PALYNOCHRONOLOGICAL CONSTRAINTS FROM HIMALAYAN FORELAND BASIN AND THEIR IMPLICATIONS ON INDIA – ASIA COLLISION

India-Asia collision took place 65-40 m.y ago averaging around 55 m.y resulted into the formation of Himalayan Foreland basin. We document the palynochronological evidence for initiation of Himalayan Foreland sedimentation in the Proterzoic basement subsidence developed as a consequence of this collision. Initial Foreland sediments of Himachal Pradesh designated as Kakara and Subathu formations are investigated in detail for the plant microbiota to generate a new evidence line of palynochronological inferences for this continental-continental collision and subsequent evolution of Himalayan Foreland basin. The plant microbiota recovered here from the Early Tertiary Subathu Formation in the stratotype point to different ecological settings depicting, marine, marginal marine, coastal transitional and freshwater depositional episodes in the Subathu Formation based on Homotryblium (52-51 my), Cordosphaeridium (52-51 my), Cleistosphaeridium (51-44 my) and Pediastrium (< 44 my) Assemblage zones from Ypresian to post-Lutetion time intervals.

Palynozones dates are designated based on global age marker palynotaxa (Williams et al. 1993). Based on the FAD and LAD limits of taxa recovered in each zone, we here propose to delimit the precise age of zones by delimiting youngest FAD and oldest LAD of taxa in the assemblage of a particular zone. The palynochronological dates so delineated in the present studies clearly point out the deposition of Subathu Formation from 52 to 44 m.y and may be even younger, for the age diagnostic palynotaxa from the uppermost part of Subathu Formation represented by Pediastrum Assemblage zone are still wanted. The Kakara Formation of Nahan area yielded marine Dinogymnium assemblage which is index of Maestrichtian.

The qualitative, quantitative and palynochronological data from Kakara and Subathu Formation of northwest Himalaya constrain that the north ward movement of Indian plate, underthrusting of Tethys crust, end Cretaceous cessation of sedimentation in Spiti basin, closure of Neotethys in the north and the eventual collision of India with Asia coincides with the initiation of marine sedimentation in Maestrichtian time in the Himalayan Foreland basin and the evolution of basin is accompanied with deposition of Subathu Formation under shallow water marine influene from 52 to 44 m.y. ago.