Biostratigraphy and palaeobiogeography of Lower Permian (lower Kungurian) conodonts from the Tak Fa Formation (Saraburi Limestone), Thailand

Lower Permian (lower Kungurian) conodonts are reported from the Indochina Block of Southeast Asia. The fauna from the Tak Fa Formation of the Saraburi Limestone Group exposed in limestone hills NNW of Khok Samrong, Thailand, includes 'Sweetognathus subsymmetricus' Wang, Ritter and Clark (early forms) and 'Pseudosweetognathus costatus' Wang, Ritter and Clark. The co-occurrence of these species indicates a Lower Permian age (upper half of the lower Kungurian) for the sampled limestones representative of the 'Mesogondolella siciliensis'–'S. subsymmetricus' Zone of South China. 'Sweetognathus' and 'Pseudosweetognathus' are for the first time reported from the Indochina terrane located in the palaeoequatorial belt in the Kungurian. 'Pseudosweetognathus' appears restricted to the Kungurian of the South China and Indochina terranes thus supporting palaeogeographic reconstructions that isolate these terranes within the Palaeo-Tethys during the Kungurian.