0.1 cal ka BP, in a core recovered from Talkin Tarn in the Brampton Kame Belt. Our new geochronology indicates progressive retreat of the TGIS from 18.7 to 17.1 ka, and becoming ice free before 16.4–15.7 ka. Initial retreat and decoupling of the TGIS from the North Sea Lobe is recorded by a prominent moraine 10–15 km inland of the present‐day coast. This constrains the damming of Glacial Lake Wear to a period before ∼18.7–17.1 ka in the area deglaciated by the contraction of the TGIS. We suggest that retreat of the TGIS was part of a regional collapse of ice‐dispersal centres between 18 and 16 ka.
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19.
The single most prominent lake associated with the retreat phase of the last British–Irish Ice Sheet (BIIS) was Proglacial Lake Humber. The present research elucidates a revised regional history of Proglacial Lake Humber from its maximum elevation to its demise using a combination of landscape mapping and luminescence dating. The results of mapping multiple Lake Humber strandlines are now best described by an eight‐stage recessional model. Erosional highstands of the lake can be shown to post‐date the BIIS advance that deposited the Skipsea Till at around 17 ka whereas new OSL ages show that Lake Humber was nearing its demise by 15.5±0.8 ka, indicating a possible short‐lived lake. Multiple lake level stands are attributed to the switching of lake outlets from the Lincolnshire Gap to the Humber Gap and to oscillations of the BIIS blocking the latter on more than one occasion and subsequently at a lower elevation with till. The horizontal or near‐horizontal shorelines confirm that isostatic adjustment did not occur during the demise of Lake Humber, indicating that BIIS advances in the North Sea region and Vale of York were not only dynamic but of short duration.  相似文献   

20.
Quaternary glaciations in the Verkhoyansk Mountains, Northeast Siberia   总被引：1，自引：0，他引：1  
Geomorphological mapping revealed five terminal moraines in the central Verkhoyansk Mountains. The youngest terminal moraine (I) was formed at least 50 ka ago according to new IRSL (infrared optically stimulated luminescence) dates. Older terminal moraines in the western foreland of the mountains are much more extensive in size. Although the smallest of these older moraines, moraine II, has not been dated, moraine III is 80 to 90 ka, moraine IV is 100 to 120 ka, and the outermost moraine V was deposited around 135 ka. This glaciation history is comparable to that of the Barents and Kara ice sheet and partly to that of the Polar Ural Mountains regarding the timing of the glaciations. However, no glaciation occurred during the global last glacial maximum (MIS 2). Based on cirque orientation and different glacier extent on the eastern and western flanks of the Verkhoyansk Mountains, local glaciations are mainly controlled by moisture transport from the west across the Eurasian continent. Thus glaciations in the Verkhoyansk Mountains not only express local climate changes but also are strongly influenced by the extent of the Eurasian ice sheets.  相似文献   

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