018613   Srivastava R K;Gautam G C (Igneous Petrology Laboratory, Geology Dep, Banaras Hindu Univ, Varanasi-221 005, Email: rajeshgeolbhu@yahoo.com) : Precambrian mafic magmatism in the bastar craton, central India. J Geol Soc India 2009, 73(1), 52-72.

The Bastar craton has experienced many episodes of mafic magmatism during the Precambrian. This is evidenced from a variety of Precambrian mafic rocks exposed in all parts of the Bastar craton in the form of volcanics and dykes. They include (i) three distinct mafic dyke swarms and a variety of mafic volcanic rocks of Precambrian age in the southern Bastar region; two sets of mafic dyke swarms are sub-alkaline tholeiitic in nature, whereas the third dyke swarm is high-Si, low-Ti and high-Mg in nature and documented as boninite-norite mafic rocks, (ii) mafic dykes of varying composition exposed in Bhanupratappur-Keskal area having dominantly high-Mg and high-Fe quartz tholeiitic compositions and rarely olivine and nepheline normative nature, (iii) four suites of Paleoproterozoic mafic dykes are recognized in and around the Chattisgarh basin comprising metadolerite, metagabbro, and metapyroxenite, Neoarchaean amphibolite dykes, Neoproterozoic younger fine-grained dolerite dykes, and Early Precambrian boninite dykes, and (iv) Dongargarh mafic volcanics, which are classified into three groups, viz. early Pitepani mafic volcanic rocks, later Sitagota and Mangikhuta mafic volcanics, and Pitepani siliceous high-magnesium basalts (SHMB). Available petrological and geochemical data on these distinct mafic rocks of the Bastar craton are summarized in this paper. Recently high precision U-Pb dates of 1891.1+0.9 Ma and 1883.0± 1.4 Ma for two SE-trending mafic dykes from the BD2 (sub-alkaline) dyke swarm, from the southern Bastar craton have been reported. But more precise radiometric age determinations for a number of litho-units are required to establish discrete mafic magmatic episodes experienced by the craton. It is also important to note that very close geochemical similarity exist between boninite-norite suite exposed in the Bastar craton and many parts of the world. Spatial and temporal correlation suggests that such magmatism occurred globally during the Neoarchaean-Paleoproterozoic boundary. Many Archaean terrains were united as a supercontinent as Expanded Ur and Arctica at that time, and its rifting gave rise to numerous mafic dyke swarms, including boninite-norite, world-wide.

14 illus, 1 table, 105 ref

018612   Srivastava R K;Ahmad T (Geology Dep, Banaras Hindu Univ, Varanasi-221 005, Email: rajeshgeolbhu@yahoo.com) : Precambrian mafic magmatism in the Indian shield: retrospect and prospect. J Geol Soc India 2009, 73(1), 7-11.

10 ref

018611   Srinivasamoorthy K;Chidambaram S;Prasanna M V;Vasanthavihar M;Peter J;Anandhan P (Earth Sciences Dep, Annamalai Univ, Annamalai-608 002, Email: moorthy_ks@yahoo.com) : Identification of major sources controlling groundwater chemistry from a hard rock terrain - a case study from mettur taluk, Salem district, Tamil Nadu, India. J Earth Syst Sci 2008, 117(1), 49-58.

The study area Mettur forms an important industrial town situated NW of Salem district. The geology of the area is mainly composed of Archean crystalline metamorphic complexes. To identify the major process activated for controlling the groundwater chemistry an attempt has been made by collecting a total of 46 groundwater samples for two different seasons, viz., pre-monsoon and post-monsoon. The groundwater chemistry is dominated by silicate weathering and (Na + Mg) and (Cl + SO₄) accounts of about 90% of cations and anions. The contribution of (Ca + Mg) and (Na + K) to total cations and HCO₃ indicates the domination of silicate weathering as major sources for cations. The plot for Na to Cl indicates higher Cl in both seasons, derived from Anthropogenic (human) sources from fertilizer, road salt, human and animal waste, and industrial applications, minor representations of Na also indicates source from weathering of silicate-bearing minerals. The plot for Na/Cl to EC indicates Na released from silicate weathering process which is also supported by higher HCO₃ values in both the seasons. Ion exchange process is also activated in the study area which is indicated by shifting to right in plot for Ca + Mg to SO₄ + HCO₃. The plot of Na - Cl to Ca + Mg - HCO₃ - SO₄ confirms that Ca, Mg and Na concentrations in groundwater are derived from aquifer materials. Thermodynamic plot indicates that groundwater is in equilibrium with kaolinite, muscovite and chlorite minerals. Saturation index of silicate and carbonate minerals indicate oversaturation during pre-monsoon and undersaturation during post-monsoon, conforming dissolution and dilution process. In general, water chemistry is guided by complex weathering process, ion exchange along with influence of Cl ions from anthropogenic impact.

7 illus, 2 tables, 14 ref

018610   Srinivasa Sarma D;Muhling J;Ram Mohan M; McNaughton N (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: dssarma@ngri.res.in) : Occurrence of hydrothermal phosphate minerals in the gold mineralized zones at hutti gold deposit, Karnataka, South India. J Geol Soc India 2008, 71(2), 223-8.

Reports for the first time, the occurrence of hydrothermal monazite and xenotime in alteration haloes associated with the gold-mineralized zones of the Hutti Gold Deposit in Karnataka, India. These minerals were identified by systematic scanning of polished thin sections in an SEM using backscattered electron and energy dispersive X-ray detectors. Most of the grains are very small (<10 μm), although some larger grains (30-40 μm) have also been identified. Hydrothermal monazite and xenotime, though volumetrically minor, have been found to be important components in many orogenic gold deposits in Australia, Canada, Brazil and South Africa, as they form a part of the primary ore mineral assemblage, either in ore-bearing veins itself or are intergrown with ore minerals in wallrock alteration zones. Both monazite and xenotime are excellent geochronometers, and their importance is that they allow precise ages to be obtained for gold mineralization events. The discovery of these minerals in hydrothermally altered rocks from the Hutti gold deposit, Dharwar Craton enables us to estimate the age of gold mineralization event(s).

4 illus, 15 ref

018609   Som S K (Earthquake Geology Div, Geological Survey of India, Eastern Region, DK-Block, Sector-II, Salt Lake City, Kolkata-700 091, Email: sksom@rediffmail.com) : U, Th enrichment in cesium bearing aplitic pegmatite of Belamu (North) area, Purulia district, West Bengal with special reference to monazite group of minerals. J Geol Soc India 2008, 71(2), 229-38.

Cesium bearing aplitic pegmatites of Chhotanagpur Gneissic Complex, Purulia district, West Bengal show enrichment in U and Th through at least one phase of lanthanide-actinide rich hydrothermal activity. Monazite group of minerals with Th and REE are hosted by the aplitic pegmatites with varying texture and composition. Monazite (Ce) occurs as inclusions within quartz and feldspar, with evolutionary trend from huttonitic monazite at core to monazite (Ce) at rim. Ce/Sm ratio varies from 8.11 to 25.67, representing a wider evolutionary trend of the melt from which monazite crystallized. Principal component analysis shows different substitution phenomenon in monazite. Chemical variations indicate the huttonitic monazite to be a primitive component, which was transformed to monazite (Ce) by interaction with LREE-P-rich fluid.

10 illus, 4 tables, 39 ref

018608   Solanki C H;Desai M D;Desai J A (Applied Mechanics Dep, SVNIT, Surat, Gujarat, Email: chs@amd.svnit.ac.in) : Empirical correlations for compressibility parameters of alluvial deposits. Indian Geotech J 2008, 38(3), 355-62.

The conventional approach is to perform subsurface investigation to obtain a sufficient number of representative soil samples which are then tested in the laboratory to obtain soil properties including compressibility parameters. Consolidation tests are time consuming and very good quality sampling and testing techniques are required. Basic physical characteristics of soil are always determined and hence correlating one or more of basic index properties with compressibility parameters derived from consolidation tests has been attempted by researchers. Use of empirical correlations for compressibility and consolidation parameters can not be generalized for all places and all soils. The correlations can be judiciously adopted for initial estimation of consolidation settlements. New empirical correlations are derived for prediction of compressibility parameters for alluvial deposits in South Gujarat region of Surat city and surroundings.

9 illus 2 tables, 4 ref

018607   Sitharam T G;Ravishankar B V;Vinod J S (NO, Indian Institute of Science, Bangalore, Email: sitharam@civil.iisc.ernet.in) : Dynamic properties of dry sands. Indian Geotech J 2008, 38(3), 334-44.

