Rabindra Nath Hota

Comparative Study of Cyclicity of Lithofacies in Lower Gondwana Formations of Talchir Basin, Orissa, India: A Statistical Analysis of Subsurface Logs

Abstract Cyclic characters of Karharbari, Barakar and Barren Measures Formations of the Talchir Gondwana basin have been studied in the subsurface logs statistically using first order Markov chain and entropy analyses. Results strongly suggest that the sediments of these formations were deposited by Markovian mechanism and all the three formations represent cyclic sedimentation. The complete cycles of all the three formations are identical and exhibit fining-upward character. Each complete cycle starts with a thin conglomerate or pebbly to coarse-grained sandstone at the base and successively followed by medium- and fine-grained sandstones, interbedded sandstone-shale, shale and terminates with a coal seam at the top. There are, however, minor variations of facies transition in different formations. Entropy analysis also corroborates these findings. The upward sequence of facies states, which is stationary at individual localities, is non-stationary over the entire area. Broad regional variations in the depositional environment, that are not significant at the local scale, may be the plausible explanation. The Karharbari, Barakar and Barren Measures sediments of the Talchir Gondwana basin fit suitably into the concept of fluvial cycles.

Cross-Association Analysis of Barren Measures Lithologies and Microfacies, Talcher Coalfield, Odisha

Cross-association analysis of lithologies and microfacies of two borehole sections of the Barren Measures Formation, Talcher coalfield situated 12 km apart show strikingly dissimilar results. In case of lithologies, one-to-one correlation becomes significant, which suggests continuity of the formation throughout the Barren Measures Formation and prevalence of braided stream depositional environment. However, lack of significant correlation of microfacies suggests existence of different sub-environments at different parts of the Barren Measures Formation during each stage of sedimentation. When channel facies were laid down at one place, homotaxial leeve, floodplain and swamp facies were deposited elsewhere.

Problems in Accepting Plate Tectonics and Subduction as a Mechanism of Himalaya Evolution.

The available geological and structural data from Chaman fault and Indus-Tsangpo regions does not support the new global tectonic concept and the presence of suture zone between Indian and the northern landmass. Instead, it is suggested that the Indus-Tsangpo is a rift valley that appeared in the Triassic and became dormant in the Cretaceous, after a spurt of volcanic activity long before the supposed suturing in the Eocene. The paleontological evidences based on plants, marine and fresh-water invertebrates, insects and vertebrates indicate that Gondwanaland was never a separate entity. Paleoclimatic continuity was maintained over this landmass of India and Tibet from the Paleozoic through Cenozoic eras up to the Pleistocene Epoch. Similarly, the widespread glacial deposits of northern Tibet bespeak of a continental landmass extending from Peninsular India up to northern Tibet, and may be beyond. Thus, Pangaea existed till its breakup beginning in the Triassic and Tethys was an epicontinental sea from west Proto-Pacific to east Proto-Pacific. At no stage was it oceanic in character, although narrow shifting belts along and across it, became rift or geosynclines in the process of crustal development. Thus, the Tethys did not form a wide, funnel shaped gulf, opening into the Pacific as depicted in many reconstructions. On the other hand, the Himalayan sequence is dominantly nongeosynclinals sediments, and therefore, genetically different from such classic mountains as the Caledonian, Hercynian, Urals, and Aravallis etc. It is significant that the Himalayan orogeny was initiated in the Cretaceous, and the major episode was Eocene, i.e. earlier than the supposed collision, rules neither out continental collision and subduction nor even in geosynclines. However, the Himalayas, could, then, not have been borne due to collision of landmasses as suggested by plate-tectonics. Instead, they are an interplatform type of mountain range formed by vertical uplift, by intrusive magmas and gravity gliding played an important part too. Terrestrial gravity, seismic (including DSS), geodetic, geomorphologic and field tectonic studies independently and collectively support the above contention. The Himalaya along with some other ranges in Central Asia may be unique in Earth history, and all the mountain ranges of the past seem apparently to have been originated in geosynclines. The plate tectonic concept, however, considers the term geosynclines redundant.

Similarity of Palaeocurrent: A Tool for Stratigraphic Correlation

Conventional stratigraphic correlations are based on similarity of lithology, order of superposition, marker bed, unconformity, grade of metamorphism, fossil content and geochronology of the rock units. The Gondwana strata have been correlated referring to the above mentioned criteria. In the present work, the Talchir and Karharbari formations of two adjacent Gondwana basins separated by over 200 Km were examined with respect to their palaeocurrent directions. The study suggests that the palaeocurrent populations of different formations in both the basins are statistically dissimilar, this is because, both are stratigraphically distinct in order of superposition and thus are not correlatable. On the other hand, the palaeocurrent populations of the same formation in both the basins are statistically similar and stratigraphically correlatable. It is suggested that the similarity of palaeocurrent can be regarded as a criterion for stratigraphic correlation at least in local and regional scale.