Late Devensian deglaciation of the Tyne Gap Palaeo‐Ice Stream,northern England          下载免费PDF全文

Stephen J. Livingstone  David H. Roberts  Bethan J. Davies  David J. A. Evans  Colm Cofaigh  Delia M. Gheorghiu 《第四纪科学杂志》2015,30(8):790-804

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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Surface cracks—geomorphological indicators for late Quaternary halotectonic movements in Northern Germany     

Jacob Hardt  Ben Norden  Klaus Bauer  Ole Toelle  Jenny Krambach 《地球表面变化过程与地形》2021,46(14):2963-2983

Loading and unloading effects of the Scandinavian Ice Sheet triggered halotectonic movements in Northern Germany. We present newly detected geomorphological features—termed surface cracks—which indicate a relation between ice sheet-induced salt movement and surface processes. As a part of the Central European Basin System, numerous Zechstein salt structures are abundant in the North German Basin. On the basis of high-resolution digital terrain data, more than 160 surface cracks were mapped in Northern Germany, which were grouped into 30 clusters. Almost all of the surface cracks occur above the top regions of Zechstein salt structures. The surface cracks can be several kilometres long, up to more than 20 m deep and more than 100 m wide. The comparison of the shape of the salt structures and the orientation of the cracks reveals a geometric dependency, indicating that the cracks preferably occur near the crest margins of the salt structures. Furthermore, 3D seismic data from two sites show that subsurface faults originating from salt movement exist beneath the surface cracks. We interpret the cracks as surface ruptures due to ice sheet-induced halotectonic movements. The cracks occur in a variety of Quaternary sediments and landforms. This indicates that widespread halokinetic movements occurred in the region after the last (Weichselian) deglaciation and likely before the thawing of the permafrost, possibly in a time frame from c. 30–20 ka until c. 15 ka.  相似文献   

A relative sea-level history for Arviat,Nunavut, and implications for Laurentide Ice Sheet thickness west of Hudson Bay     

Karen M. Simon  Thomas S. James  Donald L. Forbes  Alice M. Telka  Arthur S. Dyke  Joseph A. Henton 《Quaternary Research》2014

Thirty-six new and previously published radiocarbon dates constrain the relative sea-level history of Arviat on the west coast of Hudson Bay. As a result of glacial isostatic adjustment (GIA) following deglaciation, sea level fell rapidly from a high-stand of nearly 170 m elevation just after 8000 cal yr BP to 60 m elevation by the mid Holocene (~ 5200 cal yr BP). The rate of sea-level fall decreased in the mid and late Holocene, with sea level falling 30 m since 3000 cal yr BP. Several late Holocene sea-level measurements are interpreted to originate from the upper end of the tidal range and place tight constraints on sea level. A preliminary measurement of present-day vertical land motion obtained by repeat Global Positioning System (GPS) occupations indicates ongoing crustal uplift at Arviat of 9.3 ± 1.5 mm/yr, in close agreement with the crustal uplift rate inferred from the inferred sea-level curve. Predictions of numerical GIA models indicate that the new sea-level curve is best fit by a Laurentide Ice Sheet reconstruction with a last glacial maximum peak thickness of ~ 3.4 km. This is a 30–35% thickness reduction of the ICE-5G ice-sheet history west of Hudson Bay.  相似文献   

Geochemical evidence for Late Cretaceous marginal arc-to-backarc transition in the Sabzevar ophiolitic extrusive sequence,northeast Iran     

《Journal of Asian Earth Sciences》2013

The ophiolitic extrusive sequence, exposed in an area north of Sabzevar, has three major parts: a lower part, with abundant breccia, hyaloclastic tuff, and sheet flow, a middle part with vesicular, aphyric pillow lava, and an upper part with a sequence of lava and volcanic-sedimentary rocks. Pelagic limestone interlayers contain Late Cretaceous (Maastrichtian–Late Maastrichtian) microfauna. The supra-ophiolitic series includes a sequence of turbidititic and volcanic-sedimentary rocks with lava flow, aphyric and phyric lava, and interlayers of pelagic limestone and radiolarian chert. Paleontological investigation of the pelagic limestone and radiolarite interlayers in this series gives a Late Cretaceous age, supporting the idea that the supra-ophiolitic series formed in a trough, synchronous with the Sabzevar oceanic crust during the Late Cretaceous. Geochemical data indicate a relationship between lava in the upper part of the extrusive sequence and lava in the supra-ophiolitic series. These lavas have a calc-alkaline to almost alkaline characteristic, and show a clear depletion in Nb and definite depletions in Zr and Ti in spider diagrams. Data from these rocks plot in the subduction zone field in tectonomagmatic diagrams. The concentration and position of the heavy rare earth elements in the spider diagrams, and their slight variation, can be attributed to partial melting of the depleted mantle wedge above the subducted slab, and enrichment in the LILE can be attributed to subduction components (fluid, melt) released from the subducting slab. In comparison, the sheet flow and pillow lava of the lower and middle parts of the extrusive sequence show OIB characteristics and high potassium magmatic and shoshonitic trends, and their spider diagram patterns show Nb, Zr, and Ti depletions. The enrichment in the LILE in the spider diagram patterns suggest a low rate of partial melting of an enriched, garnet-bearing mantle. It seems that the marginal arc basin, in which the Sabzevar ophiolite was forming, experienced lithospheric extension in response to slab rollback. This process, which formed a backarc basin, may have aborted the embryonic arc, stopped arc magmatism, and led to the rise of mantle diapirs. The extrusive ophiolite sequence, north of Sabzevar probably formed during the transition from a marginal arc basin to a backarc basin during the Late Cretaceous.  相似文献   

