Evolution in Basin Fill Style During the Mesozoic Gondwana Continental Break-up in the Godavari Triple Junction, SE India

Abstract

Consistent changes are observed in the Mesozoic sedimentary lithofacies and palaeocurrents during the transition from the continental Gondwana (NW-SE trending Chintalpudi Graben - CG) to the coastal Gondwana (NE-SW trending Krishna Godavari Coastal Basin - KGCB) in the Godavari Triple Junction (GTJ). The Mesozoic continental Gondwana sediments include the Kamthi (early Triassic), Kota (Jurassic) and Gangapur (early Cretaceous) Formations. Coastal Gondwana succession comprising the Raghavapuram (early Cretaceous) and the Tirupati (Middle to late Cretaceous) Formations transversely superimpose the continental Gondwana. The Continental Gondwana is mainly cross-stratified sandstone and fossiliferous ( Glossopteris and Ptilophyllum flora) clay assemblage of alluvial environment. Palaeocurrent is towards NW in the Kamthi Formation, WNW in the Kota Formation and centripetal in the Gangapur Formation. The Raghavapuram Formation (KGCB) comprises of grey/carbonaceous clay-sandstone association of SE flowing delta plain distributories with inter-distributory swamps and fossiliferous white clay (a mix of Ptilophyllum flora and invertebrate fauna) of prodelta / shallow marine environment. The succeeding sandstone- conglomerate facies of the Tirupati Formation (Middle to late Cretaceous) with SE palaeocurrent indicates delta progradation whereas the infratrappean clay-limestone beds (mainly invertebrate fauna of Maastrichtian age) point to delta abandonment, prior to the K/T boundary volcanism. Tectono-sedimentary model presented in this communication incorporates that the change from the continental Gondwana to coastal Gondwana had occurred in four stages. During stage-I (late Carboniferous to early Jurassic) the sediments were deposited by a north-westerly flowing alluvial system whose distal source was located in southeast beyond the east coast of India. Stage -II (Middle to late Jurassic) is marked by westerly shift in palaeocurrents attributed to an obstruction caused by an upliftment of the Mailaram high parallel to the NE-SW Eastern Ghat trend. Stage-III (early Cretaceous) is heralded by the onset of deltaic sedimentation in SE due to separation of landmass that supplied detritus to the CG until the end of the Jurassic. During stage-IV, the delta progradation is accentuated by the basement uplift (Eastern Ghat Mobile Belt). It is suggested that the change over from continental Gondwana to coastal Gondwana had occurred over a time span of about 70 my between late Jurassic to Cretaceous and controlled by phase-wise upliftment of the basement as a corollary to the Gondwana continental break-up.