009569   Chandrashekhar M B;Sarnam Singh;Roy P S (NO, Indian Inst of Remote Sensing, 4, Kalidas Road, Dehradun-248 001) : Geospatial modelling techniques for rapid assessment of phytodiversity at landscape level in western Himalayas, Himachal Pradesh. Curr Sci 2003, 84(5), 663-70.

The mountainous state of Himachal Pradesh is known for its vast natural wealth, including forests, alpine meadows, rivers and valleys endowed with a rich array of life forms. However, this biodiversity hot spot is under great peril owing to human-induced disturbance factors. The findings on spatial representation of the habitat at a scale which can be used for conversation planning and rehabilitation are lacking. IRS-1D, LISS-III sensor data have been used to assess the vegetation coupling with RS and GIS techniques in the state. An approach for rapid assessment of biodiversity at landscape level using satellite remote sensing, phytosociological data and knowledge base in geospatial model has been presented. The geospatial analyses at the landscape level reveal that most of the fertile valleys of the region are occupied by the human activities and possess very low bio-richness. Inverse relationship has been observed with disturbance at landscape level vis-a-vis phytodiversity or richness of the vegetation type/habitat.

5 Illus, 2 Tables, 29 Ref

008471   Yadav S;Rajamani V (School of Environment Sciences, Jawaharlal Nehru University, New Delhi-110 067) : Aerosols of NW India - a potential Cu source. Curr Sci 2003, 84(3), 278-80.

^ssc2 illus, 1 table, 13 ref

008470   Tripathi O P;Jain S L (Radio and Atmospheric Science Div, National Physical Laboratory, New Delhi - 110 012) : Abrupt change in total ozone column over Indian Antarctic station. Indian J Radio Space Phys 2003, 32(2), 38-42.

The solar radiation at five wavelengths, namely, 300 nm, 305 nm, 312 nm, 940 nm and 1020 nm has been measured using narrow band (2.5 nm FWHM) filters with a microprocessor-based sun-photometer from January 1997 to February 1998 on hourly basis on all clear days at Maitri, and Indian Antarctic station (70°45'S, 11°45'E), during sixteenth Indian Scientific Antarctic expedition. The total column ozone has been estimated from these measurements. Very low ozone values have been observed during Antarctic spring, which confirmed the continuity of ozone hole phenomenon. Abrupt increase in total ozone column has been observed during ozone hole period. This observation has been confirmed by the same event in total ozone mapping spectrometer (TOMS) measurements and may be attributed to planetary wave phenomenon.

3 illus, 16 ref

008469   Sinha D K (Chemistry Dep, K G R (P G) College, Moradabad-244 001) : Statistical analysis of physico - chemical parameters of the water of river Sai at Rae Bareli. Indian J envir Prot 2002, 22(2), 184-7.

^ssc1 illus, 1 table, 14 ref

008468   Singh I B;Jaiswal M;Singhvi A K;Singh B K (Geology Dep, Lucknow University, Lucknow-226 007) : Rapid subsidence of western Ganga plain during late Pleistocene: evidence from optical dating of subsurface samples. Curr Sci 2003, 84(3), 451-4.

Infrared stimulated luminescence dating of sub-surface sediment core samples from about 350-190 m depths in Meerut and Yamuna Puram (Bulandshahr) regions of western Ganga Plain gave ages of 49-31 ka. Such sample depths and ages indicate rapid subsidence of the region during latest Pleistocene to create appropriate accommodation space in a relatively short time. Geochemical and clay mineralogical data indicate a humid climate during 50-30 ka. It is inferred that during 50-10 ka western Ganga Plain was rapidly subsiding and received large amount of sediment from the activity of Ganga Megafan.

3 illus, 4 tables, 16 ref

008467   Shrivastava P K;Singh G N;Shrivastava D (Phys Dep, Govt. New Sci College, Rewa (M.P.) - 486 001) : Short-term influence of coronal mass ejections on geomagnetic disturbances. Indian J Radio Space Phys 2003, 32(2), 52-4.

Coronal mass ejections (CMEs) are described as a turbulent interplanetary phenomena at IAU, which influence the interplanetary medium as well as disturbances in geomagnetic field. The CMEs represent large scale changes in the solar corona. In this note the relation of CMEs with geomagnetic activity has been studied for the period of 1988-1993. It is found that CMEs in association with B-type solar flares are most effective in producing disturbances in geomagnetic field.

1 illus, 9 ref

008466   Sarma C;Deka D K;Bhattacharyya K G (Chemistry Dep, Gauhati University, Guwahati-781 014) : Quality of water in a few urban drinking water sources. Indian J envir Prot 2002, 22(2), 173-83.

Reports on 24 physico - chemical characteristics for water samples collected seasonally over a 3 year period from 5 public ponds, 3 ring wells and 1 natural reservoir in and around Guwahati city. The water quality characteristics show the degraded nature of the water sources in an urban area.

5 illus, 1 table, 16 ref

008465   Rehan Ali S;Rao L A K (NO, National Institute of Science, Technology and Development Studies (CSI, New Delhi-110 012) : Infra red spectra of the precambrian stromatolitic phosphorites of Gandhra , Panchmahals district, Gujarat. Bull Indian Geol Ass 1999, 32(1), 43-7.

The infra red spectra of the apatite group of minerals of the precambria stromatolitic phosphorites from the Champaner belt of Gandhra Panchmahals district, Gujarat gives a vital data regarding the compositional characteristics. Infra red spectral analysis of the phosphorite samples were carried out in the 650 to 4000 cm-1 frequency region using KBr pellets on a Shimadzu-408, Infra Red Spectrophotometer. The prominent vibration bands have been assigned to various functional groups and approach to carbonate apatite and carbonate hearing hydroxyl apatite in composition with the probable and varying degree of PO4 substitution with the introduction of carbonate and hydroxyl groups.

2 illus, 2 tables, 16 ref

008464   Rastogi R G (Phys Dep, Gujarat Univ, Ahmedabad - 380 009) : New look at the ionospheric current system. Indian J Radio Space Phys 2003, 32(2), 21-37.

