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

A. K. Ray ¹, C. C. Ghosh ¹, S. Nag ¹

Affiliations
1 Geology Department, Presidency College, Calcutta 700 073, IN

Abstract

Alveolina of Kutch Middle Eocene limestones and marls is identified as A. elliptica var. nuttalli. The variety is shown to have a characteristic shape (expressed as a ratio of polar and equatorial diameters), and more or less fixed number of flosculinised whorls; the variation in the development of non-flosculinised whor1s on the flosculinised ones is attributed to an ontogenetic development correlated with size increase. The variety shows a clear case of lateral facies variation, occurring in two 'apparent' horizons in deeper parts of the basin with vertical absence in between, but continuing throughout the rock unit in marginal shallower parts. The facies-governed nature of this larger benthic foraminiferal species and its presence in the Kutch Paleogene sequence without the earlier glomalveoline forms are considered important aspects in stratigraphic studies.

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Ravi Shanker ¹, S. Nag ², S. Shome ¹

Affiliations
1 Geological Survey of India, Kolkata, IN
2 Geological Survey of India, Lucknow, IN

Abstract

Mesoproterozoic metavolcano-sedimentary sequence in and around Bhowali-Khairna area, Uttaranchal, constitute mostly metabasalts with quartzites, phyllites and variegated slates, referable to Bhimtal Formation. Our study was centred on metabasalts and the rocks occurring in close spatial association with them. Detailed petro-mineralogical and SEM-EDS studies have revealecl the presence of gold which we report here for the first time. Of the two types of metabasalts viz., massive, crudely foliated type and foliated type, both showing mineralogical assemblages of subgreenschist facies and greenschist facies respectively, gold is commonly found in the foliated type and rarely in the massive type. Presence of gold as tiny grains in disseminated fashion suggest that widespread hydrothermal activity caused precipitation of gold after the rocks had witnessed peak metamorphism.

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S. Nag ¹, R. K. Gaur ¹, Tapan Pal ²

Affiliations
1 Geological Survey of India, Lucknow, IN
2 Geological Survey of India, Calcutta, IN

Abstract

Late Cretaceous-Tertiary sediments together with the underlying Sylhet Trap and Precambrian granites/gneisses are exposed along the southern fringe of Meghalaya plateau. This huge pile of sediments is dissected by E-W and NNE-SSW striking faults. Several workers postulated a direct correlation between tectonism and sedimentation, interpreting the E-W striking Dauki fault as a 'growth fault'. The present work suggests that the sedimentation of this pile is controlled by basin transgression and regression and not by the Dauki or other faults. Dauki fjult being post-Kopili (post-Eocene) in age, could not have acted as a growth fault during the deposition of these Late Cretaceous-Palaeogene sediments.

In the plate tectonic version of Greater India in Gondwanaland, a broadly coeval lithofacies and biofacies assemblages existed in Late Cretaceous-Palaeogene sequences of the southern Tibetan plateau and southern Meghalaya plateau. While the sedimentation in Tibet during Palacogene is dominated by carbonate rocks - except at the KIT boundary (Jidula Formation), the sedimentation in southern Meghalaya is represented by arenaceous and calcareous rocks.

Keywords

Sedimentology, Lithofacies, Structure, Cretaceous, Tertiary, Faunal Assemblage, Dauki Fault, Tibetan Plateau, Meghalaya Plateau, Plate Tectonics.

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S. N. Kak ¹, A. V. Subrahmanyam ¹, S. Nag ², T. Pal ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Geological Survey of India, Sector E, Aliganj, Lucknow-226024, IN
3 Geological Survey of India, Kolkata, IN

Abstract

No Abstract.

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