Presents the results of dynamic properties such as shear modulus and damping ratio of natural dry sand samples collected from earthquake affected area of Ahmedabad of Gujarat state in India. A series of strain controlled undrained cyclic triaxial test were carried out on isotropically compressed dry sands samples and dynamic properties were evaluated from the first cycle of the hysteresis loop. Influence of parameters such as amplitude of cyclic strain, confining pressure, and frequency on the dry sand samples were evaluated and reported. The shear modulus of dry sands slightly increases with increase in the number of loading cycles for the first very few cycles and thereafter the shear modulus almost becomes constant with number of cycles. However, the influence of number of loading cycles is not significant on damping ratios of the dry sand samples. A significant influence of amplitude of cyclic strain and confining pressure on the shear modulus and damping ratio can be observed. Furthermore, it has been seen that the shear modulus is less influenced by frequency of loading. However, frequency has a significant influence on the damping ratio of dry sands. In addition, results of the present investigation irrespective of different parameters fall well with the lower and upper bound values for sands proposed by Seed and Idriss [Report, EERC 70 -10 (1970)].

13 illus, 1 table, 8 ref

018606   Sinha S;Ghosh S K;Rohtash Kumar;Islam R; Sanyal P;Sangode S J (Sedimentology Group, Wadia Institute of Himalayan Geology, Dehra Dun-248 001, Email: sinha_subho@rediffmail.com) : Role of tectono-climate factors in the neogene Himalayan foreland sediments: petrology and geochemical approach, Kangar sub-basin. J Geol Soc India 2008, 71(6), 787-807.

The Neogene Siwalik fluvial succession (12.77-4.48 Ma) of the NW Himalayan foreland basin, east of Ravi River, are deposited under varied tectono-climatic conditions. Petrography and geochemistry of the sediments were carried out to understand the relative roles of tectonics and climate in this basin. The sandstones are classified as sub-litharenites with subordinate arkosic-lithicwacke. The detrital components particularly the rock fragments are consistent with the inferred source area presently disposed towards the north of the depocenter and suggest that the Higher, Lesser and Lower Tertiary formations supplied detritus since 12.77 Ma. The Th/ Sc vs Zr/Sc ratio indicates sediment recycling. The Cr and Ni, negative Eu anomaly, LREE enrichment and moderately flat HREE in the mudstones collectively suggest dominant contribution from felsic igneous rocks beside contribution from basic, sedimentary/metamorphic lithology. Near consistent nature of the detrital modes and geochemical parameters through time suggest unvarying source since 12.77 Ma. The present study also infers that the source areas uplift owing to tectonic activity of Chail Thrust at least by 12.77 Ma with a perceptible activity of MBT after 8 Ma. The δ¹⁸O variations in soil carbonates reveals ongoing intense monsoon system since 12.77 Ma followed by a phase of aridity at 9.1 Ma. Presence of fresh and weathered feldspar, limestone, basic volcanics and mica, both in humid and arid phase indicate rapid deposition and preservation. Despite the climatic turnover from humid to arid, distinctive changes in the framework mineral compositions over time is not discernable. The petrographic and geochemical data reveals that the near similar source area, relatively rapid transport, moderate chemical weathering and sediment recycling controlled the composition of the sediments of the HFB in response to tectonics and climate.

4 illus, 11 tables, 79 ref

018605   Shukla U K;Janardhana Raju N (Geology Dep, Banaras Hindu Univ, Varanasi-221 005, Email: shukla_umakant@yahoo.com) : Migration of the Ganga river and its implication on hydro-geological potential of Varanasi area, U.P., India. J Earth Syst Sci 2008, 117(4), 489-98.

Borehole data reveals that during Late Quaternary, the Ganga river was non-existent in its present-location near Varanasi. Instead, it was flowing further south towards peripheral craton. Himalayan derived grey micaceous sands were being carried by southward flowing rivers beyond the present day water divide of Ganga and mixed with pink arkosic sand brought by northward flowing peninsular rivers. Subsequently, the Ganga shifted to its present position and got incised. Near Varanasi, the Ganga river is flowing along a NW-SE tectonic lineament. The migration of Ganga river is believed to have been in response to basin expansion caused due to Himalayan tectonics during Middle Pleistocene times. Multi-storied sand bodies generated as a result of channel migration provide excellent aquifers confined by a thick zone of muddy sediments near the surface. Good quality potable water is available at various levels below about 70 m depth in sandy aquifers. Craton derived gravelly coarse-to-medium grained sand forms the main aquifer zones of tens of meter thickness with enormous yield. In contrast, the shallow aquifers made up of recycled interfluve silt and sandy silt occur under unconfined conditions and show water-level fluctuation of a few meters during pre- and post-monsoon periods.

5 illus, 24 ref

018604   Shukla S B;Patidar A K;Bhatt N (Geology Dep, Faculty of Science, M. S. Univ of Baroda, Vadodara-390 002, Email: nilesh_geol@yahoo.com) : Application of GPR in the study of shallow subsurface sedimentary architecture of Modwa apit, gulf of Kachchh. J Earth Syst Sci 2008, 117(1), 33-40.

The study was carried out on the Modwa beach complex between Rawal Pir and Modwa, about 10 km east of Mandvi on the northern coast of the Gulf of Kachchh. The Modwa spit is a 7-km long WNW-ESE trending prograding amalgamated beach ridge complex that is about 0.5km wide at its western end and 1.5 km wide at its eastern end. This Ground-Penetrating Radar (GPR) survey delineated a variety of the radar surfaces and radar facies which reflects not only large scale sedimentary architecture, but depositional facies of the beach ridge complex. These are bounding surfaces separating the radar facies outline beach ridge (br), washover (wo), coastal dune (cd) and swale (sw) depositional environments. The internal sedimentary structures like tangential, parallel, concave and convex upward stratifications could also be visualized from the GPR profiles. The architecture suggests the formation of this complex due to a combined process of eastward littoral drift of locally derived sediments and its onshore deposition by storms and eolian activities.

5 illus, 33 ref

018603   Shome D;Bhattacharyya I (Geological Sciences Dep, Jadavpur Univ, Kolkata-700 032, Email: debashome@yahoo.com) : Pyrometamorphosed coking coals from Jharia coal basin with special emphasis on deterministic parameters suggestive of extent of thermal effect. J Geol Soc India 2008, 71(2), 271-80.

Criteria to identify the variously affected zones of a coal seam intruded by igneous bodies of variable composition and configuration is a matter of investigation long since. Changes in physical, chemical, optical and structural behavior of coal indicate an increase in rank toward the coal-intrusive contact. In present study a comparison of the above parameters reveals a distinct difference in the behavioral pattern with changing distances from the contact beyond which normal characteristics of coal seam is retained. The identification of zones of variable rank with distance from coal-intrusive contact may act as a guide during mining and proper utilization sector for coal.

6 illus, 3 tables, 17 ref

018602   Sharma R;Murthy V V S;Mishra V P;Nagaraju B V;Gouda H C;Singh R K (Geological Survey of India, GMC Div, AMSE Wing, Vasudha Bhavan, Kumaraswamy Layout, Bangalore-560 078) : Structural study through aeromagnetic data for mineral prospecting in betul-chhindwara area, M.P.. J Geol Soc India 2008, 71(6), 815-26.

The aeromagnetic map of Betul-Chhindwara area, contains two magnetic domains, namely 'A' representing high amplitude anomalies falling over Deccan Traps and domain 'B' represented by moderate amplitude anomalies falling over gneiss and Gondwana Supergroup. The qualitative interpretation of aeromagnetic data has brought out several linears and discontinuities, which show the presence of various magnetic bodies and fractures/faults/shears/ contacts respectively. The magnetic linears were found to trend mainly in ENE-WSW direction and few in E-W, NE-SW and NW-SE directions. The prominent magnetic discontinuities trending in ENE-WSW directions were found to be intersected by NW-SE, NE-SW and nearly N-S trending discontinuities at places. One of these prominent discontinuities was found to fall along granitic gneiss and others at the contact of gniesses with Gondwana Supergroup in northern part and with Deccan Traps in southern part. One prominent discontinuity was found within Gondwana Supergroup in the northern part and another in the southeastern part over the known Gavilgarh fault. The magnetic discontinuity obtained in the gneissic complex was found to fall over the known sulphide mineralisation near Banaskhapa-Piparia etc and thus assumes importance for prospecting sulphide minerals all along the discontinuity. The quantitative interpretation was carried out by computing the radial power spectrum and by 2-D modelling of selected anomalies. The Radial power spectrum yielded two interfaces at the depths of 0.871 km and 9.461 km from observation plane (1080 m above msl). The shallow layer map is similar to that of the terrain corrected map whereas the deep layer map indicated the gradients corroborating with the discontinuities mentioned above excepting the one falling over granitic gneiss which was reflected as a broad elongated magnetic low. The results of 2-D modelling over ten selected anomalies suggest that most of the bodies are very shallow excepting two. The dips of most of the bodies were found in between 6°-25° and few between 32°- 48°.

