The 'Jaunsar' Problem in the Himalaya - A Critical Analysis and Elucidation

A complex association of limestones, quartzites, slates and volcanic rocks and ashes exposed In the Garhwal Himalaya was first called as 'Jaunsar System' by Oldham. Pilgrim and West adopted the name 'Jaunsar' for their Jagas Series c - a selective quartzite-slate association, and Auden variously considered his Mandhali-Chandpur-Nagthat association of diverse lithology, and the Nagth Nagthat Series of quartzite-phyllite association as 'Jaunsar'. Later workers either adopted the classification of Pilgrim and West, or of Auden, or reclassified the Chandpur-Nagthat to include crystallines and metamorphics, without much regard to the larger stratigraphic Implications of the same. This has resulted In great confusion In the stratigraphy of the Himalayas leading to conjectural correlations of formations and hypothetical interpretation of structures.

The present study has shown that the 'Jaunsars' are variously part of the Simla group of Srikantia and Sharma or are part of the sequence of the Mandhali-Chandpur-Nagthat. The recent attempt to include rock types referable to the Jutogh as part of the Chandpur-Nagthat is mainly due to the non-recognition of a thrust contact between these two which is obscured due to post-tectonic metamorphism and deformation, and hence is not an acceptable proposition.

It is now proposed to redefine the term 'Jaunsar' and to strictly restrict it to the restored sequence of Mandhali, Chandpur and Nagthat formations. The Jaunsar group as adopted now represents a typical geosynclinal type of sediments deposited on the eroded surface of the Deoban belt. It is characterised by the association of the Bhowali volcanics and the acid intrusives of the Kharasali gneiss, and is typically eugeosynclinal. Structurally it occurs as a superficial nappe over the isopic zones of the Deoban-Simla group in the southern part of the Deoban belt.

The Jaunsar group, the Simla group and the Rampur formation are considered as contemporaneous formations in the present scheme of correlation of geosynclinal sediments In the Lesser HImalaya.