Discovery of Gondwana plant fossils and palynomorphs of Late Asselian (Early Permian) age in the Karakoram Block     

R. Upadhyay  R. Chandra  A.K. Sinha  R.K. Kar  S. Chandra  N. Jha  H. Rai 《地学学报》1999,11(6):278-283

We report the discovery of Early Permian (late Asselian, ∼280–275 Ma) plant fossils and associated palynomorphs from a marine sedimentary sequence of the eastern Karakoram plate, in northern India. These specimens show affinities with those found in marine Lower Gondwana sediments of the Indian subcontinent. This supports the contention that during the Early Permian Period, the Karakoram plate was Peri-Gondwanan. It is suggested to have had an intermediate position between the Indian plate and the Qiangtang–Lhasa microcontinents, at a latitude of about 35° south.  相似文献   

Multiple interpretive errors? Indeed. Reply to: Climate effects of the 74 ka Toba super-eruption: Multiple interpretive errors in ‘A high-precision 40Ar/39Ar age for the Young Toba Tuff and dating of ultra-distal tephra’ by Michael Haslam     

《Quaternary Geochronology》2013

We would like to thank Michael Haslam (Haslam et al., 2013) for his interest in our recent contribution on the dating of the Young Toba Tuff/Tephra (YTT) (Mark et al., 2013). However, we point out errors made by Haslam, using this opportunity to clarify and expand on our discussion while also re-emphasising the important points from our study that have been overlooked.  相似文献   

Sulcus and outline morphometrics of sagittal otolith variability in freshwater fragmented populations of dwarf gourami,Trichogaster lalia (Hamilton, 1822)     

《Limnologica》2021

Studies on the anatomy of sulcus and outline morphometrics of the three population groups of Trichogaster lalia were carried out to examine the effects of anthropogenic stressors (dams and barrages) on the function-related morphological variability of the fish. Altogether 150 samples of the fish were procured from three geographically isolated rivers namely Ganga, Gomti and Yamuna. The features based on images and morphological indices of sulcus, otolith and body shape of the fish were analysed and compared using uni and multivariate statistical procedures. Rostrum, anti-rostrum and margins of sagittal otolith and cauda of sulcus predominantly varied among three population groups of the fish. Variations in geometric morphometrics of sulcus, otolith-outline, combination of both and body shape indicated the existence of three distinct groups of the fish where individuals of river Gomti and Ganga were found to be closer to each other compared to that of river Yamuna. Mantel test showed an overall good correlation between the morphometric data-sets based on otolith and body shape in delineating three groups of the fish. Understanding of the environmental factors influencing the variations in function-related morphology of the different groups of T. lalia is essential to identify the boundaries of the different groups of the fish and to implement the appropriate strategies for their conservation.  相似文献   

基于小波分析的GPS双差观测数据消噪方法研究     

陈向阳 《测绘工程》2011,20(6):20-23

通过双差方法难以消除的多路径误差、接收机观测噪声等非模型化误差会大大影响GPS动态定位的精度.基于小波分析的理论,对GPS双差观测数据序列的消噪问题进行研究,结果表明,利用小波去噪原理,可有效地从受到强噪声干扰的GPS观测数据序列中提取变形特征信息,增强基线解算的有效性,提高GPS定位精度,解决传统技术对GPS动态监测...  相似文献   

Long-term hydroclimatic variability in monsoon shadow zone of western Himalaya, India     