9 illus, 1 table, 14 ref

018601   Sharma R;Joshi P;Pant P D (NO, Wadia Institute of Himalayan Geology, Dehra Dun-248 001, Email: sharmarajesh@wihg.res.in) : Role of fluids in the formation of talc deposits of Rema area, Kumaun lesser Himalaya. J Geol Soc India 2009, 73(2), 237-48.

Talc deposits of Rema area in the Kumaun Inner Lesser Himalaya are hosted within high magnesium carbonates of the Proterozoic Deoban Formation. These deposits occur as irregular patches or pockets mainly within magnesite bodies, along with impurities of magnesite, dolomite and clinochlore. Textures represent different phases of reactions between magnesite and silica to produce talc. Petrography, XRD and geochemistry reveal that the talc has primarily developed at the expense of magnesite and silica, leaving dolomite largely un-reacted. Early fluid inclusions in magnesite and dolomite associated with talc are filled with H₂O+NaCl+KCl± MgCl₂ ± CaCl₂ fluids, which represent basin fluid system during diagenesis of carbonates. Their varied degree of re-equilibration was although not pervasive but points to increased burial, and hence requires careful interpretation. H₂O-CO₂ fluid with Xco, between 0.06 and 0.12 was equilibrated with talc formation. The reaction dolomite+quartz → talc was not extensive because T-Xco₂ was not favourable, and talc was developed principally after magnesite+quartz.

6 illus, 2 tables, 41 ref

018600   Sharma G K;Bora J (Geology Dep, Kumaun Univ, Nainital-263 002, Email: gksharma61@yahoo.com) : Pleistocene radiolarians from the Leg 119 site 745, sections (1H to 4H) in the southern ocean region. J Geol Soc India 2009, 73(2), 165-77.

Presents a detailed record of radiolarian species from the Leg 119 Site 745 (sections 1H to 4H) in the southern ocean region. Forty five species were identified and illustrated from forty six samples. The taxonomy, two radiolarian zones namely NR1 and NR2, morphological variations and distribution of laxa have been made from these sections. Twelve new species are identified but they are not formally named. The study provides the detailed Antarctic Pleistocene radiolarian data, proposed the placement of NR1 and NR2 zonal boundary at a shallow depth of 6.63 mbsf and data is used for comparative studies with other parts of the Antarctic region.

24 illus, 1 table, 38 ref

018599   Sharada M K;Swathi P S;Yajnik K S;Kalyani Devasena C (NO, CSIR Centre for Mathematical Modelling and Computer Simulation (C-MMAC, Wind Tunnel Road, Bangalore-560 037, Email: sharada@cmmacs.ernet.in) : Role of biology in the air-sea carbon flux in the Bay of Bengal and Arabian sea. J Earth Syst Sci 2008, 117(4), 429-47.

A physical-biological-chemical model (PBCM) is used for investigating the seasonal cycle of air-sea carbon flux and for assessing the effect of the biological processes on seasonal time scale in the Arabian Sea (AS) and Bay of Bengal (BoB), where the surface waters are subjected to contrasting physical conditions. The formulation of PBCM is given in Swathi et al (2000), and evaluation of several ammonium-inhibited nitrate uptake models is given in Sharada et al (2005). The PBCM is here first evaluated against JGOFS data on surface pCO₂ in AS. Bay of Bengal Process Studies (BoBPS) data on column integrated primary productivity in BoB, and WOCE I1 data on dissolved inorganic carbon (DIG) and alkalinity (ALK) in the upper 500 meters at 9°N in AS and at 10°N in BoB in September-October. There is good qualitative agreement with local quantitative discrepancies. The net effect of biological processes on air-sea carbon flux on seasonal time scale is determined with an auxiliary computational experiment, called the abiotic run, in which the biological processes are turned off. The difference between the biotic run and abiotic run is interpreted as the net effect of biological processes on the seasonal variability of chemical variables. The net biological effect on air-sea carbon flux is found to be highest in southwest monsoon season in the northwest AS, where strong upwelling drives intense new production. The biological effect is larger in AS than in BoB, as seasonal upwelling and mixing are strong in AS, especially in the northeast, while coastal upwelling and mixing are weak in BoB.

12 illus, 3 tables, 52 ref

018598   Seshunarayana T;Senthil Kumar P;Sampath Rao V;Mysaih D;Satish Kumar K;Pavan Kishore P (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: senthilngri@yahoo.com) : Multichannel analysis of surface waves reveals ahear zones and fractures in a shallow granite basement: wailapally watershed near Hyderabad. J Geol Soc India 2008, 71(2), 261-5.

Delineation of shear zones and fracture systems in hard rock areas is essential in locating potential groundwater zones. The Multichannel Analysis of Surface Waves (MASW) is a new developing seismic geophysical technique, which has now been widely used in imaging shallow subsurface, in terms of shear wave velocity. We test its potentiality in Hyderabad granite terrain, at Wailapally watershed, for delineating shear zones and fractures in a shallow granite basement covered with thin weathering and alluvium cover. Surface wave data were obtained at three sites using 24 channel seismograph, and were used to model the shear wave velocity of the subsurface. The study clearly demarcates the bedrock depths, shear zones or faults, fractures, weathering and soil covers in the shallow subsurface up to a depth of -30 m; the results are also in good agreement with the surface geological observations. Therefore, the MASW is an excellent geophysical tool that can clearly demarcate the shallow structures favorable for groundwater in hard rock areas.

3 illus, 7 ref

018597   Satyawali P K;Singh A K (Snow and Avalanche Study Establishment, , Him Parisar Sector 37A, Chandigarh, Email: pra,odsatyawali@hotmail.com) : Dependence of thermal conductivity of snow on microstructure. J Earth Syst Sci 2008, 117(4), 465-75.

A geometrical model, including different geometrical shapes influencing thermal conductivity of snow is proposed. The geometrical model has been assumed to comprise of unit cells having solid (ice) inclusion as an aggregation of spherical, cylindrical or cubical shapes with vertical connection, arranged in a cubic packing. From the geometrical model and one-dimensional heat transfer theory, the effective thermal conductivity has been computed. For this purpose, coupled one-dimensional heat transfer equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat transfer due to water vapour sublimation through air. The model demonstrates the dependency of thermal conductivity on density, grain-spacing, grain contact ratio and temperature. Spherical inclusions give highest conductivity while cubical inclusion estimates lowest value for the same density. Thermal conductivity has been found increasing sharply near to the packing density for all three shapes. Empirical model results and results obtained from existing microstructure based models have also been compared with the present model.

5 illus, 26 ref

018596   Sanjeevi S;Bhaskar A S (Geology Dep, Anna Univ, Chennai-600 025, Email: ssanjeevi@annauniv.edu) : Satellite derived digital terrain and perspective models: an aid to teach geologic mapping. J Geol Soc India 2008, 71(2), 214-22.

Digital Elevation Models (DEMs) are a good source of data where students can easily observe how the geology and the topography relate. Most geoscientific applications using georeferenced cartographic data need a good knowledge and visualization of the topography of the Earth's surface. For example, accurate mapping of geomorphological features is hardly feasible from a single image but it needs the three-dimensional (3D) information to be added for a better interpretation of the two-dimensional (2D) data. Elucidates with examples, the potential of satellite derived DEM and DTM and illustrates how to visualize and extract geologic information from them. The aim here is to suggest a new teaching aid to make students understand the geology of an area in a better way. Examples of DTM and perspective models of certain terrains of south India (the Andipatti-Usilampatti folded metasedimentary region and the structural basin in Palaniyarpuri) have been used in this paper to make geologists and students appreciate the utility of DEMs and DTMs. It has been demonstrated that for the undergraduate and postgraduate students of geology, a preliminary, virtual tour of the terrain to be mapped can be made possible using the DEM generated from satellite stereo images.

5 illus, 1 table, 29 ref

018595   Samant B;Mohabey D M;Kapgate D K (Geology Dep, Banaras Hindu Univ, Varanasi-221 005, Email: bandanabhu@rediffmail.com) : Palynofloral record from Singpur intertrappean, Chhindwara district, Madhya Pradesh: implication for late cretaceous stratigraphic correlation and resolution. J Geol Soc India 2008, 71(6), 851-8.

