005161   Mangotra S R;Prabhakar V;Sarkar J;Rana B S; Jitendra Prasad (Regional Laboratory, , Couvery Basin, Oil and Natural Gas Corporation Ltd (ONGC), No. 3, First Lane, Gowri Building, N.H. Road, Chennai-600 034, Email: mangotra_sr@ongcl.com) : Geochemical studies in Ramnad-Palk bay sub-basin and their implication for exploration. J appl Geochem 2006, 8(2A), 299-319.

Study makes an attempt to understand genesis, expulsion and migration of gaseous hydrocarbons in Ramnad -Palk way area of Cauvery basin, India. The maturity of gases of Ramnad sub-basin is in the range of 0.9-0.95  vitrinite reflectance (VRo) equivalent on the basis of composition and isotopic values. The maturity of condensate associated with these gases on the basis of Methyl Phenanthrene Index (MPI) is 0.9 VRo equivalent and appears to have been generated by a gas prone source facies. The API gravity of condensates and methane content in gases show increasing trend with shallowing of depth of reservoirs. This is probably a result of migration/phase fractionation from possible source rocks of Albian to Pre-Albian age and effect of higher maturity of 1.3 (VRo) is ruled out. Presence of mature source rock layers and hydrocarbons is observed near the area in Palk Bay where basin fill is of more than 4km thickness. Biomarker fingerprints and isotopic data of oils and oil to source correlation studies suggest localized generation and migration of the hydrocarbons in PH-I and PH-K areas. In Ramnad area, the producing wells are all aligned in a linear trough which overlies an area, where presence of source rock is also anticipated on the basis of seismic in synrift sediments. The wells drilled in the flanks of trough have not encountered any hydrocarbon and significant mature source facies. This may suggest localized generation and migration of hydrocarbons in Ramnad sub-basin similar to Palk-Bay area.

17 illus, 6 tables, 21 ref

005160   Malkovsky V I;Pek A A (NO, Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetny per., 35. Moscow-119 017, Russia, Email: malk@igem.ru) : Influence of density-driven flow on stabilization of contaminant plume in natural traps. J appl Geochem 2006, 8(2A), 578-88.

Initial position of the plume was determined in accordance with the data obtained from tritium tests, The simulation shows that contaminant moves north- and eastward with time. More dense solutions move predominantly northward (down the clip of the aquifer) whereas dilute solutions of lower density flow eastward to the zone of decreased hydraulic resistance of the confining layer between Horizons I and II. It follows from the mathematical model of the process that contaminant migration velocity increases with an increase in transmissivity of the aquifer and a decrease of its porosity.

8 illus, 11 ref

005159   Jayaprakash C;Maran N;Kalluraya V K K;Dinesh A C (NO, , Geological Survey of India (GSI), WCO-1, Mangalore, Email: jayaprakashc@hotmail.com) : Temporal variations of major oxides, carbonate and trace metals around Kavaratti Island, Lakshadweep. J appl Geochem 2006, 8(2A), 407-16.

Five gravity core samples varying in length between 1.69m and 1.93m were collected from northwest to southeast of Kavaratti island at water depths ranging between 1747m and 2083m. from the Lakshadweep Ridge domain. The seafloor around the island is blanketed by brown to olive brown non-sticky hemi-pelagic clay with abundant foraminiferal tests Geochemical studies were undertaken on these five cores using the sub-samples collected from the top. 50 cm, 100 cm. 150 cm and from the bottom. The down core variation of SiO₂. AI₂O₃ and Fe₂O₃ follows sympathetic trend in all the cores. The SiO₂ content of the sediments ranges between 9.09 % and 36.96 %. Al₂O₃ between 2.28 % and 10.98 %, Fe₂O₃ between 1.48 % and 6.47 % and the Mn content between 208 ppm to 1608 ppm. The high Mn values can be attributed to the oxidizing bottom waters present in the area. The Readily Oxidisable Organic Matter (ROOM) content in the sediments varies from 0.67% to 1.57% and shows sympathetic relationship with other major oxides. The SiO₂ in sediments is principally contributed by terrigenous clay with negligible contribution from sand grains, radiolarian and silicoflagellate tests, whereas Al₂O₃ is wholly contributed by the clay minerals of terrigenous origin. In view of the absence of any Fe- bearing detrital minerals in the area, the iron associated with the sediments would have mainly derived from terrigenous clay minerals and a part also by the hydrothermal solutions. The CaCO₃ content ranges between 29.98 % and 77.49 % and shows an inverse relation to the major oxides. The CaCO₃ is contributed by foraminiferal tests as well as by the algal ridges. The vertical variation pattern of Cu, Zn, Ni and Cr show similarity. Sr shows antipathetic relation with the above trace metals. The chemical study of the gravity cores depicts changes in the sedimentological as well as geochemical cycle. Since SiO₂ and A1₂O₃, are mostly contributed by the terrigenous sediments, their progressive decrease from the bottom of the core to the top illustrates a corresponding reduction in the terrestrial supply. The break is more prominent towards the top of the sediment column starting from 100cm below the seabed. This trend is also imitated by trace metals such as Cu, Zn, Ni and Cr. Calcium carbonate follows a reverse trend and gets enriched towards the top of the sediment column. Since the CaCO₃ in the sediments is partially contributed by the break down of the algal ridges due to wave activity, its increased content in the sediments towards the top of the sediment column may imply an increasing order of destruction of the coral reeves in the area. On the contrary a flourished marine fauna also would have resulted in an increased supply of CaCO₃ in the sediments which in turn would have resulted in the dilution of the terrestrial borne sediments.

13 illus, 3 tables, 10 ref

005158   Dhana Raju R (Applied Geochemistry Dep, Honorary Visiting Professor, Osmania Univ, Hyderabad-500 007, Email: rdhanaraju@yahoo.co.in) : Geochemistry of the peninsular gneiss (PG) and closepet (EQ.) granite in the Rayachoti area, Andhra Pradesh, India : its implication of the concepts of age-zonation of PG in the Dharwar craton and 'Dharwar batholith'. J appl Geochem 2006, 8(2A), 558-77.

In the Dharwar Craton (DC) of southern India, Peninsular Gneiss (PG) is the most widespread gray granitic complex, occupying vast terrains in both the Western and Eastern DC (WDC and EDC). The Closepet Granite (CG) and its equivalents (Eq.) occur as several parallel linear bodies in EDC. Both PG and CG (Eq.) occur together in the southwestern environs of the Cuddapah basin in the Rayachoti area of Cuddapah district, Andhra Pradesh, and their geochemistry, along with their field and petrological aspects, is critically examined in this paper. Geochemically, PG compared to CG (Eq.) in the area is (a) marked by-relatively lesser silica, potash, Rb and U, and higher Fe, Mg, Ca, Na, Sr, Ni, Cr, V. Sc and Ce; (b) sodic, high-calcic, metaluminous to weakly peraluminous (A/CNK: 0.94-1.15) type as against potassic. low-calcic and strongly peraluminous (A/CNK: 1.08-1.42) nature of the latter; (c) tectonically of a continental/island arc type against continental collision type of the latter; (d) of<126>3.6 Ga old single-grain zircon LAM-ICPMS concordant U-Pb age (from the nearby Kalyandurg area) as against as 2.5 Ga Rb-Sr whole-rock isochron age of CG (Eq.); (e) formed from a granitic melt, produced by partial melting of basic rocks present as xenoliths in it, whereas the highly fractionated CG (Eq.) appears to have formed by partial melting of PG; and (f) essentially I-type, magnetite series 'hornblende granodiorite-tonalite' with CG (Eq.) being S-type, ilmenite series mica 'monzo-/syeno-granite'. These marked differences between PG and CG (Eq.) are also reflected in their contrasting field setting and petrography. The cumulative studies thus invalidate the hitherto held concepts that the (i) age of PG in WDC is older than that in EDC; (ii) crude isotopic age-zonation in PG from west to east in DC, reflected by <126>3.4 Ga gneisses in the Gorur-Hassan area in WDC as against <126>2.7 Ga gneisses to the east of CG in EDC; and (iii) late Archaean 'Dharwar batholith in EDC as a single unit that encompasses both PG and CG together. The radio-isotopic data rather indicate that the oldest PG in both WDC and EDC is of Mesoarchaean age (<126>3.4-3.6 Ga).

8 illus, 5 tables, 36 ref

005157   Datta G C;Sivan P;Sharma R;Bhatnagar A K (NO, , K.D.M.I.P.E., Oil and Natural Gas Corporation Ltd. (ONGC), Dehradun-248 195, Email: gourdatta@yahoo.com) : Organo-sulfur and pyrrolic nitrogen compounds in crude oils of Mumbai offshore basin. J appl Geochem 2006, 8(2A), 251-65.

