Graptolite biostratigraphy of the Lower Silurian (Llandovery and Wenlock) of Bohemia     

Petr &#x;torch 《Geological Journal》1994,29(2):137-165

Nearly 50 sections through the Llandovery and Wenlock black shales of the Barrandian area (Bohemia) have been examined bed by bed. This has made possible the compilation of an improved and well defined graptolite zonal scheme with much new biostratigraphic data included. A total of 268 graptolite species and subspecies have been found. Their stratigraphic distribution allows the recognition of 27 graptolite zones: ascensus–acuminatus, vesiculosus, cyphus, triangulatus–pectinatus, simulans, convolutus, sedgwickii, linnaei, turriculatus, crispus, griestoniensis, tullbergi, spiralis, grandis, insectus, centrifugus, murchisoni, riccartonensis, dubius, belophorus, rigidus, ramosus–perneri, lundgreni, parvus, nassa–frequens, praedeubeli–deubeli, ludensis, and several subzones. The biozones are defined by the vertical ranges of their ‘index’ species and are characterized by rich accompanying associations. The zonal scheme is correlated with graptolite sequences elsewhere.  相似文献   

川东下三叠统飞仙关组-嘉陵江组界线附近的锶同位素组成   总被引：2，自引：0，他引：2  

胡作维  黄思静  王庆东  王春梅  郜晓勇 《地层学杂志》2007,31(4)

作为化学地层学的重要分支之一,锶同位素地层学已经逐步成为全球海平面变化、造山运动、古气候和古环境等全球事件研究和对比的有效工具,根据锶同位素地层学的基本原理,在对样品进行沉积岩组构、化学成分分析和对同期海水代表性评估的基础上,测试了四川东部华蓥山地区下三叠统飞仙关组-嘉陵江组界线附近6个碳酸盐岩样品的锶同位素组成。结果表明,该界线附近的锶同位素组成与前人公布的早三叠世同期海水的锶同位素组成数据基本一致。锶同位素地层学研究的引入,可望为我国南方海相三叠系飞仙关组和嘉陵江组的年代地层学对比研究提供重要依据。  相似文献   

Sedimentology and early diagenesis of the Broadford Beds (Lower Jurassic), Skye,north-west Scotland     

Alison Searl 《Geological Journal》1992,27(3):243-270

The Broadford Beds comprise a basal carbonate-dominated unit overlain by dark muddy sandstones and an upper cross-bedded sandstone unit. The limestones include coralliferous and oolitic lithologies and the sandstones include pisolitic berthierine ironstones and abundant phosphate nodules. The Broadford Beds have a maximum thickness of 140 m and can be subdivided into 17 parasequences, each initiated by an approximately 20 m rise in relative sea level. Marine flooding surfaces are most readily recognized in the lower parts of the succession, where diagenetic data can be utilized to locate emergence surfaces. There is no diagenetic evidence of early emergence in the upper parts of the sequence, but a variety of sedimentological data can be used to identify parasequence boundaries. Deposition of the Broadford Beds occurred largely around the shores of a number of islands in the northern Hebridean area. These islands partly isolated the Skye–Applecross area from a deeper marine basin to the west, and this may have enhanced the formation of authigenic phosphates and iron silicates. It is possible to use the regional variability of parasequence thicknesses to investigate the role of active local tectonism in governing differential subsidence and sediment supply.  相似文献   

Snow cover area change and its relations with climatic variability in Kashmir Himalayas,India     

Mifta ul Shafiq  Zahoor ul Islam  P. K. Joshi  Waseem A. Bhat 《国际地球制图》2019,34(6):688-702

Snowmelt makes an essential component of the hydrological system of Kashmir Himalayas. The present study was carried out to examine the status of Snow Cover Area (SCA) using Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day Snow Cover Product between 2000 and 2016. The intra- and inter-annual variability in SCA and in meteorological parameters was observed and various statistical tests were used to study the interrelationship. Results of statistical analysis indicate decrease in maximum temperature (?0.05 °C/year) and minimum temperatures (?0.02 °C/year) while rise in precipitation (19.13 mm/year). It also showed an increase in annual mean SCA (43.5 sq km) during the study period. The analysis was also carried out on a seasonal basis. The results revealed that in Kashmir Himalayas, climate plays a dominating role in controlling the SCA. The results depict the short-term fluctuations in SCA and show the magnitude of change between two successive values being very large in SCA.  相似文献   

Distribution of diagenetic alterations within depositional facies and sequence stratigraphic framework of fluvial sandstones: Evidence from the Petrohan Terrigenous Group,Lower Triassic,NW Bulgaria     

Mohamed Ali Kalefa El-Ghali  Sadoon Morad  Howri Mansurbeg  Miguel Angel Caja  George Ajdanlijsky  Neil Ogle  Ihsan Al-Aasm  Manhal Sirat 《Marine and Petroleum Geology》2009

Sequence stratigraphy of fluvial deposits is a controversial topic because changes in relative sea level will eventually have indirect impact on the spatial and temporal distribution of depositional facies. Changes in the relative sea level may influence the accommodation space in fluvial plains, and hence have impact on types of fluvial system, frequency of avulsion, and style of vertical and lateral accretion. This study aims to investigate whether depositional facies and changes in the fluvial system of the Lower Triassic Petrohan Terrigenous Group sandstones (NW Bulgaria) in response to changes in the relative sea level have an impact on the spatial and temporal distribution of diagenetic alterations.  相似文献   

Mantle plumes and the metamorphism of the lower crust and their influence on basin evolution     