A diversified palynoassemblage has been recorded from the Singpur intertrappean of Chhindwara District, Madhya Pradesh, that has earlier yielded megafloral remains. The section is strategic as it is located between the Chhindwara-Mandla-Jabalpur (CMJ) sector to the north and Nand-Dongargaon (ND) basin to the south, that have so far produced a majority of the palynologically studied intertrappean sections associated with the Deccan Volcanic Sequence (DVS). In this context the palynological assessment of the Singpur intertrappean is critical for establishing a spatio-temporal correlations of the sediments of the two widely separated volcanic sub-provinces/regions. The Singpur palynoassemblage shows presence of marker Late Cretaceous (Maastrichtian) palynotaxa viz. Aquilapollenites bengalensis, Ariadnaesporites sp., Gabonlsporls spp. and Pulcheripollenites cauveriana, associated with primitive stephanocolpate pollen. The appearance of polyaperturate pollen grains in the central India is significant as it suggests the evolutionary trend in the angiosperms during Latest Cretaceous. The overall assemblage of the Singpur is indicated to be coeval with the Sindhi intertrappean bed of ND basin, and younger than the dinosaur bearing intertrappean beds of Mohagaon kalan (well section) and Ranipur of CMJ sector in the north. It is also indicated that the famous iridium bearing intertrappean section at Anjar (Kutch) associated with dinosaurs (Titanosaurus indicus) and deposited during 29 R, is older to the Singpur intertrappean bed.

2 illus, 40 ref

018594   Samadhiya N K;Maheshwari P;Basu P;Bhushan Kumar M (Civil Engineering Dep, Indian Institute of Technology, Roorkee-247 667, Email: nksamfce@iitr.ernet.in) : Load - settlement characteristics of granular piles with randomly mixed fibres. Indian Geotech J 2008, 38(3), 345-54.

An attempt has been made to study the behavior of granular piles with randomly mixed fibres installed in soft soil. For this purpose, an experimental program in laboratory has been planned and experiments have been carried out to study the load carrying capacity of fibre reinforced granular pile. Few experiments have also been conducted on granular piles without fibre reinforcement to study the effect of randomly mixed fibres in granular pile. Effect of depth of sand pad, placed on granular pile reinforced soft soil system, has also been studied. It has been observed that ultimate load carrying capacity of granular pile does not necessarily increase with the increase in its length for pile length to pile diameter ratio more than 4 - 5. It has been further observed that the load carrying capacity increases as depth of sand pad on soil reinforced with granular pile increases. Effect of fibre content and fibre length has also been studied by means of conducting experiments in the laboratory.

9 illus, 8 ref

018593   Sahu D D (Agrometeorological Cell, Agronomy Dep, Junagadh Agricultural Univ, Junagadh-362 001, Email: ddsahu1950@yahoo.co.in) : Annual and seasonal variability of climatic South Saurashtra agroclimatic zone. J Agrometeorol 2008, 10(1), 93-6.

^ssc6 tables, 2 ref

018592   Sahoo S C;Madhu M;Mohanraj R (NO, Central Soil and Water Conservation Research and Training Institute, R, Udhagamandalam-643 004) : Probability analysis of rainfall for Udhagamandalam. J Agrometeorol 2008, 10(1), 65-9.

Daily rainfall data of 43 years (1960-2002) of Udhagamandalam were used for annual, seasonal and monthly analysis at different probability levels to obtain the rainfall distribution pattern. At 80 per cent probability level, the rainfall available in the first (May to August) and second (September to November) season are more than the water requirement of the crops which are grown in this region. In the third season (December to April) the rainfall availability is not enough to support any crop without irrigation. Annual maximum daily rainfall was estimated at different return period which will be useful for design of any water harvesting and soil conservation structures. The annual one day maximum rainfall at 50 and 100 years return period was found to be 238.8 and 293.6 mm, respectively. The depth-duration-frequency relationship was developed for duration of 1 to 6 days maximum rainfall for different frequency.

1 illus, 4 tables, 7 ref

018591   Reddy L A K;Kulshrestha U C;Satyanarayana J; Kulshrestha M J;Krishna Moorthy K (NO, Indian Institute of Chemical Technology, Hyderabad-500 007, Email: umesh_iict@rediffmail.com) : Chemical characteristics of PM₁₀ aerosols and airmass trajectories over Bay of Bengal and Arabian sea during ICARB. J Earth Syst Sci 2008, 117(S1), 345-52.

First time, chemical characterization of PM₁₀ aerosols was attempted over the Bay of Bengal (BoB) and Arabian Sea (AS) during the ICARB campaign. Dominance of SO^2-₄, NH⁺₄ and NO^-₃ was noticed over both the regions which indicated the presence of ammonium sulphate and ammonium nitrate as major water soluble particles playing a very important role in the radiation budget. It was observed that all the chemical constituents had higher concentrations over Bay of Bengal las compared to Arabian Sea. Higher concentrations were observed near the Indian coast showing influence of landmass indicating that gaseous pollutants like SO₂, NH₃ and NO_x are transported over to the sea regions which consequently contribute to higher SO^2-₄, NH⁺₄ and NO^-₃ aerosols respectively. The most polluted region over BoB was 13°-19°N and 70°-90°E while it was near 11°N and 75°E over AS. Although the concentrations were higher over Bay of Bengal for all the chemical constituents of PM₁₀ aerosols, per cent non-sea salt (nss) fraction (with respect to Na) is higher over Arabian Sea. Very low Ca²⁺ concentration was observed at Arabian Sea which led In higher atmospheric acidity as compared to BoB. Nss SO^2-₄ alone contributed 48% of total water soluble fraction over BoB as well as AS. Ratios SO^2-₄ /NO₃ over both the regions (7.8 and 9 over BoB and AS respectively) were very high as compared to reported values at land sites like Allahabad (0.63) and Kanpur (0.66) which may be due to very low NO^-₃ over sea regions as compared to land sites. Air trajectory analysis showed four classes: (i) airmass passing through Indian land, (ii) from oceanic region, (iii) northern Arabian Sea and Middle East and (iv) African continent. The highest nss SO^2-₄ was observed during airmasses coming from the Indian land side while lowest concentrations were observed when the air was coming from oceanic regions. Moderate concentrations of nss SO^2-₄ were observed when air was seen moving from the Middle East and African continent. The pH of rainwater was observed to be in the range of 5.9-6.5 which is lower than the values reported over land sites. Similar feature was reported over the Indian Ocean during INDOEX indicating that marine atmosphere had more free acidity than land atmosphere.

5 illus, 6 tables, 14 ref

018590   Ramakrishnan M (NO, , 8, Manipallavam, 29, Balakrishna Road, Valmiki Nagar, Thiruvanmiyar, Chennai-600 041, Email: emarkay@hotmail.com) : Precambrian mafic magmatism in the western Dharwar craton, Southern India. J Geol Soc India 2009, 73(1), 101-16.

Mafic rocks of Western Dharwar Craton (WDC) belong to two greenstone cycles of Sargur Group (3.1-3.3 Oa) and Dharwar Supergroup (2.6-2.8 Ga), belonging to different depositional environments. Proterozoic mafic dyke swarms (2.4, 2.0-2.2 and 1.6 Ga) constitute the third important cycle. Mafic rocks of Sargur Group mainly constitute a komatiitic-tholeiite suite, closely associated with layered basic-ultrabasic complexes. They form linear ultramafic-mafic belts, and scattered enclaves associated with orthoquartzite-carbonate-pelite-BIF suite. Since the country rocks of Peninsular Gneiss intrude these rocks and dismember them, stratigraphy of Sargur Group is largely conceptual and its tectonic environment speculative. It is believed that the Sargur tholeiites are not fractionated from komatiites, but might have been generated and evolved from a similar mantle source at shallower depths. The layered basic-ultrabasic complexes are believed to be products of fractionation from tholeiitic parent magma. The Dharwar mafic rocks are essentially a bimodal basalt-rhyolite association that is dominated by Fe-rich and normal tholeiites. Calc-alkaline basalts and andesites are nearly absent, but reference to their presence in literature pertains mainly to carbonated, spilitized and altered tholeiitic suites. Geochemical discrimination diagrams of Dharwar lavas favour island arc settings that include fore-, intra- and back-arcs. The Dharwar mafic rocks are possibly derived by partial melting of a Iherzolite mantle source and involved in fractionation of olivine and pyroxene followed by plagioclase. Distinctive differences in the petrography and geochemistry of mafic rocks across regional unconformities between Sargur Group and Dharwar Supergroup provide clinching evidences in favour of distinguishing two greenstone cycles in the craton. This has also negated the earlier preliminary attempts to lump together all mafic volcanics into a single contemporaneous suite, leading to erroneous interpretations. After giving allowances for differences in depositional and tectonic settings, the chemical distinction between Sargur and Dharwar mafic suites throws light on secular variations and crustal evolution. Proterozoic mafic dyke swarms of three major periods (2.4, 2.0-2.2 and 1.6 Ga) occur around Tiptur and Hunsur. The dykes also conform to the regional metamorphic gradient, with greenschist facies in the north and granulite facies in the south, resulting from the tilt of the craton towards north, exposing progressively deeper crustal levels towards the south. The low-grade terrain in the north does not have recognizable swarms, but the Tiptur swarm consists essentially of amphibolites and Hunsur swarm mainly of basic granulites, all of them preserving cross-cutting relations with host rocks, chilled margins and relict igneous textures. There are also younger dolerite dykes scattered throughout the craton that are unaffected by this metamorphic zonation. Large-scale geochemical, geochronological and palaeomagnetic data acquisition through state-of-the-art instrumentation is urgently needed in the Dharwar craton to catch up with contemporary advancements in the classical greenstone terrains of the world.

