Division and correlation of Yixian Formation in western Liaoning , China

The Yixian Formation is a series of volcanic-sedimentary rocks in Biepiao area of Liaoning Province. It is mainly composed of basic and intermediate-basic volcanic lava , pyroclasts and terrestrial sedimentary rocks. Based on the regularity of volcanic activity , the Yixian Formation was divided by the present authors into four members in ascending order : the first member is of basal conglomerate , basic and intermediate-basic vol- canic rocks ; the second member is of lake phrase sedimentary rocks , or in another word , precious fossil-rich sedimentary beds ; the third is of basic volcanic rocks ; and the fourth is of upper conglomerate. Field mapping and comprehensive study also indicate that there are abundant vertebrate fossils ( mainly of Psittacosaurus ) in the first member of the Yixian Formation , and the Jehol Biota ( including Sinosauropterxy , Confuciusorns sanc- tus , Archaefructus , etc. ) is yielded in the second member of Yixian Formation. From west to east , the volcanic activity of Yixian Formation changed regularly from early to late , and from basic and intermediate-basic to acid ( alkali ) .