Hydrogeologic framework of the Deccan terrain of the Koyna River basin, India     

Pradeep K. Naik  Arun K. Awasthi  A. Anand  Prakash C. Mohan 《Hydrogeology Journal》2001,9(3):243-264

The Koyna River basin in India drew the attention of geoscientists after an earthquake (magnitude 7) in 1967. Since then, detailed geological, tectonic, and seismic investigations of this river basin have been carried out by several workers. However, very little study has been done on its hydrogeological framework. The present work aims at filling this gap. Basalts, laterites, alluvium, soils, and talus deposits form shallow unconfined aquifers, with transmissivity of 27–135 m²/d and a regional specific yield of 0.012. In shallow basaltic aquifers, the lower part of the highly weathered and highly jointed horizon above, and the poorly weathered and highly jointed horizon below, form the most potential zone for groundwater occurrence. Well yields in the deeper basaltic aquifers are directly related to the occurrence of lineaments, whereas at a shallower level they are related to geomorphic features. Spring discharges are highly dependent on their source aquifers and areas of recharge. They have a mean winter discharge of 46 m³/d and a summer discharge of 28 m³/d. Chemically, groundwaters are dominated by alkaline earths (Ca²⁺, Mg²⁺) and weak acids (HCO₃ ^–, CO₃ ^–); they are calcium-bicarbonate type (53%) and calcium-magnesium-bicarbonate type (27%) at shallower levels; and calcium-magnesium-bicarbonate type (29%), sodium-bicarbonate type (24%), calcium-bicarbonate type (19%), and calcium-magnesium-sodium-bicarbonate type (19%) in deeper aquifers. The Koyna River basin is characterized by both scarcity and abundance of groundwater. In the water-scarce areas in the dissected plateaus, artificial recharge of aquifers through construction of several recharge structures at suitable locations is highly recommended. In the water-abundant areas in the central valley, on the other hand, expanded consumptive use of water resources is encouraged. Electronic Publication  相似文献   

Spectral interpretation of gravity anomalies due to horizontal slab like bodies with lateral variation of density     

N L Mohan  S Seshagiri Rao 《Journal of Earth System Science》1982,91(1):43-54

Fourier spectrum of the gravity effect due to a horizontal slab with lateral variation of density is derived. By analysing this spectrum a procedure is formulated to determine the parameters of the causative bodyviz. depths to the upper and lower surfaces, width of the horizontal portion having the lateral density variation and the lateral density gradient. Two synthetic models and a field example are discussed to establish the validity of the procedure formulated. This is much simpler than Gendzwill’s type curves method.  相似文献   

Interpretation of gravity anomalies due to some two-dimensional structures: A Hilbert transform technique     

N Sundararajan  N L Mohan  S V Seshagiri Rao 《Journal of Earth System Science》1983,92(2):179-188

An interpretation procedure is formulated using the Hilbert transform for analysing the gravity effect of (a) two-dimensional horizontal circular cylinder, (b) semi-infinite thin fault block, and (c) a geologic contact. In all three cases the abscissa of the point of intersection of the gravity anomaly curve or the horizontal derivative curve and its Hilbert transform yields directly the depth of the body. The proposed method is tested on theoretical models. Also, the method is applied to the field data of a geologic contact taken over the Himalayan foothills across the Brahmaputra valley.  相似文献   

Gold mineralisation and alteration of Penakacherla schist belt, India, constraints on Archaean subduction and fluid processes     

C. Manikyamba  S. M. Naqvi  M. Ram Mohan  T. Gnaneshwar Rao 《Ore Geology Reviews》2004,24(3-4):199

In the Dharwar Craton, southern India, gold deposits are found mostly along the six arcuate shear zones passing through late Archaean greenstone belts (2.7 Ga). One such shear zone complex extends for about 400 km within and along the Ramagiri–Hungund schist belt. The Penakacherla sector of this shear zone is excellently exposed, enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration.Metamorphism and deformation under NE–SW compression associated with Archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists. Continued compression generated a 50–100-m-wide shear zone complex consisting of mafic phyllonites. Advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified, K-metasomatic assemblage mainly consisting of chlorite, amphibole, K-mica, plagioclase, ankerite, quartz, Fe-oxides, pyrite, chalcopyrite and arsenopyrite. Networks of quartz and carbonate veinlets, a few millimeters to a few centimeters thick, formed along the foliation planes giving rise to microscopic alteration envelope, in which individual veinlet systems are merged into one another to form a composite alteration system. Gold is found within these quartz veinlets, mafic phyllonites and at their mutual contacts.Hydrothermal fluids have modified the primary major, minor, trace and LREE compositions of host rocks such that their mutual behaviour became non-systematic. Some HFSE and HREE also show minor mobility but the overall REE pattern generally resembles that of the precursor mafic volcanic rocks. Mass and volume loss/gain by Si and Ca has made significant impact on Al, Ti and Zr abundances, which are generally immobile during hydrothermal alteration. However, element pairs such as Zr–Hf, V–Sc and Nb–Ta maintain primary inter-element ratios, although their absolute abundances are drastically diluted. Similarly, ΣREE in highly silicified and carbonatised samples are reduced, but patterns remain similar to those of relatively least altered mafic phyllonites with (La_N/Yb)_N between 1 and 3. In some samples, LREE enrichment is observed elevating in (La_N/Yb)_N from 3 to 11. Pathfinder elements and base metals such as As, Cd, Cu, Pb, Zn and Sb have been added along with the Au and Ag.δ¹³C of carbon varies from −16‰ to −21‰ suggesting a biogenic origin, whereas coexisting pyrite δ³⁴S ranges from 1‰ to 3‰, pointing towards the involvement of magmatic or average crustal sulphur. Overall concentrations of K, Rb, Sr, Ba, Nb, Ta, Ti, Cs, Cr, Co, V, Y and Sc and many of the ratios such as K/Rb, La/Sc, La/Yb indicate that metamorphism, devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks. Fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity.  相似文献   

