| Abstract | Based on recent and new sampling in Spiti (Indian Himalaya), a refined and more detailed conodont zonation of the Induan and lower Olenekian stages is presented. Spiti has one of the richest and most
diverse Lower Triassic conodont records in the world and a high-resolution calibration to the LPL ammonoid time scale. Though the P-T boundary interval is not represented due to a depositional break, a fast transgression leads to immediate onset of
offshore conditions and to the occurrence of pelagic faunas. Spiti is therefore one of the rare places in the Tethys with a Neogondolella dominated conodont biofacies in the Griesbachian, and more than 10 neogondolellinid species document a worldwide
peak in diversity as well as an alternate biozonation for this interval (Orchard & Krystyn> 1998). The base of the Dienerian is marked by a drastic change in facies from well oxygenated to disoxic and in part anoxic conditions paralleled by a sharp
drop in Neogondolella diversity and later complete loss of species. Replacement rate by the newly appearing genus Neospathodus is surprisingly low, as is the apparent evolutionary diversification. The Dienerian-Smithian boundary interval slows a
return to well oxygellated sea bollu1n conditions and to very rich conodont faunas. Within five successive, biostratigraphically useful steps, 3 new genera (Borinella, Eurygnathodus, Discretella) and about 10 new species (6 of them neospathodids)
appear during a short time interval of less than 1 myr. This explosive radiation (Orchard, 2005, Zhao et al., 2006) allows a very fine-tuned conodont zonation of the Induan- Olenekian boundary. |