滇西保山熊洞村栗柴坝组牙形石的发现及其地质意义

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

针对保山地层区熊洞剖面原属栗柴坝组的灰岩进行了牙形石样品分析,总计建立了5个牙形石带,分别为Pterospathodus pennatus procerus带、Kockelella walliseri带、Ancoradella ploeckensis带、Polygnathoides siluricus带和Polygnathus nothoperbonus带。该剖面第8层原属栗柴坝组,Polygnathus nothoperbonus分子的出现证实其为下泥盆统埃姆斯阶的地层,应归为向阳寺组。剖面总体对应志留系温洛克统底部到下泥盆统埃姆斯阶中部,中间缺失志留系罗德洛统卢德福特阶—下泥盆统埃姆斯阶之间的8~10个标准牙形石带,说明该地区后期可能受构造作用影响,志留系和泥盆系界线为断层接触。该剖面牙形石序列的建立一定程度上完善了滇西保山地层区志留系生物地层的研究程度,为下一步该区生物地层格架的建立奠定了基础。

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.