Paleogene crustal anatexis and metamorphism in Lhasa terrane, eastern Himalayan syntaxis: Evidence from U-Pb zircon ages and Hf isotopic compositions of the Nyingchi Complex   总被引：7，自引：0，他引：7  

Liang GuoHong-Fei Zhang  Nigel HarrisRandall Parrish  Wang-Chun XuZhang-Liang Shi 《Gondwana Research》2012,21(1):100-111

In the eastern Himalayan syntaxis, the southern Lhasa terrane is dominated by middle- to high-grade metamorphic rocks (Nyingchi Complex), which are intruded by felsic melts. U-Pb zircon dating and zircon Hf isotopic composition of these metamorphic and magmatic rocks provide important constraints on the tectono-thermal evolution of the Lhasa terrane during convergent process between Indian and Asian continents. U-Pb zircon data for an orthogneiss intruding the Nyingchi Complex yield a protolith magma crystallization age of 83.4 ± 1.2 Ma, with metamorphic ages of 65-46 Ma. This orthogneiss is characterized by positive ε_Hf (t) values of + 8.3 and young Hf model ages of ~ 0.6 Ga, indicating a derivation primarily from a depleted-mantle or juvenile crustal source. Zircons from a quartz diorite yield a magma crystallization age of 63.1 ± 0.6 Ma, with ε_Hf (t) values of − 8.2 to − 2.7, suggesting that this magma was sourced from partial melting of older crustal materials. Zircon cores from a foliated biotite granite show ages ranging from 347 to 2690 Ma, with age peaks at 347-403 Ma, 461-648 Ma and 1013-1183 Ma; their zircon ε_Hf (t) values range from − 30.6 to + 6.9. Both the U-Pb ages and Hf isotopic composition of the zircon cores are similar to those of detrital zircons from the Nyingchi Complex paragneiss, implying that the granite was derived from anatexis of the Nyingchi Complex metasediments. The zircon rims from the granite indicate crustal anatexis at 64.4 ± 0.7 Ma and subsequent metamorphism at 55.1 ± 1.3 and 41.4 ± 2.3 Ma. Our results suggest that the late Cretaceous magmatism in the southern Lhasa terrane resulted from Neo-Tethys oceanic slab subduction and we infer that Paleocene crustal anatexis and metamorphism were related to the thermal perturbation caused by rollback of the northward subducted Neo-Tethyan oceanic slab.  相似文献   

东南极冰盖上新世大规模退缩事件          下载免费PDF全文

刘小汉  韦利杰  黄费新  方爱民  琚宜太  李潇丽  周学君 《地质科学》2013,(2):419-434

笔者近年对东南极内陆格罗夫山(Grove Mountains)开展了上新世以来冰盖表面波动的综合研究,运用冰川地质、地貌、土壤、沉积岩、孢粉组合及宇宙核素等各种方法手段,提出东南极大冰盖形成以后并非稳定演化至今,而在上新世早期时发生过大规模退缩,其前缘至少曾经退缩到格罗夫山地区,距现今冰盖边缘约400 km。之后,冰盖又迅速膨胀,到距今2.3 Ma时,冰面至少超过现今高度约400 m。以后冰面缓慢平稳下降,至1.6 Ma时,东南极冰盖进入第四纪振荡期,但重新上升的冰面再也没有超过现今高度的100 m以上。东南极冰盖大规模消融事件在全球尺度上也有所响应,例如北半球大冰盖形成,青藏高原整体剧烈隆升,塔里木盆地黄土出现等。这类行星尺度的气候变化可能与直布罗陀海峡关闭与地中海盐化事件,巴拿马地峡关闭等大地构造事件有关。  相似文献   

Using in situ cosmogenic 10Be to identify the source of sediment leaving Greenland          下载免费PDF全文

