Magnetic Polarity Stratigraphy of the Upper Siwalik Subgroup, East of Chandigarh, Punjab Sub-Himalaya, India

Abstract

An approximately 900m thick succession of pre-Pinjor (Tatrot) and Pinjor beds of the Upper Siwalik Subgroup is exposed in the Khetpurali section which lies to the east of Chandigarh. Samples collected from the mudstone interval from forty-nine fluvial cyclic units exhibit a stable detrital remanent magnetisation. The study of magnetic polarity of these samples reveals the presence of six normal and six reverse magnetozones. The Tatrot-Pinjor faunal boundary has been interpreted to approximately lie at the Gauss-Matuyama boundary. Based on this interpretation, the Olduvai Event in Matuyama reversed polarity epoch spans 160m of the middle part of the Pinjor Formation. The local Pliocene/Pleistocene boundary in this section is interpreted to lie 170m higher in the sequence with reference to the Tatrot-Pinjor faunal boundary.

Changes in the fluvial domain in the post-Gauss Epoch are interpreted to reflect changes from 'meander belt' deposits to 'braided stream' deposits. The first appearance of conglomerates in the section has been interpreted to occur in the post-Olduvai time.