Describes some regional anomalies in the solar daily variations of the northward X and eastward Y geomagnetic field by examining the data from individual stations during the International Geophysical Year (IGY) 1957-58. Around 30-40°N dip latitude the daily range of X showed a minimum and the range of Y a maximum, which is the characteristic of the S_q focus. No definite indications of such phenomenon were seen in the southern hemisphere. The low latitude maximum of ΔX around noon changed to midday minimum at high latitudes, not through a flat daily variation at focus latitudes. A forenoon minimum and an afternoon maximum of ΔX occurred at northern focus latitudes. A reverse feature occurred at southern focus latitude. It is suggested that the mid-latitude S_q current system is greatly affected by another low latitude current system as well as by the polar S_q current system. The daily variation of YF128><68>Y was reversed in the two hemispheres (the latitude of reversal at around 15°S in J-solstices and around 10°N during D-solstices) which suggests the invasion of summer current system over the winter current system.

15 illus, 1 table, 18 ref

008463   Patel S J;Bhatt N Y (Geology Dep, M S University of Baroda, Vadodara-390 002) : Alignment of the larger forminifers in the Thalassinoides burrows of the Paleogene rocks of Western Kachchh, Gujarat. Bull Indian Geol Ass 1999, 32(1), 27-31.

Larger foraminifers such as Nunmulites. Discocyclina and Lepidocyclina are found in the matrix as well as in the various burrow systems (Arenicolites, Laminites, Thalassinoides, Palaeophycus, Beaconites) of palaeogene rocks of the Western Kachchh. Thalassinoides are the largest burrow system amongst the available trace fossils. These are made up of aligned larger foraminifers whose equatorial (larger) axes are perpendicular to the burrow system forming meniscus structures. This alignment is quite different from those foraminifers placed in the matrix and in other burrow systems. The substrate modification and alignment of the foraminiferal tests within Thalassinoides burrow systems show characteristics of sediment processes either by advection or diffusion or both types during the forward movements of the thalassinidean decapod crustaceans. Polished and unbroken nature of the larger foraminifers in the burrows indicate that the shells have been transported short distance from their place of excavation.

1 illus, 23 ref

008462   Naval Kishore;Rai B;Singh V P;Sharma R K (CAS Geology, Punjab University, Chandigarh-160 014) : Geology and geochronology of the Baragaon Gneisses Satluj Valley, Himachal Pradesh. Bull Indian Geol Ass 2002, 35(1), 43-50.

Baragaon gneisses form a part of the Chail Formation, which overlie the Shali Formation and are overlain by the rocks of the Jutogh Formation. The Na₂O content in these gneisses is less than 3.2 wt %. Chemistry of the gneisses indicates that the gneisses are metaluminous as well as peraeuminous and have generated between 4 to 4 Kb pressure and 670 to 685°C temperature. Rb-Sr whole rock isochron yield an age of 1861±81 Ma with initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70506±0.00691. Relatively low initial ⁸⁷Sr/⁸⁶Sr ratio, low Sodium and Aluminium saturation index indicate that melt for the granitic gneisses has been derived from upper mantle/lower crust and the higher grade of metamorphism has caused depletion of alkalies which eventually reduce ⁸⁷Sr/⁸⁶Sr ratio.

7 illus, 3 tables, 23 ref

008461   KUMar S N;Prasannakumar V;Nair P K R (Geology Dep, University College, Trivandrum-695 034) : Temporal relations between deformation and granite emplacement at Kalpatta, South India. Bull Indian Geol Ass 2002, 35(1), 51-6.

Kalpatta granite intrudes into the Precambrian crystalline rocks which show three phases of structures. Mesoscopic analysis of major as well as minor structures and microfabric analysis of quartz c-axis patterns and poles to (001) of biotite indicate two major deformational events, the first one being more intense. As the Kalpatta granite has elliptical and is free from deformational effects, it is considered a post-kinematic diapiric type of intrusion.

3 illus, 7 ref

008460   Kulshrestha S K;Singh R Y;Saha S K (CAS in Geology, Punjab University, Chandigarh-160 014) : Eocene ostracods from Dauki Nala Section, Sylhet Bangladesh. Bull Indian Geol Ass 1999, 32(1), 49-53.

Embodies the first record of 6 species belonging to 4 genera of ostracods from the outcrops of Sylhet Limestone and Kopili Shale Formation from Dauki Nala Section (Ballaghat), Sylhet District, Bangladesh. Among them one species is new. The present assemblage is suggestive of Middle-Late Eocene age for the sediments.

2 illus, 1 table, 9 ref

008459   Khan A Z;Ahmad A H M (Geology Dep, Aligarh Muslim University, Aligarh) : Texture and heavy minerals study of Dharangadhra Group of sandstones (Lower Cretaceous), Saurashtra Basin, Gujarat. Bull Indian Geol Ass 1999, 32(1), 33-42.

The overall textural study of the Dharangadhra Group of sandstones suggest that the sandstones have not suffered high energy environment. The heavy minerals indicate that they were derived from acid igneous rocks and metamorphic rocks.

5 illus, 1 table, 8 ref

008458   Gupta L N;Ravindra Kumar;Jagmohan Singh (NO, I C A S in Geology, Punjab University, Chandigarh-160 014) : Mineral chemistry and petrogenesis of Matiana phyllites, Himachal Pradesh. Bull Indian Geol Ass 1999, 32(1), 13-25.

The stratabound sultide mineralisation occurs in green phylite and grey (calcareous) phyllite of the Chail Group of rocks (Precambrian) at Matiana, Himachal Pradesh. It is comprised of mainly pyrite in the form of stringers, pockets and disseminations. Clorite. muscovite, pyrite and carbonate minerals of both the rock types have been investigated. The calcareous phyllites consist of repidolite muscovite, quartz and calcite whereas the green phyllites are made up of thuringite, ankerite, muscovite, quartz and repidolite. The muscovite in calcareous phyllites is relatively poorer in potash and alumina as compared to those of green phyllites. Mineral chemistries of these rock types suggest that the calcareous phyllites are of sedimentary metamorphic origin whereas the green phyllites are volcanoclastic tuff. The pyrites occurring in both the rock types are volcanogenic.

5 illus, 5 tables, 14 ref

008457   Gupta D C;Saxena R N;Chatterjee A C (Applied Geology Dep, Barkatullah University, Bhopal) : Petrochemistry of the Deccan Trap lava flows from Mandu cliff region, Dhar district, Madhya Pradesh. Bull Indian Geol Ass 2002, 35(1), 13-28.

