Astronomical time scale for the Middle Oxfordian to Late Kimmeridgian in the Swiss and French Jura Mountains     

André Strasser 《Swiss Journal of Geoscience》2007,100(3):407-429

Detailed investigation of facies and sedimentary structures reveals that, during the Middle Oxfordian to Late Kimmeridgian, the shallow carbonate platform of the Swiss and French Jura Mountains recorded high-frequency sea-level fluctuations quite faithfully. The cyclostratigraphic analysis within the established biostratigraphic and sequence-chronostratigraphic framework implies that the resulting hierarchically stacked depositional sequences formed in tune with the orbital cycles of precession (20 kyr) and eccentricity (100 and 400 kyr). The astronomical time scale presented here is based on the correlation of 19 platform sections and 4 hemipelagic sections from south-eastern France where good biostratigraphic control is available. The cyclostratigraphic interpretation suggests that the interval between sequence boundaries Ox4 and Kim1 (early Middle Oxfordian to earliest Kimmeridgian) lasted 3.2 myr and that the Kimmeridgian sensu gallico has a duration of 3.2 to 3.3 myr. The astronomical time scale proposed here is compared to time scales established by other authors in other regions and the discrepancies are discussed. Despite these discrepancies, there is a potential to estimate the durations of ammonite zones and depositional sequences more precisely and to better evaluate the rates of sedimentary, ecological and diagenetic processes. Editorial handling: Hanspeter Funk, Helmut Weissert, Stefan Bucher  相似文献   

大兴安岭摩天岭雨养泥炭沼泽多环芳烃分布特征与来源分析   总被引：3，自引：0，他引：3  

史彩奎  贾益群  王国平 《湿地科学》2007,5(3):260-265

运用气相色谱—质谱(GC-MS)技术对大兴安岭摩天岭(47°22′23″N,120°38′45″E)雨养泥炭沼泽泥炭柱中的多环芳烃(PAHs)污染物进行了分析。结果表明,研究区雨养泥炭沼泽表层PAHs总含量的质量比为1 874.4 ng/g,与国内外雨养泥炭沼泽表层相比,其污染水平相对较高。由于研究区气候冷湿,雨养泥炭沼泽中的有机质腐殖化程度较低,有机碳含量较高,这和其PAHs含量的相关性较小。研究区样品中检测出的PAHs主要以2~3环的多环芳烃为主;由PAHs分子标志物指标分析结果可知,研究区雨养泥炭沼泽PAHs污染物的主要来源是当地森林火灾与大气远距离沉降;沉降的PAHs污染物是原油开采、石油生产和化石燃料燃烧的共同贡献。在距地表15~34 cm处,柱状剖面层的PAHs含量显著增加,这是由于1987年和1998年大兴安岭发生森林火灾树木燃烧所致。  相似文献   

Responses of streamflow to climate change in the northern slope of Tianshan Mountains in Xinjiang: A case study of the Toutun River basin     

Li WeiHong  Chen YaNing  Hao XingMing  Huang Xiang  Chen YaPeng 《中国科学D辑(英文版)》2007,50(1):42-48

A case study on the responses of streamflow to climate change in the Toutun River basin was carried out based on data analysis of streamflow, precipitation, and temperatures during the past 50 years.Temporal series of the streamflow change in the Toutun River basin was analyzed and tested using the Mann-Kendall nonparametric test. Results revealed that the annual runoff of the Toutun River had been in a monotonic decreasing trend for the past 50 years. Compared with the 1950s and 1960s, the annual runoff in the 1990s decreased by 4.0×105 m3 and 7.2×105 m3. The precipitation did not show monotonic trend during the past 50 years, but the annual temperature increased by 1.12℃ since the 1950s. Further data analysis indicated that the monthly runoff of the Toutun River decreased significantly from August to October, with precipitation displaying the similar pattern of seasonal change. Analysis suggests that the reduction of streamflow in the Toutun River basin is possibly caused by the seasonal change of precipitation, especially the precipitation reduction in summer, and temperature increases.  相似文献   

Feedbacks between erosion and sediment transport in experimental bedrock channels     

Joel P. Johnson  Kelin X. Whipple 《地球表面变化过程与地形》2007,32(7):1048-1062

Natural bedrock rivers flow in self‐formed channels and form diverse erosional morphologies. The parameters that collectively define channel morphology (e.g. width, slope, bed roughness, bedrock exposure, sediment size distribution) all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes. To explore the mechanics of river incision, we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate (sand and cement), a single sediment size primarily transported as bedload, a single erosion mechanism (abrasion) and sediment‐starved transport conditions. We find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field, sediment transport and bottom roughness. Abrasion only occurs where sediment impacts the bed, and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows. However, the spatial focusing of erosion results in tortuous flow paths and erosional forms (inner channels, scoops, potholes), which dissipate flow energy. This energy dissipation is a negative feedback that reduces sediment transport capacity, inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Subduction of Continental Crust in the Early Palaeozoic North Qaidam Ultrahigh-Pressure Metamorphic Belt, NW China:Evidence from the Discovery of Coesite in the Belt   总被引：3，自引：0，他引：3  

YANG Jingsui  XU Zhiqin  SONG Shuguang  ZHANG Jianxin  WU Cailai  SHI Rendeng  LI Haibing  Maurice BRUNEL  Paul TAPPONNIER Institute of Geology  Chinese Academy of Geological Science  Baiwanzhuang Rd.  Beijing  China Department of Earth Sciences  University of Montpellier II  Montpellier  France Institut de Physique du Globe  Paris Cedex  France 《《地质学报》英文版》2002,76(1):63-68