9 illus, 87 ref

018589   Raj R (Geology Dep, Faculty of Science, M. S. Univ of Baroda, Vadodara-390 002, Email: naveenrachna@gmail.com) : Occurence of volcanic ash in the quaternary alluvial deposits, lower Narmada basin, Western India. J Earth Syst Sci 2008, 117(1), 41-8.

Reports the occurrence of an ash layer intercalated within the late Quaternary alluvial succession of the Madhumati River, a tributary of the lower Narmada River, Petrographic, morphological and chemical details of glass shards and pumice fragments have formed the basis of this study. The ash has been correlated with the Youngest Toba Tuff. The finding of ash layer interbedded in Quaternary alluvial sequences of western Indian continental margin is significant, as ash being datable material, a near precise time-controlled stratigraphy can be interpreted for the Quaternary sediments of western India. The distant volcanic source of this ash requires a fresh re-assessmerit of ash volume and palaeoclimatic interpretations.

5 illus, 2 tables, 40 ref

018588   Radhakrishnan K (Space Dep, National Remote Sensing, Balanagar, Hyderabad-500 037, Email: director@nrsa.gov.in) : Major thrust areas of remote sensing and GIS applications in geosciences. J Geol Soc India 2008, 71(2), 153-70.

8 illus, 82 ref

018587   Radhakishna T (NO, Centre for Earth Science Studies, Trivandrum-695 031, Email: tradha1@rediffmail.com) : Precambrian mafic magmatism in South Indian granulite terrain. J Geol Soc India 2009, 73(1), 131-42.

South Indian granulitc terrain had witnessed significant part of Precambrian mafic igneous activity in the form of episodic mafic dyke intrusions of the Palaeoproterozoic period. Strike trends of these dykes are not uniform over the region and the dykes are generally fresh, massive, black dolerites except in the Bhavani shear zone bordering the southern fringes of Nilgiri massif. In Agali-Coimbatore area of our study in the western Bhavani shear zone, the dykes appear to be penecontemporaneous with shearing. Isotopic data place age of Agali-Coimbatore dyke intrusions at about 2.1 Ga. The age of these dykes is significant to constrain an early Palaeoproterozoic age for major shearing event in the Bhavani shear zone. Other dyke emplacement ages are placed at about 1.8 Gaand 1.65 Ga based on the Ar/Arand K-Ar isotopic results of dykes in Dharmapuri and Tiruvannamalai areas. Older ages comparable to those of the Dharwar craton are not known and in this respect future isotopic dating is vital. Geochemically, these dykes are quartz/hypersthene normative subalkalic tholeiites. An attempt is made here to provide insights into the general petrogenetic history of the Precambrian dykes. Compositional trends are explained by the fractional crystallization of ferromagnesian phases and plagioclase control is conspicuous at the advanced stages of fractionation. Geochemical characteristics suggest that the dykes have tapped Fe-rich non-pyrolite mantle sources with LIL and LREE enrichment as in many continental basalts. The data suggest that role of crustal contamination is limited in petrogenesis; crustal signatures are noticed in the more mafic end members formed in early stage of evolution suggesting that contamination was temperature controlled with most primitive high temperature magmas being most vulnerable to the process. Nd-Sr isotopic data, at present restricted to Agali-Coimbatore dykes, suggest that Palaeoproterozoic magmas tapped subcontinental lithosphere that may have stabilized in the Archaean times at about 3 Ga during the major crustal building activity in the shield region. Further work coupled with isotopic and mineral chemistry will improve our knowledge on the petrological evolution of the dyke magmas and mafic magmatism in general.

5 illus, 1 table, 50 ref

018586   Rachhpal Singh (NO, , Geological Survey of India, Bachittar Complex, Bye Pass, NH-1A, Chhanni Himmat, Jammu-180 015, Email: gsijammu@rediffmail.com) : On the nature of Ladakh granitoid complex (LGC), Leh and Kargil districts, Jammu and Kashmir. J Geol Soc India 2008, 71(2), 281-2.

The work based on systematic geological mapping in the southeastern part of Ladakh and traverse geological mapping in the remaining part of the Ladakh range and adjacent areas has revealed that the Ladakh granitoid complex is composed of rock sequence which is formed by the granitisation of the rocks of volcano-sedimentary parentage.

3 illus, 8 ref

018585   Purnanandam K;Rajagopal K (Civil Engineering Dep, IIT Madras, Chennai-600 036, Email: purnanandamk@yahoo.co.in) : Lateral earth pressure reduction due to controlled yielding technique. Indian Geotech J 2008, 38(3), 317-33.

The heavily compacted backfills behind rigid retaining walls exerts much higher lateral earth pressures on the wall than the at-rest pressures because of locked in lateral stresses in the soil. In such cases, controlled yielding method, in which vertical layers of compressible medium are introduced between the retaining wall and the backfill soil, is an ideal technique to reduce the lateral earth pressures on rigid retaining walls. The much softer compressible medium will allow the soil to expand into it as the compressible layer compresses. Because of the resulting lateral deformations and local arching in the soil, the earth pressures in the soil will either reach active state or below active state. The earth pressures could be further reduced by introducing horizontal layers of reinforcement in the backfill. The introduction of reinforcement layers will also increase the stiffness of the soil. This paper presents some results from laboratory investigations and field tests applying the controlled yielding technique for reducing the lateral earth pressures.

16 illus, 1 table, 15 ref

018584   Purandara B K;Varadarajan N;Venkatesh B (NO, National Institute of Hydrology, Hard Rock Regional Center, Belgaum-590 001, Email: purandarabk@yahoo.com) : Simultaneous transport of water and solutes under transient unsaturated flow conditions. J Earth Syst Sci 2008, 117(4), 477-87.

The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows. In the study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid (upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in downstream parts of the study area, Study characterized the soil salinity and groundwater quality in both areas. An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and measured results indicating the applicability of the model.

3 illus, 1 table, 23 ref

018583   Praveen Kumar R;Dodagoudar G R (Civil Engineering Dep, Indian Institute of Technology, Madras, Chennai, Email: praveenkumar.rachakonda@gmail.com) : Modelling of 1 - D contaminant migration through unsaturated soils using RPIM. Indian Geotech J 2008, 38(3), 363-71.

An attempt is made to model the contaminant transport through unsaturated porous media using Radial Point Interpolation Method (RPIM) with polynomial reproduction. The RPIM is used for solving the governing differential equation involving one-dimensional advection-dispersion-sorption-decay processes. Thin plate spline radial basis functions are used in the analysis. The van Genuchten model is used for describing the hydraulic properties of the unsaturated soil. Numerical examples are presented to illustrate the applicability of the proposed method; the results are compared with those obtained from the finite element method and it is found that they agree well.

5 illus, 1 table, 5 ref

018582   Pradeep Kumar T B;Tiwary A;Fahmi S (Atomic Minerals Directorate for Exploration and Research, , Western Region, AMD Complex, Sector V Extn., Pratap Nagar, Sanganer, Jaipur-302 030) : Nature of uranium mineralisation in the Kerpura-Tiwari-ka-bas area, Sikar district, Rajasthan. J Geol Soc India 2009, 73(2), 220-8.

