Palynostratigraphy of the Devonian-Carboniferous transition in the Tulong section in South Tibet: A Hangenberg Event sequence analogue in the Himalaya-Tethys zone

Palynological assemblages from the Tulong succession in South Tibet enabled the recognition of three miospore biozones within the Zhangdong and 'Yali' formations. In ascending order, they are the Retispora lepidophyta-Verrucosisporites nitidus (LN) Biozone, the Vallatisporites vallatus-Foveosporites pellucidus (VP) Biozone and the Rugospora polyptycha-Tricidarisporites arcuatus (PA) Biozone. The LN Biozone in the Tulong section can be correlated to the LN Biozone of Western Europe, based on the first and last appearances of many index miospore species. However, Tournaisian palynological assemblages of Western Europe and South Tibet show compositional differences. The VP and PA biozones of South Tibet are correlated tentatively to the VI-HD and BP-TC biozones of Western Europe based on the occurrences of rare miospore index species in both regions. The Zhangdong and 'Yali' formations are now dated as Famennian to possibly earliest Visean. This age assessment is supported by rare conodonts and ammonoids recovered from intercalated limestones in the basal part of 'Yali' Formation. In the Everest region, the Devonian-Carboniferous boundary is now placed c. 10 m above the lower boundary of the 'Yali' Formation, which was originally suggested by Lin and Qiu (1985) to be position of the D-C boundary. Unlike western Gondwana, i.e. Bolivia and Brazil, the Himalaya-Tethys zone at the northeastern margin of Gondwana does not show obvious lithological evidence for glaciations. The new palynostratigraphic data, including information on sea-level changes reflected by variations in palynological composition and lithology around the Devonian-Carboniferous boundary allow, an interregional, approximate correlation with the classical Hangenberg Event sequence in the Rhenish Massif. The analogous Hangenberg Event sequence in South Tibet further supports the hypothesis that the rapid Hangenberg Event regression/transgression was a global eustatic event of significant magnitude. The co-occurrence of probably reworked Frasnian Geminospora lemurata and Archaeoperisaccus spores in the Himalaya-Tethys zone indicates the palaeogeographical proximity of the northern margin of Gondwana to the South China Block in the palaeoequatorial belt.