Detrital iron-ore deposits in the Iron Ore Group of rocks,northern Orissa,eastern India     

B. K. Mohapatra  P. P. Singh  P. Mishra  K. Mahant 《Australian Journal of Earth Sciences》2013,60(8):1139-1152

Detrital iron deposits (DID) are located adjacent to the Precambrian bedded iron deposit (BID) of Joda near the eastern limb of the horseshoe-shaped synclinorium, in the Bonai–Keonjhar belt of Orissa. The detrital ores overlie the Dhanjori Group sandstone as two isolated orebodies (Chamakpur and Inganjharan) near the eastern and western banks of the Baitarani River, respectively. The DID occur as pebble/cobble conglomerates containing iron-rich clasts cemented by goethite. Mineralogy, chemistry and lamination of these clasts are similar to that found in the nearby BID ores. Enrichment of trace and rare-earth elements in the DID relative to the BID is attributed to their concentration during the precipitation of cementing material. The detrital iron orebodies formed when Proterozoic weathering processes eroded pre-existing BID outcrops located on the Joda Ranges, and the resulting detritus accumulated in the paleochannels. In situ dissolution in association with abundant organic material produced Fe-saturated groundwater, which re-precipitated as goethite within the aggraded channel to cement the detritals. Growth of microplaty hematite in the goethite matrix suggests some level of subsequent burial metamorphism.  相似文献   

Trend analysis and ARIMA modelling of pre-monsoon rainfall data for western India   总被引：1，自引：0，他引：1  

Priya Narayanan  Ashoke Basistha  Sumana Sarkar  Sachdeva Kamna 《Comptes Rendus Geoscience》2013,345(1):22-27

Spatial and temporal variability of rainfall over different seasons influence physical, social and economic parameters. Pre-monsoon (March, April and May – MAM) rainfall over the country is highly variable. Since heat lows and convective rainfall in MAM have an impact on the intensity of the ensuing monsoons, hence the pre-monsoon period was chosen for the study. The pre-whitened Mann Kendall test was used to explore presence of rainfall trend during MAM. The results indicate presence of significant (at 10% level) increasing trend in two stations (Ajmer, Bikaner). The practical significance of the change in rainfall was also explored as percentage changes over long term mean, using Theil and Sen's median slope estimator. Forecast using univariate ARIMA model for pre-monsoon months indicates that there is a significant rise in the pre-monsoon rainfall over the northwest part of the country.  相似文献   

Authigenic Gypsum in Gas-Hydrate Associated Sediments from the East Coast of India (Bay of Bengal)   总被引：2，自引：0，他引：2  

M. KOCHERLA 《《地质学报》英文版》2013,87(3):749-760

Authigenic gypsum crystals, along with pyrite and carbonate mineralization, predominantly calcites were noticed in distinct intervals in a 32 m long piston core, collected in the gas hydrate- bearing sediments in the northern portion of the Krishna-Godavari basin, eastern continental margin of India at a water depth of 1691 m. X-ray diffraction and energy dispersive spectrum studies confirm presence of pyrite, gypsum, calcite, and other mineral aggregates. The occurrence of gypsum in such deep sea environment is intriguing, because gypsum is a classical evaporite mineral and is under saturated with respect to sea water. Sedimentological, geochemical evidences point to diagenetic formation of the gypsum due to oxidation of sulphide minerals (i.e. pyrite). Euhedral, transparent gypsum crystals, with pyrite inclusions are cemented with authigenic carbonates, possibly indicating that they were formed authigenically in situ in the gas hydrate-influenced environment due to late burial diagenesis involving sulphate reduction and anaerobic oxidation of methane (AOM). Therefore, the authigenic gypsums found in sediments of the Krishna-Godavari and Mahanadi offshore regions could be seen as one of the parameters to imply the presence of high methane flux possibly from gas hydrate at depth.  相似文献   

AN EVALUATION OF SURFACE HARDNESS OF NATURAL AND MODIFIED ROCKS USING SCHMIDT HAMMER: STUDY FROM NORTHWESTERN HIMALAYA, INDIA     

BY VIKRAM GUPTA  RUCHIKA SHARMA  MADHO PRASAD SAH 《Geografiska Annaler: Series A, Physical Geography》2009,91(3):179-188

Four rock types (quartz mica gneiss, schist, quartzite and calc-silicate) located in the Satluj and Alaknanda valleys were used to test whether a Schmidt hammer can be used to distinguish rock surfaces affected by various natural and man-induced processes like manual smoothing of rock surfaces by grindstone, surface weathering, deep weathering, fluvial polishing and blasting during road construction. Surfaces polished by fluvial process yielded the highest Schmidt hammer rebound (R-) values and the blast-affected surfaces yielded the lowest R-values for the same rock type. Variations in R-value also reflect the degree of weathering of the rock surfaces. It has been further observed that, for all the rock types, the strength of relationship between R-values for the treated surfaces (manual smoothing of rock surface by grindstone) and the unconfined compressive strength (UCS) is higher than for the fresh natural surfaces.  相似文献   

