New observations on Devonian in the Baoshan Block of western Yunnan, China

Abstract

The Devonian Heyuanzhai Formation was re‐investigated in its type area in Shidian, Baoshan Block, western Yunnan, China. The sequences crop out at the Douyashan section adjacent to the Heyuanzhai village where they were measured. They are represented by thick fossiliferous successions of carbonate deposits interbedded with calcareous shale and mudstone. A great number of fossils were collected from the formation, with detailed documentation of brachiopods, crinoids, and ostracods in this paper. In the lower and middle parts of the Heyuanzhai Formation, the brachiopod Gypidula‐Schizophoria‐Spinatrypa assemblage is recognized and generally correlated to the Eifelian–Givetian. Whereas, in the upper part, the brachiopod Pugnax‐Hypothyridina‐Tenticospirifer assemblage is recognized for the first time, indicating an Early‐Middle Frasnian by occurrences of new species of rhynchonellid and cyrtospiriferid brachiopods, as well as the middle Late Devonian crinoids (Megaradialocrinus, Halocrinites, and Melocrinites) and ostracods (Palaeocopida, Platycopida, Metacopina, Podocopida). The sedimentary facies association and fossil assemblages herein indicate that the Heyuanzhai faunas from the Douyashan section inhabited a turbulent mid‐ramp with depth between the fair‐weather wave‐base and storm wave‐base, and were possibly accumulated in an environment that was derived from immediately adjacent habitats after short‐distance transportation.