RADIOLARIAN EVIDENCE FOR THE STRATIGRAPHY AND PALAEO-OCEANOGRAPHY OF THE DEEP-WATER PASSIVE MARGIN OF THE INDIAN PLATE (KARAMBA FORMATION, INDUS SUTURE ZONE, LADAKH HIMALAYA)

New radiolarian biostratigraphical information sheds light on the Meso zoic sedimentary, tectonic and palaeoceanographic evolution of a south -Tethyan margin in northern India. Radiolarian cherts studied here for m part of deformed deep-water successions within the Indus Suture Zone (Ladakh Himalaya); these are defined as the Karamba Formation and int erpreted as the stratigraphically higher and palaeogeographically more distal parts of a passive margin (Lamayuru Group). This formation inc ludes radiolarites, pelagic carbonates, redeposited limestones, ferrug inous shales, sandstones, and abundant mafic extrusive rocks. Radiolar ian assemblages of early and late Middle Jurassic, mid-Cretaceous (mid -Albian to Cenomanian) and Late Cretaceous (Santonian) age were obtain ed from four measured sequences. Results indicate: (i) long, intact Ju rassic-Cretaceous successions, rather than disrupted melange, are pres ent in the Karamba Formation; (ii) extensive basic volcanism took plac e during the Middle Jurassic and can be correlated with an extensional phase affecting the NW Indian continental margin; (iii) non-calcareou s radiolarian-rich sediments accumulated during the Middle Jurassic, r eflecting the influence either of a broad Jurassic equatorial upwellin g zone, or a more localised coastal upwelling system. After drowning o f the Zanskar elastic shelf in the late Albian, sedimentation on the d istal shelf and upper slope was restricted by bottom current activity. Late Albian-Cenomanian radiolarites of the Karamba Formation are cont emporaneous with stratigraphic gaps and glauconite-phosphorite deposit ion on the Zanskar shelf. A well-developed eastward boundary current o ff the northern margin of India may have persisted until near the end of the Late Cretaceous. During the late Albian-Cenomanian, current act ivity and coastal upwelling were probably strong and radiolarian-rich sediments accumulated on the distal margin beneath the CCD. Pelagic li mestones accumulated during the Turonian over the entire margin, possi bly related to eustatic sea-level rise and consequent reduction in bot tom current activity. Intense oceanic circulation apparently was renew ed during the Coniacian-Santonian, as indicated by sedimentary hiatuse s in the Zanskar shelf succession and accumulation of carbonate-free r adiolarian ooze in the Karamba Formation.