Abstract

Raghavapuram Shale of Aptian-Turonian age represents a 2nd order sequence which is further subdivided into a transgressive systems tract (TST) representing the AptianAlbian high gamma-high resistivity (HGHR) Lower Raghavapuram and overlain by highstand systems tract (HST) of Cenomanian-Turonian low gamma-low resistivity (LGLR) Upper Raghavapuram Members. The Lower Raghavapuram has been further sub-divided into 3rd orders TST-HST-TST followed by Upper Raghavapuram into 3rd order HST-TST-HST. A comprehensive geological model is thus attempted by superimposition of depositional facies over paleogeographic maps at 4 levels (Aptian-Albian for Lower and CenomanianTuronian for Upper Raghavapuram) in a sequence stratigraphic framework. During Aptian, initially marine transgressions due to breakup of Elan Bank from India led to basal TST-I with prevalence of isolated, restricted marine, anoxic and lagoonal environment. This is followed by middle HST in which coarser clastics were delivered from basin margin (W or NW side) by fluvial processes over innershelf-intertidal sandflat/tidal channels and mixed siliciclastic-carbonate deposition (Kaikalur high). Upper part of Lower Raghavapuram (Albian) indicates further transgression with inundation of horsts (TST-II). In Upper Raghavapuram, initially during Early Cenomanian, increase in sedimentation rate has resulted HST-I with coarser clastics towards western margin. In Late Cenomanian, SE tilting of the basin led to basin-wide transgression (TST). Paleogeographic map at Upper Raghavapuram top (Turonian) depicts seaward shift of paleoshoreline indicating progradation of delta/slope fan (HST-II). The comprehensive depositional model through integrated sedimentological, log signature and other G&G data coupled with high resolution sequence stratigraphic studies will help to identify better reservoir within 3rd order HST and extent of short-term T-R cycles.