In the mandu Cliff region, seventeen lava flows of simple and compound nature have been delineated along a hilly tract from 240 m to 705 m above msl. These lava flows are basalt to basaltic andesite with some transitional types. On the basis of variation in major oxide composition with stratigraphic height, the 465 m thick pile of lava flows have been divided into group - 1 and Group - 2, separated from each other by a marker horizon of GPB (Giant plagioclase Basalt). On the basis of field relations, petrography and behaviour of major elements, the Group - 1 lavas have been further divided into subgroups A, B, C, D, E, and F, while Group - 2 lavas are classified into subgroup G and H. Gour lava flows of basaltic andesite occur in Group - 1, while Group - 2 consists two lava flows of basaltic andesite composition. The flow-units of compound lava flows in group 1 show varied chemical composition. Magma mixing, assimilation and slight contamination are probably the main processes producing magmas of different composition from tholeiitic parental magma. Crystal fractionation of `open system' type (O'Hara Type) generated the lava flows of diverse mineralogical and chemical composition. On the basis of CaO/Al₂O₃ vs Mg #, it is seen that Group - 1 lavas may be produced by plagioclase fractionation, while Group - 2 lavas are produced by clinopyroxene fractionation. These magmas probably erupted through different feeders in the area.

8 illus, 4 tables, 19 ref

008456   Gupta D C;Chatterjee A C;Jain P K (Applied Geology Dep, Barkatullah University, Bhopal) : Geochemical stratigraphy of the Deccan traps of Manmad district Nasik (Maharashtra) India. Bull Indian Geol Ass 2002, 35(1), 29-41.

Based on detailed geological mapping and petrochemical studies, the 350-400m thick Deccan Trap lava pile of Manmad Formation has been divided into six members i.e. Anakwade (AN), Ankaiwari (AK), Ankai Cave (AC), Agastha Rishi (AR), Lower Tankai (LT) and Upper Tankai (UT). These members are consituted of 18 lava flows. On the basis of break in MgO contents, trace elements and REE data, these lava flows are grouped into three Chemical Types namely CT 1, CT 2 and CT 3. The MgO, TiO₂, P₂O₅, Zr and Y gradually decreases in the sequence from CT 3 → CT 2 → CT 1. Since CT 3 has high concentration of MgO, Ni, Cr and LiL elements in comparison to CT 2 and CT 1 types, it is presumed to be the primitive magma responsible for the formation of CT 2 and CT 1 by the process of fractional crystallization. The petrogrenesis of chemical types is discussed in the light of new set of trace elements and REE data.

5 illus, 5 tables, 4 ref

008455   Dhirendra Kumar;Saravanan B (Atomic Energy Dep, Atomic Minerals Directorate for Exploration and Research, R K Puram, New Delhi-110 066) : Geochemical features of early eocene volcanism in north-eastern Himalaya, Arnachal Pradesh, India. Bull Indian Geol Ass 2002, 35(1), 1-12.

The early Eocene Abor volcanics mainly comprise basalt and andesite with minor trachyte and rhyolite, occasionally interbedded with thin agglomerate, tuffaceous shal and volcanic breccia. Chemically, the volcanics support two divisions - basalt and andesite, and closely resemble calc-alkaline basalt. The ratios Zr/Nb (7.43-31.8), La/Nb (0.7-2.4), Rb/Nb (0.6-3.5), Ba/La (1.5-28.3) and Eu/Sm (0.20-2.75) of the volcanics lying between average ratios of continental crust and premordial mantle indicates low degree crustal contamination. The trend of magmatic crystallisation and wide range K/Rb (285-705), Ba/La (1.5-28.3) ratios indicate the volcanics to have been produced at island-arc setting. The emplacement is coeval to the formation of Indian Ocean and Ninety East Ridge ODP-site 121-756 (43.2±0.5 Ma). This period is characterized by rifting, deepening and subsidence of large chunk of Indian Ocean floor which seems to have triggered volcanic activity along the ancestral line of weakness of Siang fracture.

6 illus, 2 tables, 27 ref

008454   Devi N R;Dutta S;Maswood M;Sarma K P (Geological Sciences Dep, Gauhati Univ, Guwahati-781 014) : Deformational history of the precambrain rocks around Garchuk of Greater Guwahati, Kamrup district, Assam, India. Bull Indian Geol Ass 2002, 35(1), 63-7.

The Precambrian metamorphites of the Garchuk area of Greater Guwahati of Assam-Meghalaya Plateau witnessed four deformation showing multiple interference patterns in the ductile to brittle fields. Firest phase deformation affected all the preexisting depositional fabrics under progressive metamorphic phase leading to the formation of most dominant, highly penetrative schistose and gneissose fabrics of rocks of amphibolite facies. The second phase of deformation was responsible for layer parallel shortening (buckling) of the mechanically active S₀ and S₁ fabrics in the NW-SE longitudinal compressive tectonics leading to the formation of NE-SW trending up and down facing folds of probable plane non-cylindrical nature and sub-horizontal plunge with associated minerals of retrograde phases. The third phase folds are non-coaxial, open, warp type, gently plunging with near vertical axial plane striking NW-SE direction and refolded earlier set of folds into non-plane non-cylindrical nature. The fourth phase deformation is related to brittle phase and the emplacement of porphyritic granite that exerted lateral pressure on the country rocks at the contact zone.

4 illus 15 ref

008453   Chhabra J;Dhirendra Kumar;Sharma M;Rawat T P S (Atomic Energy Dep, West Block VII, R K Puram, New Delhi-110 066) : Role of sulphur and organic carbon in uranium mineralisation of Dagshai sanstones, Solan district, H.P., India. Bull Indian Geol Ass 2002, 35(1), 57-62.

Biochemically and physico-chemically degraded organic matter, occuring in radioactive sandstones of Dagshai Formation around Tarol, maltu and Lohanji areas have been analysed for total organic carbon, uranium and sulphur. The data show negative correlation between organic carbon and uranium (r=-0.8479) and organic carbon and sulphur (r=-0.7228) but positive correlation between uranium and sulphur (r=+0.5293). The results reveal the reduction of soluble U⁺⁶ and insoluble U⁺⁴ species by elemental S and H₂S produced by sulphate reducing bacteria associated with detrital organic matter. It is contented that total organic carbon supplied energy to sulphate - sulphide system through biogenic processes. Sulpur played an essential role in the fixation of uranium in Dagshai sediments.

2 illus, 17 ref

008452   Chadha D K (NO, Central Ground Water Board, Jamnagar House, Mansingh Road, New Delhi-110 011) : Ground water resources - need for protection from depletion and pollution. Bull Indian Geol Ass 1999, 32(1), 1-12.