Changes in the source and transport mechanism of terrigenous input to the Indian sector of Southern Ocean during the late Quaternary and its palaeoceanographic implications     

M. Thamban  S. S. Naik  R. Mohan  A. Rajakumar  N. Basavaiah  Witty D’Souza  Sarita Kerkar  M. M. Subramaniam  M. Sudhakar  P. C. Pandey 《Journal of Earth System Science》2005,114(5):443-452

Changes in the terrigenous sediment source and transport mechanisms during the late Quaternary have been investigated using four sediment cores within the Indian sector of Southern Ocean, using the magnetic susceptibility (MS) and sedimentological records. Sediments deposited during the Holocene and other interglacial periods were characterised by low MS, low sand content, reduced ice-rafted detritus (IRD) input and increased illite possibly transported via hydrographic advection from the south. The glacial intervals are characterised by high MS, high sand content, increased IRD input and reduced illite clays, derived from both local as well as Antarctic sources. Significant reduction in clay fraction and illite content during glacials suggests that the erosive and transporting capabilities of the deep and bottom waters could have reduced compared to the interglacial times. The changes in terrigenous influx to this region were significantly influenced by the rhythmic glacial-interglacial fluctuations in bottom circulation and the position of the Polar Front.  相似文献   

Postcolonial geographies of development: Introduction   总被引：1，自引：0，他引：1  

Marcus Power  Giles Mohan  Claire Mercer 《Singapore journal of tropical geography》2006,27(3):231-234

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Constrained regularization of digital terrain elevation data     

Mohan  A. Bartesaghi  A. Sapiro  G. 《Geoscience and Remote Sensing Letters, IEEE》2006,3(1):59-62

A framework for geometric regularization of elevation maps is introduced in this letter. The framework takes into account errors in the data, which form part of standard elevation maps specifications, as well as possible additional user/application-dependent constraints. The algorithm is based on adapting the theory of geometric active surfaces to the problem of regularizing elevation maps. We present the underlying concepts and numerical experiments showing the effectiveness and potential of this theory.  相似文献   

Selection of optimum frequency of a wind scatterometer     

Abhijit Sarkar  Raj Kumar  Mannil Mohan 《Journal of Earth System Science》1988,97(2):192-192

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Spatial continuity measures for probabilistic and deterministic geostatistics   总被引：3，自引：0，他引：3  

E. H. Isaaks  R. Mohan Srivastava 《Mathematical Geology》1988,20(4):313-341

Geostatistics has traditionally used a probabilistic framework, one in which expected values or ensemble averages are of primary importance. The less familiar deterministic framework views geostatistical problems in terms of spatial integrals. This paper outlines the two frameworks and examines the issue of which spatial continuity measure, the covarianceC (h) or the variogram (h), is appropriate for each framework. AlthoughC (h) and (h) were defined originally in terms of spatial integrals, the convenience of probabilistic notation made the expected value definitions more common. These now classical expected value definitions entail a linear relationship betweenC (h) and (h); the spatial integral definitions do not. In a probabilistic framework, where available sample information is extrapolated to domains other than the one which was sampled, the expected value definitions are appropriate; furthermore, within a probabilistic framework, reasons exist for preferring the variogram to the covariance function. In a deterministic framework, where available sample information is interpolated within the same domain, the spatial integral definitions are appropriate and no reasons are known for preferring the variogram. A case study on a Wiener-Levy process demonstrates differences between the two frameworks and shows that, for most estimation problems, the deterministic viewpoint is more appropriate. Several case studies on real data sets reveal that the sample covariance function reflects the character of spatial continuity better than the sample variogram. From both theoretical and practical considerations, clearly for most geostatistical problems, direct estimation of the covariance is better than the traditional variogram approach.This paper was presented at MGUS 87 Conference, Redwood City, California, 14 April 1987.  相似文献   

Geology and geomorphology of Cumbum valley and Varushanadu hills,Madural district,Tamil Nadu through remote sensing     

R. Palanivelu  M. Jayaraman  C. Mohan Doss  R. Arul Selvan  R. Mamallan 《Journal of the Indian Society of Remote Sensing》1988,16(1):73-78

The Varushanad hills forms the eastern offshoot of the Western Ghats and the Cumbum valley divides the Varushnad hills from the Western Ghats. Investigations were carried out in about 1700 sq Km comprising the Cumbum valley and the Varushanad hills of the Western Ghats situated in Periakulam Srivalliputhur and Usilampatti taluks of Tamil Nadu on the geological and geomorphological aspects. Remote sensing techniques were used and limited field checks were made. Visual interpretation of aerial photographs on 1:60,000 scale was carried out for identifying the geomorphological features, drainage pattern and lithology. Digital analysis of the Landsat computer compatible tape (CCT) path-row 154–053 was also carried out to delineate major lithological variations. Major lineaments were also mapped from the Landsat imagery and false colour composite. The rock types of the Cumbum valley and the Varushanad hills are mainly charnockites, granite gneiss and pink granites which have been deformed by folds and faults. The various geomorphological units of the area are ridges, valleys, bazada zone and pediment zone of mountain complex. Resources evalution studies on the potential zone of ground water and possible construction materials were also discussed.  相似文献