DISCOVERY OF THE SINIAN SYSTEM IN THE HAIYUAN AREA, NINGXIA, AND ITS FEATURES

Sinian strata were for the first time found in the Haiyuan area, Ningxia, which are named the Wenchangshan Group. This group is divided in ascended order into two formations. The Dundunliang Formation in the lower part, 9—80 m thick, is composed of massive to thick-bedded conglomerate and overlies the Xihuashan Group of the Jixian System unconformably; the Gaojiashan Formation, 16—46.5 m thick, consists of sandstone and siltstone and is unconformably overlain by Upper Silurian clastic rocks. Both the above-mentioned two formations contain abundant plant microfossils, including 10 genera （26 species）, e. g.: Pseudozonos phaera, Trachys phaeridium, Leiopsophos phaera, Leiafusa, Lophosphos phaeridium and Monotromatos phaeridium. Many species of theirs are Late Sinian representative elements. This group is broadly equivalent to the Toushantuo Formation-Dengying Formation in western Hubei of China.