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

T. S. Ramakrishna ¹

Affiliations
1 "The Anomaly" 1250 B, Road 62, Jubilee Hills, Hyderabad - 500 033, IN

Abstract

No Abstract.

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T. S. Ramakrishna ¹

Affiliations
1 Geological Survey of India, Hyderabad 500001, IN

Abstract

When the regional Bouguer gravity anomalies do not corroborate with the surface geology, the general tendency of many interpreters is to take recourse to the undulations in the Moho, ignoring the Conrad in between, inspite of the fact that Conrad has been traced in several parts of the country by DSS as well as by gravity. Further, while inferring basic intrusives to explain some of the gravity highs, the corresponding magnetic data is also not taken into account. This note shows how Conrad may be creating disorder in regional gravity interpretations and how ignoring magnetic data leads to weak and suspect inferences.

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T. S. Ramakrishna ¹, A. Y. S. R. Chayanulu ¹

Affiliations
1 Geological Survey of India, Hyderabad 500 001, IN

Abstract

Out of the six Purana basins, namely Cuddapah, Kaladgi, Bhima, Pakhal, Chattisgarh and Vindhyan, Cuddapah, Pakhal and Chattisgarh appear to be filled with rocks of higher than normal density, whereas the other three comprise low density rocks. Their gravity picture, however, are not found to be simple highs or lows as to be expected from their densities but are distorted by both deepseated causes as in the case of Cuddapah, Chattisgarh and Vindhyan basins, as well as the overlying sediments as in the case of Pakhal basin. Major earth movements appear to have been associated with Cuddapah, Pakhal, Vindhyan and Chattisgarh basins whereas Kaladgi and Bhima basins represent mere depressions. The thickness of sediments in these basins is estimated to vary from 2 to 10 km.

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T. S. Ramakrishna ¹

Affiliations
1 Training Institute, Geological Survey of India, IN

Abstract

The gravity and aeromagnetic maps of the Cuddapah basin present some very interesting results that may help in understanding the configuration of the basin better and also plan exploration strategies. Based on the gravity field along 79"E longitude, the Nallamalai sub-basin can be divided into three minor basins separated by two ridges along Obalam-Vanipenta and Racherla-Nandikotkur axis, besides the Palnad basin at the northeastern end which also might be underlain by Nallamalais.

The aeromagnetic picture divides the basin and adjoining crystallines on the east into two domains roughly along a line joining Srisailam and Srikalshasti. To the east of this magnetic divide, the dense high frequency contours inside the basin, like those on the outside, suggest a shallow basement for the Nallamalais. To the west of it, it is the low frequency E-W regional trends that dominate. The corresponding magnetic profile (along 79°E) brings out a major E-W regional magnetic high with a width of about 10km at its peak; along Pedda Ahobilam-Panem axis. While this high falls off regionally both towards south and north, the northern fall is interrupted by two low closures, one west of Racherla and the other corresponding to the Srisailam basin. The Macherla-Agnigundala gravity ridge and the associated dipolar magnetic anomaly could be due to sources responsible for mineralisation near Agnigundala and as such the entire ridge trending NW-SE needs a closer geological scrutiny.

Keywords

Gravity, Aeromagnetics, Cuddapah basin, Nallamalai.

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T. S. Ramakrishna ¹

Affiliations
1 1250B, Road 62, Jubilee Hills, Hyderabad-500 004, IN

Abstract

No Abstract.

Full Text

   

T. S. Ramakrishna

Abstract

No Abstract.

Full Text