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Sengupta, S.
- Petrology of Post -Archaean Magmatic Rocks in the Eastern Indian Craton
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Affiliations
1 Geological Survey of India, 15, KYD Street, Calcutta 700 016, IN
1 Geological Survey of India, 15, KYD Street, Calcutta 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 51, No 1 (1998), Pagination: 31-42Abstract
Minor rhyolite intrusives spatially associated with granophyric granites occur along the eastern and southwestern fringe of the Archaean Singhbhum Granite batholith in the eastern Indian Craton. Some minor trachyte dykes occur within the batholith and both are of post-Archaean age. On the basis of major and trace element studies it has been inferred that a process more complex than simple fractional crystallisation has controlled the observed chemical variation in both the rocks. However, the two are genetically unrelated and have been generated from different sources. All the rhyolites, which are scattered as small bodies over an extensive area, are produced from similar source compositions. The chemical variation among the rhyolites is the result of a difference in degree of melting and the samples enriched in LREE and other incompatible elements represent a lower degree of partial melt. Composition of the rhyolites suggests that neither muscovite nor aluminosilicates were present in the source. The likely source is therefore the trondhjemites and mafic-ultramafic rocks constituting the Archaean crust of the region. Similar source for rhyolites distributed over a large area indicates a homogeneous composition for the Archaean crust.Keywords
Rhyolite, Trachyte, Eastern Indian Craton, Geochemistry, Partial Melting.
- Geology of Scotland
Abstract Views :205 |
PDF Views:128
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Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 7 (1985), Pagination: 505-506Abstract
No Abstract.Full Text
- Unusual Composition from the Cumulate Section of Andaman Ophiolite
Abstract Views :183 |
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Authors
Affiliations
1 Geological Survey of India, 4, Chowringhee Lane, Calcutta, IN
2 I.T.C., Kanaalweg, 3, Delft, NL
1 Geological Survey of India, 4, Chowringhee Lane, Calcutta, IN
2 I.T.C., Kanaalweg, 3, Delft, NL
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 30, No 4 (1987), Pagination: 249-254Abstract
Mafic and acid cumulates from Andaman ophiolite contain hornblende and magnetite as primary cumulus phases. Four samples with higher SiO2range, contain in addition apatite and quartz crystallised from intercumulus liquid. These have lower Ni, Cr and higher total REE abundances than ophiolitic gabbros and plot away from the field of ophiolitic cumulates in the AFM diagram. Strong negative Eu-anomaly is in striking contrast to ophiolitic cumulates.No volcanic rocks are associated with these cumulates. Volcanic rocks occurring in a different thrust slice are similar to 'transitional' ridge basalts. It is suggested that the cumulates have crystallised from melts more evolved than ridge tholeiites and possibly from melts similar to basaltic andesites of Andaman ophiolite. in a shallow magma chamber.
- Trabecules in Assilina exponens (Sowerby) (:Foraminiferida) – A Preliminary Report
Abstract Views :259 |
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Authors
Affiliations
1 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata - 700 019, IN
2 Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
1 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata - 700 019, IN
2 Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No 6 (2008), Pagination: 750-752Abstract
Preliminary report on trabeculae bearing B Form tests of Middle Eocene larger foraminifera Assilina exponens (Sowerby) from Lakhpat, NW Kutch is provided here for the first time. Taxonomic significance of trabecules in nummulites in general and Assilina exponens in particular is discussed.Keywords
Foraminifera, Assilina exponens (Sowerby), Trabeculae, Middle Eocene, Kutch, Gujarat.- Arsenic Rich Phases in Aquifer Sediments from Southern West Bengal
Abstract Views :176 |
PDF Views:172
Authors
Affiliations
1 Central Petrological Laboratory, Geological Survey of India, 15, Kyd Street, Kolkata 70001 6, IN
1 Central Petrological Laboratory, Geological Survey of India, 15, Kyd Street, Kolkata 70001 6, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 2 (2001), Pagination: 173-176Abstract
No Abstract.Full Text
- Association of Microbes with Arsenic-Bearing Siderite Concretions from Shallow Aquifer Sediments of Bengal Delta and its Implication
Abstract Views :196 |
PDF Views:129
Authors
Affiliations
1 Geological Survey of India, Kolkata - 700 016, IN
1 Geological Survey of India, Kolkata - 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 3 (2001), Pagination: 269-271Abstract
No Abstract.Full Text
- Arsenic Rich Phases in Aquifer Sediments Prom Southern West Bengal
Abstract Views :175 |
PDF Views:134
Authors
Affiliations
1 Publication Division, Geological Survey of India, Eastern Region, Kolkata, IN
2 Central Petrological Laboratory, Geological Survey of India, 15 Kyd Street, Kolkata - 700 016, IN
1 Publication Division, Geological Survey of India, Eastern Region, Kolkata, IN
2 Central Petrological Laboratory, Geological Survey of India, 15 Kyd Street, Kolkata - 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 6 (2001), Pagination: 552-553Abstract
No Abstract.Full Text
- Striate Nummulites (:Foraminiferida) from the Early Oligocene Rocks of Southwestern Kutch
Abstract Views :203 |
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Authors
Affiliations
1 Department of Geology, University of Calcutta, 35 Ballygaunge Circular Road, Kolkata - 700 019, IN
1 Department of Geology, University of Calcutta, 35 Ballygaunge Circular Road, Kolkata - 700 019, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 74, No 5 (2009), Pagination: 597-600Abstract
Megalospheric form of a striate Nummulites, provisionally identified here as Nummulites sp. aff. chavannesi de la Harpe, is documented from the Early Oligocene rocks of SW Kutch, Gujarat. This striate Nummulites occurs in association with N. fichteli-clipeus Group, N. cf. fichteli, Heterostegina, Operculina and Gypsina. High abundance of microspheric tests of reticulate Nummulites and virtual absence of microspheric tests of striate Nummulites reflect contrasting success of growth and sexual reproduction of the two groups of sympatric Nummulites.Keywords
Nummulites sp. aff. chavannesi de la Harpe, Oligocene, Kutch, Gujarat.References
- ADAMS, C.G., BUTTERLIN, J. and SAMANTA, B.K. (1986) Larger foraminifera and events at the Eocene/Oligocene boundary in the Indo-West Pacific region. In: Ch. Pomerol and I. PremoliSilva (Ed.), Terminal Eocene Events. Elsevier Sci. Publ., Amsterdam, pp.237-252.