The static ground water resources of the country have been assessed as 10812 BCM and dynamic resources as 432 BCM. The present stage of development of the replenishable resources is 32%. However, certain areas in the country, particuraly in the states of Punjab and haryana, the stage of development has exceeded the annual recharge leading to depletion of the resource. On the other hand implementation of major and medium irrigation projects have led to problem of water logging. Unplanned development of water resources, haphazard disposal of municipal and undertrial wastes and application of agricultural inputs have led to ground water quality deterioration pollution. The next millenium, therefore, needs to be devoted to exercising various management options including conservation and augmentation of ground water resources for increasing the availability of the resource and to protect the resource from pollution to meet the requirements of increasing population.

8 illus, 6 tables, 7 ref

008451   Bowman G G;Mortimer I K (Phys Dep, The Univ of Queensland, Qld 4072, Australia) : Influence of geomagnetic activity on the occurrence of midlatitude ionogram-recorded spread-F. Indian J Radio Space Phys 2003, 32(2), 16-20.

Delayed spread-F occurrence as recorded by ionograms, following geomagnetic activity (GA) has been investigated using data from 88 stations located around the world. The spread-F occurrence is delayed progressively from one to three days, from subauroral to midlatitude regions. The equatorial latitudes show suppressed activity. An examination of daily spread-F occurrence values relative to the AE index reveals not only a main delay of one day, but also delays of two and three days involve principally GA occurring around 0600 hrs LT.

3 illus, 1 table, 19 ref

008450   Bose S K;Bhattacharya A B (Phys Dep, Kalyani Univ, Kalyani - 741 235) : Solar plasma activated decametric radio emission of non-Io origin from Jupiter magnetosphere. Indian J Radio Space Phys 2003, 32(2), 43-51.

The interaction between solar plasma with Jovian magnetosphere has been highlighted by studying the correlation between decametric radio emission from the Jupiter with different solar plasma parameters and also with the interplanetary magnetic field feature and the heliospheric current sheet extent. Significance of the correlation is tested with usual statistical technique. Also the Chree-superposed-epoch analysis has been performed with lag-days correction for the observed solar plasma parameters at IAU, considering high values of occurrence probability of decametric radio-emission of non-Io origin from Jupiter as epoch days. The results of Chree analysis support the correlation study.

15 illus, 2 tables, 34 ref

008449   Bordoloi R K;Kotoky P;Baruah J;Haque I;Borah G C (Chemistry Dep, D K D College, Dergaon-785 614) : Physico - chemical parameters of Toklai river, Assam. Indian J envir Prot 2002, 22(2), 151-3.

Physico - chemical parameters of the Toklai river water are monitored for 2 different seasons in and around Jorhat city, Assam. Indicates a fluctuating behaviour of different parameters throughout the course. However, an anthropogenic incorporation from the urbanised part of the city is attributed and warrants continuous geochemical monitoring of the soil/water systems is warranted.

1 illus, 1 table, 7 ref

008448   Ahmad S;Nayak V K (Geochemical Lab, Geology Dep, A M U, Aligarh-202 002) : The X-ray diffraction and Geochemical studies of flourite from Chandidogri deposit, district Rajnandgaon, Madhya Pradesh. Bull Indian Geol Ass 1999, 32(1), 55-64.

The fluorite of the Chandidongri fluorite deposit contains various proportions of different species of fluorite as revealed from mineralogical and geochemical studies, the coloured and white varieties contain traces of yettrofluorite, cerofluorite and borofluorite while the colourless transparent variety is predominantly a yettrofluorite. The geochemical analyses of fluorite show the presence of U. The some rare earths (La, Ce and Nd) and a host of trace elements (Ga, Rb, Y, Nb, Sr, Zr, Ba, V, Cr, Ni, Cu, Pb, and Zn). As U and Th have great geochemical affinity for aforementioned rare earths and trace elements and morover fluorite samples also exhibit natural themoluminescence, the possibility of uranium and thorium mineralization is strong in the area. The presence of traces of Cu, Pb and Zn both in fluorite as well as in associated Dongargarh granite indicated that these elements may have been transported along with fluorine from the late derivatives of associated granitoid magmatism. This would account for the fluorite with some Cu-Pb-Zn mineralization. The violet colouration of fluorite may be due to radioactive effects and/or prolonged exposure to sunlight.

4 illus, 3 tables, 9 ref

007554   Mohanlal Purshottamdas Tank (NO, , 482, Old Aerodrome Road, Bhavnagar-364 001) : Device for producing artificial rain. 0000, (NULL), (NULL).

007553   Stephen J;Gokarn S G;Manoj C;Singh S B (NO, National Geophysical Res Institue, 60 Hyderabad-500 007) : Effects of galvanic disortions on magnetotelluric data: interpretation and its correction using deep electrical data. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 27-36.

The non-inductive galvanic disturbances due to surficial bodies, lying smaller than high frequency skin depth, cause serious interpretational errors in magnetotelluric data. These frequency independent disatortions result in a quasi-static shift between the apparent resistivity curves know as static shift. Two-dimensional modelling studies, for the effects of surficial bodies on magnetotelluric interpretation, show that the transverse eletric (TE) mode apparent resistivity curves are hardly affected compared to the transverse magnetic (TM) mode curves, facilitating the correction by using a curve shifting method to match low frequency asymptotes. But in the case of filed data the problem is rather complicated because of the random distribution of geometry and conductivity of near surface inhomogeneities. Presents the has been presented of deep resistivity soounding (DRS) data to constrain MT static shift. Direct current sensitivity studies show that the behaviour of MT static shift can be estimated using DC resistivity measurement close to the studies show that the behaviour of MT sounding station to appreciable depths. The distorted data set is corrected using the MT response for DRS model and further subject to joint inversion with DRS data. Joint inversion leads to better estimation of MT parameters compared to the separate inversion of data sets.

6 illus, 26 ref

007552   Sengupta S (Geo Dep, Presidency Coll, 86/1 College Street, Kolkata - 700 073) : On a middle eocene granulate nummulites (:foraminiferida) from umrangshu, mikir-north cachar hills, Assam, Eastern India with observations on test growth and chamber protoplasm extrusion in morphologically complex taxa of the genus. Indian J Earth Sci 2003, 28(1-4), 32-7.

Dimorphic pair of a Middle Eocene granulate Nummulites (:Foraminiferida) from Umrangshu, Mikir-North Cachar Hills, Assam, provisionally identified as N. ex. gr. acutus (Sowerby) is described and illustrated for the first time. The microspheric form of the taxon reveals complex morphological features. It is suggested that multiple spire and septal filament pattern were instrumental in regulating test growth and chamber protoplasm extrusion respectively in large and morphologically complex taxa of the genus.