Mineralisation of uraninite and brannerite occurs in the albitised metasedimentary and intrusive igneous rocks of Kerpura-Tiwari-ka-bas area in Sikar district, Rajasthan. Samples collected from well dumps contain 0.016 to 1.52% U₃O₈ with very low ThO₂. The host rocks show wide variation in chemical composition due to varying degree of alkali metasomatism, associated alteration and composition of protoliths. The spatial distribution of uranium in groundwater as well as rock samples from well dumps indicates localisation of the uranium mineralisation along NNE-SSW and NW-SE directions in Kerpura block. Petrographic and lithogeochemical studies point towards close genetic relationship between alkali metasomatism and uranium mineralisation. The mineralisation seems to be due to mobilisation of uranium and other LILEs by metasomatising fluids and their deposition along shear zones at a later stage, which may not be spatially related to zones of intense albitisation.

3 illus, 5 tables, 13 ref

018581   Pophare A M;Mendhe V A;Varade A (Post Graduate Dep of Geology, RTM Nagpur Univ, Law College Square, Amravati Road, Nagpur-440 001, Email: apophare@yahoo.com) : Evaluation of coal bed methane potential of coal seams of seams of sawang colliery, Jharkhand, India. J Earth Syst Sci 2008, 117(2), 121-32.

The coal seams of Sawang Colliery, East Bokaro Coalfields are bituminous to sub-bituminous in nature and categorized as high gaseous seams (degree II to degree III level). These seams have the potential for coal bed methane (CBM) and their maturity increases with increasing depth, as a result of enhanced pressure-temperature conditions in the underground. The vitrinite maceral group composition of the investigated coal seams ranges from 62.50-83.15%, whereas the inertinite content varies from 14.93-36.81%. The liptinite content varies from 0.66% to 3.09%. The maximum micro-pores are confined within the vitrinite group of macerals. The coal seams exhibit vitrinite reflectance values (Ro% calculated) from 0.94% (sample CG-97) to 1.21% (sample CG-119). Proximate analyses of the investigated coal samples reveal that the moisture content (M%) ranges from 1.28% to 2.98%, whereas, volatile matter (VM%) content is placed in the range of 27.01% to 33.86%. The ash content (A%) ranges from 10.92% to 30.01%. Fixed carbon (FC%) content varies from 41.53% to 55.93%. Fuel ratio variation shows a restricted range from 1.53 to 1.97. All the coal samples were found to be strongly caking and forming coke buttons. The study is based on the adsorption isotherm experiments carried out under controlled P-T conditions for determination of actual gas adsorption capacity of the coal seams. This analysis shows that the maximum methane gas adsorbed in the coal sample CG-81 is 17m3/t (Std. daf), at maximum pressure of 5.92MPa and experimental temperature of 30°C. The calculated Langmuir regression parameters P_L and V_L range from 2.49 to 3.75 MPa and 22.94 to 26.88m 3/t (Std. daf), respectively.

5 illus, 7 tables, 43 ref

018580   Pattan J N;Parthiban G;Banakar V K;Tomer A; Kulkarni M (NO, National Institute of Oceanography, Dona Paula, Goa-403 004, Email: pattan@nio.org) : Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian ocean basin. J Earth Syst Sci 2008, 117(2), 113-19.

Three sediment cores in a north-south transect (3°N to 13°S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (x) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest x (12.32 x 10^-7 m³ kg^-1), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate x (29.93 x 10^-7 kg^-1) but highest Al (6.84%), Fe (5,20%) and Ti (0.44%), and siliceous ooze core with highest x (38.06 x 10^-7m³kg^-1) but moderate Al (4.49%), Fe (2. and Ti (0.19%) contents. The distribution of x and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of X is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source. The occurrence of phillipsite in terrigenous clav is evident by the Al-K scatter plot where trend line intersects K axis at more than 50% of total K suggesting excess K in the form of phillipsite. Therefore, the presence of phillipsite might be responsible for negative correlation between x and Al (r = -0.52). In siliceous ooze the strong positive correlations among x, Al_exc and Fe_exc suggest the presence of authigenic Fe-rich smectite. High Mn content (0.5%) probably in the form of manganese micronodules is also contributing to x in both calcareous and. siliceous ooze but not in the terrigenous core where mean Mn content (0.1%) is similar to crustal abundance. Thus, x systematically records the terrigenous variation in both the biogenic sediments but in terrigenous clay it indirectly suggests the presence of authigenic minerals.

4 illus, 3 tables, 35 ref

018579   Parameswaran K;Nair S K;Rajeev K (Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram-695 022, Email: k_parameswaran@ussc.gov.in) : Impact of aerosols from the Asian continent on the adjoining oceanic environments. J Earth Syst Sci 2008, 117(1), 83-102.

Aerosol optical, depth (AOD) at 630 nm wavelength over the oceanic regions adjoining the Asian Continent is examined using a seven-year long data base derived from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA satellite to study the mean spatial and temporal variations as well as to understand the impact of aerosols advecting from the continent. Depending on the prevailing meteorological conditions and nature of synoptic circulation, the AOD over the oceanic region shows a systematic annual variation. This annual pattern inturn also shows an inter-annual variability because of the corresponding variations in the meteorological features over the continent as well as small-scale deviations in the nature of synoptic circulation. The annual variation over the oceanic regions also shows a pronounced spatial heterogeneity depending on the influence of continental aerosols. Making use of the wind speed dependence of sea-salt AOD at far-oceanic environments and monthly mean wind speeds at small grids of size 5° x 5°, the annual variation of sea-salt AOD at different locations is studied to understand the spatial heterogeneity of this component. The residual component obtained by subtracting this from the measured AOD is the non-oceanic component due to advection from continent. The source regions for major continental advections are delineated from the analysis of air-mass back trajectories at appropriate locations identified from the annual pattern of non-oceanic component. The long-term effect of the continental impact is examined from the mean trend of AOD over the three major oceanic regions. This study shows that the continental influence is most significant over the Arabian Sea, followed by the Bay of Bengal and is almost insignificant in most of the regions over the Southern Hemispheric Indian Ocean, except for the effect of smoke aerosols over a few locations near Indonesia and Madagascar.

9 illus, 54 ref

018578   Naseema Beegum S;et al. (Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram-695 022) : Characteristics of spectral aerosol optical depths over India during ICARB. J Earth Syst Sci 2008, 117(S1), 303-13.

Spectral aerosol optical depth (AOD) measurements, carried out regularly from a network of observatories spread over the Indian mainland and adjoining islands in the Bay of Bengal and Arabian SIM. are used to examine the spatio-temporal and spectral variations during the period of ICARB (March to May 2006). The AODs and the derived Angstrom parameters showed considerable variations across India during the above period. While at the southern peninsular stations the AODs decreased towards May after a peak in April, in the north Indian regions they increased continuously from March to May. The Angstrom coefficients suggested enhanced coarse mode loading in the north Indian regions, compared to southern India. Nevertheless, as months progressed from March to May, the dominance of coarse mode aerosols increased in the columnar aerosol size spectrum OUT the entire Indian mainland, maintaining the regional distinctiveness. Compared to the above, iad stations showed considerably low AODs, so too the northeastern station Dibrugarh, indi-: the prevalence of cleaner environment. Long-range transport of aerosols from the adjoining regions leads to remarkable changes in the magnitude of the AODs and their wavelength dependencies during March to May. HYSPLIT back-trajectory analysis shows that enhanced long-range transport of aerosols, particularly from the west Asia and northwest coastal India, contributed significantly to the enhancement of AOD and in the flattening of the spectra over entire regions; if it is the peninsular regions and the island Minicoy are more impacted in April, the north Indian regions including the Indo Gangetic Plain get affected the most during May, with the AODs soaring as high as 1.0 at 500 nm. Over the islands, the Angstrom exponent (a) remained significantly.

10 illus, 2 tables, 30 ref

018577   Naqvi S M;Srinivasa Sarma D;Sawkar R H;Ram Mohan M;Rana Prathap J G (NO, National Geophysical Research Institute, Hyderabad-500 007, Email: naqvimahmood@yahoo.com) : Role of adakitic magmatism and subduction in gold endowment of Dharwar neoarchaean greenstone belts, India. J Geol Soc India 2008, 71(6), 875-88.

Acid volcanics found in auriferous greenstone belts of the Dharwar Craton are rhyolites, adakitic rhyolites and high silica adakites. Adakites are compositionally similar to TTG and characterized by high Na₂O/K₂O, depleted MgO, Cr, Ni, Y and Yb. The adakitic melts were most probably generated by the partial melting of the basaltic slab below a mantle wedge. LILE and LREE enriched IAB are the dominant volcanic members of the greenstone belts. IAB of the greenstone belts were generated from partial melting of the mantle wedge under the influence of slab derived fluids. The wedge derived IAB and slab derived adakites were deformed and metamorphosed to generate fluids responsible for the gold endowment of these belts. Rhyolites and possibly rhyolitic adakites were generated by the melting of the sialic continental crust forming top of the descending slab. Identification of adakites in auriferous greenstone belts strengthens the genetic link between adakite magmatism, subduction and Neoarchaean gold endowment.

