Evolutionary History of Mammalian Fauna and Paleoenvironments-Late Cenozoic Eurasia and North America-

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The purpose of this research is to interpret the paleoenvironments and biostratigraphy of Late Cenozoic mammalian fauna heretofore undescribed for the Eastern Eurasia.In 1993, the Japanese and Chinese joint expedition conducted stratigraphical, sedimentological and paleontological survey in the Leijiahe Formation of Lingtai County, Gansu Province, China. The field work was done during the end of August and the first part of September 1993. Paleontologists excavated Locality 4 in detail, and collected small mammalian fossils from Locality 4 and 6 by screen and washing method.The following conclusions are reached :1. stratigraphic structure of the Leijiahe Formation consists conglomerate bodies and interbeded mudstone. Sedimentological data indicate that the sedimentological environment of the Leijiahe Formation is meandering river system and its flood plain.2. About 2,200 fossils are excavated from the Leijiahe Formation. Mammalian fossil evidence suggests that the Leijiahe Formation is Pliocene in age.3. Taphonomy of mammalian fossils from the Locality 4 of the Leijiahe Formation indicate that mammalian fossils were not transported from far away.4. Paleomagnetic data from the Locality 6 by Dr.Cheng of the Institute of Geology, Academia Sinica indicate that the Leijiahe Formation ranges in age during 3 million years.5. Paleoenvironmental analysis by microfossils is not yet finished. However, preliminary result of pollen analysis shows that the paleoenvironment of Leijiahe Formation is mixed forest and openland.From available evidences, it is concluded that the paleoenvironment of Leijiahe Formation is alluvium sedimentary basin under the dry climate.