DIVISION OF THE LOWER CRETACEOUS YIXIAN FORMATION AND ITS OSTRACOD FOSSILS IN JIANCHANG BASIN, WESTERN LIAONING

The Yixian Formation of Jianchang Basin, represented by the Shangpingfang-Qingshiyan, ShangbaimiaoLuojiagou and Xiaolangjiagou-Sanmendian stratigraphic sections in Yaolugou area, may be subdivided into five members. The first member is characterized mainly by sandy conglomerate (Yaolugou layer). The second member is composed of sandy mudstone and shale intercalated with tuff, including the ostracod Cypridea (C.) biventricostata-Yumenia luojiagouensis assemblage subzone (in Shangbaimiao layer), Cypridea(C.) luanpingensis-Yumenia unidorsalta-Djungarica camarata assemblage subzone (in Luojiagou layer), and the fossil birds and reptiles etc., but the Houshigouli layer contains mainly fossil fishes and conchostracas. The third member consists of acidic-intermediate lavas and its pyroclastic rocks. The fourth member, called Qianshizigou layer, is characteristic of sandshale intercalated by andesite, containing the ostracod Yumenia luojiagouensis-Jianchangella dorsicostata assemblage subzone. The fifth member is of acid volcanic rocks. All the above mentioned ostracod assemblage subzones are put under the Cypridea (C.) biventricostata-Yumenia luojiagouensis-Djungarica camarata assemblage zone of Yixian Formation in Jianchang Basin, to be the early stage of Early Cretaceous in age. This paper describes the fossil ostracods of one new genus and seven new species.