Presents geochemical investigations of several aromatic biomarkers in the crude oils from Bombay High, northwest of Bombay High and Bassein area of the Mumbai Offshore Basin, in order to understand the paleoenvironment, thermal maturity level of their source rocks and also to trace secondary migration pathways. Dibenzothiophene to phenanthrene (DBT/Phe) parameter represents the ratio of organo-sulfur compounds present in the oils. Low ratios indicate that the oils have been generated from the clastic terrestrial sources where as the high ratios indicate mixed source inputs predominantly marine. This ratio ranges from 0.09 to 0.87 for studied oils suggesting a wide variation of fades and depositional environments. The cross plot of DBT/Phe and pristane/phytane (Pr/Ph) ratios shows that the oils of northwest Bombay High and Bassein were generated from predominantly terrestrial organic matter deposited in suboxic to oxic conditions. The oils from west of Bombay High, Wedge Out structures and Bombay High were derived from mixed source input with lateral variations in redox conditions. On the basis of trimethylnaphthalenes. tetramethylnaphthalenes and other geochemical data the Mumbai Offshore basin oils were classified into different groups. The aromatic maturity parameter reveals that the oils have been generated at early to peak oil window (VRc 0.65 to 0.90%). The concentration of pyrrolic nitrogen compounds, low in Bombay High oils and higher in oils from Bassein area, Wedge Out structures and northwest of Bombay High, suggest that Bombay High oils have undergone a long distance migration as compared to Bassein, Wedge Out and northwest of Bombay High oils.

8 illus, 3 tables, 20 ref

005156   Das M (Petroleum Technology Dep, Dibrugarh Univ, Assam) : Clay minerals and their influence on hydrocarbon production potential of Tipam reservoir sands in Jorajan oil field, Assam basin, India. J appl Geochem 2006, 8(2A), 266-76.

Clay minerals have a definite role in modifying the reservoir properties of reservoir rock. This study is mainly based on analysis of clay minerals of Tipam reservoir sands in Jorajan oilfield. The study reveals that both allogenic and authigenic clays are present in the Tipam reservoir sands. Smectite and kaolinite are the dominant and most frequently occuring clay minerals found in the matrix of these reservoir sands, Illite. chlorite and mixed layers are also present in small amounts. Grains, pores and channels are coated with clays. The high degree of clay coatings over the detrital grains result in an extremely high surface area of the pore-system which creates porosity and permeability variation in the Tipam reservoir sands. This clay coating also increases the irreducible water saturation zone which in turn lowers the resistivity of the oil bearing sands. The nature and abundance of clay minerals affect the oil potentiality of the formation of the study area.

4 illus, 14 ref

005155   Das Gupta S C (NO, , Coal Wing (OP), Geological Survey of India, Kolkata) : Perspective of exploration and resource evaluation of coal bed methane (CBM) in India vis-a-vis the role of the geological survey of India. J appl Geochem 2006, 8(2A), 359-65.

Coal Bed Methane(CBM). an alternate source of energy, is a clean and eco-friendly gas. Its extraction from the coal bed . sections not only augments energy resources, but also keeps the source coal bed intact in place for future mining. Further the risk of gas explosion in the coal bed. from which the gas has been drawn, is alleviated. Viewing the global scenario, it is noted that only a few major coal-bearing countries like USA, Russia, China, Australia, Poland. U.K.. Germany, and lately. India have taken keen interest in the exploration and development of CBM gas. USA, the forerunner, had initiated its venture in exploration and development of CBM as early as in 1970s and worked out a resource of 400-700 TCF of gas from two major and a few minor coalfield areas. The other countries are also following the USA to make headway. India is endowed with a resource of 247 billion tonne of coal with 38% (94 billion tonne) lying in the depth range of 300 to 1200m below the surface. The coal occurs mainly within the Lower Gondwana sequence in the eastern and southeastern parts of the country. A conservative gas-in-place resource of 564 billion cubic metres of CBM gas has been prognosticated from the major coalfields of India. Presently, the CBM activities in the country are limited to sinking of several exploratory wells in parts of Damodar valley areas and Sohagpur Coalfields by ONGC and other agencies: the commercial production of gas is yet to come. The Geological Survey of India (GSI). since its inception in 1851, had initiated activity in the search and exploration of coal. On the basis of most of exploration done by the GSI. coal resource of the country could be established at 247 b.t. It is now felt that the GSI has to play a significant role in the exploration and evaluation of CBM. In fact, the basic documents prepared on various coalfields by the GSI at the instance of the Directorate General of Hydrocarbons (DGH) laid a foundation for lessing out the blocks by the DGH to private bidders for CBM exploration and development. Formation of methane gas in viable quantity in a particular coal bed is much dependent on-thickness of the coal bed, degree of coalification/rank of the coal, its depth of occurrence, permeability, etc. Keeping these basic precincts in view, the GSI. in association with some other nationalised organizations, has taken up CBM studies in the country. The drill-core samples of coal collected during the course of regional exploration by the GSI are being examined in various ways-petrography including micro-cleat/fracture determinations, reflectance and maceral study, chemical analyses of samples for determination of ranks, gas desorption studies, etc. From certain coalfields like Raniganj, Rajmahal, Birbhum, East Bokaro, Sohagpur, etc.. the data generated in respect of CBM gas by direct measurement in GSI boreholes indicated gas content of 0.14 to 12.70 cubic metre/tonne.

3 tables, ref

005154   Chaudhuri S N;Datta D R;Datta A (NO, , Geological Survey of India, Coal Wing, Saltalake, Kolkata) : Petrographic characteristics and depositional environment of early permian coals of Ramkola-Tatapani coalfield vis-a-vis coal bed methane. J appl Geochem 2006, 8(2A), 366-75.

The two most important variables e.g. petrographic composition and rank character (by vitrinite reflectance %) influencing the qualitative character of the coal seams in parts of Tatapani-Ramkola coalfield of the Son valley area were studied in delail. The coal seams in Tatapani basin (Meghuli area) show higher vitrinite and low exinite compared to coal seams of Ramkola basin (Sondiha area), which are characterised by high inertinite and exinite content. High mineral and shaly matter in the seams attribute to high ash content in the seams of both the blocks. Potentiality for Coal Bed Methane (CBM) depends mainly on coal characteristics viz. rank, composition and permeability. The amount of CBM entrapped in a coal bed is a joint function of depth, seam thickness, rank and petrographic composition of coal seams. Bulk of methane gas remains adsorbed in the micropore or intermolecular space of coal. More the internal surface area of these micropore, more is the adsorbtion capacity of the coal. Compositionally vitrinite has a greater proportion of micro pores and more surface area and thus a higher methane adsorption capacity. Minor portion of methane is held within the macroporocity i.e. cleat and fracture network of the coal seam, mostly as free gas. Seam thickness, its lateral continuity and depth of occurrence are important parameters from CBM point of view. The coal seams of Meghuli area of Tatapani Coalfield show gradual increase in oil reflectance values from 0.48 to 0.56% along depth from 9.53 to 200.58m. This suggests coalification gradient of 0.04%/100m. In Sondiha area of Ramkola Coalfield the oil reflectance value increases from 0.43 to 0.51% in one borehole along depth from 72.75 to 182.05m and from 0.42 to 0.55% in other borehole along depth from 79.22 to 204.63m. The coalification gradient is computed to be 0.09%/100m which is higher than that of Tatapani block. This range of 0.04-0.09%/100m is comparable with that of other areas of moderately high rank coal (e.g. Sohagpur Coalfield) and is implying that higher geothermal gradient influenced coalification in the basin. Although the rank character of Ramkola-Tatapani Coalfield is not very encouraging in the CBM point of view so far studied, better rank coal can be expected at the deeper part of the basin. Favorable petrographic composition of coal seams represented by thick vitrite bands at greater depths in Sondiha area could possibly be a potential. Coal facies analysis suggests defferent level of bio chemical degradation under different palaeo environment and sub environments that had influenced the gross petrographic composition of the seams. On the basis of relationship between coal facies indices and petrographic characteristics, a few coal seams of Meghuli area of Tatapani basin showing higher reactive constituents were formed under palaeoenvironments indicating high to low TPI (Tissue Preservation Index) and GI (Gelification Index). The depositional milieu for peat formation in the basin is interpreted from microlithotype assemblages. This indicates that the deposition was mainly under fluvio-deltaic plain environmental set up. Vitrinite and exinite content, in general appears to be higher in upper delta setting compared to lower delta plain which shows diminution of inertinite, inertmediates and mineral matter content. The upper delta plain setting is more fluvial, dominated and characterised by fresh ground water condition with no marine influence. The biochemical coalification was thus influenced by elevated (neutral to just alkaline) pH. This alkaline environment favored growth of bacteria, promoted decomposition and led to higher gelification. It further set the process of vitrinisation as observed in seams of sondiha area.

