The Inner Sedimentary Belt:

The Inner Sedimentary Belt of the Kumaon Lesser Himalaya extends from the Garhwal region in the west to beyond the Kali River marking the eastern boundary of the Kumaon Himalaya.  The oldest rock unit of this belt is termed the Rameshwar Formation (Ahmad, 1975)  and consists of slate, siltstone, greywacke, protoquartzite, limestone and phyllite.  This formation is correlated with the Rautgara Quartzites (Valdiya, 1964) and Hatsila Formation (Misra and Bhattacharya 1972, 1973). 

The Pithoragarh Formation, overlying the Rameshwar Formation include stromatolite bearing dolomitic limestone with magnesite, talc, chert, pebble beds with some slate and calcareous slates.  Three rock units constitute the Pithoragarh Formation.  The Thalkedar Limestone constituting the lowermost unit consists of thinly bedded limestone with minor gray shale/slate.  The Sor Slates overlying this unit consist of gray slate and shale with minor dolomitic bands.  The topmost unit of the Pithoragarh Formation are the massive Gangolihat Dolomites with stromatolites.  These are, in places, phosphatic, and are intebedded with magnesite and talc schists.  This zone is apparently the same as the main calcareous unit of the Calc Zone of Pithoragarh (Valdiya, 1962; Misra and Banerjee, 1968; Misra and Valdiya, 1969), the Calc Zone of Tejam (Heim and Gansser, 1939; Gansser, 1964), and the Kotaga Banali of Saklani (1971, 1978), as well as the Doya Dolomite (Misra and Bhattacharya, 1972) of Pugar valley and the Jhatkwali Formation (Mehdi et al., 1972).  Dolomitization and recrystallization are common features of the limestone.  On the basis of the discovery of stromatolites (Valdiya, 1969; Kumar and Tiwari, 1977, 1978; Kumar, 1978; Bhattacharya, 1976a), a Middle Riphean age has been assigned to the rocks of this Formation.

Phyllitic rocks with gray, green and black slates with minor calcareous interbeds constitute the rock formations overlying the Pithoragarh Formation.  These rocks are the same as, or directly correlatable with the Kanalichina Formation (Mehdi et al., 1972) of the Pithoragarh district and the Betalghat Formation (Raina and Dungrakoti, 1975) of the Bhimtal-Bhowali area in Nainital district.  They are also termed the Saling Formation (Bhattacharya, 1980). 

The Berinag Formation constituting the topmost horizon of the Inner Sedimentary Belt is seen surrounding the crystalline masses of the Almora, Askote, and Baijnath units.  The rock types consists of fine to coarse grained massive quartzite, often sericitic and schistose, with pebble beds, chlorite beds, and interbedded metabasites.  Kumar (1978) has correlated the Berinag Formation with the Kaimur Formation of Upper Vindhyans.  Jain (1971) classified this unit as the Garhwal Group. 

The rock formations constituting the Inner Sedimentary Belt have been tightly folded into a few E-W to ESE-WNW trending folds.  At places there is strong evidence of thrusting and dislocation by a number of faults.

Based on field evidences, some workers (Valdiya, 1962, 1964, 1969, 1973; Misra and Kumar, 1968; Misra and Banerjee, 1968; Misra and Bhattacharya, 1972; Saklani, 1971, 1972; Jain, 1971; Pachauri, 1972; and Bhattacharya, 1976b) are of the opinion that a thrust plane separates the Berinag Formation from the underlying units, and that this sedimentary sequence is inverted.  Other workers (Heim and Gansser, 1939; Gansser, 1964; Mehdi et al., 1972; Banerjee and Bisaria, 1975; Ramji, 1976; Kumar and Tiwari, 1977; Kumar, 1978; and Bhattacharya, 1980) maintain that the entire sedimentary pile is in a normal position except for locally inverted sequences.




Wallrock Alteration



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