芬兰的冰川作用与冰川地貌     

齐利.  Н 《冰川冻土》1990,12(1):17-30

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中国东部末次冰期风沙沉积的基本特征及其相模式   总被引：4，自引：0，他引：4  

张明书  刘健 《海洋地质与第四纪地质》1993,13(1):1-10

依据中国东部已发现的两种不同类型的末次冰期风沙沉积剖面,总结出空间分布上的局限性,类型上的多样性,序列上的旋回性,盛行风向的恒定性,物质组成的近源性,伴生物的一致性,层理类型的典型性,序次界面的特定性以及控制因素的一致性等十大特征,并提出了风沙沉积的相模式。  相似文献   

南海北部周边地区倒数第二次冰期—末次间冰植被演化   总被引：9，自引：0，他引：9  

罗运利  孙湘君 《海洋地质与第四纪地质》2003,23(1):19-26

为了研究倒数第二次冰期旋回(氧同位素6/5期)中的环境变迁,对南海北部大洋钻探(ODP)1144站(20°3.18′N、 17°25.14′E, 水深2 037 m)总共385个孢粉样品进行了分析研究,时间分辨率为530 a/样.孢粉谱的主要特征是松属花粉和草本植物花粉百分含量交替占优势,并且大致和冰期旋回对应间冰期时松属花粉占优势,冰期时草本植物花粉占优势.详细的对比表明,在氧同位素6/5期的冰期-间冰期过渡阶段,孢粉组合的变化要早于氧同位素记录指示的冰盖体积的变化,表明中低纬度地区气候变暖早于冰盖后退.还讨论了孢粉组合变化对轨道和亚轨道旋回以及季风变化的响应.  相似文献   

山东荣成成山头“柳夼红层”的层序、划分与成因及其气候意义(Ⅱ)   总被引：1，自引：0，他引：1  

张明书  刘健 《海洋地质与第四纪地质》1992,(2)

四、“柳夼红层”的物质组成 本文(Ⅰ)所列“柳夼红层”剖面地层层序进行了物相、粒度、X衍射和ESR年代测定,其结果与宏观观察结果相吻合。 “柳夼红层”,剖面序列,层位和时代有所不同,成因有别,而在物质组成上却大同小异,表现出从晚更新世早期至全新世地层,其物源供应基本相同,都来源于燕山期斑状花岗岩的风化破碎产物,属就地近源搬运。  相似文献   

Evaluation of ASTER GDEM and SRTM and their suitability in hydraulic modelling of a glacial lake outburst flood in southeast Tibet     

Weicai Wang  Xiaoxin Yang  Tandong Yao 《水文研究》2012,26(2):213-225

The resolution and accuracy of digital elevation models (DEMs) can affect the hydraulic simulation results for predicting the effects of glacial lake outburst floods (GLOFs). However, for the Tibetan Plateau, high‐quality DEM data are often not available, leaving researchers with near‐global, freely available DEMs, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) and the Shuttle Radar Topography Mission data (SRTM) for hydraulic modelling. This study explores the suitability of these two freely available DEMs for hydraulic modelling of GLOFs. Our study focused on the flood plain of a potentially dangerous glacial lake in southeastern Tibet, to evaluate the elevation accuracy of ASTER GDEM and SRTM, and their suitability for hydraulic modelling of GLOFs. The elevation accuracies of ASTER GDEM and SRTM were first validated against field global position system (GPS) survey points, and then evaluated with reference to the relatively high precision of 1:50 000 scale DEM (DEM5) constructed from aerial photography. Moreover, the DEM5, ASTER GDEM and SRTM were used as basic topographic data to simulate peak discharge propagation, as well as flood inundation extent and depth in the Hydrologic Engineering Center's River Analysis System one‐dimensional hydraulic model. Results of the three DEM predictions were compared to evaluate the suitability of ASTER GDEM and SRTM for GLOF hydraulic modelling. Comparisons of ASTER GDEM and SRTM each with DEM5 in the flood plain area show root‐mean‐square errors between the former two as ± 15·4 m and between the latter two as ± 13·5 m. Although SRTM overestimates and ASTER GDEM underestimates valley floor elevations, both DEMs can be used to extract the elevations of required geometric data, i.e. stream centre lines, bank lines and cross sections, for flood modelling. However, small errors still exist in the cross sections that may influence the propagation of peak discharge. The flood inundation extent and mean water depths derived from ASTER GDEM predictions are only 2·2% larger and 2·3‐m deeper than that of the DEM5 predictions, whereas the SRTM yields a flood zone extent 6·8% larger than the DEM5 prediction and a mean water depth 2·4‐m shallower than the DEM5 prediction. The modelling shows that, in the absence of high‐precision DEM data, ASTER GDEM or SRTM DEM can be relied on for simulating extreme GLOFs in southeast Tibet. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late Quaternary vegetation dynamics in a biodiversity hotspot, the Uluguru Mountains of Tanzania     

Jemma Finch  Melanie J. Leng  Rob Marchant 《Quaternary Research》2009,72(1):111-122

Late Quaternary vegetation history and environmental changes in a biodiverse tropical ecosystem are inferred from pollen, charcoal and carbon isotope evidence derived from a ∼ 48,000-yr sedimentary record from the Uluguru Mountains, a component of the Eastern Arc Mountains of Kenya and Tanzania. Results indicate that Eastern Arc forest composition has remained relatively stable during the past ∼ 48,000 yr. Long-term environmental stability of the Eastern Arc forests has been proposed as a mechanism for the accumulation and persistence of species during glacial periods, thus resulting in the diverse forests observed today. The pollen and isotope data presented here indicate some marked changes in abundance but no significant loss in moist forest taxa through the last glacial maximum, thereby providing support for the long-term environmental stability of the Eastern Arc. Anthropogenic activities, including burning and forest clearance, were found to play a moderate role in shaping the mosaic of forest patches and high-altitude grasslands that characterise the site today; however, this influence was tempered by the inaccessibility of the mountain.  相似文献   

