Revision of Miange Formation and establishment of Lucan Member, western Sichuan

The revised Miange Formation is interpreted as intermediate acidic volcanics of subalkline calc alkaline, potassium alkaline series, with intercalations of slates. This sequence is part of the Yidun paleo island arc, lying on a sequence boundary, which is underlain by the Qugasi or Genlong Formation of an island stage to an immature island arc stage. A fossil rich, argillaceous and carbonate member at the top of the Miange Formation is assigned as Lucan Member. The Miange Formation is overlain by the turbidite facies Lamaya Formation.