Middle Devonian brachiopods from Qujing of eastern Yunnan, China and their biostratigraphical and palaeoecological implications

The Middle Devonian Qujing Formation at its type locality in eastern Qujing City, Yunnan was investigated for the first time. At the Wutaishan section, the formation is characterized by fossiliferous limestone and marls with massive terrigenous inputs. About 1292 individual specimens and several fragmented stringocephalid brachiopods were collected and systematically identified in this study. They are assigned into 18 species of 13 genera from 9 families in 6 orders. Undispiriferoides species and their detailed internal structures are for the first time illustrated, with a new species Undispiriferoides qujingensis being established. We recognize the assemblages of Stringocephalus and Ambothyris-Spinatrypa. The former is characterized by Stringocephalus burtini and accompanied with plenty of Meristella kütsingensis, M. flayelli, and Desquamatia sp. that are commonly present in the middle Givetian in South China. Whereas the latter is identified in the late Givetian and mainly contains small-sized, smooth spiriferides (e.g., Emanuella takwanensis, Ambothyris panxiensis) and atrypides Spinatrypa. The brachiopod assemblages in the section were largely correlated with environmental parameters and ecological factors in the near-shoal belt, where alternating clastic and marine carbonate depositions were disrupted by sea-level fluctuations. The Stringocephalus fauna favorably diversified in reefal and carbonate-dominated substrates and was replaced by the soft-bottom dwelling habitants of the Ambothyris-Spinatrypa assemblage, coinciding with multiple and progressive sea-level fluctuations in the Givetian.