The discovery of conodonts from the Lichaiba Formation in Xiongdong Village, Baoshan area, western Yunnan Province, and its geological significance

This research is mainly focused on the conodonts sequence of "Lichaiba Formation" in Xiongdong area. Detailed investigation has revealed five conodont zones, which are in ascending order of Pterospathodus pennatus procerus Zone, Kockelella walliseri Zone, Ancoradella ploeckensis Zone, Polygnathoides siluricus Zone, and Polygnathus nothoperbonus Zone. Because of the recognition of conodont Polygnathus nothoperbonus from Bed 8, it is argued that the strata should belong to Lower Devonian, named Xiangyangsi Formation. To sum up, the strata of Xiongdong section range from Wenlock Stage of the Silurian to Emsian Substage of Lower Devonian, with the lack of 8~10 conodont zones from the upper part of Ludlow Stage of the Silurian to the lower part of Emsian Substage of Lower Devonian between them. These data indicate that the area was affected by regional tectonism, resulting in the faulted contact relationship in the Silurian-Devonian interval. As for stratigraphic thickness, Xiongdong section is a highly concentrated section compared with other typical sections which are equally situated in the west of Yunnan Province.