北票-义县地区义县组以火山-沉积地层为主体,具有4个火山活动亚旋回,生物化石主要形成于第一、第二、第四亚旋回期间,构成了3个产出层位.以中华龙鸟、孔子鸟、辽宁古果为代表的珍稀化石组合产在义县组二段中,形成于125～127Ma期间.枕状熔岩、淬火岩等特殊岩石的出现和高频层序地层研究表明,北票、义县地区的含珍稀化石沉积层(义县组二段)都处于相对较深的湖盆沉积环境,表现为湖扩展体系域沉积,两地含珍稀化石沉积地层层位基本相当.义县组形成于135～120Ma期间,属于早白垩世.多方面证据表明侏罗系-白垩系界限应当置于义县组底界. The Beipiao-Yixian area, the Yixian Formation, has volcanic-sedimentary strata as its main body and has 4 volcanic sub-cycles. The fossils mainly formed during the first, second and fourth sub-cycles and formed three output strata The rare fossil assemblage, represented by Chinese dragon bird, Confucius bird and Liaoning ancient fruit, was formed in the second member of Yixian Formation during 125 ~ 127 Ma.The occurrence of special rocks such as pillow lava and quenched rock and high frequency sequence The stratigraphic studies show that the rare fossil sedimentary layers (the second member of Yixian Formation) in Beipiao and Yixian are all in a relatively deep lacustrine sedimentary environment and are characterized by the deposition of the lake system tract and the deposition of stratigraphic layers The Yixian Formation formed during the period of 135-120 Ma and belonged to the Early Cretaceous.According to various evidences, the limit of Jurassic-Cretaceous should be placed at the bottom boundary of Yixian Formation.