Stratigraphy and sedimentary history of the Nepal Tethys Himalaya passive margin

The sedimentary history of the Nepal Tethys Himalaya began with deposition of thick carbonates in the Cambro?–Ordovician, followed by a mixed siliciclastic–carbonate epicontinental succession recording two major deepening events in the Early Silurian and Late Devonian. Fossiliferous carbonate ramp deposits in the Tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins (“rift stage”). Break-up in the mid-Early Permian, locally associated with effusion of tholeiitic lava flows, was followed by a transgressive sandy to shaly, locally coal-bearing or bioclastic unit capped by condensed pelagic carbonates in the Middle to Late Permian (“juvenile ocean stage”). Subsidence of the cooling stretched crust led close to bathyal water depths in the Olenekian, but then slowed down in the Middle Triassic to increase again sharply in the Late Triassic owing to renewed extensional tectonic activity and sediment loading during up- and out-building of the Indian continental terrace. Deposition of tropical platform carbonates finally became widespread in the middle Liassic (“mature passive margin stage”). The initial fragmentation of Gondwana in the Middle Jurassic led to rejuvenation of the Indian craton and deposition of quartzo-feldspathic hybrid arenites, capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late Bathonian/middle Callovian. Next, a discontinuous pelagic grey marly limestone unit was followed by the ammonoid-rich offshore Spiti Shale in the Late Jurassic. The final disintegration of Gondwana began in the Berriasian, when quartzose siliciclastics derived again from the rejuvenated Indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the Valanginian? followed in the Hauterivian to Albian by more felsic differentiates such as the trachyandesites exposed in the Lesser Himalaya 120 km to the south. A widespread drowning episode, fostered by waning volcaniclastic supply during a global eustatic rise, is documented by a major glauconitic horizon deposited at middle southern latitudes in the late Albian, overlain by “Scaglia-like” pelagic limestones in the latest Albian. The final part of sedimentary history, during the rapid northward flight of India and its collision with Eurasia, is not documented anywhere in Nepal due to later erosion of Upper Cretaceous to Lower Tertiary strata.