6 illus, 3 tables, 17 ref

005153   Bhishm Kumar;Rai S P;Nachiappan R P;Saravana Kumar U;Surjeet Singh;Diwedi V K (NO, National Institute of Hydrology, Roorkee-247 667, Email: bk@nih.ernet.in) : Sedimentation rate in North Indian lakes estimated using <. Curr Sci 2007, 92(10), 1416-20.

In the present study, recent sedimentation rates in Na-inital. Bhimtal, Sattal and Naukuchiatal lakes, Uttara-khand; Mansar and Dal lakes, Jammu and Kashmir, and Sagar and Bhopal lakes, Madhya Pradesh have been determined employing ²¹⁰Pb and ¹³⁷Cs dating techniques. The results indicate comparatively higher sedimentation rates in certain western Himalayan lakes such as Dal, Nainital and Bhimtal than in Sattal, Naukuchiatal and Mansar. The Bhopal lake is getting silted at a higher rate than the Sagar lake. The observed sedimentation pattern reveals that sedimentation rate decreases from near-shore to far-shore and is a minimum at the central and deepest part in lakes of western Himalayas, while Sagar and Bhopal lakes have a different pattern of sedimentation.

4 illus, 2 tables, 18 ref

005152   Bhatnagar A K;Bisht R S;Goswami R G;Dutta G C;Singh R R (NO, , K.D.M.I.P.E., Oil & Natural Gas Corporation Limited (ONGC), Dehradun-248 195, Email: ashok_suman@rediffmail.com) : Geochemical characterisation and oil - source correlation studies in south Cambay basin, India. J appl Geochem 2006, 8(2A), 332-58.

Geochemical studies in Gandhar and Nada area reveal that source rock potential and organic matter richness is high in shale sections in Hazad, Cambay Shale and Olpad formations. In Broach block, Cambay shale and Olpad sediments in the western flank were deposited in sub-oxic environment with mixed source input while in the basinal areas, these sediments were deposited in sub-oxic to anoxic environments having mixed source input and experienced more marine influence. The Hazad sediments in Broach block and Cambay Shale and Olpad sediments in Narmada block, deposited in sub-oxic environment, have more terrestrial input. Cambay Shale and Olpad sediments in Broach block are sufficiently mature while these sediments in Narmada block and Hazad sediments in Broach block have just entered the oil window and are in early catagenetic stage. Western flank oils of Nada and South Malpur of Broach block have been generated by mixed source facies deposited in sub-oxic environment. The oils of central and eastern fields of Broach block (Gandhar, Dahej, Pakhajan, Dabka and Padra) and Ankleshvar and Kosamba fields of Narmada block have been generated by mixed source facies deposited in sub-oxic to anoxic environment. All the studied oils are of moderate maturity. The oils of South Cambay basin are clubbed in three groups (1) Western group oils of Nada and South Malpur of Broach block, (2) Central and eastern group oils of Gandhar, Dahej. Pakhajan. Dabka and Padra of Broach block and Ankleshvar and Kosamba oils of Narmada block and (3) Jambusar oils in North-central part of Broach block. Oils of Nada and South Malpur show correlation to the source sequences of Cambay shale and Olpad formations of Nada-A(3400-3800m) and Barkhodra-A(2900-3200m). Oils of Gandhar, Dahej, Pakhajan, Dabka and Padra fields of Broach block and Ankleshvar and Kosamba fields of Narmada block correlate with source rocks of Cambay Shale and Olpad formations ftom wells Gandhar-A(3300-4000m) and Dahej-A (3250-3700m). The Jambusar oils do not correlate with source sequences of western flank and south-central part of basinal area of Broach block. These may have localized contribution from north-central part of Broach block. Ankleshvar and Kosamba oils do not match with source sediments of Narmada block. The depocenters of Narmada block are relatively small and good source rocks with adequate maturity did not develop. Hence. Narmada block reservoirs were possibly charged from Broach and Tankari depressions of Broach block. The study suggests that main centers for hydrocarbon generation were in Tankari and Broach depressions from where the oil migrated to central and eastern fields of Broach block and also migrated to the Narmada block reservoirs probably along the faults. Western flank oils and north-central oils from Broach block were generated within the localized depressions.

20 illus, 4 tables, 15 ref

005151   Balaram V (NO, National Geophysical Research Institute, Hyderabad-500 007, Email: balaramv1951@yahoo.co.in) : Exploration for platinum group elements (PGE) in peninsular India - status, problems and scope. J appl Geochem 2006, 8(2A), 441-57.

Discovery of new platinum group of elements (PGE) desposits/mineralized zones is of great economic importance for the country. An account of the formation mechanisms of different PGE deposits and their reported occurrences across the world are presented. In India till date only the Baula-Nuasahi layered Complex in Orissa, mafic-ultramafic Hanmalapura Complex in Karnataka, and the layered Sittampundi Anorthosite Complex in Tamil Nadu, are the three known promising PGE occurrences. Recent studies show that there is a tremendous potential for PGE-mineralisation in mafic-ultramafic complexes, ophiolite complexes and the fine grained sediments such as sulfide bearing black shales, occurring in different parts of our country. Determination of PGE at extremely low concentrations with the accuracy and precision and at high throughputs required for exploration studies needs optimization of critical steps such as selection of a representative sample and application of sensitive analytical techniques, etc. For identifying economically viable deposits and their mining, detailed geological, petrological and geochemical studies are essential on massive potential areas. These aspects are discussed in detail with examples.

5 illus, 8 tables, 56 ref

004289   Yadava M G;Ramesh R;Pandarinath K (Planetary and Geosciences Div, Physical Research Laboratory, Navrangpura, Ahmedabad-380 009, Email: rramesh@prl.res.in) : Positive 'amount effect' in the Sahayadri (Western Ghats rainfall. Curr Sci 2007, 93(4), 560-4.

Authors present stable oxygen isotopic ratios (δ¹⁸⁰) of rainfall collected over three years (July to October 2000-02) at Mangalore. Authors observe an apparent positive correlation between the monthly, amount-weighted mean oxygen isotopic ratio of the rainwater and monthly total rainfall, contrary to the generally expected negative trend in many island and continental stations. We offer an explanation for this observation and propose that the 'amount effect' in the annual rainfall still remains with a negative slope, and thus can be useful in palaeomonsoon reconstruction using oxygen isotopic variations of annually laminated speleothems.

3 illus, 23 ref

004288   Yadav D N;Sarin M M;Krishnawami S (NO, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, Email: dny@apsara.barc.ernet.in) : Hydrogeochemistry of Sambhar salt lake, Rajasthan: implication to recycling of salt and annual salt budget. J Geol Soc India 2007, 69(1), 139-52.

Geochemical analysis of groundwater samples and brines from the Sambhar Salt lake shows a predominance of NaCl with respect to total salt content (TDS), which varies from 0.5 to <126>400 g/L. All brine (lake + shallow sub-surface) samples indicate a Na-Cl type alkaline solutions with pH varying from 8.5 to 10. All this suggests a general provenance for halite or dissolution of desiccated salt minerals in the catchment and drainage areas of the lake. Adjacent groundwaters are mostly neutral Na-Cl type with TDS ranging from 0.5 to 13 g/L. In contrast to groundwaters, the river waters from Roopangarh and Mendha reflect that out of the TDS, the major ions constitute Na, Alk and Cl with an average equivalent Na/Cl ratio of 2.7, indicating dissolution of Na from silicate weathering of rocks. However, the lake water composition overwhelms the river water upon mixing during the recharge period. A complete annual wetting and drying cycles of evolution of lake brine shows generation of Na-Cl type of brine with steady increase in major ions except Ca and Mg ions which decrease in successive stages of evaporation. Relative change in Na and Cl ions is also observed during the late stage of evaporation at or beyond halite saturation stage. Observation of such chemical change in brine composition is in line with the identification of salt minerals in lake sediments and salt encrustation by XRD technique. In present-day hydrologic set-up, the estimated salt inventory in lake is <126>10⁶ tons as compared to riverine input of 6xl0⁴ tons and an upper limit of aeolian input of about 5xl0⁴ tons. Such an estimate indicates that majority of salt is derived from the recycling and re-solution of salt encrustation from the lake bed during recharge period.

6 illus, 8 tables, 26 ref

004287   Vijaya Rao V;Sain K;Rajendra Prasad B (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: vijayraov@yahoo.co.in) : Dipping Moho in the Southern part of Eastern Dharwar craton, India, as revealed by the coincident seismic reflection and refraction study. Curr Sci 2007, 93(3), 330-6.

