Quantitative Evaluation of Bouguer Anomalies in Puranpur Area of the Ganga Basin

Bouguer gravity data of the Ganga basin could not be interpreted earlier quantitatively, as it was believed that the isostatic effect of the Himalayas masked all the local anomalies. The present work, however, suggests that the contribution of substantially thick low density post-unconformity sediments is more in masking the local anomalies than the isostatic effect.

The gravity data in Puranpur area of the Ganga basin have been interpreted in terms of basement depths after removal of the effect of the post-unconformity sediments, whose disposition is fairly well known from the seismic data. In the Puranpur depression the maximum sedimentary thickness is about 6000 metres. The pre-unconformity sediments in this depression may be different from those in the adjoining areas, to the west and south. The northeastern limit of this depression is a basement ridge on which interesting structural features are located.

In the northern part of the area the basement structures exhibit a WNW-ESE trend indicating that this area probably belongs to the Krol basin. In the southern part, the trend is dominantly E-W, but is disturbed by a number of NE-SW trending features. The former is probably governed by the basement rocks belonging to the Bundelkhand massif while the latter are due to the continuance of the Aravalli trend of the peninsular area.