- BISWAS, S.K. (1992) Tertiary stratigraphy of Kutch. Jour. Pal. Soc. India, v.37, pp.1-29.
- BLONDEAU, A. (1972) Les Nummulites. Vuibert, Paris, 255p.
- DASGUPTA, A. (1970) Further studies on reticulate Nummulites (Foraminifera) from Oligocene Beds of Cutch, India. Jour. Geol. Min. Metal. Soc. India, v.42, pp.159-172.
- JAIPRAKASH, B.C. and KUMAR, P. (1993) Late Eocene-Early Oligocene biostratigraphy of Mansa-Indrora area, Cambay Basin. Jour Geol. Soc. India, v.42, pp.357-367.
- LEE, J.J., FABER (JR.), W.W., ANDERSON, O.R. and PAWLOWSKI, J. (1991) Life-cycles of foraminifera. In: J.J. Lee and O.R. Anderson (Ed.), Biology of Foraminifera. Academic Press, London, pp.285-334.
- MEHROTRA, K.K. and WANI, M.R. (1985) Middle Eocene-Early Oligocene biostratigraphy and palaeoecology of B-57 structure, Bombay offshore area. Bull. Geol. Min. Met. Soc. India, no.52, pp.78-87.
- MOHAN, M. (1965) Variation in Nummulites fichteli Michelotti. Bull. Geol. Soc. India, v.2, pp.93-96.
- MOHAN, M. and PANDEY, J. (1971) Foraminiferal control in the Tertiary basins of India. Jour. Pal. Soc. India, v.16, pp.78-88.
- MUKHOPADHYAY, S. K. (2003) A rare foraminiferal assemblage with new species of Nummulites and Globigerina from the EoceneOligocene transition strata of Cambay Basin, India. Micropal., v.49, pp.65-93.
- NUTTALL, W.L.F. (1925) Indian reticulate Nummulites. Ann. Mag. Nat. Hist., v.15, pp.661-669.
- RACEY, A. (1995) Lithostratigraphy and larger foraminiferal (nummulitid) biostratigraphy of the Tertiary of northern Oman. Micropal., v.41 (Suppl.), pp.1-123.
- SAMANTA, B. K. (1968) Nummulites (Foraminifera) from the Upper Eocene Kopili Formation of Assam, India. Palaeontol., v.11, pp.669-682.
- SENGUPTA, S. (2000) Problems of classifying early Oligocene reticulate Nummulites (Foraminiferida) from southwestern Kutch, Gujarat. Jour. Geol. Soc. India, v.56, pp.673-677.
- SENGUPTA, S. (2002) A note on test shape of Nummulites cf. fichteli Michelotti Form A (:Foraminiferida) from the Early Oligocene deposit of southwestern Kutch, India. Jour. Geol. Soc. India, v.60, pp.223-224.
- SUKLA, S. (2008) Atlas of taxonomic and bio-chronostratigraphic studies on Paleogene larger benthic foraminifera from Indian sedimentary basins. Paleontographica Indica, no.9, pp.1-183.
- Macroseismic Study of 20th May 2007 Sikkim Earthquake - Its Seismotectonic Implications for the Region
Abstract Views :218 |
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Authors
Affiliations
1 Geological Survey of India, Northern Region, Lucknow-226 024, IN
2 Geological Survey of India, Eastern Region, Gangtok - 737 101, IN
1 Geological Survey of India, Northern Region, Lucknow-226 024, IN
2 Geological Survey of India, Eastern Region, Gangtok - 737 101, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 75, No 2 (2010), Pagination: 383-392Abstract
An earthquake of magnitude 5.0 with its epicenter in the West Sikkim district occurred on the evening of 20th May 2007. The macroseismic study revealed an ENE-WSW isoseismal pattern indicating a trend conforming to that of the major tectonic discontinuities in this part of the Himalaya.
The relatively moderate event, felt even at far away places like, Siliguri, Darjeeling, etc induced a maximum intensity of VI (MSK) in the form of development of cracks in the walls, fall of thick chunks of plaster in Type A or even Type BC structures at localities like Tashiding, Ralang, Rabang, Keozing, Sakyong, etc.
The study also revealed that the NW-SE trending Tista lineament is playing an important role in the release of the tectonics strain in this region and that the rupture initiated under the influence of the northward directed tectonic stresses at an asperity formed at one of the decollements within the crust by the intersection of this tectonic discontinuity was interpreted to be responsible for this seismic event.