Seismic reflection study along the Kuppam-Bommidi profile in the Southern Granulite Terrain (SGT) shows a south-dipping Moho extending from 10.5 to 14.5 s two-way time in the southern part of the Eastern Dharwar Craton (EDC), which corresponds to a depth ranging from <126>34 to <126>46 km. A similar Moho feature is also observed from the seismic section of the coincident refraction study. The Moho depth is also constrained by gravity data and other seismic studies of the region. Presence of such an unusual Moho feature in the Archean terrain is due to thermal and tectonic stability of the craton. In contrast, the reflection Moho could not be observed in the Mettur Shear Zone, located further south of the EDC. This may be due to crustal structure developed during the Proterozoic tectono-thermal activities in the SGT. However, the refraction study suggests a Moho depth of <126>42 km for the SGT along the profile. The Moho seems to be a lithological boundary in the EDC, whereas it is a rheological boundary in the SGT. The present study demonstrates the complimentary nature of reflection and refraction datasets and usefulness of the coincident study.

8 illus, 27 ref

004286   Vashisht A K;Sharma H C (Irrigation and Drainage Engineering Dep, G.B. Pant Univ Agriculture and Technology, Pantnagar-263 145, Email: akvashisht74@yahoo.com) : Hydrological behaviour of a natural spring. Curr Sci 2007, 93(6), 837-40.

In the middle and greater Himalaya, natural springs are the main source of domestic water consumption, but their discharge does not remain constant with time. Erratic rainfall directly affects the recharging of the spring catchment. In this communication, the behaviour of a perennial spring with rainfall variation is analysed from eight years' data recorded daily. It is concluded that the time required for the water from the remotest part of the feeding catchment of the spring to reach the outlet (time of concentration) is equal to 57 days.

6 illus, 1 table, 7 ref

004285   Tiwari M;Ramesh R (Planetary and Geosciences Div, Physical Research Laboratory, Ahmedabad-380 009, Email: manish@ncaor.org) : Solar variability in the past and palaeoclimate data pertaining to the southwest monsoon. Curr Sci 2007, 93(4), 477-87.

Significant part of the earth's climate variability is caused by changes in the solar emission. Instrumental observation of the sun gives us some idea about decadal variability in the solar radiation. On longer timescales, author look to palaeoclimate proxies to learn about solar variability. In this review authors discuss various palaeo-records and what author have learnt from them. In addition, author outline important questions that need to be addressed.

8 illus, 80 ref

004284   Thakur S S;Patel S C (Earth Sciences Dep, Indian Institute of Technology, Powai, Mumbai-400 076, Email: satyajeet@iitb.ac.in) : Low pressure granulite facies Sukma supracrustal rocks near Nagaras, Southern Bastar craton. J Geol Soc India 2007, 69(1), 75-9.

This communication discusses the metamorphism of low pressure granulites in the Sukma supracrustal suite near Nagaras in the southern Bastar craton. The area shows occurrence of Mg-Al rocks of both amphibolite and granulite facies. Amphibolite facies Mg-Al schist usually contains cordierite and a low-Ca amphibole, which is commonly cummingtonite and rarely gednte. Low-Ca amphibole and sillimanite are never found together in the same rock. Mg-AI granulite is characterised by the presence of orthopyroxene in lieu of low-Ca amphibole. Most of the Mg-Al rocks are silica saturated.

3 illus, 9 ref

004283   Sridharan S;Muthuchami A (NO, Regional Meteorological Centre, Chennai) : Some salient features of the Arabian sea severe cyclonic storm of 5-10 may 2004. Mausam 2007, 58(1), 122-30.

9 illus, 9 ref

004282   Solomon Raju P;Purnachandra Rao N;Arun Singh; Ravi Kumar M (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, Email: raonpc@ngri.res.in) : 14 February 2006 Sikkim earthquake of magnitude 5.3. Curr Sci 2007, 93(6), 848-50.

On 14 February 2006, an earthquake of magnitude 5.3 struck to the west of Phodong, a small town in the Himalayan State of Sikkiin. The earthquake was followed by a large number of aftershocks that were recorded by a network of digital seismic stations operated by the National Geophysical Research Institute, Hyderabad. The study indicates an east-west trend of the epicentral distribution of earthquakes, which is correlated with the decollement plane of the Main Boundary Thrust dipping northward in Sikkim Himalaya. The Sikkiin region is surrounded by several damaging earthquakes of the past, although it has not experienced a magnitude 8.0 earthquake so far. However, it remains to be seen whether the Sikkim region is a potentially less hazardous zone or there is likelihood of occurrence of a great earthquake in the near future.

3 illus, 10 ref

004281   Singh O P;Lal B;Onkar Prasad (India Meteorological Dep, , New Delhi-110 003, Email: opsingh@imdmail.gov.in) : Value addition in district level dynamical forecast during monsoon depressions and storms. Mausam 2007, 58(1), 1-8.

The trials of district level forecasts yielded encouraging results during 2005 monsoon. The purpose to document the methodology followed in the value addition during the periods of monsoon depressions and storms. The focus is on the use of Mean Sea Level (MSL) positions and the 850 hPa circulation features predicted by different model centres, especially the European Centre for Medium-Range Weather Forecasts (ECMWF). The ECMWF-predicted 72 hr MSL position of the monsoon depression centre was found to be significantly correlated to the actual position of the system and the central location of the realized rainfall zone associated with the system. Even the predicted location of the system at 850 hPa by the ECMWF has been found useful in identifying the districts that received heaviest rainfall associated with the monsoon systems. MM5 and T-SO - predicted locations of the system at 850 hPa yielded lower correlations with the location of the actual rainfall zone associated with the system. As ECMWF - predicted rainfall was not available the rainfall predicted by MM5 and T-80 were used in the computations of the correlations with actual rainfall amounts associated with monsoon depressions and storms. The correlations between MM5 and T-80 - predicted average and maximum rainfall associated with systems and corresponding actual were poor. Though it is not difficult to identify the districts that are likely to be affected by the heavy rainfall associated with monsoon depressions/storms, the prediction of exact rainfall amount for each district (beyond heavy, very heavy or exceptionally heavy categories) is difficult from the mode! outputs which makes such forecasts a very challenging task. Therefore, the value addition using other inputs such as satellite information, synoptic charts, climatology etc. are very useful in the prediction of rainfall amounts associated with monsoon systems.

2 illus, 3 tables, 7 ref

004280   Singh O P (India Meteorological Dep, New Delhi-110 003, , Email: opsingh@imdmail.gov.in) : Long-term trends in the frequency of severe cyclones of Bay of Bengal : observations and simulations. Mausam 2007, 58(1), 59-66.

The east coast of India and the coasts of Bangladesh, Myanmar and Sri Lanka are vulnerable to the incidence of tropical cyclones of the Bay of Bengal. Every year these cyclones inflict heavy loss of life and property in this region. Global climate change resulting from anthropogenic activity is likely to manifest itself in the weather and climate of the Bay of Bengal region also. The long-term trends in the frequency and intensity of tropical cyclones of the Bay of Bengal during intense cyclonic months May, October and November is one such problem which has been addressed. Utilizing the existing data of 129 years (1877-2005) pertaining to the tropical cyclone frequency and intensity in the Bay of Bengal during May, October and November, a study was undertaken to investigate the trends in the frequency of severe Cyclonic Storms (SCS) during past decades. The results of the trend analysis reveal that the SCS frequency over the Bay of Bengal has registered significant increasing trends in past 129 years during the intense cyclonic months. It may be emphasized that these trends are long-term trends for more than hundred years based on statistical analyses which do not necessarily imply that SCS frequency has increased continuously decade after decade. As a matter of fact there has been a slight decrease in SCS frequency after peaking in the pentad 1966-1970, but this does not alter the long-term trend much. The intensification rate during November, which accounts for highest number of intense cyclones in the north Indian Ocean, has registered a steep rise of 26% per hundred years, implying that a tropical depression forming in the Bay of Bengal during November has a high probability to reach to severe cyclone stage. A regional climate model simulation revealed the enhanced cyclogenesis in the Bay of Bengal during May, October and November as a result of increased anthropogenic emissions in the atmosphere.

3 illus, 2 tables, 12 ref

004279   Singh D;Singh V (Science and Technology Dep, Technology Bhawan, New Mehrauli Road, New Delhi-110 016, Email: dschahar_ds@yahoo.com) : Impact of tropical cyclone on total ozone measured by TOMS-EP over the Indian region. Curr Sci 2007, 93(4), 471-6.

Impact of tropical cyclones formed over the Arabian Sea and Bay of Bengal on the total ozone derived from the Total Ozone Mapping Spectrometer aboard the Earth Probe satellite has been studied. Authors have analysed the perturbations caused in the total amount of ozone due to four severe tropical cyclones. The daily total ozone anomalies have been calculated for the lifespan of each ropical cyclone. Theses anomalies were observed to be local in character and moved with the tropical cyclone. Further, these anomalies are related to the intensification of the cyclonic systems. In general, negative anomalies were observed to be more than 20 Dobson Units at the time of maximum intensity of cyclones. Variations in daily total ozone anomalies, from development to intensification stage and then to decaying stage of each cyclone have brought out clearly the impact of tropical cyclone on the total ozone, which got depleted considerably over the affected region.