Heinz-Jürgen Brink 《Marine and Petroleum Geology》2009

Since the stretching model appears to be not applicable to the subsidence of accretionary crust, basins located on this crust type may have an alternative origin. Examples of such basins are the West Siberia Basin and the North German Basin. Both basins showed intensive volcanism and magmatism during the initial phase of their development. Remarkably, the West Siberia Basin is closely located to the (hotspot related) Siberian flood basalts with a similar Permo-Triassic age, and the location of the North German Basin in Permian times is identical with the present day position of the Tibesti hotspot in Northern Africa. These two basins may have specific relations to hotspot heat sources of the Earth's underlying mantle. Due to these heat sources, thermal metamorphism within the lower layers of the (accretionary) crust may occur, resulting in rock density increase and subsequent shrinkage of the affected rock volumes. These shrinkage processes will lead to the development of topographic lows, their filling with sediments, and the subsequent start of an exponentially declining isostatic/metamorphic basin subsidence. In addition to the analyses of metamorphic processes, potential field anomalies, temperature fields, and histories of subsidence have been integrated into one single model that can explain the development of the North German Basin. Similarly, the East African Rift and Eifel Hotspots affected parts of the overriding continental plates. The East African Rift Hotspot can be traced back to the Afar flood basalts and the Dniepr–Donets Basin, whereas the Eifel Hotspot can be linked to the North Sea Basin. Continental drift templates, present day hotspot locations, flood basalt areas, metamorphic facies as function of temperature, and crust categories are taken as published in recent literature.  相似文献   

苏皖下扬子区晚白垩世以来的构造-热历史：浦口组砂岩磷灰石裂变径迹证据     

张沛  周祖翼  许长海 《海洋地质译丛》2009,(4):26-32

对苏皖下扬子区上白垩统浦口组（K2P）的三个砂岩样品进行了磷灰石裂变径迹（AFT）研究。结果显示：2个样品的AFT合并年龄为（88．8±4．4）Ma（径迹长度为（12．0±0．3）μm）和（82．1±6．8）Ma（径迹长度为（14．4±0．3）μm）与浦口组沉积年龄相近,说明它们沉降的幅度达到但没有超过AFT部分退火区间,1个样品的AFT合并年龄（117．3±5．9）Ma（径迹长度为（13．3±0．3）μm）大于浦口组沉积年龄,代表物源区抬升、剥露的冷却年龄。根据热历史模拟结果,识别出黄桥事件（110～90Ma）、仪征事件（70～60Ma）和三垛事件（35～22Ma）三期重要的构造事件,并将下扬子区晚白垩世以来的盆地演化划分为四个阶段：110～70Ma断坳复合型伸展盆地、70～35Ma拉张断陷盆地、35～22Ma挤压抬升阶段和22Ma至今坳陷盆地。  相似文献   

Spatial Variability of Mass Movements in the Satluj Valley,Himachal Pradesh during 1990～2006     

Vikram Gupta  M. P. Sah 《山地科学学报》2008,5(1):38-51

Satluj Valley is known to have a history of landslides and related mass movement activities since the geological times. Geological and geomorphological settings combined with anthropogenic activities constitute a propensity towards slope failure. During the last two decades,the area witnessed substantial increase in athropogenic pressure,mainly due to the exploitation of hydropower potential,changing landuse pattern and population growth. In addition,a shift of the climatic patterns in the form of larger area falling under the influence of rains was observed. These natural as well as anthropogenic changes in the area have resulted in increased spatial coverage of landslide in the area. This paper documents these changes during 1990～2006.  相似文献   

The shipway limestone of gower: Sedimentation on a storm-dominated early carboniferous ramp     

T. J. Faulkner 《Geological Journal》1988,23(1):85-100

A detailed sedimentary study of the Lower Carboniferous (Courceyan) Shipway Limestone Formation at Three Cliffs Bay on the Gower Peninsula (South Wales) has shown that the bioclastic limestones represent a storm-dominated sequence that contains the storm-related sedimentary structure hummocky cross-stratification (HCS). Conformably overlying the Shipway Limestone is a cross-stratified oolitic sandbody with evidence of subaerial exposure. Six sedimentary lithofacies are identified in these two formations which record a distal to proximal, shallowing-upward trend that passes from beneath mean wave-base to above fairweather wave-base. The shallow marine facies model constructed by Wu (1982) from his study of the Lower Carboniferous limestone sequences of South Wales is re-evaluated. Modifications proposed for the model include the addition of two distal tempestite facies and a proximal oolite sand body. The Shipway Limestone and Brofiscin Oolite record the first major, basin-wide, shallowing-upward phase of the Lower Carboniferous in South Wales.  相似文献   

2001-2020年新疆伊犁河谷植被主要生长季NDVI时空变化与水热因子关系研究     

武鹏飞  玉奴斯&#;唐阿塔尔  代鹏超  王小军  高海涛  梁凤超 《沙漠与绿洲气象(新疆气象)》2024,18(4):150-157

植被是陆地生态系统的重要组成部分,在气候和生物化学循环中对水和能量的交换起到至关重要的作用。利用MODIS-NDVI数据,采用Theil-Sen中值趋势分析、Mann-Kendall检验及变异系数的方法,研究了2001-2020年伊犁河谷植被主要生长季（5-9月）归一化植被指数（NDVI）的时空变化特征,结合气温降水数据采用相关性分析的方法,探究了植被主要生长季的影响因素。结果表明：（1）2001-2020年伊犁河谷植被主要生长季NDVI在空间上存在明显的差异性,NDVI多年均值较高。（2）区域尺度上,NDVI年际变化趋势较为平缓;像元尺度上,微量减少和微量增加的面积占比较大,显著增加与显著减少的区域较集中,占比较小。（3）伊犁河谷生长季植被的稳定性较好,CV≤0.10基本分布在整个区域,0.3相似文献