Coesite was discovered as inclusions in zircon separates from pelitic gneiss associated with a large eclogite body in the North Qaidam ultrahigh-pressure (UHP) terrane. Some graphite inclusions were also found. This finding suggested the occurrence of in-situ UHP metamorphism and that the terrane was most likely recrystallized at pressures below the diamond stability field. It supported other previous indirect UHP evidence, such as polycrystalline quartz inclusions in eclogitic garnet, quartz lamellae in omphacite and P-T estimates for both eclogite and garnet peridotite. The U-Pb and Sm-Nd ages of the North Qaidam eclogite indicated that subduction of continental crust occurred in the Early Palaeozoic, which probably recorded a collision between the Sino-Korean and Yangtze plates.  相似文献   

On Continent-Continent Point-Collision and Ultrahigh-Pressure Metamorphism   总被引：4，自引：0，他引：4  

DONG Shuwen  Chinese Academy of Geological Sciences  Baiwanzhuang Ro  Beijing WU Hongling  LIU Xiaochun  XUE Huaimin Institute of Geomechanics  Chinese Academy of Geological Sciences  Beijing Fei Zhenbi 《《地质学报》英文版》2002,76(1):69-80

Up to now it is known that almost all ultrahigh-pressure (UHP) metamorphism of non-impact origin occurred in continent-continent collisional orogenic belt, as has been evidenced by many outcrops in the eastern hemisphere. UHP metamorphic rocks are represented by coesite- and diamond-bearing eclogites and eclogite facies metamorphic rocks formed at 650-800℃ and 2.6-3.5 GPa, and most of the protoliths of UHP rocks are volcanic-sedimentary sequences of continental crust. From these it may be deduced that deep subduction of continental crust may have occurred. However, UHP rocks are exposed on the surface or occur near the surface now, which implies that they have been exhumed from great depths. The mechanism of deep subduction of continental crust and subsequent exhumation has been a hot topic of the research on continental dynamics, but there are divergent views. The focus of the dispute is how deep continental crust is subducted so that UHP rocks can be formed and what mechanism causes it to be subducte  相似文献   

Discovery of Radiolarian Fossils from the Aiketik Group at the Western End of the South Tianshan Mountains of Chinaand Its Implications   总被引：1，自引：0，他引：1  

LI Yuejun  WANG Zhaoming  WU Haoruo  HUANG Zhibin  TAN Zejinand LUO Juncheng Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing Tarim Oil Field Company  PetroChin  Korl  Xinjiang Zhu Xiling 《《地质学报》英文版》2002,76(2):146-154

The Aiketik Group, distributed at the western end of the South Tianshan Mountains, China, is an important lithostratigraphic unit involved in the South Tianshan orogen. It is separated from the adjacent rocks by faults. Generally, the geologists ascribed it to the Upper Carboniferous according to Pseudostaffella sp., Profusulinella sp. and Fusulinella sp. found from the limestone and sandy limestone of Aiketik. Our radiolarian fossils were obtained from the chert samples collected from the Haladaok section located at the upper Tuoshihan River. The fossils mainly include Albaillella undulata Deflandre, Albaillella paradoxa Deflandre, Albaillella sp. aff. A. paradoxa Deflandre, Albaillella sp. cf. A. deflandrei Gourmelon, Albaillella sp., Albaillella excelsa Ishiga, Kito and Imoto (?), Belowea variabilis (Ormiston et Lane), Callella cf. C. parvispinosa Won, Entactinia cf. E. tortispina Ormiston et Lane, Entactinia aff. E. tortispina Ormiston et Lane, Entactinia variospina Won, Entactinia sp., Eostylodicty  相似文献   

川西龙门山前陆盆地构造沉降初步分析   总被引：7，自引：0，他引：7       下载免费PDF全文

张箭  徐强  廖仕孟  朱同兴 《沉积与特提斯地质》2002,22(4):67-72

研究表明，龙门山冲断带是川西前陆盆地的主要物源区，它的逆冲推覆活动直接控制着川西前陆盆地的沉积类型和沉积物供给量，晚三叠世诺利期，瑞替期和晚侏罗世早中期是川西前陆盆地构造沉降速率较高时期，反映龙门山冲断带在这些时期的逆冲推覆速率较大，是逆冲推覆作用构造抬升的强烈时期；而早侏罗世是该地区构造沉降时，估算龙门山逆冲推覆体在各个不同时期的抬升高度和抬升速率。  相似文献   

北祁连山东段新元古代火山岩的年代学证据   总被引：4，自引：2，他引：4       下载免费PDF全文

于福生王春英  杜国民 《中国地质》2002,29(4):360-363

在1∶5万石门川幅、老龙湾幅区域地质调查时发现,北祁连山东段上吊吊坡地区存在一套不同于下奥陶统阴沟群的火山岩,经全岩样品Sm-Nd同位素测定,获得Sm-Nd等时线年龄为(723±25.0)Ma,表明其形成时代为新元古代。地球化学特征表明该套火山岩形成于岛弧环境,说明当时北祁连东段仍处于洋壳俯冲挤压环境。  相似文献   

天目山柳杉树轮δ¹³C对华东地区降水序列的重建          下载免费PDF全文

吕军  屠其璞  钱君龙 《大气科学学报》2001,24(3):350-355

对采自天目山的柳杉树轮进行交叉定年后,得到树轮的δ¹³C年序列。将δ¹³C年序列去除大气CO₂的影响,保留其高频振荡部分。利用华东地区部分气象站的降水资料,通过主成份分析,分析了降水与树轮δ¹³C之间的关系。考虑滞后效应,利用回归方法重建了过去一百多年来的华东地区不同时段的降水序列,并分析其变化特征。  相似文献