Late Permian to Middle Triassic radiolarian faunas from northern Thailand

Moderately well-preserved Late Permian to Middle Triassic radiolarians are identified in chert beds that occur in the Shan-Thai Block of northern Thai land. These radiolarians are identical to the faunas of the Late Permian Ne oalbaillella ornithoformis and N. optima Assemblage Zones and the Triassic Parentactinia nakatsugawaensis and Triassocampe coronata Assemblage Zones r eported in chert sequences of Japan. We discovered the radiolarian faunas, apparently indicating Late Permian and Early Triassic ages, in almost conti nuous sequences of chert and shale exposed in the north of Chiang Mai. The occurrence of these radiolarian faunas provides important data to solve the P/T (Permian/Triassic) boundary in pelagic sequences. Our present discover y also furnishes significant data to reconstruct the paleobiogeography of M ainland Thailand during Late Permian to Middle Triassic times. Fifty specie s belonging to 35 genera, including three unidentified genera, are investig ated taxonomically. Four new species Pseudospongoprunum? chiangdaoensis, Ce nosphaera igoi, Cenosphaera? rugosa, and Tlecerina? apsornae are described.