Environmental significance of bedrock jointing in Southern Ontario,Canada     

N. Eyles  A. E. Scheidegger 《Environmental Geology》1995,26(4):269-277

The bedrock surface of many glaciated areas is obscured by thick drift deposits. In southern Ontario, Canada, the buried bedrock surface is dissected by channels, infilled with glacial deposits as much as 150 m thick, that are part of a wider mid-continent preglacial fluvial system that predates formation of the modern Great Lake basins. The infills of bedrock channels form major groundwater aquifers, influence regional groundwater flows and contaminant migration to Lake Ontario, and may localize the release of thermogenic methane and radon within heavily urbanized surface environments. A quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident. Buried bedrock channels in south-central Ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying Pleistocene sediments. Joints in sediments are of considerable environmental significance (for example, subsurface contaminant and gas migration in fine-grained clayey sediments) and of many origins (stress release, desiccation, etc.) but are widely assumed to be a predominantly surface-related phenomena; the existence of deeper joints has been noted by some authors but their origin is obscure. Data presented herein from south-central Ontario confirm that, in addition to surface-related joints, a second population of bedrock-related joints, reflecting the upward propagation of bedrock fractures, is present in Pleistocene sediments of south-central Ontario.  相似文献   

Cenozoic uplift of Nuussuaq and Disko, West Greenland—elevated erosion surfaces as uplift markers of a passive margin   总被引：1，自引：0，他引：1  

Johan M. Bonow  Peter Japsen  Karna Lidmar-Bergstrm  James A. Chalmers  Asger Ken Pedersen 《Geomorphology》2006,80(3-4):325-337

Remnants of a high plateau have been identified on Nuussuaq and Disko, central West Greenland. We interpret the plateau as an erosion surface (the summit erosion surface) formed mainly by a fluvial system and graded close to its former base level and subsequently uplifted to its present elevation. It extends over 150 km east–west, being of low relative relief, broken along faults, tilted westwards in the west and eastwards in the east, and having a maximum elevation of ca. 2 km in central Nuussuaq and Disko. The summit erosion surface cuts across Precambrian basement rocks and Paleocene–Eocene lavas, constraining its age to being substantially younger than the last rift event in the Nuussuaq Basin, which took place during the late Maastrichtian and Danian. The geological record shows that the Nuussuaq Basin was subjected to subsidence of several kilometres during Paleocene–Eocene volcanism and was transgressed by the sea later during the Eocene. By comparing with results from apatite fission track analysis and vitrinite reflectance maturity data, it is suggested that formation of the erosion surface was probably triggered by an uplift and erosion event starting between 40 and 30 Ma. Surface formation was completed prior to an uplift event that started between 11 and 10 Ma and caused valley incision. This generation of valleys graded to the new base level and formed a lower erosion surface, at most 1 km below the summit erosion surface, thus indicating the magnitude of its uplift. Formation of this generation of valleys was interrupted by a third uplift event also with a magnitude of 1 km that lifted the landscape to near its present position. Correlation with the fission-track record suggests that this uplift event started between 7 and 2 Ma. Uplift must have been caused initially by tectonism. Isostatic compensation due to erosion and loading and unloading of ice sheets has added to the magnitude of uplift but have not significantly altered the configuration of the surface. It is concluded that the elevations of palaeosurfaces (surfaces not in accordance with present climate or tectonic conditions) on West Greenland's passive margin can be used to define the magnitude and lateral variations of Neogene uplift events. The striking similarity between the landforms in West Greenland and those on many other passive margins is also noted.  相似文献   

Quaternary glaciation and hydrologic variation in the South American tropics as reconstructed from the Lake Titicaca drilling project     

Sherilyn C. Fritz  Paul A. Baker  Geoffrey O. Seltzer  Ashley Ballantyne  Pedro Tapia  Hai Cheng  R. Lawrence Edwards 《Quaternary Research》2007,68(3):410-420

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon.  相似文献   

Palynological evidence for a latest Carboniferous-Early Permian glaciation in Northern Ethiopia     

Robert Bussert  Eckart Schrank 《Journal of African Earth Sciences》2007,49(4-5):201-210

Palynomorphs extracted from glacigenic sediments in Northern Ethiopia are latest Carboniferous-Early Permian in age. These sediments were hitherto thought to be either of Upper Ordovician or of Late Carboniferous-Early Permian age. The predominantly glaciolacustrine and glaciofluviatile sediments were deposited in glacial troughs and valleys that were eroded into Precambrian basement rocks and into Early Palaeozoic deposits, possibly equivalents of Upper Ordovician sediments in Eritrea. In the latest Carboniferous-Early Permian, glaciated uplands to the north of Ethiopia must have existed in Eritrea and/or in southern or central Saudi Arabia.  相似文献   

Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska     

Gerald F. Wieczorek  Eric L. Geist  Roman J. Motyka  Matthias Jakob 《Landslides》2007,4(3):205-215

An unstable rock slump, estimated at 5 to 10 × 10⁶ m³, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3–4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green’s law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours.  相似文献   

青藏高原东部当子沟末次冰期冰川演化光释光测年   总被引：1，自引：0，他引：1  

欧先交  张彪  赖忠平  周尚哲  曾兰华 《地理科学进展》2013,32(2):262-269

青藏高原东部横断山脉沙鲁里山北支雀儿山北麓的当子沟, 保留了4 组末次冰期冰碛垄, 每组冰碛垄由若干道小冰碛垄组成, 是末次冰期多次冰川波动的理想地貌证据。为恢复该地末次冰期冰川演化历史, 从这4 组冰碛垄中采集了7 个光释光测年样品进行年代测定。等效剂量采用单片再生法(SAR)和标准生长曲线法(SGC)进行测试。年代结果显示:第1~3 组冰碛垄形成于22.4-16.5 ka BP, 属深海氧同位素2 阶段(MIS-2), 大致与全球末次盛冰期(LGM)相当。第4 组冰碛垄形成于MIS-3。MIS-3 冰川规模大于MIS-2。第1~3 组9 道次一级小冰碛垄表明, 约在22.4-16.5 ka BP期间当子沟冰川经历了9 次小波动。冰川在稍早于22.4 ka BP达到MIS-2 的最大范围, 此后规模在波动中逐渐萎缩, 可能是冰川对MIS-2 后期太阳辐射增强、气温回升的响应。最里侧冰碛垄形成于16.5 kaBP, 可能标志着该地冰消期的开始。此后, 当子沟冰川大幅快速退缩。冰川融水在最里侧冰碛垄里侧低洼谷地汇集并被阻塞形成当子错。  相似文献   

末次冰期冰碛垄系列的形态特征及其形成探讨 ——以帕隆藏布江谷地为例   总被引：1，自引：0，他引：1  

陈仁容  周尚哲  邓应彬 《冰川冻土》2012,34(4):836-847

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   

玉龙雪山冰川沉积序列OSL定年   总被引：3，自引：3，他引：0  

何则  何元庆  张志刚  和丽华  齐翠姗  刘婧 《冰川冻土》2016,38(6):1544-1552

位于青藏高原东南缘的玉龙雪山分布有欧亚大陆纬度最低的海洋型冰川,其主峰及周边地区保存了大量清晰完整的第四纪冰川遗迹。研究该区第四纪冰川作用遗迹及其冰川作用史,具有重要的理论与实际价值。应用光释光（OSL）测年技术对玉龙雪山冰川沉积物进行了定年,结合前人研究资料,重建玉龙雪山冰川作用史。研究结果表明：玉龙雪山东麓的末次冰期冰碛物主要形成于晚更新世末次冰期最盛时期,其平均年代约在25ka,西麓末次冰期冰碛物形成年代约为50ka,对应于深海氧同位素3阶段中期（MIS3b）。而倒数第二次冰期的年代在240ka左右,处于中更新世晚期,对应于MIS8阶段,当时玉龙雪山存在多条复式山谷冰川。该研究可为玉龙雪山第四纪冰川作用历史的重新认识以及光释光测年技术在该区的应用提供基础资料。  相似文献   

黄土高原北缘中部末次冰期冰楔假型的发现及意义     

王建勇  张绪教  何泽新  赵秋晨  何祥丽  盛余应 《现代地质》2015,29(4):816-824

冰楔假型是反映古气候环境的重要标志,其蕴涵的气候地层信息对地貌演化过程具有重要的指示意义。通过对黄土高原北缘中部环江T1阶地上新发现的冰楔假型群特征的研究和光释光(OSL)测年,结果显示这些发育在冲积砂砾石中的冰楔假型的充填砂体的年代为 (30.01±3.31) ka B.P.,形成环境推测当时的年平均地温比现今要低17.7 ℃。该冰楔假型的发现也为末次冰期阶段性冻土南界的位置和变迁提供了证据。另外,据冰楔与阶地冲积物的关系推测,在冰楔形成的冰冻期河流阶地的堆积缓慢甚至停滞,在(28.64±3.13) ka B.P.之后的气候温暖期河流快速下切、T1阶地形成。这为河流阶地成因机制的探讨提供了依据,反映了气候波动对阶地发育的控制。  相似文献   

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