8 illus, 8 ref

004278   Siddhartha Singh;Giri R K;Attri S D (India Meteorological Dep, , New Delhi) : Cyclonic disturbances over Indian seas during 1991 - 2004. Mausam 2007, 58(1), 113-22.

5 illus, 2 tables, 6 ref

004277   Sharma R K;Ray S (NO, , Geological Survey of India, Email: geodata@sancharnet.in) : Geology of the newly discovered copper-gold mineralization at Dhani-Basri, Dausa district, Rajasthan. J Geol Soc India 2007, 69(1), 153-60.

The auriferous copper mineralisation at Dhani Basri, Dausa district, Rajasthan, occurring in the Archaean basement rocks (MangaJwar complex of Gupta at el. 1980), discovered and explored recently, is a significant and sole occurrence in North Rajasthan. This find assumes significance as no such Cu-Au mineralisation has been found hosted in the oldest rocks of Rajasthan east northeast of Jaipur. The mineralisation is localized within the silicified hybrid granite gneisses and controlled by shear zones trending N-S to N 10°W -S 10°E, which are sympathetic to the N-S and NNW-SSE trending faults cutting through the cover sequence, namely Alwar Group of Delhi Supergroup and Raialo metasediments. The principal sulphides are chalcopyrite, pyrite, pyrrhotite, pentlandite and cubanite. Magnetite occurs as oxide phase. Free gold grains embedded in the chalcopyrite and gangue is also associated with this basemetal mineralisation. The gangue minerals are quartz, sericite, chlorite, biotite and amphiboles. Occurrence of pyrrhotite - cubanite exsolution suggests the temperature of mineralisation to be of the order of 350°C. The coarsely crystalline nature, straight grain boundaries of the ore minerals, temperature of formation and fluid homogenization temperature collectively suggest this mineralisation to be of hydrothermal, remobilized nature of epigenetic type and suggests acidic environment of deposition.

5 illus, 1 table, 13 ref

004276   Satyanarayana K;Nallapa Reddy A;Jaiprakash B C;Chidambaram L;Srivastava S;Bharktya D K (Regional Laboratory, , ONGC, Cauvery Basin, Chennai) : A note on foraminifera, grain size and clay mineralogy of tsunami sediments from Karaikal-Nagore-Nagapattinam beaches, Southwest coast of India. J Geol Soc India 2007, 69(1), 70-4.

Analysis of tsunami sediments collected along Karaikal to Nagapattinam beaches revealed that all the sediments are of silty/clay lithology consisting of predominantly montomorillonite, chlorite with rare presence of glauconite. Well preserved foraminiferal tests including long spines of Asterorotalia trispinosa and Ammonia dentata indicate no grain-to-grain abrasion during transportation of sediments. The fine grained lithology and foraminiferal assemblage data strongly point that there was only transfer of energy through tidal waves and there was no reworking of oceanic sediments.

1 illus, 2 tables, 6 ref

004275   Saraswat R;Khare N;Chaturvedi S K;Rajakumar A (NO, National Centre for Antarctic and Ocean Research, Headland Sada, Vasco-da-Gama, Goa-403 804, Email: rs.niog@gmail.com) : Sea water pH and planktic foraminiferal abundance: preliminary observations from the Western Indian ocean. Curr Sci 2007, 93(5), 703-6.

Planktic foraminiferal abundance has been calculateoin a set of 28 surface sediment samples collected from the equatorial and southwestern Indlan Ocean. In order to understand the influence of changing seawater pH on the planktic foraminiferal abundance, the latter has been compared with average sea-water pH of the top 500 m of the water column, measured in situ. Though water depth shows a marked influence on the planktic foraminiferal abundance, pH also appears to affect the overall abundance of planktic foraminifera. The preliminary results indicate that the planktic foraminiferal abundance is directly proportional to sea-water pH.

2 illus, 1 table, 16 ref

004274   Sangun M K;Ozdilek H G (Chem Dep, Faculty of Arts and Science, Mustafa Kemal Univ, 31024 Antakya, Hatay, Turkey, Email: ksangun@gmail.com) : Determination of soil and water contamination around an industrialized town, Kazanli, Mersin, Turkey. Asian J Chem 2007, 19(1), 706-10.

In this study, concentrations of selected metals, namely chromium and nickel, in groundwater and soil were investigated. It was found that extensive chromium and nickel levels in soil that had been used for building materials and this could probably impair public and environmental health, such as in sea turtles, in the area. Toxicological risk assessment from water quality criteria indicated that aquatic toxicity from both acute and chronic nickel and chromium does not exceed estimated ecotoxicoiogy levels.

4 illus, 8 ref

004273   Ravikumar D;Ravindra Singh G;Umesh N; Chikkaramappa T;Jagadeesh B R;Manjula M N;Rajashekarappa K S (NO, , Karnataka State Remote Sensing Application Center (KSRSAC), Bangalore-560 034) : Identification of structural parameters for groundwater development in hard rock terrain using remote sensing, GIS and geophysical methods. Envir Ecol 2007, 25(2), 341-5.

Fractures and lineaments exercise a dominant control on groundwater occurrence and movement in hard rock terrain. Groundwater development at a given site is critically controlled by third order fractures and lineaments such as joints and shears. The usual concept that depth to water table decreases from hill to a valley region, and that its movement occurs towards the valley, may hold good for groundwater of weathered horizons and where an effluent relation of water table to stream bed exists. Water held in deep seated joints, may however, have a movement in different direction depending upon attitude and density of joints. Hence harnessing of deep groundwater by bore wells should always be planned in the light of joints characterizing a particular area. Remote sensing data helps in delineating the fracture and lineament and potential zones with less time and cost effective manner than conventional methods. The thematic layers on geology, geomorphology, drainage, hydrology, structures, soil and land use generated from satellite data, are being used in GIS platform for identifying the ground water prospect zones. Geophysical investigations adopting electrical resistivity methods are carried out in Bangarapet town, Kolar district, Karnataka state. To delineate the vertical variations along the depth, like thickness of the over burden, depth to bed rock, depth to fracture geophysical survey was carried out. Electrical resistivity 'Schlumberger Array Technique' survey was adopted to analyze the resistivity variation along different vertical horizons.

4 illus, 6 ref

004272   Ramasamy S;Singh T S;Madhavaraju J;Asir G G (Geology Dep, School of Earth and Atmospheric Sciences, Madras Univ, Guindy Campus, Chennai-600 025) : Petrography and geochemistry of pre-Ariyalur sequence in Perambalur district, Tamil Nadu - implications on depositional environment and palaeoclimate. J Geol Soc India 2007, 69(1), 121-32.

Maruvattur quarry section (Dalmiapuram Formation) is located near the Archaean-sedimentary boundary at the western margin of the Ariyalur-Pondicherry sub-basin. The lithofacies observed in the quarry include boulder-algal limestone and clastic limestone alternating with siltstone and claystone. This amply reveals that the depositional conditions fluctuated between carbonate facies to fine clastic facies. The coarse clastic materials are not found in the litho-sequence suggesting that the source area reached a peneplanation stage. This stage released only fine clastic materials to develop silty clay and siltstone lithologies. The clastic deposition was fine grained, hence it is interpreted that the depositional basin experienced a calm environment. The limestone units are mostly bedded types pointing out that the older biohermal limestone underwent erosion and redeposited as clastic limestone to form biostromal limestone. The clastic limestone has a few impressions of trace fossils suggesting the slower rate of sedimentation in a comparatively deeper marginal basin. The Anaipadi river traverse representing Garudamangalam Formation indicates a variable lithological association along the dip direction. The claystone is the bottom most unit of this traverse. The clastic deposition is followed by a muddy carbonate phase, which further indicates a calm neritic environment that existed for sometime before deposition of subarkosic-arkosic lithofacies towards the top in the traverse. The varied distribution of elastics has been useful to synthesise information on tectonics and sedimentation. The trilinear plots such as Q, F, L (quartz, feldspar and lithic fragments), and Qm, K, P (quartz monocrystalline, potash and plagioclase feldspars) derived through modal analysis suggest a granitoid source area. The petrographic study and modal analysis suggest that the bottom quartz rich sequence formed in a semi-humid type climate, which gradually became semi-arid as evidenced by the subarkosic-arkosic sands towards upper level along the Anaipadi river traverse.

6 illus, 2 tables, 19 ref

004271   Ramana Murty T V;Mohana Rao K;Malleswara Rao M M;Lakshminarayana S;Murthy K S R (NO, National Institute of Oceanography, Regional Centre, 176 Lawsons Bay Colony, Visakhapatnam-530 017, Email: kmrao@nio.org) : Sediment - size distribution of innerself off Gopalpur, Orissa coast using EOF analysis. J Geol Soc India 2007, 69(1), 133-8.