4 illus, 23 ref

007551   Rao P L S;Mohanty U C;Raju P V S;Iyengar G (Cen for Atmospheric Sciences, Indian Inst of Technol Delhi, Hauz Khas, New Delhi-110 016) : The Indian summer monsoon as revealed by the NCMRWF system. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 95-111.

Mean seasonal features of the Indian summer monsoon circulation in the National Centre for Medium Range Weather Forecasting (NCMRWF) global data assimilation and forecast system. The large-scale budgets of heat and moisture are examined in the analyzed and model atmosphere. The daily operational analyses and forecasts (day 1 though day 5) produced for the summer seasons comprising June, July and August of 1995 and 1993 have been considered for the purpose. The influence of the systematic errors over the Indian summer monsoon and performance of the model in capturing the interseasonal variability were studied. The heat and moisture balances show reduction in the influx of heat and ,moisture in the model forecast compared to the analyzed atmosphere over the monsoon domain. Consequantly, the diabatic heating also indicates reducing trend with increase in the forecast period. In effect, the strength of Indian summer monsoon, which esentially depends on these parameters, weakens considerably in the model forecasts. Despite producing feeble monsoon cicrulation, the model captures interseasonal variability realistically. Although, 1995 and 1993 are fairly normal monsoon seasons, the former received more rainfall compared to the latter in certain pockets of the monsoon domain. This is clearly indicated by the analyzed and model atmosphere in terms of energetics.

15 illus, 18 ref

007550   Rajesh R S;Mishra D C (NO, National Geophysical Research Institute, Hyderabad-500 007) : Admittance analysis and modelling of satellite gravity over Himalayas-Tibet and its seismogenic correlation. Curr Sci 2003, 84(2), 224-30.

The averaged admittance function computed from six long-range profiles (1650 km) of the merged satellite free air anomaly across Himalayas and Tibet shows good fit for a regional compensation model with an effective elastic thickness of 50 km and depth of compensation as 70 km. This suggests that the crustal strength resides in the upper 50 km of the crust which represents the brittle part of the crust. The earth-quake focal-depth distribution in this area suggests that most of the seismic activities are confined with in the upper 50 km, confirming that this part of the earth's crust is brittle and inferring that the lower crust of 20 km is ductile in nature, which has been confirmed from megnetotelluric studies over Tibet. Modelling of Bouguer anomaly aong 90°E longitude across Himalayas and Tibet, constrained from the results of INDEPTH seismic profiles across Tibet, suggests that the crustal thickness varies from 40 km under the Indo-Gangetic Plains to 70 km under the Indus Tsangpo Suture Zone (ITSZ) which remains almost flat at 70 km under the Tibet and reduces to 40 km north of Altyn Tagh Fault (ATF).

4 illus, 30 ref

007549   Purnachandra Rao V;Rajagopalan G;Vora K H; Almeida F (National Inst of Oceanography, , Dona Paula, Goa-403 004) : Late quaternary sea level and environmental changes from relic carbonate deposits of the western margin of India. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 1-25.

Relic carbonate deposits along the western margin of India occur as dolomite crusts, aragonite sands (pelletal/oolitic) and aragonite-cemented limestones, oyster shells, corals, encrusted coralline algal and foraminiferal-dominated nodules. Radiocarbon dates were measured for 62 relic deposits covering the entire margin. The age of these deposits on the continental shelf off Cape Comorin and Mangalore, between 110 and 18 m depth, ranges between 12,619 ¹⁴C yr BP and 6.390 ¹⁴C yr BP. On the northwestern margin of India, especially on the carbonate platform (between 64 and 100m), the age ranges from 17,250 to 6,730 ¹⁴C yr BP. The relic deposits of the Gulf of Kachchh at depths between 35 and 25 m are dated at 12,550-9,630 ¹⁴C yr BP. The age vs. depth plot of the relic deposits further indicates that the Gulf of Kachchh was inundated much early, atleat by 15 ka, after the Last Glacial maximum, and was subjected to uplift and subsidence during the Holocene. The carbonate platform subsided during the early Holocene. Some of the relic deposits between Cape Comorin and Mangalore plot on or, closely follow the glacio-eustatic sea level curve. Despite abundant siliciclastic flux discharged by the Narmada and Tapti during the early Holocene, carbonate sedimentation continued until 6.700 ¹⁴C yr BP. It is suggesd that the rive-derived sediment flux diverted southrards under the influence of the SW monsoon current and, thereby, increased the turbidity on the shelf and slope southeast of the carbonate platform and facilitated the formation of deeper water foraminiferal nodules off Vengurla-Goa.

22 illus, 2 tables, 59 ref

007548   Pal S K;Majumdar R K (Centre for Study of Man and Environment, , CK 11, Sector 2, Salt Lake, Kolkata - 700 091) : Determination of groundwater potential zones using iso-resistivity maps in alluvial areas of Munger district, Bihar. Indian J Earth Sci 2001, 28(1-4), 16-26.

Forty six vertical electrical soundings (VES) were conducted over alluvial areas, adjacent to Chotanagpur plateau fringe areas of Munger district, Bihar., with maximum electrode spacing (AB/2) of 250 m. VES data were interpreted to obtain layer parameters using modified inversion programme. The resistivity variations of different formations have been presented in the form of iso-resistivity contour maps at different depths from the surface. Drill log data were compared for understanding the resistivity range of different formations. The iso-resistivity maps have been interpreted for understanding the subsurace lithological variation and thereby relative groundwater potential zones of the area were estimated. Depth to groundwater level and water table contour map with groundwater flow directions during pre-monsoon period have been presented for better understanding of groundwater availability and sitting of dugwell and tubewell in the area.

4 illus, 1 table, 34 ref

007547   Olowofela J A (Phy Dep, Univ of Ibandan, Ibandan, Nigeria) : Location of hydrocarbon reservoirs by spontaneous potential method. Indian J Earth Sci 2003, 28(1-4), 51-4.

Presence of an electric field in the atmosphere is a well-documented fact. This field presents a source of constant electric field in the earth. Hydrocarbon reservoirs have always associated with them gas, water and hydrocarbon. Presence of gas in the reservoir which has a dielectric different from the adjoining rock matrix leads to an approximation of the reservoir to a dielectric sphere in the region of constant electric field. Analysis carried out show various potential of the area of the hydrocarbon reservoir shows minimum of anomally.

