First documentation of late Silurian and earliest Devonian (Lochkovian) conodonts from biostromes and mud mounds in Truong Son Terrane of the Indochina Composite Terrane: Geological significance

Late Silurian to Early Devonian conodonts are first documented from the marl–limestone alternations, with biostromes and mud mounds, succession in the north of the Loei fold belt, in the Truong Son Terrane of the Indochina Composite Terrane in NE Thailand. Species found include Wurmiella excavata, Panderodus unicostatus, Zieglerodina eladioi, Belodella resima, Neopanderodus aequabilis, Belodella anomalis, and Icriodus? sp. indet. Eight major lithofacies of sedimentary rocks were identified and interpreted as shallower to deeper marine environments in a warm, tropical zone. The sequence was deposited to the east of a Silurian rhyolitic volcanic arc with which it interdigitates and is regarded as a part of an arc or back-arc basin. A Siluro-Devonian arc shows that this part of the Indochina Composite Terrane rifted away from Gondwana in or prior to the Silurian.