New opinions on the sedimentary environment of the Upper Devonian Nanguang Formation in Jinghong, southern Yunnan

The Devonian strata distributed in southeastern Jinghong of Yunnan were partly named the Padang Formation for the strata composed of coarse clastic rocks, and partly named the Nanguang Formation for the strata characterized by fine clastic rocks and tuff. The Padang Formation was assigned to Middle Devonian according to the brachiopeds fauna whereas the Nanguang Formation to Upper Devonian according to Lepotophloeum rhombicum. Much controversy has existed concerning their sedimentary environments, and the opinions include continental environment, alternating environments between continent and marine, neritic shelf, and subabyss-abyss environments. The authors' investigation indicates that the index fossil of Late Devonian, Lepotophloeum rhombicum, is also discovered from the Padang Formation and that the Padang Formation is younger than the Nanguang Formation on the basis of the sedimentary sequence. Therefore, it is suggested that the name of Padang Formation should be abolished and that the whole sequence should be named the Nanguang Formation belonging to Upper Devonian. The Nanguang Formation is characterized by typical Bouma sequences with fossil radiolarians and represents deep-sea turbidite fan successions.