4 illus, 1 ref

007546   Mandal M;Mohanty U C;Potty K V J;Sarkar A (Centre for Atmospheric Sciences, Indian Inst of Technol, Hauz Khas, New Delhi-110 016) : Impat of horizontal resolution on prediction of tropical cyclones over bay of Bengal using regional weather prediction model. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 79-93.

Examined the performance of a regional atmospheric model in forecasting tropical cyclones over the Bay of Bengal and its sensitivity to horizontal resolution. Two cyclones, which formed over the Bay of Bengal during the years 1995 and 1997, are simulated using a regional weather prediction model with two horizontal resolutions of 165 kmand 55 km. The model is found to perform reasonably well towards simulation of the storms. The structure intensity and track of the cyclones are found to be better simulated by finer resolution of the model as compared to the coarse resolution. Rainfall amount and its distribution are also found to be sensitive to the model horizontal resolution. Other important fields, viz., vertical velocity, horizontal divergence and horizontal moisture flux are also found to be sensitive to model hiorizontal resiolution and are better simulated by the model with finer horizontal grids.

11 illus, 2 tables, 24 ref

007545   Maithani D D (H.N.B. Garhwal Univ, , Srinagar (Garhwal)) : Slope analysis and tectonic influence on the slope of lower Alaknanda basin, Garhwal Himalaya. Natn Geogr 2000, 35(1-2), 115-21.

Slope analysis of the lower Alaknanda basin of Garhwal Himalaya has been attempted using Raise and Henry's method and classified into six slope categories. Attempt has also been made to examine the tectonic influence on the slope i.e. steep slope has been noticed along the structure linement, while gently slope has been developed in the tributary valleys and on the summit surfaces.

3 illus, 1 table, 5 ref

007544   Mahajan R R;Murty S V S (Planetary and Geosciences Div, Physical Res Lab, Ahmedabad-380 009) : Laser microprobe for the study of noble gases and nitrogen in single grains: a case study of infividual chondrules from the Dhajala meteorite. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 113-27.

A laser microprobe capable of analysing nitrogen and noble gases in individual grains with masses less than a milligram is described. It can be used in both continuous wave (CW) mode, useful for stepwise heating of an indicidual grain, as well as in pulsed mode, useful for ablating material from a small selected area of a sample for gas extraction. Low blanks (in ccSTP units) for ⁴He(4.8x10^-12), 2²²Ne(1.0x10^-12), ³⁶ Ar(1.0x10^-13), 84^x Kr(2.9x10¹⁴), ¹³² Xe(2.6x 10¹⁴), and N (87 pg), using this system. Preliminary data for individual chondrules from the Dhajala meteorite show that noble gases and nitrogen from grains as small as 170 microgram can be analysed using the laser microprobe setup. The amount of trapped neon in Dhajala chondrules is very small, and nitrogen in the chondrules is isotopically heavier as compared to the bulk meteorite.

11 illus, 6 tables, 29 ref

007543   Kumar D;Ahmed S (Indo-French Centre for Groundwater Research, National Geophysical Research Institute, Hyderabad-500 007) : Seasonal behaviour of spatial variability of groundwater level in a granitic aquifer in monsoon climate. Curr Sci 2003, 84(2), 188-96.

Universal kriging technique with a linear drift was applied to analyse the available groundwater levels during different periods for one cycle during the year 2000. The bounded variograms, i.e. without the effect of a drift, were calculated using the directional variogram in the direction perpandicular to the major mean flow. All the variograms were then cross-validated to get final acceptable models for each time period. Subsequently, two variograms, one for the monsoon period with the presence of recharge component and the other for the non-monsoon period without the presence of recharge component were evolved. A common variogram was also determined to represent the average over all time periods. Cross-validation tests were done to check that the variograms representing monsoon and non-monsoon periods were able to reproduce field values for the corresponding periods more satisfactorily than a single common variogram. Thus application of geostatistics could be simplified for time-varying parameters such as water level.

5 illus, 4 tables, 22 ref

007542   Gupta S K;Deshpande R D (NO, Physical Research Laboratory, P O Box 4218, Navrangpura, Ahmedabad-380 009) : Dissolved helium and TDS in groundwater from Bhavnagar in Gujarat: unrelated to seismic events between August 2000 and January 2001. Proc Indian Acad Sci-Earth Planet Sci 2003, 112, 51-60.

Temporal variations have been observed in both dissolved helium and TDS in the form of increase in basaltic and decrease in alluvial aquifers. The increase in basaltic aquifers has been explained by enhanced pumping of old groundwater with relatively higher concentration of dissolved helium and salt, whereas the decrease in alluvial aquifers has been explained by dilution from the post monsoon groundwater recharge. Therefore, the observed temporal variations cannot be ascribed to the contemporary enhanced seismic activity in this region since August-September 2000.

4 illus, 2 tables, 16 ref

007541   Goswami B N;Rajagopal E N (Cen for Atmospheric and Oceanic Sciences, Indian Inst of Sci, Bangalore-560 012) : Indian Ocean surface winds from NCMRWF analysis as compared to quikSCAT and moored buoy winds. Proc Indian Acad Sci-Earth Planet Sci 2003, 112(Mar), 61-77 .

The quality of the surface wind analysis at the national Centre for Medium Range Weather Forecasts (NCMRWF), New Delhi over the tropical Indian Ocean and its improvement in 2001 are examined by comparing it with in situ buoy measurements and satellite derived surface winds from NASA Quik SCAT satellite (QSCT) during 1999, 2000 and 2001. The NCMRWF surface winds suffered from easterly bias of 1.0-1.5 ms^-1 in the equatorial Indian Ocean (IO) and northerly bias of 2.0-3.0 ms^-1 in the south equatorial IO during 1999 and 2000 compared to QSCT winds. The amplitude of daily variability was also underestimated compared to that in QSCT. In particular, the amplitude of daily variability of NCMRWF winds in the eastern equatorial IO was only about 60<3> of that of QSCT during 1999 and 200. The NCMRWF surface winds during 2001 have significantly improved with the bias of the meaqn analyzed winds considerably reduced everywhere bringing it to within 0.5 ms^-1 of QSCT winds in the equatorial IO. The amplitude and phase of daily and intraseasonal variability are very close to that in QSCT almost everywhere during 2001. It is shown that the weakness in the surface wind analysis during 1999 and 200 and its improvement in 2001 are related to the weakness in simulation of precipitation by the forecast model in the equatorial IO and its improvement in 2001.

13 illus, 33 ref

007540   Gopalswami P M;Kumar P E;Kulandaivelu A R (Chem Dep, Erode Arts College (Autonomous), Erode-638 009) : Quality of water in the Bhavani river. Asian J Chem 2003, 15(1), 306-10.

