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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.
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.
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.
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.
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.
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.
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