Earlier studies on grain-size analysis of sediment samples collected over the innershelf of Gopalpur coast have revealed two significant depositional environments viz. beach and dune. Sediment samples from water depth of <60>15 m show the representation of dune type of environment and the samples beyond 15 m in the study area are characterised of beach type of environment suggesting submergence of two physiographic units of beach and dune due to Holocene transgression. Empirical Orthogonal Function (EOF) analysis carried out for the above units on grain-size distribution of the sediments in the φ- size class revealed that the first three φ- dependant eigen function viz. c₁ (φ), c₂ (φ) and C₃ (φ) account for more than 95% of variance predominantly represented by the first - dependent function c₁ (φ) alone. This first function c₁ (φ) of deeper sediments (15 - 30 m depth) contribute 76.34 % of the total distribution representing coarser sands, in general, and characterized by predominance of very coarse sand to the extent of 40%. Shallow sediments (0- 15 m depth) contribute 70% of the distribution-representing medium to fine sand with the dominance of 40% of fine sand. This eigen function c₁ (φ) showed significant differences in the concentration of grain size particles across the innershelf reflecting the change in the energy condition that prevailed in the area during the emergence of the innershelf.

4 illus, 8 tables, 26 ref

004270   Raj Y E A;Asokan R;Revikumar P V (NO, Regional Meteorological Centre, Chennai, Email: yearaj@satyam.net.in) : Contrasting movement of wind based equatorial trough and equatorial cloud zone over Indian southern peninsula and adjoining bay of Bengal during the onset phase of northeast monsoon. Mausam 2007, 58(1), 33-48.

The northeast monsoon sets in over southern parts of peninsular India after the retreat of southwest monsoon and in association with the southward movement of equatorial trough The INSAT satellite imageries scrutinised during the past several years revealed that the cloud bands at the time of northeast monsoon onset moved from south Bay into the southern peninsula, a feature that contrasts with the north to south movement of the equatorial trough. The paper investigates this aspect based on a dataset of lower level upper winds of the peninsula, rainfall data and INSAT OLR data for the 20 year period 1981-2000. The super epoch profiles of zonal winds, latitudinal position of equatorial trough with reference to northeast monsoon onset dates have been derived and studied. The region with OLR values less than 230 W/m² was defined as the equatorial cloud zone and the movement of northern limit of ECZ was studied based on the normal pentad OLR data and also the superposed epoch profiles. From these analysis it has been established that at the time of northeast monsoon onset, the wind based equatorial trough moves south of Comorin whereas the cloud zone in the Bay of Bengal moves from south to north. Reasons for the occurrence of such a contrasting feature have been ascribed to features such as decreasing strength of lower level easterlies from north to south over coastal Tamil Nadu, reversal of temperature gradient between Chennai and Thiruvananthapuram at the time of onset and the dynamics of 40-day oscillation. The northeast monsoon activity over coastal Tamil Nadu has been found to be negatively correlated with the low level zonal winds over the coast, the degree of relation decreasing from north to south and also from October to December. Based on the results derived in the study and also the other known features of northeast monsoon a thematic model of northeast monsoon onset listing the events that precede and succeed the onset has been postulated.

10 illus, 5 tables, 16 ref

004269   Quadir D A;Hussain A;Ahasan M N;Chhophel K; Sonam K (NO, SAARC Meteorological Research Centre (SMRC), Dhaka, Bangladesh, Email: dquadir@yahoo.com) : Climatic characteristics of temperature and precipitation of Bhutan. Mausam 2007, 58(1), 9-16.

An attempt has been made to study the characteristics of the climate of Bhutan using the data of temperature and precipitation of 44 stations for the years 1990-1999. Annual profile of monthly minimum and maximum temperature shows the unimodal character attaining maximum in July and minimum in January for most of the stations of Bhutan. Extreme highest temperature was 37.2° C at Phumsholing in the southwest Bhutan and extreme lowest temperature is -8.2° C at Drukgyel Dzong in the west central Bhutan. Spatial distribution of temperature shows that the mountainous areas of the central, west central and northern part of Bhutan are characterized by low temperature and the southern valleys by high temperature. Annual profile of monthly precipitation manifests the unimodal nature attaining maximum mostly in July and minimum in January. The highest annual precipitation was 5866 mm at Sipsoo and lowest annual precipitation of 628 mm at Gidakom. The central and northern part of Bhutan has relatively low precipitation. The country average precipitation shows that Bhutan gets 1679.4 mm of annual precipitation of which about 70 % occurs in the monsoon season and 19.9% in the pre-monsoon season. The yearly time series of country average monsoon precipitation for 10 years shows a variation with timescale of 3-4 years with a coefficient of variation (CV) of 5.5%. Comparison of monsoon precipitation of Bhutan with All India Monsoon Precipitation (A1MP) shows that the former undergoes more or less opposite phase of variations with respect to A1MP. The correlation analysis shows negative correlation with correlation coefficient of -0.64 which is significant at 0.05 levels.

8 illus, 1 table, 3 ref

004268   Praveen M N;Ghosh B;Srivastava H S;Dora M L; Gaikwad L D (NO, , Geological Survey of India, Bhopal-462 016, Email: bghosh_geol@hotmail.com) : Sulphide mineralisationin betul belt: classification and general characteristics. J Geol Soc India 2007, 69(1), 85-91.

Sulphide mineralisation and syn-volcanic hydrothermal alteration in the Betul Belt is associated with submarine bimodal volcanism. Felsic volcaniclastics form the favourable host rocks in most areas. Alteration zones have been metamorphosed to middle to upper-amphibolite facies giving rise to various metamorphic mineral assemblages. Based on metal ratios, mineralisation can be classified into Zn-Cu and Zn-Pb-Cu types. The difference between the two types might be related to the composition of the footwall volcanics. Zn-Cu types are in close proximity to mafic volcanics towards their footwall side whereas, Zn-Pb-Cu types occur in areas dominated by felsic volcanics with little mafic volcanics towards the footwall. The sub-parallel sheet like nature of the ore bodies and strata-bound alteration might be related to the permeable nature of the host volcaniclastics.

4 illus, 1 table, 17 ref

004267   Prasad S;Jain R L;Srivastava M S (NO, , Geological Survey of India, Western Region, Jaipur) : Record of middle jurassic (Bathonian) ammonite genus Clydoniceras blake from Jaisalmer Basin, western Rajasthan. J Geol Soc India 2007, 69(1), 53-6.

A single specimen of Middle Jurassic (Bathonian) Ammonite Genus Clydoniceras BLAKE has been collected from the sandy limestone of the base of Bada Bag Member of Jaisalmer Formation of Charu area of Jaisalmer District, Western Rajasthan. This specimen is described and figured in the present text to update the stratigraphy of rocks of pre-Kuldhar Member of the Jaisalmer Formation.

2 illus, 2 tables, 16 ref

004266   Pattanaik J K;Balakrishnan S;Bhutani R;Pramod Singh (Earth Sciences Dep, School of Physical, Pondicherry Univ, Chemical and Applied Sciences, Puducherry-605 014, Email: sbala_2002@yahoo.com) : Chemical and strontium isotopic composition of Kaveri, Palar and Ponnaiyar rivers: significance to weathering of granulites and granitic gneisses of southern Peninsular India. Curr Sci 2007, 93(4), 523-31.

Strontium (Sr) isotope ratios and major ion abundance were determined on water samples of Kaveri, Palar and Ponnaiyar rivers, collected during the NE monsoon of 2005, when there was unusually heavy rainfall. Sr isotope ratios combined with major ion concentrations were used to determine relative contribution of Sr and major ions by weathering of various rock types exposed in the drainage basin. ⁸⁷Sr/⁸⁶Sr ratios were well correlated to Ca/Sr and Mg/Sr ratios in water samples indicating mixing of water with solute load essentially derived by weathering of granitoid gneisses, mafic volcanics and carbonates of the Archean schist belts in the upper reaches with the water draining felsic granulites in the lower reaches.

6 illus, 2 tables, 33 ref

004265   Pandey V K;Bhatt V;Pandey A C;Das I M L (K. Banerjee Centre for Atmospheric and Ocean Studies, Institute of Int, Allahabad Univ, Allahabad-211 002, Email: vivekkpandey@rediffmail.com) : Impact of Indonesian throughflow blockage on the southern Indian Ocean. Curr Sci 2007, 93(3), 399-406.

Deals with the numerical simulation of the Indonesian throughflow (ITF) via three major passages, namely Lombok strait (115°E, 8°S), Savu strait (122°E, 9°S) and Timor strait (128°E, 11°S), its seasonal variability and impact on the sea surface parameters due to its blockage. The model is initialized with the Levitus94 climatological dataset for annual mean temperature and salinity fields, and is forced by the seasonal and yearly varying da Silva SMD 1994 and Hellerman and Rosenstein wind datasets. The spin-up of the model has been carried out separately for open and closed Indonesian channels using both the surface wind climatologies. Numerical simulations confirm that the ITF is mainly towards Indian Ocean in a year. It has been observed that surface winds have an impact on the phase as well as magnitude of the ITF. The net effect of blockage is reduction in temperature of the Southern Indian. Ocean and no significant change is seen in surface salinity.

