Simla Slates: The Precambrian Flysch of the Lesser Himalaya, Its Turbidites, Sedimentary Structures and Paleocurrents
The Precambrian Simla Slates group of Himachal Pradesh and Garhwal is a shaly flysch made up of graywackes and related finer sediments deposited primarily by lateral turbidity currents in the distal part of the basin. Two trends of paleocurrents have been recognized in this flysch. Various scour and tool markings indicate turbidity currents that flowed oblique or even transverse to the general tectonic strike of the Himalayan chain. These turbidity currents demonstrate diverging trends northwest to north-northwest in the Simla area, north in the Tons Valley in the middle, and north-northeast to northeast in Garhwal. They seem to have originated on the shelf of the north-by-northeasterly prolongation of the now profoundly eroded and peneplaned Aravalh, which lies buried under the sands of the Ganga and Yamuna Rivers. The Archean Aravallis, and possibly the Ajabgarhs of the Proterozoic Delhi System probably served as the mam source of the sediments. Erosional structures in the graywackes and related sediments indicate indigenous bottom currents sweeping consistently in an easterly direction across the slope. The directly overlying Blaini Boulder Beds of the Simla area arc interpreted as slide conglomerates, representing submarine slides generated on steep structural slopes as a result of severe tectonic movements toward the end of the Simla time.