Juxtaposition of India and Madagascar: A Perspective     

M. Yoshida  H.M. Rajesh  M. Santosh 《Gondwana Research》1999,2(3):449

Proterozoic terrains in South India and Madagascar provide important clues in understanding the Gondwanaland tectonics, especially the assembly of this mega-continent during the Pan-African period. The Archaean terrains in both Madagascar and India are characterized by N-S trending greenstone belts occurring within gneissose granitic rocks in the northern part. Extensive development of K-rich granitic rocks of ca. 2.5 Ga is also characteristic in both areas. Such a broad age zonation of younger Dharwar (ca 2.6–3.0 Ga) in the north and the older Sargur (ca 3.0–3.4 Ga) in the south as in South India remains to be identified in future studies from Madagascar. The occurrence of greenschist facies rocks in the northeastern part and higher grade rocks in most of other parts in the north-central terrain of Madagascar is comparable with the general tendency of increasing metamorphic grade from northwestern to southern areas ranging from greenschist to granulite facies in South India. The Proterozoic crystalline rocks in both continents show pronounced lithological similarity with the wide occurrence of graphite-bearing khondalite in association with charnockitic rocks. While the Archaean-Proterozoic boundary is well defined in southern India by the Palghat-Cauvery or the KKPT shear zones as recently identified, this boundary is ill-defined in Madagascar due to extensive Pan-African overprinting, as well as the development of the Proterozoic cover sequence, the Itremo Group. There is also a possible general correlation between the Mesoproterozoic cover sequences in Madagascar and India, such as between the Itremo Group of west-central Madagascar and the Kaladgi and Cuddapah sequences of South India. The Pan-African granulite facies metamorphism of ca. 0.5 Ga extensively developed in both India and Madagascar is generally comparable in intensity and extent. P-T conditions and P-T-t paths also appear comparable, with the general range of ca. 700–1000°C and 6–9 kb, and near-isothermal decompressional paths. A-type granite plutons and alkaline rocks including anorthosites and mafic plutonic rocks of ca. 500–800 Ma develop in both terrains, provide strong basis for the correlation of both terrains, and define a Pan-African igneous province within East Gondwanaland. Major shear zones in both continents are expected to play a critical role in the correlation, albeit are still poorly constrained. Detailed elucidation of the tectonic history of the shear zones, and the timing of various events along the shear zones would provide important constraints on the correlation of the two continental fragments.  相似文献   

Mid–late Holocene hydrological changes in the Mahi River, arid western India   总被引：1，自引：0，他引：1  

Alpa Sridhar   《Geomorphology》2007,88(3-4):285-297

This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was  55 000 m³ s^− 1 and that of the historic channel was  9500 m³ s^− 1, some  25 times and  5 times greater than that of the present river (2000 m³ s^− 1), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene.  相似文献   

长江、黄河大洪水前期地球系统演变的分析   总被引：21，自引：14，他引：7  

汤懋苍  高晓清  柳艳香  郭维栋  王钟睿 《高原气象》2000,19(4):441-449

通过分析江、淮、黄、海四大洪共１４个大洪水年的前期地震场特征,发现大洪水前在青藏高原东南地区、亚欧中纬地带和台湾以东洋面三处的有强地震发生,若强震出现在中印缅热点则对应着江淮大小;强震出现在川青甘地区则对应着黄海河大水。引发大水的直接原因是本地区地热涡的强烈发展,它因刚好位于数组”同向等距地热涡族”的相交点上,交相干共振的结果,文中详细分析了１９５４和１９８２年两个个例。最后分析了“中印缅热点”的  相似文献   

Groundwater targeting in a hard-rock terrain using fracture-pattern modeling, Niva River basin, Andhra Pradesh, India   总被引：1，自引：0，他引：1  

Y. Srinivasa Rao  T. Reddy  P. Nayudu 《Hydrogeology Journal》2000,8(5):494-502

In hard-rock terrain, due to the lack of primary porosity in the bedrock, joints, fault zones, and weathered zones are the sources for groundwater occurrence and movement. To study the groundwater potential in the hard-rock terrain and drought-prone area in the Niva River basin, southern Andhra Pradesh state, India, Landsat 5 photographic data were used to prepare an integrated hydrogeomorphology map. Larsson's integrated deformation model was applied to identify the various fracture systems, to pinpoint those younger tensile fracture sets that are the main groundwater reservoirs, and to understand the importance of fracture density in groundwater prospecting. N35°–55°E fractures were identified as tensile and N35°–55°W fractures as both tensile and shear in the study area. Apparently, these fractures are the youngest open fractures. Wherever N35°–55°E and N35°–55°W fracture densities are high, weathered-zone thickness is greater, water-table fluctuations are small, and well yields are high. Groundwater-potential zones were delineated and classified as very good, good to very good, moderate to good, and poor. Electronic Publication  相似文献   

基于知识的旱地生理趋势的评价模型     

R Jana  M V Khire 《地理学报(英文版)》2004,14(1):25-31

The present study aims the evaluation of bio-physical characteristics towards soil-water-vegetation stress and a rule is envisaged to assess the degree of temporal changes. The digital rule for assessment is initialized through the index of land Instability (ILI) where the variance indicates the temporal instability of the pixel I.e., smallest land unit. It is assumed that the biophysical characteristic of land is in command of land-dynamics where there is no change in Land Use/Land Cover (LU&LC). The intensity map on tendency of albedo (IALB) assesses the intensity of soil erosion and water stress whereas intensity map on tendency of NDVI (INDVI) appraises the stress on vegetation. The carry-out study covers a part of semiarid Western India. Primarily remote sensing technique, which carries the digital information of land temporally and spatially, is adopted in this paper. A part of the study area is represented using two sets of IRS 1A/lB LISS-I data of March with a decadal time domain (1989-1998) as a test area. It is assumed that the soil-water-vegetation stress is maximum during summer(March-April-May) in any tropical belt and decadal data will stretch the possibility of climate as well as man-made activity over the land.  相似文献   

INDIA/ASIA CONVERGENCE AND HIMALAYAN SHORTENING   总被引：1，自引：0，他引：1  

Stphane Guillot    David Baratoux    Eduardo Garzanti    Didier Marquer    Julia de Sigoyer  WT  ”BX 《地学前缘》2000,(Z1)

INDIA/ASIA CONVERGENCE AND HIMALAYAN SHORTENING  相似文献