Fusiline foraminiferal biostratigraphy and carbonate facies of the Permian Ratburi Limestone, Saraburi, central Thailand

Abstract. A succession of Permian carbonates outcropping along the highway north of Saraburi, central Thailand, has yielded a prolific and diverse fusiline-algal assemblage of Early Permian (Sakmarian) to early Late Permian (Midian) age. Six major units representing dominantly carbonate platform environments are recognised: turbidite and basin slope deposits, a platform margin algal reef, a back reef, an interior platform with patch reefs, a protected lagoon inner platform, and supratidal, dolomitised algal mats. Archaeolithoporella and Tubiphytes form major reef frameworks analogous to those described from the Middle Permian reefs of Trogkofel (southern Austria) and El Capitan (western Texas). The associated dasycladacean floras are assignable to the Eastern Circum-Pacific Realm, whilst the fusiline fauna has Arctic-Tethyan affinities in the Early Permian and Tethyan affinities in the Middle Permian. Eight fusuline assemblage zones are recognised and the Robustoschwagerina-Nagatoella Zone, representing the Sakmarian (early Artinskian) stage, is recorded for the first time from central Thailand. Phylogenetic studies of the fusulines, coupled with an examination of the diagenetic fabrics and field observations, indicate the presence of an unconformity during the late Early Permian-early Middle Permian, which may be correlatable with a worldwide eustatic sea-level fall or may be due to local tectonic movements.