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TheMesozoic sedimentary strata of Yanheying Basin have been regarded as the Early Cretaceous Jiufotang Formation by 1 /200 000 regional geological survey report and geological annals in recent thirty years. Through the research on1 /50 000 regional geological investigations of horizon, lithologic association, sequence, chronological ages and biologic assemblage, the authors consider that it is inconsistent with the finger-like interactive relationship between Jiufotang Formation and Yixian Formation regionally. Moreover, its rock association and sedimentary cycle are difficult to correlate the Jiufotang Formation in the studied area. The conchostracan fossils of this sedimentary strata consist of Yanjiestheria and Orthestheria which surface ornament features show a p rogressive types in conchostracan evolution, indicating generally the Earty Cretaceous in age. Consequently, the authors corsider the fluvial-lacustrine facies strata overlying the Yixian Formation are aged in the Early Cretaceous, correlated to the Nantianmen Formation according to its characteristics of lithologic association and sedimentary sequence.