Alice H. Nelson  Paul R. Bierman  Jeremy D. Shakun  Dylan H. Rood 《地球表面变化过程与地形》2014,39(8):1087-1100

We use the concentration of in situ ¹⁰Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland's sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized (n = 19) and non‐glacerized terrain (n = 10), from channels where sediment from glacerized and non‐glacerized terrain is mixed (n = 28), from Holocene glacial‐fluvial terraces (n = 4), and from one sand dune. In situ ¹⁰Be concentrations in sediment range from 1600 to 34 000 atoms g^‐1. The concentration of in situ ¹⁰Be in sediment sourced from non‐glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ ¹⁰Be concentration in bedrock (n = 5) and boulder (n = 6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5 ka. The isotope concentration in sediment sourced from non‐glacerized terrain is higher than in sediment sourced from glacerized terrain because the non‐glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of ¹⁰Be that probably accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of ¹⁰Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

地域生态环境保护与城市规划布局中的地下水资源评价——以鄂西岗地董市幅1:50 000水文地质图数据集为例          下载免费PDF全文

肖攀  何军  彭轲  许珂 《中国地质》2019,46(S2):93-101

鄂西岗地1：50 000水文地质图数据集是在董市幅实施水文地质测绘、地球物理勘探、遥感地质解译、水文地质钻探、水样品采集测试及地下水位监测与统测等工作基础上完成原始数据采集,综合前期收集资料的整理分析与最新采集数据集成编制而成。原始数据采集主要包括遥感地质解译面积450 km²,机（民）调查点226个,地质调查点125个,环境地质调查点16个,水文地质钻探孔12眼,工程地质钻探孔8眼,水样品（全分析、同位素及有机污染样）合计采集80组,丰、枯水期地下水位统测各40点次,以及机（民）井监测12点位（一个水文年监测）等,数据采集严格遵守《水文地质调查规范》（DZ/T 0282-2015）《水文水井地质钻探规程》（DZ/T 0148-2014）等规范与技术要求组织实施,保证数据的准确可靠。数据集采用MapGIS 6.7平台辅助制图,坐标系为1984年西安坐标系,投影方式为高斯-克吕格投影（6度带）。水文地质图编制是以地下水系统理论为指导,充分展现关键水文地质信息与地下水资源现状条件,为区域地下水资源开发利用远景规划与有效保护提供直接依据,能够促进长江中游生态文明建设与长江中游经济带快速发展。  相似文献   

基于InSAR和ICESat的南极冰盖地区DEM提取和精度分析   总被引：3，自引：1，他引：2  

万雷  周春霞  鄂栋臣  邓方慧 《冰川冻土》2015,37(5):1160-1167

结合InSAR和ICESat测高数据,以东南极PANDA断面4个实验区为例,进行DEM生成研究.在干涉相位转换成高程前,引入ICESat测高数据作为控制点优化干涉对基线,消除基线线性误差趋势的影响.利用控制点之外的ICESat测高数据分析4个实验区的DEM精度及其差异,并探讨了引起DEM误差的原因.冰流和地貌特征是影响InSAR生成冰盖DEM精度的重要因素.针对冰流的影响,从理论上进行了分析并结合冰流速数据进行了分析验证.最后利用克里金插值法改正InSAR DEM残余误差,并利用GPS实测控制点对改正效果进行验证.结果表明:对于高纬区流速较小且分布一致的区域,改正效果很好,DEM精度可达3 m;而对于冰流速较大且复杂的地区,需采用多基线等算法进一步消弱冰流引入的误差.  相似文献   

南极冰盖的物质平衡研究:进展与展望   总被引：2，自引：0，他引：2       下载免费PDF全文

温家洪  孙波  李院生  潘增弟 《极地研究》2004,16(2):114-126

南极冰盖物质平衡最新的研究进展表明,西南极洲表现出两种变化模式,西部在增厚,而北面在更快地减薄。西南极冰盖总体可能正在减薄,其物质损失的速率可能足以使海平面每年上升近0.2mm。东南极冰盖物质不平衡可能很小,甚至其符号还不能被确定。南极半岛正在经历着快速变化。目前还不能可靠地估算南极冰盖的物质平衡状态。同时,大型冰川的停滞,一些冰川流速加快,冰盖大范围加速减薄,冰架大面积的快速崩解和支流冰川的加速,以及着地线强烈的底部融化等显示出南极冰盖存在快速变化。南极冰盖物质平衡未来的重点研究领域是开展冰盖表面高程变化的监测与模拟,确定表面物质平衡及其在各冰流盆地的分布,着地线的冰流通量,冰架底部的融化,了解冰后期冰盖退缩的动力过程,以及开发、对比和改进与冰盖物质平衡模拟和预测相关的各种模型。  相似文献