Abstract: The Zhangjiatian Formation newly built on the eastern margin of the Zhengkang landmass in the Longtangzhai area,Changning,western Yunnan is made up of the slope-basin clastic rock-siliceous rocklimestone-basalt formation,in which three types of sedimentary sequences can be recognized:distal low-density turbidity sequence composed of thin-bedded sandstones and mudstones,Bouma sequence representing proximal turbidity current deposits,and deep-sea static deposits composed of siliceous rocks,mudstone/siliceous mudstone and limestones. In the recent geological survey,abundant Tournaisian-Xiangbogian conodonts are collected in the limestones of the Zhangjiatian Formation. Especially,the occurrence of Visean-Tournaisianpelagic conodonts Gnathodusbilineatus and Scaliognathodusanchoralis indicates that a deep-sea trough basin was initiated during the Early Carboniferous. The Al/(A1 + Fe + Mn) ratios ranging between 0.22 and 0.40 suggest that the siliceous rocks in the Zhangjiatian Formation may be assigned to the thermally-affected biogenic siliceous rocks. Furthermore,the siliceous rocks have MnO/TiO₂ ratios ranging between 0.13 and 0.59,abnormal Ce value of 1.0, (La/Yb)_N ratios between 0.93 and 1.93,(La/Ce)_N ratios between 1.01 and 1.09,and relatively flat NASCnormalized REE patterns. All these data have reflected the characteristics of continental-margin siliceous rocks. Referenced to the regional geological data,it is inferred that during the Late Palaeozoic,there once occurred a rift trough developed between the Zhengkang landmass and Gengma passive continental margin,which was associated with the tectonic evolution of the Changning-Menglian Ocean. The slope-basin turbidity deposits in the Zhangjiatian Formation just represent the sedimentary records of the tectonic events during this period.