Ram R. Yadav 《Climate Dynamics》2011,36(7-8):1453-1462

Tree-ring-width data of Himalayan cedar [Cedrus deodara (Roxb.) G. Don] from 11 homogeneous moisture stressed sites in the monsoon shadow zone of the western Himalaya were used to develop a mean chronology extending back to ad 1353. The chronology developed using Regional Curve Standardization method is the first from the Himalayan region of India showing centennial-scale variations. The calibration of ring-width chronology with instrumental precipitation data available from stations close to the tree ring sampling sites showed strong, direct relationship with March?CApril?CMay?CJune (MAMJ) precipitation. This strong relationship was used to supplement the instrumental precipitation data back to ad 1410. The precipitation reconstruction showed extended period of drought in fifteenth and sixteenth centuries. Increasingly pluvial conditions were recorded since eighteenth century, with the highest precipitation in the early part of the nineteenth century. The decreasing trend in reconstructed precipitation in the last decade of the twentieth century, consistent with the instrumental records, is associated with the decreasing trend in frequency of western disturbances. MAMJ precipitation over the monsoon shadow zone in the western Himalaya is directly associated with the North Atlantic Oscillation (NAO) and NINO3-SST index of El Nino-Southern Oscillation (ENSO), the leading modes of climate variability influencing climate over large parts of the Northern Hemisphere. However, the relationship between ENSO and MAMJ precipitation collapsed completely during 1930?C1960. The breakdown in this relationship is associated with the warm phase of Atlantic Multidecadal Oscillation (AMO). A spectral analysis of reconstructed MAMJ precipitation indicates frequencies in the range of the variability associated with modes of NAO, ENSO and AMO.  相似文献   

三种再分析气温资料在中国西部地区的可信度评价   总被引：1，自引：0，他引：1  

钞振华 《南京气象学院学报》2011,34(2):162-169

再分析资料质量检验和可信度分析是其合理使用的必要前提,是提高气候变化研究成果可靠性的根本保证,为了评价NCEP-II、ERA-40和JRA-25三种再分析资料在中国西部地区的可信度,研究对比分析了2m气温产品的质量。结果表明,这三种再分析气温产品都能较好地反映中国西部地区气温的空间分布特征,在地形复杂区域与站点气温的差异比较大,而在地势相对平缓的地区这三种再分析资料都能提供高质量的气温产品。由于同化了地面观测资料,ERA-40、JRA-25气温产品的可信度相对较高,且能够提供更为详尽的大尺度气温变异性。总体上,ERA-40的质量优于其他两种再分析资料。  相似文献   

Organic walled microbiota from the silicified algal clasts, Bhander limestone, Satna area, Madhya Pradesh     

S. K. Pandey  S. Kumar 《Journal of the Geological Society of India》2013,82(5):499-508

A good assemblage of organic-walled microbiota has been discovered from the petrographic thin sections of the black-bedded chert of the Bhander limestone, exposed at Sajjanpur area of Satna district and Ramnoi area of Rewa District, Madhya Pradesh. The assemblage is made up of the following forms: Synodophycus euthemos, Myxococcoides minor, Coniunctiophycus gaoyuzhuangense, Siphonophycus kestron, Siphonophycus robustum, Eoentophysalis magna, Glenobotrydion aenigmatis and Huroniospora microreticulata. The assemblage comprises both filamentous as well as coccoidal forms of cyanobacterial affinity. The forms are associated with algal clasts.  相似文献   

Late Pleistocene-Holocene morphosedimentary architecture, Spiti River, arid higher Himalaya     

Pradeep Srivastava  Yogesh Ray  Binita Phartiyal  Anupam Sharma 《International Journal of Earth Sciences》2013,102(7):1967-1984

The Spiti River drains the rain shadow zone of western Himalaya. In the present study, the fluvial sedimentary record of Spiti valley was studied to understand its responses to tectonics and climate. Geomorphic changes along the river enable to divide the river into two segments: (i) upper valley with a broad, braided channel where relict sedimentary sequences rise 15–50 m high from the riverbed and (ii) lower valley with a narrow, meandering channel that incises into bedrock, and here, the fluvio-lacustrine sediments reside on a bedrock bench located above the riverbed. The transition between these geomorphic segments lies along the river between Seko-Nasung and Lingti villages (within Tethyan Himalaya). Lithofacies analyses of the sedimentary sequences show six different lithofacies. These can be grouped into three facies associations, viz. (A) a glacial outwash; (B) sedimentation in a channel and in an accreting bar under braided conditions; and (C) formation of lake due to channel blockage by landslide activities. Seventeen optically stimulated luminescence ages derived from ten sections bracketed the phases of river valley aggradation between 14–8 and 50–30 ka. These aggradation phases witnessed mass wasting, channel damming and lake formation events. Our record, when compared with SW monsoon archives, suggests that the aggradation occurred during intensified monsoon phase of MIS 3/4 and that proceeded the Last Glacial Maxima. Thus, the study reports monsoon modulated valley aggradation in the NW arid Himalaya.  相似文献   

