Early Carboniferous onset of Gondwanian glaciation and Neo-tethyan rifting in South Tibet

Abstract

At least four diamictite-bearing intervals of Early Carboniferous age, containing faceted pebbles, trapezoidal cobbles and boulders up to 1000 m 3 in volume, have been recognized and traced for over 200 km along the Tethys Himalayan Zone of South Tibet, from east of Everest to west of Shishapangma. These largely glacio-marine sediments, intercalated within the Rakyang Formation, which overlies lower Tournaisian limestones and underlies lower Bashkirian black shales, were deposited during the Visean to Serpukhovian. Shore ice thus began to form in this region of northern Gondwana several tens of million years earlier than previously thought. This glacial event occurred at middle southern latitudes and was triggered by basin inversion and tectonic uplift in the first stages of Neo-tethyan rifting, as documented by the close association of diamictites with olistoliths and olistostromes in Lower Carboniferous units. After a transgressive interglacial episode in the Bashkirian, a much more widespread glaciation occurred in the latest Carboniferous, and was shortly followed by continental break-up and opening of Neo-tethys in the late Early Permian.