The Autocthonous Zone
Between the North Almora and Berinag Thrusts lies the autochthonous zone of sedimentary groups discernible in the large elongate windows, mostly in the inner Lesser Himalayas. The Damtha group (Chakrata and Rautgara Formations), an Early Riphean flysch, and the conformable calcargillaceous Tejam Group (Deoban and Mandhali Formations) of Middle Ripliean to Vendian age, constitute the framework of the autochthonous unit. Very mildly metamorphosed dolerite dykes and sills and basalt lavas are characteristic features of the upper part of the Damtha group. Complexly folded and severely deformed, particularly in the proximity of the thrust planes, the autochthonous zone exhibits a series of tight asymmetrical to overturned and locally isoclinal folds, many of them being split up by faults or thrusts causing repetition and even local inversion under the overthrust Berinag sheet. The Darntha group of rocks, with thin and impersistent cappings of Subathu, are also exposed in the windows in the outer Lesser Himalayas in Garhwal - the Deoprayag-Byasghat-Satpuli window of the Ganga-Nayar valleys, and the Phart and Bidhalna windows in the neighborhood of Narendranagar. The Nayar Fault, which developed along the anticlinal axial plane of the synclinally folded Krol Nappe, is responsible for bringing up and exposing the Damtha (mainly Chakrata flysch) rocks in these windows.
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