Abstract
The Simla Group of the western Lesser Himalaya comprises a prograding muddy delta sequence that was built by the collapse of a carbonate shelf during Late Precambrian time. The Simla sequence consists of a thick, about 1500 m, coarsening-upwards clastic succession which is divisible into the Basantpur, Chhaosa and Sanjauli Formations. Carbonate appears only in the basal formation (Basantpur Formation). Three subfacies for the basal Simla have been discerned: a carbonate platform to the northeast (Basantpur subfacies), shallow water with more clastic influence to the south (Kunihar subfacies) and relatively deep water adjacent to a fault scarp to the northwest (Kashlog subfacies). The first signs of deltaic sediments appear in the middle of the Basantpur Formation and are well developed in the overlying Chhaosa Formation. The overall characteristics of the Chhaosa facies are those of a delta-front and distributary mouth bar where floods from distributaries and shelf storms lead to very rapid deposition, mostly above wave base. The uppermost Sanjauli Formation is relatively thick bedded, coarse grained and more frequently cross-bedded representing delta platform and distributary channel deposits. A significant change in environment of deposition is observed in the overlying beds, previously known as the Upper Sanjauli Member, and now being separated as the Jagas Formation. The Jagas facies suggests major uplifts and a climatic change to semi-arid conditions. The detritus of the Simla delta came from the Indian Shield situated to the south of the delta. Most constituents indicate mature sediments with occasional lithoclasts of sedimentary and intraformational characters. Faulting presumably continued during the deposition of the Simla Group as is characteristic for rifted continental margins.
Published Version
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