Over time and space changing characteristics of estuarine suspended particles in the German Weser and Elbe estuaries     

《Journal of Sea Research》2014

Fine cohesive, suspended sediments appear in all estuarine environments in a predominately flocculated state. The transport and deposition of these flocs is influenced by their in-situ and primary particle size distribution. Especially the size of the inorganic particles influences the density and hence the settling velocity of the flocculated material. To describe both the changes in primary particle size of suspended particulate matter as well as the variability of floc sizes over time and space, the data of In-Situ Particle-Size Distributions (ISPSDs), Primary Particle Size Distributions (PPSDs) and Suspended Sediment Concentrations (SSCs) were collected. For this, Laser In-Situ Scattering and Transmissiometry (LISST) measurements as well as the water samples were collected in the German Elbe and Weser estuaries, covering seasonal variability of the SSC.The data of the ISPSDs show that the inorganic and organic Suspended Particulate Matter (SPM), as found in the Elbe and Weser estuaries, mostly appears in a flocculated state. The substrate for organic matter is mainly imported from the seaside and transported into the estuaries as indicated by an upstream decrease of the amount of fine particles. In winter, when the freshwater discharge is high, different PPSDs are found in the case of the Elbe estuary in the Turbidity Maximum Zone (TMZ) as well as in the landward and in the seaward sections close to the TMZ. In summer, the distance between the seaward and the landward section is too low to obtain an individual PPSD within the Elbe TMZ.A missing correlation between the PPSD and ISPSD shows that the inorganic constituents do not have an influence on the in-situ floc size. Although flocs aggregate and disaggregate over a tidal cycle and with changing SSC, they do not change their PPSD. The microflocs are therefore strong enough to withstand further breakage into their inorganic constituents.  相似文献   

Spike in phytoplankton biomass in Greenland Sea during 2009 and the correlations among chlorophyll-a,aerosol optical depth and ice cover     

瞿波  路海浪  林道荣 《中国海洋湖沼学报》2014,32(2):241-254

The distributions and correlations of chlorophyll-a(Chl-a),aerosol optical depth(AOD)and ice cover in the southeast Arctic Ocean-Greenland Sea(10°W–10°E,70°–80°N)between 2003 and 2009 were studied using satellite data and statistical analyses.Regression analysis showed correlations between Chl-a and AOD,Chl-a and ice cover,and AOD and ice cover with different time lags.The time lag of Chl-a and AOD indicated their long-term equilibrium relationship.Peaks in AOD and Chl-a and generally occurred in May and July,respectively.Despite the time lag,the correlation between Chl-a and AOD in the study region was as high as 0.7.The peak gap between Chl-a and AOD shifted for about 6 weeks during 2003–2009.In the summer and autumn of 2009,Chl-a and AOD levels were much higher than during the other years,especially in the northern band of the study region(75°–80°N).The driving forces for this localized increase in phytoplankton biomass could be mainly attributed to the very high rate of ice melting in spring and early summer and the high wind speed in autumn,together with the increased deposition of aerosol throughout the year.The unusually high AOD in the spring of 2003 was mainly due to a massive fi re in Russia,which occurred in the fi rst half of the year.Over the 7 years of the study,the sea surface temperature generally decreased.This may have been due to the release of dimethylsulfi de into the air,excreted in large amounts from abundant phytoplankton biomass,and its subsequent reaction,form large amounts of aerosol,and resulting in regional cooling.  相似文献