Lower Permian conodonts from Palaeo-Tethys Ocean Plate Stratigraphy in the Chiang Mai-Chiang Rai Suture Zone, northern Thailand

Lower Permian (lower Sakmarian) conodonts are reported from a coherent section of Ocean Plate Stratigraphy, and from a limestone block in the Palaeo-Tethys suture zone between Lamphun and Lampang, south of Chiang Mai, northern Thailand. Conodont species from both the pelagic limestones of the OPS section and the limestone block are deep-water forms with distinctive biogeographic affinities comparable to faunas of the Urals and North American Mid-Continent. A new name, Chiang Mai-Chiang Rai Suture Zone, is here proposed for the Palaeo-Tethys suture in northern Thailand that forms the boundary between the Sibumasu Terrane and the Sukhothai Arc terrane. The Inthanon Zone of northern Thailand is interpreted as representing a fold and thrust belt west of the Chiang Mai-Chiang Rai Suture Zone, which comprises Sibumasu Terrane continental margin rocks and remnant klippen of Chiang Mai-Chiang Rai Suture Zone rocks thrust as a nappe westward during the Triassic collision between Sibumasu and the Sukhothai Arc/Indochina Terrane.