Lithostratigraphy of Permian marine sequences, Khao Pun area, central Thailand: Paleoenvironments and tectonic history

Geologic mapping and subsurface lithostratigraphic investigations Tt ere ca rried out in the Khao Pun area (4 km(2)), central Thailand. More than 250 h and specimens, 70 rock slabs, and 70 thin sections were studied in conjunct ion with geochemical data in order to elucidate paleoenvironments and tecto nic setting of the Permian marine sedimental uv sequences. This sedimentary succession (2485 m thick) was re-accessed and re-grouped into three lithos tratigraphic units, namely in ascending order the Phu Phe, Khao Sung and Kh ao Pun Formations. The Lower to lower Upper Permian sedimentary facies indi cated the transgressive/regressive succession of shelf sea/platform environ ment to pelagic or abyssal environment below the carbonate compensation dep th. The sedimentological and paleontological aspects, together with petroch emical and lithological points of view reveal that the oldest unit might in dicate an Early Permian shelter ed shallow or lagoonal environment. Then th e depositional basin became deeper as suggested by the prolonged occurrence of bedded chert-limestone intercalation with the local exposure of shallow er carbonate build-up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicu cullus sp.) cher ts. This cryptic evidence might indicate the abyssal envir onment during middle Middle to early Late Permian; whereas, previous studie s advocated shelf-facies environments. Following this, the depositional con dition might be a major regression on the microcontinent close to Indochina , from the minor transgressive/regressive cycles that developed within a sk eletal barrier; and, through the lagoon with limited circulational and anae robic conditions, on to the tidal fiat to the sheltered lagoon without effe ctive land-derived sediments.