Palaeoglaciation of Bayan Har Shan,northeastern Tibetan Plateau: glacial geology indicates maximum extents limited to ice cap and ice field scales   总被引：1，自引：0，他引：1  

Jakob Heyman  Arjen P. Stroeven  Helena Alexanderson  Clas Hättestrand  Jon Harbor  Yingkui Li  Marc W. Caffee  Liping Zhou  Daniel Veres  Feng Liu  Martin Machiedo 《第四纪科学杂志》2009,24(7):710-727

Key locations within an extensive area of the northeastern Tibetan Plateau, centred on Bayan Har Shan, have been mapped to distinguish glacial from non‐glacial deposits. Prior work suggests palaeo‐glaciers ranging from valley glaciers and local ice caps in the highest mountains to a regional or even plateau‐scale ice sheet. New field data show that glacial deposits are abundant in high mountain areas in association with large‐scale glacial landforms. In addition, glacial deposits are present in several locations outside areas with distinct glacial erosional landforms, indicating that the most extensive palaeo‐glaciers had little geomorphological impact on the landscape towards their margins. The glacial geological record does indicate extensive maximum glaciation, with local ice caps covering entire elevated mountain areas. However, absence of glacial traces in intervening lower‐lying plateau areas suggests that local ice caps did not merge to form a regional ice sheet on the northeastern Tibetan Plateau around Bayan Har Shan. No evidence exists for past ice sheet glaciation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

The Baykonurian glaciohorizon of the Late Vendian     

N. M. Chumakov 《Stratigraphy and Geological Correlation》2009,17(4):373-381

Glacial deposits occurring close to the Vendian-Cambrian boundary were discovered long ago in several regions of Asia and West Africa. New data of recent years confirm earlier observation and specify age constraints of these deposits. In certain sections, glacial sediments rest on beds with the Upper Vendian fossils (Vendotaenia sp., Sabellidites remains, and microfossils). In the Hoggar Highland, they discordantly overlie magmatic rocks ca. 560 Ma old. In the East Sayan Mts., the Upper Vendian Cloudina sp. have been found in the diamictite matrix. In Central Asia and Northwest China, cap dolomites conformably overlying glacial deposits grade upward into the chert-phosphatic sediments containing fossils (Tarim region), which are characteristic of the Anabarites trisulcatus Zone in the Nemakit-Daldynian Stage. Fossils of this zone have been found directly above glacial deposits in the East Sayan. According to all these data, the respective Baykonurian glaciation, as it is termed in this work, either antedated the Nemakit-Daldynian Age or was concurrent to its commencement. The glaciation is correlative with a significant negative δ¹³C excursion of ?5 to ?10‰. Judging from recent paleotectonic reconstructions, the Baykonurian glaciation was not regional in rank and left records in both hemispheres of the Earth. This glaciation resumes the well-known succession of the great glaciation event in the terminal Late Precambrian, i.e., the Sturtian, Marinoan, and Gaskiers glaciations. Hence, one cannot ignore the Baykonurian glaciation when analyzing the geological, biospheric, and biotic history of the Late Precambrian.  相似文献   

冲绳海槽末次盛冰期孢粉组合的古环境指示意义   总被引：1，自引：0，他引：1  

邓韫  郑卓 《地球科学》2005,30(5):597-603

冲绳海槽西陆坡末次冰期的高沉积速率为高分辨率研究提供了良好的材料,DGKS-9602钻孔通过氧同位素年代对比,总长931cm的岩心保存了相当于氧同位素阶段1～3的沉积记录．孢粉分析的结果表明,OIS1和OIS三阶段松属花粉含量占优势,平均含量达65％以上,而OIS2阶段松属百分含量明显降低,草本植物花粉含量增加,超过50％．松属与蒿属等草本花粉间的相互消长指示了海平面的升降,并与氧同位素曲线的变化趋势相似．末次盛冰期中国东部大陆架覆盖的植被以草地为主,由于冲绳海槽在末次盛冰期时的绝大部分沉积物质与大陆架的剥蚀作用有关,来自长江中上游山地较远距离带来的物质和山地花粉相对减少．与中国东部尘土花粉结果对比发现,现代东海表层蒿属与禾本科比值（A／P）所指示的纬度正好与长江中下游平均纬度相当,而冲绳海槽末次盛冰期的A／P比值所指示的陆地环境比现代高7个纬度,证明末次盛冰期植被带南移,与前人陆地记录的结果相吻合．  相似文献   

北京西山第四纪冰川遗迹——三十届国际地质大会地质旅行路线指南(T204)     

吴锡浩  蒋复初  徐和聆  肖华国 《地质力学学报》2003,9(4):289-302

北京西山的第四纪冰川遗迹考察和研究,始于20世纪50年代。但自80年代以来部分学者对有关冰川现象提出了异议,其中最主要的观点是有关现象可用冰缘气候下的雪蚀作用和寒冻泥石流作用给予解释。本路线介绍了可判识北京西山是否发育第四纪冰川关键的模式口冰溜面、管坨岭冰碛层、太平庄冰碛层、鲁家滩冰水沉积和大富庄冰碛层等五处第四纪冰川遗迹的古冰川宏观和微观特征。   相似文献