The stratigraphy of the Tethys Himalaya

This article reviews the entire late Neoproterozoic to Eocene evolution of the northern Indian continental margin. In the NW Himalaya, the Cambrian succession is overlain with angular unconformity by Ordovician conglomerates, testifying to a Pan-African orogenic event. At the top of the pre-rift sequence, an unconformity truncates Tournaisian limestones or older strata testifying to the onset of Neotethyan rifting. The up to ~1.5 km thick rift sequence chiefly consists of quartz-rich white sandstones and black mudrocks. Four diamictite intervals in South Tibet testify to shore ice in the Visean-Serpukhovian, followed by two transgressive fossiliferous intervals (Bashkirian Fenestella Shales and Moscovian Chaetetid Shales). Glacio-marine diamictites containing volcanic detritus document renewed glaciation at Kasimovian-Gzhelian to Asselian times during the climax of rifting. At the base of the drift sequence, mid-Sakmarian glauconitic arenites are followed by basaltic eruptions during the initial development of the Neotethyan volcanic passive margin. Final submergence of rift shoulders is documented by middle to upper Permian strata followed by condensed ammonoid-bearing Lower Triassic pelagic limestones and by Middle Triassic shelfal marls and marly limestones. Thick UpperThis article reviews the entire late Neoproterozoic to Eocene evolution of the northern Indian continental margin. In the NW Himalaya, the Cambrian succession is overlain with angular unconformity by Ordovician conglomerates, testifying to a Pan-African orogenic event. At the top of the pre-rift sequence, an unconformity truncates Tournaisian limestones or older strata testifying to the onset of Neotethyan rifting. The up to ~1.5 kmthick rift sequence chiefly consists of quartz-rich white sandstones and black mudrocks. Four diamictite intervals in South Tibet testify to shore ice in the Visean-Serpukhovian, followed by two transgressive fossiliferous intervals (Bashkirian Fenestella Shales and Moscovian Chaetetid Shales). Glacio-marine diamictites containing volcanic detritus document renewed glaciation at Kasimovian-Gzhelian to Asselian times during the climax of rifting. At the base of the drift sequence, mid-Sakmarian glauconitic arenites are followed by basaltic eruptions during the initial development of the Neotethyan volcanic passive margin. Final submergence of rift shoulders is documented by middle to upper Permian strata followed by condensed ammonoid-bearing Lower Triassic pelagic limestones and by Middle Triassic shelfal marls and marly limestones. Thick Upper Triassic strata containing bimodal volcanic detritus indicate intraplate extension during the separation of the Lhasa Block from Gondwana. The Lower Jurassic carbonate platform contains a dark-mudrock interval with frequent storm layers testifying to the early Toarcian “oceanic anoxic event”. The disconformity at platform top is onlapped by widespread upper Middle Jurassic condensed horizons with iron ooids, overlain by ammonoid-rich Upper Jurassic black shales. Lower Cretaceous sandstones indicate renewed intraplate extension and volcanic activity during the final breakup of Gondwana. Condensed glauco-phosphorites deposited during the latest Albian to latest Cenomanian “oceanic anoxic events” OAE1d and OAE2 marked the synchronous drowning of the clastic shelf. Upper Cretaceous foraminiferal oozes are overlain by a regressive marly/sandy sequence deposited during the initial impingement of the Deccan plume at the base of Indian lithosphere. After the India/Asia collision onset at ~60 Ma, shallow-marine carbonates record a Paleocene/Eocene disconformity interpreted as induced by the flexural wave propagating from the suture zone. The passive-margin succession is unconformably sealed by volcaniclastic redbeds containing grains of ultramafic mantle rocks fed by the Transhimalayan arc-trench system during obduction onto India and initial development of the Himalayan thrust belt. Triassic strata containing bimodal volcanic detritus indicate intraplate extension during the separation of the Lhasa Block from Gondwana. The Lower Jurassic carbonate platform contains a dark-mudrock interval with frequent storm layers testifying to the early Toarcian “oceanic anoxic event”. The disconformity at platform top is onlapped by widespread upper Middle Jurassic condensed horizons with iron ooids, overlain by ammonoid-rich Upper Jurassic black shales. Lower Cretaceous sandstones indicate renewed intraplate extension and volcanic activity during the final breakup of Gondwana. Condensed glauco-phosphorites deposited during the latest Albian to latest Cenomanian “oceanic anoxic events” OAE1d and OAE2 marked the synchronous drowning of the clastic shelf. Upper Cretaceous foraminiferal oozes are overlain by a regressive marly/sandy sequence deposited during the initial impingement of the Deccan plume at the base of Indian lithosphere. After the India/Asia collision onset at ~60 Ma, shallow-marine carbonates record a Paleocene/Eocene disconformity interpreted as induced by the flexural wave propagating from the suture zone. The passive-margin succession is unconformably sealed by volcaniclastic redbeds containing grains of ultramafic mantle rocks fed by the Transhimalayan arc-trench system during obduction onto India and initial development of the Himalayan thrust belt.