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

本研究的目的是解释迄今为止未描述的欧亚大陆东部晚新生代哺乳动物区系的古环境和生物地层。1993年，中日联合考察队在中国甘肃省灵台县雷家河组进行了地层学、沉积学和古生物学调查。实地工作是在1993年8月底和9月初进行的。古生物学家对4号地点进行了详细挖掘，并通过筛洗法在4号和6号地点收集了小型哺乳动物化石。得出以下结论：1。雷家河组地层结构由砾岩体和互层泥岩组成。沉积学资料表明，雷家河组沉积环境为曲流水系及其冲积平原。从雷家河组出土了约2200块化石。哺乳动物化石证据表明，雷家河组为上新世，年龄为3岁。3 .对雷家河组4地哺乳动物化石的地形学分析表明，哺乳动物化石并非来自遥远的地方。中国科学院地质研究所程博士从6地采集的古地磁资料表明，雷家河组的年龄在300万年左右。微化石古环境分析尚未完成。而花粉分析的初步结果表明，雷家河组的古环境为森林与开阔混交林。根据已有证据，认为雷家河组古环境为干燥气候下的冲积沉积盆地。

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.