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

D. Haldar ¹, T. Laskar ¹, P. C. Bandyopadhyay ¹, N. K. Sarkar ¹, J. K. Biswas ¹

Affiliations
1 Geological Survey of India, IN

Abstract

Geotectonically the Barren and Narcondum islands lie on the Neogene Inner volcanic are, which proceeds from the recent volcanoes of Central Burma in the North to the Miocene to Recent volcanoes of Indonesia in the SE and are believed to have evolved as a result of eastward subduction of the Indian Ocean lithosphere below the SE Asian plate. The Barren island volcano is characterised by resurgent volcanism; so far, three distinct volcanic episodes have been recorded. An initially submarine volcanism, possibly taking place in late to Post-Pleistocene time formed a giant volcanic cone representing the ancestral Barren island. This ancient volcanic cone was at times, blown out and a thick pile of pyroclastics got deposited over the surface of the relict cauldron. Historical records reveal that the volcano became active again in 1789 when the existing cone with a crater and three subsidiary vents were developed. The present eruption initially starting from the NE subsidiary vent, subsequently merged with the main crater. The intensity of volcanic eruption gradually gathered momentum and continued unabated with thundering explosions till the end of September, 1991. Since November it is lying dormant. There is no major disastrous effect.

The lava of the first phase was olivine basalt and that of the second pbase a high-alumina olivine basalt.

Keywords

Volcanoes, Ezrren-Island, Andaman Sea, Natural Hazards.

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Asru K. Chaudhuri ¹, Somnath Dasgupta ², Goutam Bandyopadhyay ², Subir Sarkar ², P. C. Bandyopadhyay ², K. Gopalan ³

Affiliations
1 Geological Studies, Unit, Indian Statistical Institute, Calcutta, IN
2 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN
3 National Geophysical Research Institute, Hyderabad, IN

Abstract

The Proterozoic sequence around Adilabad, Andhra Pradesh comprises a distinct lithostratigraphic unit of 'Group' status and has been given the name Penganga Group. The Penganga Group has been classified into three Formations which are, in order of younging, Pranhita Sandstone, Chanda Limestone and Sat Nala Shale. The sequence is dominated by limestones and shales which were deposited in relatively deep water environment and, thus, contrast sharply with the conglomerate, sandstone and shallow water limestones of the Pakhal Group. Radiometric dating of fresh glauconites from middle part of the Penganga Group gives an age of 770 ± 30 Ma. Thus, the Penganga Group is the youngest of all other Proterozoic sequences in Pranhita-Godavari Valley.

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