Informatics Publishing Limited

Joydip Mukhopadhyay ¹, Gautam Ghosh ¹, N. J. Beukes ², Jens Gutzmer ³

Affiliations
1 Department of Geology, Presidency College, Kolkata -700 073, IN
2 Department of Geology, University of Johannesburg, AuckIand Park, ZA
3 Department of Geology, University of Johannesburg, Auckland Park, ZA

Abstract

Conglomerates correlatable with the late Meso-Neoproterozoic Kolhan Group in the vicinity of Chamakpur and Baljori villages flanking the Iron Ore Group of rocks of the Jamda-Koira valley, Jharkhand and Orissa, include pebbles of hard high-grade iron ore, which are mined as iron ore. The mode of occurrence and character of these orebearing conglomerates suggest them to have been deposited in a proximal alluvial fan setting. The iron ore pebbles are composed of martite and microplaty hematite, and are very similar in appearance to the BIF-hosted iron ores of the Noamundi-Joda deposits of the Iron Ore Group. The ore-bearing conglomerates provide evidence that the hard hematite-rich iron ores of the western Iron Ore Group, from whlch ore pebbles are most probably derived, must have predated the Kolhan sedimentation and are not related to modern lateritic weathering.

Keywords

Iron ore, Precambrian, Iron Ore Group, Colluvial, Hydrothermal, Singhbhum, Jamda-Koira valley, Jharkhand, Orissa.

Full Text

     

Anupendu Gupta ¹, Joydip Mukhopadhyay , Gautam Ghosh , N. J. Beukes , Jens Gutzmer

Affiliations
1 Geological Survey of India, Kolkata, IN

Abstract

No Abstract.

Full Text

   

Joydip Mukhopadhyay ¹, Asru K. Chaudhuri ²

Affiliations
1 Department of Geology, Presidency College, 86/1 College Street, Kolkata - 700 073, IN
2 Geological Studies Unit, Indian Statistical Institute, 203 B.T. Road, Kolkata - 700 108, IN

Abstract

Stratigraphic classification of apparently monotonous lithographic limestone of the Proterozoic Penganga Group leads to the understanding of the depositional setting and palaeogeography of a deep-water limestoneshale succession. The Penganga Group around Adilabad unconformably overlies granitic basement, and includes three formations, namely, the Pranhita Sandstone (c. 25 m), the Chanda Limestone (c. 250 m), and the Sat Nala Shale (>2000 m). The Pranhita Sandstone is a cross-stratified subarkosic sandstone deposited in a shoreface environment. The Chanda Limestone developed as a deep-water, below wave-base platform. It is essentially micritic, and includes a number of slope-related autoclastic limestone mass-flow deposits, a lentil of glauconitic sandstone emplaced as submarine fan deposit (c. 25 m), and two regionally persistent horizons of deep-water bedded chert interstratified with manganese ore. The Sat Nala Shale is a deep-water, brown shale without any siliciclastic coarser than mud. On the basis of stratigraphically-controlled variations in colour, bedding character and composition, the Chanda Limestone can be subdivided into a number of mappable (1:25,000) units, that can be organized into three formal members, the Bhimsari, Bilari and Ramai Members, and one informal Brown heterolithic member. The members were deposited in different parts of the platform, at different stages of its evolution, under varied state of oxidation and reduction. Detailed mapping of the units reveals the presence of two major thrust faults that divide the succession into a southern autochthonous package successively over-ridden by a para-autochthonous package and an allochthonous package, occurring in the northern and northeastern part of the area. The autochthonous package includes sandstone and shale of the Pranhita Sandstone deposited in shoreface and inner shelf environments. The para-autochthonous package is dominated by lithographic limestone of the Bhimsari and Bilari Members, and a thin horizon of the Sat Nala Shale. The allochthonous package is dominated by slope to basinal deposits of the Ramai Member and the Bhimsari Member, and a thick sequence of the Sat Nala Shale. This package also includes the stratified bedded chert and manganese ore indicating open ocean up welling circulation. The attitude of the thrust planes and the vergence of thrust-related folds suggest southerly propagation of thrust sheets. The allochthonous northern package was transported from a terrain beyond the northern limit of the study area, implying that the Penganga sea was open towards north. Northward opening of the basin along with upwellingrelated bedded chert and manganese deposits point to the existence of an open marine basin in the central part of peninsular India, north of the Dharwar craton.

Keywords

Proterozoic, Lithographic Limestone, Stratigraphic Classification, Thrust, Palaeogeography. Penganga Group, Adilabad, Andhra Pradesh.

Full Text