With a view to create awareness among the public about the quality of water in the Bhavani River, which is one of the important rivers of Tamilnadu, a study was been udertaken. The samples of water have been collected at varios points along the course of the Bhavani river from the Nilgiris to Bhavani Kuduthurai. The samples of water were colleged using standard procedural methods. The physicochemical analysis and biological examinations were extensively carried out on each sample using known standard methods. The results of these analyses point out the fact that the Bhavani river water is being highly polluted by letting out industrial effluents, industrial waste water, agricultural run off and sewage into the stream. The presence of inorganic ions such as hexavalent chromium, sulphate ions, etc., and biological waste has contributed to the pollution of the river water. As a result, water borne diseases have become common in this area and the raw water cannot be used as such for industrial purposes. The Bhavani river water should be treated properly and disinfected before being supplied for industrial purposes and human consumption.

2 tables, 9 ref

007539   Chakroborty A;Bhattacharya B (Geology Dep, Jogamaya Devi Coll, 92, S.P. Mukherjee Road, Kolkata - 700 026) : Evidences of faunal activities in the Talchir formation, Raniganj basin, Eastern India. Indian J Earth Sci 2003, 28(1-4), 55-6.

^ssc6 ref

007538   Bhattacharya D K;Barla V C (Post Graduate Geology Dep, Ranchi Coll, Ranchi - 834 008) : Geochemistry and petrogenesis of granitic rocks around hazaribagh, Jharkhand. Indian J Earth Sci 2003, 28(1-4), 38-45.

The granitic rocks occuring around Hazaribag include gneiss and granites. The latter being younger, though the former are abundant. Mineralogically they are granitic to granodioritic in composition and show characteristic of peraluminous S-type granites. Both of them show a limited range of variation in major and trace elements in terms of their chemistry. There is a depletion of CaO, MgO, FeO, TiO₂ Sr, V, Cr, Y, Zr and enrichment of Rb with increase in SiO₂. It is envisaged that partial melting of crustal rocks have generated the granitic melts. The latter have given rise to the granitic rocks of the area by a process of fractional crystallisation.

9 illus, 3 tables, 11 ref

007537   Bandyopadhyay D N;Ghosh A (Geological Sci Dep, Jadavpur Univ, Calcutta - 700 032) : Lithofacies analysis and palaeoenvironmental significance of Barakar and Barren measure formations of chati nala mccluskieganj, north karanpura coalfield, Ranchi district, Bihar. Indian J Earth Sci 2001, 28(1-4), 1-15.

Stratification, bedforms and facies assemblages establish that the Barakar and barren Messure formations were deposited in meandering and low sinuosity braided channels respectively. Fining upward sequences showing facies assemblages having ordered distribution of grain size along with characteristic palaeocurrent pattern, mud draped accretionary planes within sandy units and large clay plug deposits reasonably establish the sinuousity of the Barakar channels. Against this dominating fluvial framework the sediment column in Barakar at places are interspersed with coarser clastics deficient in plant and carbonaceous remains. Internal structures in different bed and bar forms in accompanying sediments bear the resemblance with those form in braided channel. Preponderance of trough cross-bed cosets reveal the dominant bed forms being the dunes in the Barren Measure where large-scale solitary sets of planar tabular cross-beds occurring either parallel or oblique to local current directions are respectively the medial and cross-channel bars. Small-scale planar tabular cross-beds were formed either from nuclei on cross-channel bars or migrating sandwaves at the shallower part of channels. Contrasting facies association characterizing the Kolpara section had been possibly the result of abrupt changes in slope and discharge triggered by syndepositional faulting. Major differences in facies assemblages of Barakar and Barren Measure Formations may be attributed to differential rate

5 illus, 1 table, 44 ref

006365   Tiwari A;Dube V S;SInha M N;Vineet Kumar (P G Dep of Geol, B N College, Patna-4) : Depositional environment of basal sandstones of Bhaunathpur, Garhwa, Jharkhand. J Indian Ass Sedimentologists 2001, 20(2), 151-65.

Basal sandstone of the Meso-Proterozoic Semri Group of te Vindhyan basin occupies the lower most horizons along with conglomerate and is exposed in and around Bhaunathpur, Garhwa District, Jharkhand. Textural, mineralogical and geochemical studies together with physical features of the sandstone indicate environmental condition of deposition. The bulk chemical compositions and mineralogy reflect the composition of weathering profiles mantling source rock, rather than bed rock. It is bi-to tri-modal, moderately well sorted, mostly slightly skewed, platykurtic and with high ZTR index. It has been derived from a distributive provenance. The overall study suggests a fluvial environmental condition of deposition.

20 illus, 4 tables, 57 ref

006364   Suresha K J;Srikantappa C;Shankara M A (Geo Dep, Mysore Univ, Manasagangotri, Mysore-570 006) : Retrograde metamorphism of charnockitic granulites around Dharapuram, Tamilnadu, India. Indian Mineralogist 2002, 36-37(2,1), 94-101.

Retrograde metamorphism of charnockitic granulites is recorded all along the Dharapuram shear zone in Tamil Nadu. Charnockitic granulites show evidence of bleaching and retrograde metamorphic alterations along ductile and ductile/brittle shear zone either along the shears parallel to foliation or cross cutting the regional fabric. Petrographic study shows alteration of orthopyroxene into secondary biotite and anthophyllite. Plagioclase shows alteration to epidote and chlorite. Both quartz and plagioclase show innumerable micro-fractures and quartz grains show recovery and recrystallization, exhibiting polygonal and sutured grain boundaries. Co₂-rich and mixed CO₂-H₂O inclusions are recorded in both the charnockitic granulites and gneiss. Based on the intersections of co-existing CO₂ and CO₂-H₂O inclusions in retorgressed gneiss, their entrapment pressures is estimated at 1.5 to 2.4 Kb at temperatures of 250°C to 400°C. Presence of empty inclusions in some of the gneisses with in the Dharapuram shear zones is attributed to removal of fluids during ductile/ductile to brittle shear deformation

6 illus, 1 table, 8 ref

006363   Sreedevi P D;Srinivasulu S;Kesava Raju K; Srinivasa Gowd S (Department of Geology, S V University, Tirupati-517 502) : Evaluation of land resources in Pageru river basin by using remote sensing data. Indian J agric Res 2002, 36(2), 71-9.

