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H. N. Sinha ¹, S. S. Srivastava ², James Peters ³

Affiliations
1 Department of Geology, Vinoba Bhave University, Hazaribagh - 825 301, IN
2 Department of Earth Sciences, Indian Institute of Technology, Roorkee - 247 667, IN
3 KDMIPE, Geology Division, ONGC, Dehra Dun-248 195, IN

Abstract

The present study is an interdisciplinary approach to put forward a precise picture of Ordovician-Silurian acritarcha and other associated microfossil distribution in the Lower Palaeozoic Tethyan sequence of the Garhwal Himalaya, lndia For the purpose, sedimentological data, macrofauna and microflora from the Shiala and Yong Formations have been considered to constrain the environmental distribution of the microfossils It has been found that chitinozo and melanosclerites as well as acritarcha of Garhwal Tethys Himalaya have a wide range of adaptation The acritarcha bloomed during cool marine condition whereas chitinozoa and melanosclerites preferred mainly In warm-water condition of blooming The Shlala Formation was deposited under cool-water conditions In a shallow pulsating basin with a rapid variations In the depositonal environment and frequent sea-level changes This formation has been affected by the fluvial influx intermittently and possibly there was a sea-level drawdown at Ordovician-Silurian boundary An attempt has been made to correlate this phenomenon with a possible Late Ordovician glacioeustatic event and it is found that the Hirnantian glaciation was probably not situated in the Himalayan region The Yong Formation was deposited mainly in a shallow subtidal setting in a tranquil and low energy ancient warm-water mass.

Keywords

Microfossil flora and fauna, Acntarcha, Palaeoenvironment, Ordovician-Silurian, tethys Hlmalaya, Garhwal, Uttaranchal.

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James Peters ¹, S. K. Singh ¹

Affiliations
1 Keshava Deva Malaviya Institute of Petroleum Exploration, 9 Kaulagarh Road, Dehra Dun - 248195, IN

Abstract

The Satpura basin, located in central India, is the westernmost exposed Gondwana basin. This basin is situated south of the Narmada-Son Geofracture (NSG) and north of the Betul-Chhindwara plateau. The basin is spindle-shaped with a length to breadth ratio of 4:1. The shape of the basin is governed by the intersection of three prominent tectonic grains. These are (1) ENE-WSW strain parallel to the NSG strain in the north, (2) NW-SE trend conforming to thc Dharwar tectonic strain in the southwest and (3) NE-SW trend parallel to the Eastern Ghat tectonic strain.

The basin is subdivided into the Pench-Kanhan sub-basin in the south and Denwa sub-basin in the north. These sub-basins are separated by the Malni-Tamiya high which runs subparallel to the strike of the basin. The basin is occupied by outcropping Gondwana sediments of Permian, Triassic and Cretaceous age. These sediments are subdivided into the lower unit comprising Talchir, Barakar, Motur and Bijori Formations, the middle unit of Pachmarhi and Matkuli Formations and the upper unit of Jabalpur Formation and Infra-trappean sediments.

The evolution of the Satpura basin could be considered in terms of pre-rift, syn-rift and post-rift phases. The pre-rift phase is characterised by the development of sag in which sediments of the Talchir Formation were uniformly deposited. Sediments deposited in prograding fluvial and paludal environments, representing the Barakar Formation followed this. Tectonic readjustments related to initial break up of the Gondwanaland resulted in the development of a rift system in which remaining sediments of the Barakar Formation and entire Motur and Bijori Formations were deposited in a "Venetian blind" pattern due to progressive subsidence, rapid sedimentation and northward shift of depocentres caused by a northward migration of the rift. Thesc pre-rift and syn-rift phases were initiated in the Early Permian and culminated in Latest Permian. The post-rift phase, which was initiated in the Late Lower Triassic, witnessed the deposition of sediments of Pachmarhi and Matkuli Formations. Subsequent to the Jurassic hiatus, sediments of Jabalpur Formation were deposited overlapping thc older sediments. Deposition of Infra-trappean sediments was the last episode of the post-rift phase. These are essentially calcretes formed on the peneplained surfaces of the older Gondwana sediments.

Keywords

Narmada-Son Geofracturc (NSG), Satpura Basin, Central India, Gondwana, Rift sedimentation.

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