Contents of January, 2001 - Vol. XXII No.1

COMPARISON OF THE AERO AND MARINE MAGNETIC DATA OVER PENINSULAR INDIA
Mita Rajaram, P. Harikumar and T.S. Balakrishnan

SURFACE AND VOLUME BASED ATTRIBUTE ANALYSIS REVEALED A POSSIBLE PALEO-RIVER CHANNEL FROM 3D SEISMIC DATA : A CASE STUDY FROM UPPER ASSAM, INDIA
S.N.Singh, B.N. Singh & Y.S. Rathore

RADIOMETRIC AND ELECTRICAL STUDIES OVER THE GADWAL SCHIST BELT – A QUALITATIVE ANALYSIS
D.Himabindu, G.Ramadass, N.Srinivasulu & M.Venkata Chary

GEOELECTRICAL INVESTIGATION TO LOCATE GROUND WATER RESOURCES FOR URBAN DEVELOPMENT: A CASE STUDY IN PARTS OF GREATER GUWAHATI URBAN AREA, ASSAM
B.Pathak and M.Venkateshwar Rao

THE EVOLUTION OF THE WEST COAST OF INDIA FROM A PERSEPECTIVE OF GLOBAL TECTONICS
Colin Reeves * & Jim Leven **

AN ANALYSIS OF MAGNETOTELLURIC (MT) DATA OVER GEOTHERMAL REGION OF BAKRESHWAR, WEST BENGAL
Rajib K. Sinharay, Shalivahan and Bimalendu B. Bhattacharya


COMPARISON OF THE AERO AND MARINE MAGNETIC DATA OVER PENINSULAR INDIA

Mita Rajaram, P. Harikumar and T.S. Balakrishnan.

Indian Institute of Geomagnetism, Colaba, Mumbai 400 005.

Abstract

Rigorous reprocessing of the degree sheet aero magnetic maps over peninsular India up to 170 N acquired from the Geological Survey of India was undertaken. These degree sheet maps include surveys that have been carried out by different agencies at different epochs and altitude and have not been corrected for the main field. The data grid spacing has a crucial effect on the nature of the map prepared. In order to utilise the aeromagnetic data for studying the deep crust, we have manually redigitised the degree sheet maps at 6’ interval and corrected for the main field using IGRF (International Geomagnetic Reference Field) model corresponding to the epoch and altitude of the data collection. Within the Cuddapah region the aeromagnetic data were not available with us; we have therefore merged our ground magnetic data in this region. In a similar manner the published marine magnetic anomaly data were re-digitised. To be able to prepare a composite magnetic anomaly map the aeromagnetic data were downward continued to the mean sea level. The two data sets are handled independently, as the errors in the two are of different nature. We do not merge the data sets, but just place them adjacent to each other to study the trends of the anomalies. The colour shaded aero cum marine magnetic anomaly map over Peninsula India, thus prepared brings out several features that are presented. From the analysis of the aeromagnetic data, we find that the source rocks of the aeromagnetic anomalies are the host province of Charnokites in the Southern Granulite Terrain (SGT) and the intrusives/iron ore bodies in the Dharwar belt (Harikumar et al, 2000). The marine magnetic data is also analysed in a similar manner, to be able to locate the position of the magnetic sources. We find that the SGT continues to the offshore between Madras and south of Karaikal. North of Madras the trends change in the offshore region. Results of the combined aero and marine magnetic sources are presented.

Back to Contents of this issue


SURFACE AND VOLUME BASED ATTRIBUTE ANALYSIS REVEALED A POSSIBLE PALEO-RIVER CHANNEL FROM 3D SEISMIC DATA : A CASE STUDY FROM UPPER ASSAM, INDIA

S.N.Singh, B.N. Singh & Y.S. Rathore

Oil India Limited., Duliajan, Assam

Abstract

The effective utilization of 3D Seismic survey, as a tool for solving the perplexities in hydrocarbon exploration and production (E&P) business, has made the acquisition of more and more 3D seismic data inevitable in the industries. The world statistics reveals that the 3D revolution has given a big jump to global “Reserve-Production curve” from 35 to 45 years for oil and 50-60 years for gas, over past decades. This has construed to the obvious industry forecast that 3D seismic technology will continue to grow in the forefront to lead the E&P business in future.

The overwhelming success and the increasing demands of the 3D seismic data for hydrocarbon exploration and production, are forcing more and more onus in the involved geoscientists to suffice the expectations of industries in the midst of growing challenges due to the need of extending explorations to inaccessible and frontier areas, efforts on identifying deep seated, seismically invisible reservoirs, imaging the subsurface in depth, the extensive demands of geophysical inputs for optimization of production from new, old or depleting reservoirs (IOR: Improved Oil Recovery) schemes and so on. Therefore, conventional data acquisition, processing and interpretation of 3D seismic data is proving to be merely inadequate in meeting the desired standards and is thus; in continuous need for further nourishment in all stages of acquisition, processing and more so in the concluding stages of interpretation to facilitate the harnessing of maximum information that could be derived and/or inferred.

