SEQUENCE STRATIGRAPHIC FRAMEWORK OF THE PALEOGENE SUCCESSION OF THE HIMALAYAN FORELAND BASIN: A CASE STUDY FROM THE SHIMLA HILLS

摘要

The Subathu Formation (Late Thanetian-Early Priabonian) of the Himalayan Foreland Basin constitutes a 2~(nd) order depositional seque a subaerial unconformity at the base and a tidally influenced transitional sequence at the top. Three 3~(nd) order T-R successions - A, B and C are recognized. Succession A (late Thanetian-late early Cuisian) includes seven facies association (FA) and commenced with transgression (TST; A.1), followed by MFS and a condensed section (A.2; P4, SBZ 4-9), carbonate-siliciclastic coarsening upward sequence (A.3-4; HST), tectonically driven deposits (A.5-7), formation of back barrier lagoon with tidal inlet inhabited by sharks, ray fish; poor circulation in the lagoon caused mortality of the vertebrate fauna (A.6) and Early stage base level rise (A.7). Succession B. (Middle-Upper Cuisian, SBZ 11-12) includes seven FAs, B.1. Minor flooding surfaces, B.2-3. Coarsening upward succession, tidalflat, subtidal setting, B.4. Muddy tempestites, in inner shelf, B.5-6. Several benthic foraminifera and crabs indicate rise in sea level, B.7. Amalgamated sequence of proximal tempestites of shoreface in inner shelf setting. Succession C. (Early Lutetian-Early Priabonian) constitutes four FAs, C.1. Begins with flooding marked by Assilina spira abrardi zone, succeeded by Biotic condensation (C.2) passing into the Passage Bed (C.3; FSST) displaying textural inversion in delta influenced setting, and coastal sand (C.4; White Quartzarenite). Conformably overlying basal part of the Dagshai Formation comprises three tidally influenced parasequences (D.1-3; LST) separated by two calcrete levels. The C.4 and D.1 mark tidally influenced transgressive ravinement surfaces