Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Madan Mohan ¹, P. Kumar ¹, V. Narayanan ¹

Affiliations
1 Institute of Petroleum Exploration, Oil and Natural Gas Commission, Dehradun, IN

Abstract

The authors favour the placement of Palaeocene-Eocene boundary at the Pseudohastigerina wilcoxensis datum. In the Cauvery basin subsurface, seemingly continuous late Palaeocene-Early Eocene successions are known only in the basinal depressions, which have been exemplified by the Chidambaram well data. Unless the sequences are well represented by cores, problems arise in delineation of Palaeocene-Eocene boundary in the flanks of ridges/highs in Cauvery basin as the index Palaeocene planktonic foraminifera are sometimes found reworked in the Eocene zones.

The occurrence of Nummulites, whose earliest occurrence is lately being attributed to the basal Eocene in the European basins, in the Cauvery basin Palaeocene corresponding to the Globorotalia velascoensis and Globorotalia pseudomenardii Zones - has been stressed. Further research is necessary in order to establish the evolutionary appearance level of these camerinids in the Indian subcontinent.

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B. C. Jaiprakash ¹, P. Kumar ¹

Affiliations
1 Palaeontology Laboratory, KDM Institute of Petroleum Exploration, ONGC, Dehra Dun 248 195, IN

Abstract

Late Eocene-Early Oligocene succession from two well sections of north-eastern margin of Cambay Basin was analysed for their foraminifera1 content. It has yielded rich larger foraminifera a few planktonic and benthonic foraminifera. Three larger foraminiferal biozones have been recognised for the succession in geologically ascending order. These are Nummulites fabianii Partial Range Zone (? 39.4 m.y. to 37.4 m,y., i.e., ? P 15 to 16); Discocyclina dispansa - Nummulites fabianii Concurrent Range Zone (37.4 m.y. to 36 m.y.. i.e., Zone P 17) and Nummulites fichteli Partial Range Zone (36 m.y. to? 35 m.y., i.e., Zone P18), The environment of deposition has varied from shallow marine to inner and outer shelf conditions in the course of the development of the succession.

Keywords

Foraminifera, Cambay Basin, Gujarat, Micropalaeontology, Stratigraphy.

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J. R. Kayal ¹, V. K. Srivastava ¹, P. Kumar ², Rima Chatterjee ¹, P. K. Khan ¹

Affiliations
1 Department of Applied Geophysics, Indian School of Mines, Dhanbad - 826 004, IN
2 National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad - 500 007, IN

Abstract

A three-component broadband seismograph is in operation since January 2007 at the Indian School of Mines (ISM) campus, Dhanbad. We have used the broadband (BB) seismograms of 17 teleseismic events (M ≥ 5.8) recorded by this single BB station during 2008-09 to estimate the crust and upper mantle discontinuities in Dhanbad area which falls in the peninsular India shield. The converted wave technique and the Receiver function analysis are used. A 1-D velocity model has been derived using inversion. The Mohorovicic (Moho) discontinuity (crustal thickness) below the ISM observatory is estimated to be ~41 km, with an average Poisson ratio of ~0.28, suggesting that the crust below the Dhanbad area is intermediate to mafic in nature. The single station BB data shed new light to the estimate of crustal thickness beneath the eastern India shield area, which was hitherto elusive. Further, it is observed that the global upper mantle discontinuity at 410 km is delayed by ~0.6 sec compared to the IASP-91 global model; this may be explained by a slower/hotter upper mantle; while the 660 km discontinuity is within the noise level of data.

Keywords

Broadband Seismograms, Teleseismic Events, Receiver Function, Crust and Upper Mantle, Moho Discontinuity.

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