6 illus, 2 tables, 57 ref

018576   Nair V S;et al. (Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum-695 022) : Size segregated aerosol mass concentration measurements over the Arabian sea during ICARB. J Earth Syst Sci 2008, 117(S1), 315-23.

Mass concentration and mass size distribution of total (composite) aerosols near the surface are essential inputs needed in developing aerosol models for radiative forcing estimation as well as to infer the environment and air quality. Using extensive measurements onboard the oceanographic research vessel. Sugar Kanya, during its cruise SK223B in the second phase of the ocean segment of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARE), the spatial distribution of the mass concentration and mass size distribution of near-surface aerosols are examined for the first time over the entire Arabian Sea, going as far as 58°E and 22°N, within a span of 26 days. In general, the mass concentrations (M_T) were found to be low with the mean value for the entire Arabian Sea being 16.7 ± 7 μg m^-3; almost 1/2 of the values reported in some of the earlier campaigns. Coarse mode aerosols contributed, on an average, 58% to the mass, even though at a few pockets accumulation mode contribution dominated. Spatially, significant variations were observed over central and northern Arabian Sea as well as close to the west coast of India. In central Arabian Sea, even though the M_T was quite low, contribution 6f accumulation aerosols to the total mass concentration was greater than 50%. Effective radius, a parameter important in determining scattering properties of aerosol size distribution, varied between 0.07 and 0.4 μm with a mean value of 0.2 μm. Number size distributions, deduced from the mass size distributions, were approximated to inverse power-law form and the size indices (v) were estimated. It was found to vary in the range 3.9 to 4.2 with a mean value of 4.0 for the entire oceanic region. Extinction coefficients, estimated using the number-size distributions, [were well-correlated with the accumulation mode mass concentration with a correlation coefficient of 0.82.

8 illus, 1 table, 33 ref

018575   Murugavel P;Gopalakrishnan V;Pant V;Kamra A K (NO, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, NCL Post, Pune-411 008) : Airborne measurements of submicron aerosols across the coastline at Bhubaneswar during ICARB. J Earth Syst Sci 2008, 117(S1), 273-80.

Airborne measurements of the number concentration and size distribution of aerosols from 13 to 700 nm diameter have been made at four vertical levels across a coastline at Bhubaneswar (20°25'N, 85° 83'E) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) programme conducted in March-April 2006. The measurements made during the constant-level at 0.5, 1, 2 and 3 km altitude levels extend ~ 100 km over land and ~ 150 km over ocean. Aerosol number concentrations vary from 2200 to 4500 cm^-3 at 0.5 km level but are almost constant at N 6000cm^-3 and ~ 800 cm^-3 at 2 arid 3km levels, respectively. At 1km level, aerosol number concentration shows a peak of 18,070 cm^-3 around the coastline. Most of the aerosol size distribution curves at 0.5 km and 1 km levels are monomodal with a maxima at 110 nm diameter which shifts to 70 nm diameter at 2 and 3km levels. However, at the peak at 1 km level, number concentration has a himodal distribution with an additional maximum appearing in nucleation mode. It is proposed that this maxima in nucleation mode at 1 km level may be due to the formation and transport of new panicles from coastal regions.

7 illus, 22 ref

018574   Murali Krishna A;Madhav M R (Civil Engineering Dep, Indian Institute of Technology Guwahati, Guwahati-781 039, Email: adapamk@gmail.com) : Densification and dilation effects of granular piles in liquefaction mitigation. Indian Geotech J 2008, 38(3), 295-316.

Amongst several alternate measures available to strengthen loose saturated sand deposits to withstand earthquake effects, provision of gravel drains/granular piles/stone columns is the most commonly adopted ground treatment methodology. The process of installation of granular piles in to loose granular deposits leads to densification in addition to reinforcement effect because of which the ground withstands better the effects of earthquakes and of liquefaction. Moreover, densified soils experience volume increase during shearing. Very high negative pore pressures generated due to suppression of the tendency for dilation further enhance the mitigation of liquefaction. In this paper, liquefaction mitigation of the ground treated by granular piles (GP) is assessed by applying the model of pore pressure generation and dissipation developed by Seed and Booker (1977), with modifications to account for the effects of densification and dilation on the ground. The combined effect of densification and dilation of the granular piles have proved to be more effective in mitigating the liquefaction potential of sand deposits than just the drainage effect.

14 illus, 37 ref

018573   Mondal S K (Geological Sciences Dep, Jadavpur Univ, Kolkata-700 032, Email: sisir.mondal@gmail.com) : Chromite and PGE deposits of mesoarchaean ultramafic-mafic suites within the greenstone belts of the Singhbhum craton, India: implications for mantle heterogeneity and tectonic setting. J Geol Soc India 2009, 73(1), 36-51.

The Archaean cratonic nuclei of the continents are important as they contain the most significant evidences for the evolution of Earth e.g. the greenstone sequences. In the Indian Shield, one of the important cratons is the Singhbhum craton, where nearly 95% of the Indian chromite deposits and only PGE deposits are located which are hosted within Mcsoarchaean ultramafic-mafic rock sequences. The ultramafic units occur as sill like intrusions within the Iron Ore Group (IOG) greenstone belts and often associated with gabbroic intrusions. In the Nuasahi and Sukinda mining districts of these occurrences, detailed petrological, geochemical and isotopic studies have been carried out in the last decades. Petrological and geochemical studies indicate a supra-subduction zone (SSZ) tectonic settings in Archaean for the origin of these ultramafic-mafic sequences. The Os isotopic and platinum group element (PGE) geochemical studies of chromites from the two mining districts indicate presence of a subchondritic source mantle domain beneath and within the Singhbhum craton similar to the Zimbabwean craton of southern African continent. The Os model age calculation indicates melt extraction from a subcontinental lithospheric mantle (SCLM) before 3.7 Ga which is similar to the other ancient cratons. As a whole the study supports the premise that India was part of the African continent in pre-Gondwana times and even in early Archaean and suggest possible amalgamation and building up of a supercontment during late Archaean. However, in comparison with other occurrences, the Singhbhum craton of the Indian Shield and the Zimbabwean craton in southern Africa are characterized by the presence of subchondritic lithospheric mantle domains within the SCLM, which were developed prior to 3.7 Ga.

9 illus, 1 table, 92 ref

018572   Mondal N C;Das S N;Singh V S (NO, National Geophysical Research Institute, Hyderabad-500 007, Email: ncmngri@yahoo.co.in) : Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram district, Andhra Pradesh, India. J Earth Syst Sci 2008, 117(2), 133-44.

Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable within short distance and contributing to near-surface inhornogeneity. In such situations topographic, hydrogeological and geomorphological features provide useful clues for the selection of suitable sites. Initially, based on satellite imagery, topographical, geomorphological and hydrogeological features, an area of about 149 km² was demarcated as a promising zone for groundwater exploration in the hard rock tract of Seethanagaram Mandal, Vizianagaram District, Andhra Pradesh, India. A total of 50 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration. An interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Ten sites were recommended for drilling. Drilling with Down-The-Hole Hammer (DTH) was carried out at the recommended sites down to 50 to 70m depths. The interpreted VES results matched well with the drilled bore well lithologs. The yields of bore wells vary from 900 to 9000 liters per hour (lph).

8 illus, 2 tables, 22 ref

018571   Misra D K (NO, Wadia Institute of Himalayan Geology, Dehra Dun-248 001, Email: dkmishra@wing.res.in) : Litho-tectonic sequence and their regional correlation along the Lohit and Dibang valleys, Eastern Arunachal Pradesh. J Geol Soc India 2009, 73(2), 213-19.

Geological mapping between Lohit and Dibang valleys of eastern Arunachal Pradesh reveals the existence of five thrust bound tectonostratigraphic units. In ascending structural order from SW to NE these are: (1) Sewak Group, (2) Lalpani Group, (3) Mayodiya Group, (4) Tidding Formation and (5) Lohit plutonic complex. This differs from previous mapping, because the three tectonostratigraphic units (Sewak, Lalpani and Mayodiya) were grouped under a single unit, referred as the Mishmi crystallines. The low-grade metamorphics of the Sewak Group occur at two different tectonic levels, one as persistent belt in the foothills and the other in the tectonic window beneath the high-grade metamorphics of the Mayodiya thrust sheet in the Higher Himalaya. The Tidding suture is the southeastern extension of the Indus-Tsangpo suture zone.

