New Ostracod Fossils From The Lower Jurassic Changliangzi Formation In Benxi Area Of Liaoning

The Changliangzi Formation is the Early Jurassic coal-bearing strata in Tianshifu basin and Saima-Qianyang basin of Benxi area,eastern Liaoning.The formation is mainly composed of dark gray mudstone and mudy siltstone intercalated with coal seams,showing typical sedimentary characteristics of continental shallow lake and swamp facies.Due to the abundant fossils of animals and plants,this formation has been concerned by the geological and paleontological circles for a long time.The fossils of plants,bivalves and insects from this formation have been studied a lot,but the fossil ostracods are not studied in detail.This paper reports the ostracod fossils from the Upper Member of Changliangzi Formation in Benxi area,in which there are 11 species of Darwinula,the well-known ostracod fossils in the Jurassic,discovered by the author for the first time.The species of Darwinula include D.taochunensis,D.huaqiaoensis,D.anhuiensis and D.yibinensis,D.parva,D.medialis,D.stenimpudica,D.giganimpudica,D.lufengensis,D.incurva,D.maanshanensis,and D.fengtaiensis.Based on the detailed descriptions of these ostracods mentioned above and the comparison with their related fossils,this paper proposes that the ostracod assemblage from the Upper Member of the Changliangzi Formation is characterized by the Assemblage of Darwinula huaqiaoensis--D.taohuanensis,dominated by the taxon Darwinula huaqiaoensis.The new funding has improves the classification level of the ostracod fossils in the studied area.Meanwhile,based on the geological ranges of Darwinula taohuanensis,D.huaqiaoensis and D.anhuiensis only recorded in the Lower Jurassic,combined with the comprehensive study of the fossil plant and bivalves associated with these ostracods,and the regional stratigraphic correlation,the Upper Member of the Changliangzi Formation is considered as the Early Jurassic,and probably the late Early Cretaceous age.In addition,combined with the lithological features of the Upper Member of the Changliangzi Formation and the indications of the bivalves and plants associated with the ostracods,this paper proposes that the Member of the Formation is probably deposited in the lakeside and swamp facies in environment,and the fossil ostracods show the benthic characteristics in shallow lake environment,close to those of the Lower Member of Ziliujing Formation in Beipei of Chongqing and Weiyuan of Sichuan.In sum,the discovery of Darwinula fossils from the Upper Member of the Lower Jurassic Changliangzi Formation fills a gap in the study of ostracods in this Formation,and would be very significant for the further study of the distribution and evolution of the Early Jurassic ostracods in Northeast China,and for the study of the Changliangzi Formation in dating,regional stratigraphic correlation,and paleoenvironment.