8 illus, 31 ref

004264   Pandey K K;Mishra K S;Pandey U K;Ramesh Babu P V (NO, Atomic Minerals Directorate for Exploration & Research CR, Nagpur-440 001) : Rb-Sr geochronology and petrochemistry of the granitoids hosting rare element pegmatites, Jharsuguda district, Orissa. J Geol Soc India 2007, 69(1), 61-4.

Whole-rock isochron dating of granite gneiss, hosting rare element - bearing pegmatites from Jharsuguda district, Orissa defines an isochron age of 2762 ± 200Ma with initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7082 ± 0.0027 (MSWD = 36.8). High ⁸⁷Sr/⁸⁶Sr ratio indicates involvement of crustal source for its formation. Petrography of the granitoids characterizes them as 'hornblende granite gneiss'. The ASI of the granite gneiss reveals its meta-aluminous nature. It is a significant host to the zoned and complex type of 'Rare Elements-bearing Pegmatites' , containing columbite-tantalite (oxide of Nb + Ta) and beryl. Based on the whole-rock isochron data, the granite gneiss of the Jharsuguda area can be equated with the Bamra and Tamparkola granite and phase III of the Singhbhum granite. Further, it postdates the Bonai and Kaptipada granite but is older to the Nilgiri and Ramapahari granite, with all these forming part of the Singhbhum-North Orissa Craton.

3 illus, 2 tables, 15 ref

004263   Naresh Kumar;Ahmad N;Roy Bhowmik S K; Srivastava K;Awadesh Kumar;Hatwar H R (NO, , Meteorological Office, Patial) : Mountain wave across 2-D orographic barriers for variable wind. Mausam 2007, 58(1), 107-13.

4 illus, 13 ref

004262   Murali Krishna N;Murthy G V G K;Paul A K; Maithani P B (Atomic Energy Dep, Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad-500 016) : Thorium-rich zircon from the Idar pegmatite, Sabarkantha district, Gujarat. J Geol Soc India 2007, 69(1), 171-6.

Cyrtolite variety of zircon rich in thorium occurs as pockets of radiating, multiple intergrowth crystals in a pegmatite emplaced in the Idar granite, Sabarkantha district, Gujarat. It has a lower specific gravity (3.86-4.4) and micro- hardness (676-835), compared to crystalline zircon (4.71 and 841-1468) respectively. The mineral analysed lower contents of SiO₂ (23.89%) and ZrO₂ + HfO₂ (43.36%), compared to normal zircon, and high contents of ThO₂ (5.06%), UO₂ (0.74%), Rare Earth Oxides (REO) (7.88%), FeO (4.44%), CaO (1.98%), MnO (1.26%), H₂O (7.95%). Accumulated damage to the crystal structure caused by the presence of appreciable amount of radioelements (5.06% ThO₂ and 0.74% UO₂) and also REO (7.88%) in the phase, aided in its metamictisation, hydration and alteration resulting in cyrtolite formation. On heating at 900°C the re-crystallised material yielded zircon x-ray pattern. The "d" spacings, intensities of the reflections obtained and increase in the size of unit cell determined for the specimen, compared to that of standard zircon, matches well with the observations made for similar metamict cyrtolites studied by others.

2 illus, 4 tables, 14 ref

004261   Mohapatra M (India Meteorological Dep, , New Delhi-110 003, Email: mohapatra_imd@yahoo.com) : Relative contribution of synoptic systems to monsoon rainfall over Orissa. Mausam 2007, 58(1), 17-32.

The low/depression over northwest (NW) Bay of Bengal is the largest contributor to seasonal monsoon rainfall over all stations in Orissa and Orissa as a whole. The Low Pressure Systems (LPS) and cyclonic circulation (cycir) extending upto 500 hPa level over NW Bay of Bengal alone contribute about 22% to the seasonal monsoon rainfall through about 12 days. The monsoon trough without any significant embedded systems over Orissa and adjoining regions contributes about 28% to seasonal rainfall through about 55 days. All types of LPS including low, depression and cyclonic storm yield maximum rainfall in their left forward (southwest) sectors. The maximum rainfall belt lies more southward due to a depression compared to that due to a low. The spatial distribution of rainfall due to cycir is less systematic. The interaction due to Eastern Ghat plays a significant role in spatial distribution of rainfall over western and eastern sides of the Eastern Ghat due to monsoon lows and depressions over Orissa and adjoining Bay and land regions. The orographic interaction due to Eastern Ghat with the cycirs over Orissa and adjoining Bay and land regions is significantly less leading to no significant difference in spatial distribution of rainfall over eastern and western sides of the Eastern Ghat.

10 illus, 4 tables, 11 ref

004260   Misra K S et al (NO, , Geological Survey of India, Seminary Hills, Nagpur) : Occurrence of fullerene bearing shungite suite rock in Mangampeta area, Cuddapah district, Andhra Pradesh. J Geol Soc India 2007, 69(1), 25-8.

Black carbonaceous slates, interbedded within the Proterozoic volcano-sedimentary sequence of Cuddapah Supergroup in the vicinity of Mangampeta are found to the fullerene bearing and belonging to the shungite suite of rocks. Presence of fullerene in powdered rock samples is identified from the characteristic spectra obtained by laser desorption/ionization spectrometry. This is further confirmed by making soxhlet extract using toluene and exposing it to different laser powers to avoid any possibility of it being analytical artifact. Both carbon allotrope fullerene C₆₀ and C₇₀ are identified within these rocks. Two geological samples collected from the prominent rock units within this thick sequence of black carbonaceous unit belonging to the shungite suite of rock are found to have fullerenes. This reporting of fullerene is first of its kind from any geological material from India. The only other occurrence of fullerenes in geological samples is recorded from the Shunga locality of the Karelean province of Russia.

1 illus, 8 ref

004259   Mandal P;Chadha R K;Kumar N;Raju I P; Satyamurty C (NO, National Geophysical Research Institute, Hyderabad-500 007, Email: prantikmandal@yahoo.com) : Estimation of source parameters of the 8 october 2005 Kashmir earthquake of M_w 7.6. Curr Sci 2007, 93(5), 660-8.

Aiming at mainly recording aftershock activity of the 2001 Bhuj earthquake of M_w 7.7, a semi-permanent network of five broadband seismographs has been in operation since last six years in the Kachchh area, Gujarat, India. The 8 October 2005 Kashmir earthquake of M_w 7.6 and its aftershocks have been well recorded by this network as well as by the Hyderabad Geoscope station. These data enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of peninsular India. First, author measured Rayleigh- and Love-wave group velocity dispersion curves in the period range of 8 s to 35 s and inverted these curves to estimate the crustal and upper mantle structure below peninsular India. Our best model suggested a two-layer crust; 13.8 km thick upper crust with a shear velocity (V_s) of 3.2 km/s and a 24.9 km thick lower crust with V_s 3.7 km/s. V_s for the upper mantle was found to be 4.65 km/s. Based on this structure, we then performed a moment tensor inversion of the bandpass (0.05-0.02 Hz) filtered seis-mograms of the 2005 Kashmir earthquake. The best fit was obtained for a source located at a depth of 30 km, with a seismic moment M₀, of 1.6 x 10²⁷ dyne-cm, and a focal mechanism with strike 19.5°, dip 42° and rake 167°. The long-period magnitude (M_A <126> M_w) of this earthquake was estimated to be 7.31. Analysis of well-developed sP_n and sS_n regional crustal phases from the bandpassed (0.02-0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggested a focal depth of 30.8 km.

11 illus, 2 tables, 33 ref

004258   Mallik T K;Bhattacharya A K (NO, , FD-317, Sector - III, Salt Lake, Kolkata-700 106) : Kaolinite from Bagru Hills, Lohardaga, Bihar. J Geol Soc India 2007, 69(1), 177-81.

Samples from the Kaolinite deposits at Bagru Hills, Lohardaga, Bihar have heavy mineral assemblage of rutile, opaque, tourmaline, biotite, staurolite, pyroxene, sphene, epidote, zircon, kyanite, muscovite and tremolite/actinolite derived from igneous and metamorphic sources. The lighter fraction includes iron hydroxides, chlorite, feldspar, carbonate and some muscovite or limonite. The major, minor and trace elements remain nearly the same irrespective of colouration of samples. The chemical composition and the size of the kaolinite grains coupled with its purity clearly indicate that it can be used in a number of industries.