The land use/land cover classification of Pageru river basin was done with the help of IRS-1B-LISS II FCC on 1: 50,000 scale by visual interpretation techniques and in conjunction with SOI topo sheets (57 J/6, 7, 10 and 11). Based on the remote sensing data, the land use/land cover patterns were interpreted. The built-up land in the basin area is only 1.02 per cent, while agricultural land occupies a large area covering 72.92 per cent. The double cropped area is very limited occupying 3.18 per cent only. The area under degraded/open forest occupy only 3.99 per cent and the waste lands occupy 14.42 per cent. The area occupied by surface water bodies is only 1.97 per cent and the grass land/grazing land occupies 2.04 per cent. Even though the agricultural land available in the basin area is substantial, the total land could not be brought into cultivation due to meagre surface and groundwater resources present in the catchment area.

3 illus, 2 tables, 4 ref

006362   Sinha D K;Niranjan Kumar S;Saran V;Fahmi S (Atomic Minerals Directorate for Exploration and Research, , 5/496 Pratapnagar-Sanganer, Jaipur-303 906) : Association of uranium with organic matter and clay in quartz arenite of bundi hills sandstone formation of bhander group, near Arnetha and Pancholas, Bundi and Sawai Madhopur districts, Rajasthan. J Indian Ass Sedimentologists 2001, 20(2), 141-50.

Bundi Hill formation of Lower Bhander Group, Vindhyan Supergroup, exposed near Arnetha and Pancholas villages of Bundi and Swami Madhopur districts, contains quartz arenite with shaly intercalations. In Arnetha, quartz arenite comprises of monocrystalline quartz, subordinate amounts of coarse chert and altered alkali fieldspars. Matrix of clay occupies interstitial spaces. Pyrite and organic matter (OM) are randomly distributed throughout the rock. Euhedral to subhedral pyrite occurs as single sporadically distributed grains and clusters. OM is finely distributed in the rocks and also as fracture fillings. Lower density alpha tracks are observed on CN film. These tracks correspond to OM at Arnetha, which indicates that uranium is adsorbed on OM. Alpha tracks corresponding to clayey cement are dispersed throughout the cement at Pancholas. Organic matter is absent in this locality. Presence of low density tracks pertaining to low grade uranium mineralisation at Arnetha and at Pancholas with negligible thorium is significant in this geological setup, which is favourable for Proterozoic Unconformity Related Uranium Deposit (PURUD). These preliminary features are important for the search of PURUD in the environs of Vindhyan basin.

10 illus, 2 tables, 6 ref

006361   Singh A K;Vallinayagam G (Earth Sci Dep, Kurukshetra Univ, Kurukshetra-136 119) : Petrochemical characteristics of acid volcanics from Kundal area, Barmer district western Rajasthan. Indian Mineralogist 2002, 36-37(2,1), 1-12.

The acid volcanics exposed in the Kundal area are trachyte, rhyolite (porphyritic, non-porphyritic), welded tuff and volcanic ash flow. Trachyte flow is associated with rhyolite. Volcanic ash bed with rhyolite agglomerate exposed within the trachyte flow. Minor amount of welded tuff which are streaky in nature, associated with rhyolite is also encountered. Occurrence of xenoliths of basic rocks within the acid volcanics suggests the younger nature of acid volcanics. The porphyritic rhyolite has affinity to peraluminous and non-porphyritic rhyolite has affinity to peralkaline. Hornblende and muscovite are present in peraluminous type whereas alkali amphilole and alkali pyroxene are present in peralkaline rhyolite type. The former has normative corundum and anorthite (<60>1AI) and latter has acmite normative (<62>1AI). Acid volcanics are high in SiO₂, Na₂O, K₂O, Zr, Nb, Y, REEs (except Eu) and low in MgO, Fe₂O₃ (t), CaO, Cr, Ni, Sr, Eu indicating that they are A-type and anorogenic in nature. They are also high potassic volcanic rocks. Geochemical characteristics suggest their crustal origin.

5 illus, 2 tables, 14 ref

006360   Sharma D P;Jayasheela H K (Geo Studies Dep, Karnataka Univ, Dharwad-580 002) : Geochemistry and grade distribution pattern and controlling factors of phosphorite deposit at Jhamarkotra, Rajasthan. Indian Mineralogist 2002, 36-37(2,1), 85-93.

Phosphorite occurring at Jhamarkotra of Udaipur region is apparently found in seven forms viz., stromatolite (Columnar structures), bedded, pelletal, modular, brecciated, fragmental and botryoidal. Several varieties of apatite viz., flour-apatite, chlor-apatite, hydroxyapatite, carbonate-apatite and oxy-apatite (voelckerite) are reported. A general formula may be written as Ca₁₀(PO₄, CO₃)₆ (F, Cl, OH)₂. Apatite is the primary mineral, but a number of other minerals are common in deposits formed during weathering of phosphate rock and guano. Phosphorite exhibits a variable chemical composition. A general bimodal character of the grade of the ore with distinct P₂O₅ percentage is indicated in the selective association of relatively high silica and extremely low MgO content in the high-grade ore, while there is an inverse relation in the low-grade ore. Weathering appears to be the most important factor causing enrichment of grade. Besides weathering, the dense population of the stromatolite per unit area also has a bearing on the grade variation.

2 illus, 3 tables, 11 ref

006359   Roy S;Banerjee S (Dep of Earth Sci, IIT Bombay, Powai, Mumbai-400 076) : Facies and petrography of the porcellanite formation around Chopan, Uttar Pradesh. J Indian Ass Sedimentologists 2001, 20(2), 195-205.

The Paleoproterozoic Porcellanite Formation of the Semri Group, Vindhyan Supergroup, consists dominantly of pyroclastics. The formation is well exposed and considerably thick (205 m) south of Chopan, U.P. Presence of abundant pumice, euhedral quartz grains, presence of magmatic corrosion within quartz and feldspar crystals, euhedral and zoned magmatic zircon crystals within the constituent facies indicate its volcanic affinity. Seven distinct lithofacies have been identified in the area. They are alternate dark and whilte banded facies, clast rich facies, shale facies, thick-bedded facies, lapilli bearing facies, crudely stratified facies and chert facies. Presence of outsized bombs (upto 45 cm) within the lapilli rich facies indicates its near vent origin. Inferred depositional environment vary from subaqueous to subaerial. Survival of delicate pumice suggests deposition in a less agitated environment like lake or lagoon. This intrabasinal volcaniclastic product has been correlated with major rifting phase of the Vindhyan.

12 illus, 20 ref