Back to Contents of this issue


RADIOMETRIC AND ELECTRICAL STUDIES OVER THE GADWAL SCHIST BELT – A QUALITATIVE ANALYSIS

Himabindu.D, Ramadass.G, Srinivasulu.N & Venkata Chary.M

Centre of Exploration Geophysics, Osmania University, Hyderabad

Abstract

The NNW-SSE trending Gadwal schist belt in the eastern Dharwar craton in the south Indian peninsular shield is interesting both from the geological as well as the geophysical points of view. However, relatively few geophysical studies over the schist belt have been reported. In this paper, semi-detailed radiometric and electrical resistivity (both profiling and vertical electrical sounding) studies were conducted along profiles laid across the schist belt. Interpretation of these results brought out the structural features and trends – faults, contacts and shear zones.

Back to Contents of this issue


GEOELECTRICAL INVESTIGATION TO LOCATE GROUND WATER RESOURCES FOR URBAN DEVELOPMENT: A CASE STUDY IN PARTS OF GREATER GUWAHATI URBAN AREA, ASSAM

B.Pathak* and M.Venkateshwar Rao**

*Geological Survey of India, N.E.R., Shillong.
**Geological Survey of India, S.R., Hyderabad.

Abstract

Electrical resistivity soundings employing Schlumberger electrode configuration were carried out around kerakuchi Senmela, Jutikuchi, Garchug, Pamohi and Tetelia areas of Guwahati to delineate the bedrock topography and estimate the thickness and nature of the overlying sediments to assess the ground water resources for urban development.

The area under study is a plain with Granite inselbergs, projecting through Quaternary sediments which comprising primarily of clay, sand and silt.

Electrical resistivity sounding curves in the area are of ‘H’ type and a combination of ‘H’ and ‘A’ or ‘H’ and ‘K’ type and could identify three to four layers apart from thin shallow surface layers of varying resistivities and thicknesses. Basement contour map prepared from Electrical Resistivity Sounding data indicate the presence of several basement ‘depressions’ and ‘ridges’. The depressions in the basement could be favourable locations point for groundwater developments. The results of Vertical Electrical Resistivity Soundings correlated well with known bore hole informations and good agreement have been found pertaining to nature and thickness of overburden and location of probable aquifer zones.

Back to Contents of this issue


THE EVOLUTION OF THE WEST COAST OF INDIA FROM A PERSEPECTIVE OF GLOBAL TECTONICS

Colin Reeves * & Jim Leven **

*International Institute for Aerospace Survey and Earth Sciences (ITC), Kanaalweg 3, 2628 EB Delft, The Netherlands.
** Mauritius Oceanography Institute, Quatre Bornes, Mauritius.

Abstract

We describe an animated global tectonic model for the development of the Indian Ocean and discuss its relevance to the geological history of India’s west coast continental margin. This feature started with a line of weakness (megashear) separating what is now India and Madagascar that fractured rocks within the Gondwana supercontinent affected by the Pan-African orogeny. Prolonged dextral transtension across this zone from earliest Cretaceous to Turonian times (140 to 90 Ma approximately) led to a zone of extended crust with some continental content some 200 km wide created during about 1000 km of southward movement of India away from Madagascar. Most of this extended crustal material remains with India even today, though other fragments were scattered widely following the outbreak of the Marion hotspot at about 89 Ma and the start of India’s rapid movement northwards. A multiplicity of mid-ocean ridges and ridge-jumps characterises the post-89 Ma development of the ocean crust between India and Madagascar but these can be explained with a minimum of hypothesis, beyond what is necessary to explain the observed ocean-floor topography and the presently-incomplete record of ocean-floor magnetic anomalies. The interruption of long periods of steady, regular ocean floor creation in the Indian Ocean by a finite number of ridge jumps and plate reorganisations can be recognised in the sedimentary record from oil wells drilled around all the coasts of Africa and also in the African interior. They can therefore also be expected to be of significance in the stratigraphy and petroleum potential of India’s west continental margin.

Back to Contents of this issue


AN ANALYSIS OF MAGNETOTELLURIC (MT) DATA OVER GEOTHERMAL REGION OF BAKRESHWAR, WEST BENGAL

Rajib K. Sinharay, Shalivahan and Bimalendu B. Bhattacharya

Department of Applied Geophysics, Indian School of Mines, Dhanbad - 826004

Abstract

Magnetotelluric (MT) reconnaissance survey has been carried out over the geothermal region of Bakreshwar, West Bengal to study the resistivity, strike direction and dimensionality of the subsurface conductivity structure. This paper is an effort to get most from the already acquired data before planning for more data. The results of sequential analysis of polar diagrams, Swift’s strike, rotation angle, tipper magnitude and skew have been presented for three MT soundings: (1) 500 m NE, (2) 1.2 km SW and (3) 9 km away in NE direction from the hot spring respectively. 1-D models have been prepared by very fast simulated annealing (VFSA), a nonlinear inversion technique, for both transverse electric (TE) and transverse magnetic (TM) modes and their resolutions at different depths have been compared. The nearest sounding to the hot spring shows two low resistive zones of about 100 ohm-m and 15 ohm-m at a depth of about 8 km and 12 km respectively in TM mode. The thicknesses of these two low resistive zones are 2.3 km and 3.4 km respectively. These zones, however, are local in nature as they are not seen even in the sounding 1.2 km away on the other side of the hot spring. It is seen that the TM mode gives better resolution at shallower depths than TE mode. Tipper and skew parameters indicate that near surface structure is 1-D or 2-D in nature but for larger depths it is 3-D in nature.

Back to Contents of this issue