2 illus, 2 tables, 36 ref

018570   Mascarenhas A (NO, National Institute of Oceanography, Dona Paula-403 004, Email: mascarenhas@nio.org) : Sand fences: an environment-friendly technique to restore degraded coastal dunes. J Geol Soc India 2008, 71(6), 868-70.

An experiment to rebuild a dune field is attempted at Miramar beach, Goa. Installation of sand fences, a simple, cheap and environment friendly method of inducing accretion of sand is proposed as a remedial management option.

2 illus, 4 ref

018569   Manu M S;Anirudhan S (Geology Dep, Kerala Univ, Kariavattom P.O., Thiruvananthapuram-695 581, Email: geomanu@rediffmail.com) : Drainage characteristics of Achankovil river basin, Kerala. J Geol Soc India 2008, 71(6), 841-50.

Achankovil River sets in one of the major shear zones of Southern India which separates the Kerala Khondalite Belt (KKB) and Charnockite terrain. In this paper morphometric characteristics of the river basin developed in a shear zone is reported. Major basin parameters like linear, aerial and relief parameters of the basin indicate that the basin architecture is much influenced by this prominent shear zone. Development of rectangular, parallel and trellis drainage patterns and parameters like bifurcation ratio, elongation ratio, are clear evidences for the structural control. Further, main river course is oriented in WNW-ESE direction, which follow the trend of the Achankovil shear zone and most of the lower order streams are developed roughly at right angles to the main river course.

7 illus, 5 ables, 16 ref

018568   Manjit Singh;Darshan Singh;Pant P (Physics Dep, Punjabi Univ, Patiala-147 002) : Aerosol characteristics at Patiala during ICARB-2006. J Earth Syst Sci 2008, 117(S1), 407-11.

The spectral AOD measurements have been made for the first time over Patiala during multi-platform field campaign ICARB-2006 using a Multi-Wavelength Radiometer (MWR) along with the suspended particulate matter measurements with a high volume sampler. Spectral AOD has higher values in May in comparison to March and April. The monthly mean AOD values at 500 nm are 0.26 ± 0.08, 0.36 ± 0.19 and 0.58 ± 0.20 for the months of March, April and May respectively. The mean AOD is more during afternoon in comparison to forenoon at all wavelengths. The atmospheric turbidity is higher in May and is attributed to dust transported by southerly winds prevailing during this month. The Angstrom parameter a varies between zero and 0.68 while β ranges from 0.1 to 0.9. The columnar water vapour content ranges from 0.12 to 2.92 cm, having a mean value of 1.06 ± 0.648cm. The mean total suspended particulate matter is 334.41 ± 97.56 μgm/m³, an indication of high aerosol loading over Patiala during the campaign period.

8 illus, 11 ref

018567   Manglik A;Thiagarajan S;Mikhailova A V; Rebetsky Y (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: ajay@ngri.res.in) : Finite element modelling of elastic intraplate stresses due to heterogeneities in crustal density and mechanical properties for the Jabalpur earthquake region, central India. J Earth Syst Sci 2008, 117(2), 103-11.

Deep lower crustal intraplate earthquakes are infrequent and the mechanism of their occurrence is not well understood. The Narmada-Son-lineament region in central India has experienced two such events, the 1938 Satpura,earthquake and the 1997 Jabalpur earthquake, having a focal depth of more than 35km. It is estimated elastic stresses due to the crustal density and mechanical properties heterogeneities along the Hirapur-Mandla profile passing through the Jabalpur earthquake region to analyse conditions suitable for the concentration of shear stresses in the hypocentral region of this earthquake. Elastic stresses have been computed by a finite element method for a range of material parameters. The results indicate that the shear stresses generated by the density heterogeneities alone are not able to locally enhance the stress concentration in the hypocentral region. The role of mechanical properties of various crustal layers is important in achieving this localization of stresses. Among a range of material parameters analysed, the model with a mechanically strong lower crust overlying a relatively weak sub-Moho layer is able to enhance the stress concentration in the hypocentral region, implying a weaker mantle in comparison to the lower crust for this region of central India.

7 illus, 1 table, 44 ref

018566   Mallikharjuna Rao J;Poornachandra Rao G V S; Sarma K P (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: mallikharjun_ngri@yahoo.co.in) : Precambrian mafic magmatism of Shillong plateau, Meghalaya and their evolutionary history. J Geol Soc India 2009, 73(1), 143-52.

The Archaean gneissic basement of Shillong plateau has been traversed by number of mafic dyke swarms. At least two suites of dykes are identified in the region represented by Proterozoic Khasi greenstone related dolerites and younger Cretaceous dolerite dykes in addition to mafic alkaline dykes. The older Khasi greenstone dolerites are altered and have undergone low-grade metamorphism compared to fresh Cretaceous dykes, which are well exposed in the West Garo Hills region. All the Khasi greenstone dolerites are tholeiite in composition and range from basalt to basaltic andesite in composition and show olivine or quartz normative character. Most of the dykes show continental nature of emplacement with some overlapping oceanic tectonic setting of origin. Petrochemical study suggests that they were derived from picrites that subsequently undergone low- pressure fractionation. Palaeomagnetic study of the older Khasi greenstone related dolerites show a direction of magnetization of Dm=17, Im= +57 (α₉₅= 23.34; K= 31.5; N= 24) with a palaeolatitude of 29.7°N to the Indian subcontinent that clearly support the Proterozoic dyke/dyke swarm emplacement in the region. The magnetic carrier as inferred from K-T studies is in multi domain 3 size and cation deficient (CD) domain states.

13 illus, 28 ref

018565   Malik J N;Morino M;Mishra P;Bhuiyan C;Kaneko F (Civil Engineering Dep, Indian Institute of Technhnology Kanpur, Kanpur-208 016, Email: javed@iitk.ac.in) : First active fault exposure identified along Kachchh mainland fault: evidence from trench excavation near Lodai village, Gujarat, Western India. J Geol Soc India 2008, 71(2), 201-8.

Reports first identified active fault exposure from Kachchh region along the Kachchh Mainland Fault (KMF) other than the 1819 Allah Bund earthquake. The active fault scarps striking E-W were identified near Lodai village along KMF. North facing scarps with height from 10-15 m are the manifestation of the displaced alluvial fan surface along this fault. Occurrence of discontinuous linear mound ranging in height from 3-5 m aligned along the strike about 100 m north of the main scarp are suggestive of younger tectonic movement and progressive shift of tectonic activity towards north along new imbricated fault. Three low to high angle reverse fault strands (F1, F2 and F3) displacing young Quaternary deposits (late Pleistocene-Holocene?) classified as A to F units comprising gravel and sand-silt facies were identified in a trench excavated at the base of the linear mound along KMF. Our preliminary observations revealed occurrence of at least two large magnitude earthquakes along the F3 fault, and may be older events along the F1 and F2. Latest event (Event-I) occurred along F3 after the deposition of unit B registering the displacement of -33 cm, penultimate event (Event-II) occurred after the deposition of unit C with -40 cm of displacement. The maximum displacement of about 73 cm along F3 indicates cumulative displacement accommodated during more than one event. The total displacement of -98 cm along F2 strand displacing the E and F units is the result of more than one event, and since the F2 probably displaced the unit C suggests that the movements occurred during penultimate (Event II) and during the Event III, older than penultimate. Displacement of Mesozoic succession during older events and unit B during the latest Event I along Fl suggests repetitive movement along this fault. The fragile nature of -3-4 m wide shear zone formed in Mesozoic rocks (shale+sandstone) also point towards repetitive tectonic movement along KMF.

4 illus, 15 ref

018564   Luirei K;Bhakuni S S (NO, Wadia Institute of Himalayan Geology, Northeast Unit, Itanagar, Email: ashing_luirei@rediffmail.com) : Ground tilting in likhabali area along the frontal part of Arunachal Himalaya: evidence of neotectonics. J Geol Soc India 2008, 71(6), 780-6.

The study along frontal part of the Sub-Himalayan terrain suggests neotectonic activities along thrusts and faults. Neotectonics is evident from geomorphic features such as development of terraces, stream incision, preferred stream migration and the thrusting of the Siwalik rocks over the Quaternary deposits. Southward Himalayan foreland propagation thrusting has resulted in ground tilting in the frontal part of the Himalaya and has led the streams to migrate towards southwest. On the other hand the stream in the Sub-Himalayan terrain flows parallel to the trend of the Arunachal Himalaya, and has migrated southward. The calculated mountain front sinuosity index reflects relative tectonic activity in the mountain front. Thrusts and faults have controlled the drainage channels of major streams. Recent seismic activities have triggered massive landslides, which blocked the streams temporarily.

5 illus, 21 ref