2 illus, 3 tables, 9 ref

004257   Malik J N;Sahoo A K;Shah A A;Rawat A; Chaturvedi A (Civil Engineering Dep, Indian Institute of Technology Kanpur, Kanpur-208 016, Email: javed@iitk.ac.in) : Farthest recorded liquefaction around Jammu caused by 8 October, 2005 Muzaffarabad earthquake of Mw=7.6. J Geol Soc India 2007, 69(1), 39-41.

Reports the farthest recorded liquefaction phenomenon near Jammu as sequel to the Mw 7.6, 8 October, 2005 Muzaffarabad earthquake of Kashmir. The most common liquefaction features were sand blows and longitudinal en echelon fissures. Based on the occurrence of liquefaction and minor damage to the pakka houses it is suggested that the intensity would have been around VI-VII on MSK scale in this region.

3 illus, 4 ref

004256   Luis A J;Pednekar S M;Sudhakar M (NO, National Centre for Antarctic and Ocean Research, Headland Sada, Goa-403 804, Email: alvluis@ncaor.org) : Post-tsunami impact study on thermohaline structure in the bay of Bengal. Curr Sci 2007, 93(5), 699-703.

Temperature and salinity profiles measured on-board ORV Sagar Kanya, during 18 January-17 February 2005, in the vicinity of the Chennai coast and west of the Andaman (AN) Islands, have been employed to assess and quantify the post-tsunami impact on the upper-ocean thermohaline structure, by comparing these with previous year's data. In the vicinity of the AN Islands, the sea surface temperature increased by 0.5°C and surface salinity decreased from 33.5 to 32 psu, between 90°E and 92°E along 10°N. This freshening has been attributed to westward geostrophic flow from the AN Sea facilitated by a sea surface height gradient inferred from the merged multi-mission satellite data. Significant temperature variations exceeding 1øC were observed between 50 and 250 m, west of the AN Islands. Near the Chennai coast (10°N, 80.9°E), influx of freshwater from the northern Bay of Bengal reduced salinity by 0.8 psu and stratification in the upper 100 m was observed. Upward shift in the 20°C isotherm was observed at all locations, suggesting a vertical entrain-ment. In general, this study reveals that considerable thermohaline variability has occurred in the upper 300 m water column, which is expected to have a significant impact on primary production and fisheries.

4 illus, 1 table, 9 ref

004255   Kore P A;Das H P;Jadhav V N;Mondal S S (NO, , Meteorological Office, Pune) : Heavy rainfall pattern over North Western parts in dry farming region of India. Mausam 2007, 58(1), 134-8.

6 illus, 2 tables, 9 ref

004254   Kolvankar V G (Seismology Div, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, Email: vkolvankar@yahoo.com) : Earthquake patterns based on diurnal and semidiurnal electromagnetic emissions related to earthquakes volcanoes observed with 24 h periodicity. Curr Sci 2007, 93(5), 710-17.

Electromagnetic (EM) emissions related to earthquakes and volcanoes were observed in a very wide frequency band from VLF to microwave. These were found to be diurnal and semidiurnal type occurring only during certain hours of the day. It was also found in these examples that the occurrences of earthquakes/eruption of volcanoes were simultaneous with the timings of these EM emissions. From this study, it can be concluded that the semidiurnal stresses on the earth and on the moon are solely caused by the position of the Sun. The causes of diurnal stresses are not precisely known. In order to study the variation of the stress devetoped over a longer period of time, the earthquakes for various regions of the globe were mapped for number of years on 24h basis. The histogram of earthquakes thus genetated on 24 h basis (HE24H) provided various patterns. It was observed that most earthquakes were aligned to some curvature representing some kind of stress fronts of different strenghts and lasting up to over 100 years. They were also found in different shapes and sizes. The study of HE24H also supports the hypothesis that the occurrence of earthquakes is synchronous to the eauth's rotation.

9 illus, 13 ref

004253   Kessarkar P M;Purnachandra Rao V (NO, National Institute of Oceanography, Dona Paula-403 004, Email: pratimak@nio.org) : Organic carbon in sediments of the Southwestern margin of India: influence of productivity of monsoon variability during the late quaternary. J Geol Soc India 2007, 69(1), 42-52.

Texture, organic carbon (OC), CaCO₃ and Rock-Eval parameters of the sediments from two gravity cores collected at depths below the oxygen minimum zone (OMZ) of the southwestern margin of India are presented and compared the results with those within the OMZ. Clayey silt / silty clays are the characteristic sediments. The OC in the core top sediments between Cape Comorin and Mangalore is higher below the OMZ than those from the OMZ. However, it is higher within the OMZ than those below the OMZ in the sediments between Mangalore and Goa, The down-core variations of OC are identical in these cores. In both the cores, relatively high OC content and low sedimentation rates correspond to the intervals of late Holocene and Last Glacial Maximum (LGM) and, low OC and high sedimentation rates to the early Holocene sediments. The CaCO₃ follows sand content in a core off Cape Comorin, with low values at the core top, increase marginally in the early Holocene and LGM and then decrease in the late Pleistocene sediments. The CaCO₃ values in a core off Mangalore are higher in the intervals of the late Holocene and early deglaciation than in early Holocene and LGM intervals. Rock-Eval parameters distinguish the sources of organic matter only at high OC concentrations. The high OC during the LGM may be related to the productivity, associated with convective mixing occurring during the NE monsoon. The low OC/CaCO₃ and high clay content during the early Holocene may be the consequences of the intensified SW monsoon that results in stronger near-surface stratification leading to low productivity. High OC and low CaCO₃ during the late Holocene suggest increased productivity and early diagenesis in the near surface sediments. It is suggested that the variations in productivity and downslope transport of sediment controlled the OC enrichment.

7 illus, 1 table, 44 ref

004252   Karmakar S;Alam M (Bangladesh Meteorological Dep, , Agargaon, Sher - E - Bangla Nagar, Dhaka-1207, Bangladesh, Email: malam@phy.kuet.ac.bd) : On the tropospheric zonal and meridional fluxes of moisture in relation to nor' westers in Bangladesh during the pre-monsoon season. Mausam 2007, 58(1), 67-74.

Attempts have been made to study the zonal and meridional fluxes of moisture of the troposphere prior to the occurrence of nor' westers in Bangladesh during the pre-monsoon season. The study reveals that the westerly fluxes (positive) of moisture (WFM) dominate in the troposphere over Dhaka at 0000 UTC from 925 to 200 hPa level having maximum frequency of WFM from 61.08 to 96.26% in the layer from 925 to about 300 hPa level. The maximum WFM over Dhaka at 0000 UTC on the dates of occurrence of nor' westers may be more than 200 gm kg^-1 x ms^-1 in the lower troposphere and the maximum easterly (negative) fluxes of moisture (EFM) over Dhaka at 0000 UTC may be -128.3 gm kg^-1 x ms^-1 at 1000 hPa. In the upper troposphere the zonal fluxes of moisture (ZFM) become nil in most of the cases. The ZFM over Dhaka at 0000 UTC are mainly westerly and more westerly in the lower and middle troposphere on the dates of occurrence of nor' westers as compared to the fluxes on the dates of non-occurrence. The southerly fluxes (positive) of moisture (SFM) dominate in the troposphere over Dhaka at 0000 UTC from 1000 to 300 hPa level. The meridional fluxes of moisture (MFM) are mainly southerly and more southerly in the lower and middle troposphere on the dates of occurrence of nor' westers as compared to the dates of non-occurrence. In the upper troposphere the MFM become nil in most of the cases. The vertically integrated ZFM and MFM from 1000 to 100 hPa over Dhaka at 0000 UTC on the dates of occurrence of nor' westers in Bangladesh have been computed, compared and inference has been drawn. The present study also deals with the spatial distribution of the vertically integrated ZFM and MFM from 925 to 400 hPa level over control.

7 illus, 2 tables, 13 ref

004251   Kanungo D R;Malpe D B;Radhakrishnan C J (Ore Dressing Div, , Indian Bureau of Mines, Hingna Road, Nagpur-440 016, Email: dbmalpe@yahoo.com) : Chrome-rich green garnets from mesoproterozoic Sausar fold belt, Tirodi area, central, India. J Geol Soc India 2007, 69(1), 65-9.

Uvarovite is rarest of the species of garnet group. Green chromiferous garnets with uvarovite, as subordinate molecules are also known. Chrome rich green garnets (uvarovite) has been reported from the Tirodi manganese deposit of Central India. The X-ray data (unit cell a= 11.98 angastrum) of these garnets is comparable with the synthetic uvarovite data. The end-member calculations based on electron microprobe studies show dominance of andradite and uvarovite with minor spessartine molecules. Distinct spatial association between chrome garnets, Mn ore and intrusive pegmatites has been observed. Chrome rich green garnets are probably pre-Sausar in age and formed in association with older supracrustals whose enclaves occur in Tirodi gneisses.

3 illus, 2 tables, 32 ref