基于区域河湖地貌演化历史的大荔人化石层位年代分析

目前对含大荔人化石的地层年代认识仍存很大争议。采用黄土—古土壤序列定年法广泛调查渭河盆地东北部区域和大荔人化石点附近洛河上下游河段过去的河湖环境演变历史;在此基础上,结合产出大荔人化石的地貌沉积体特征,分析其形成时所处的区域演化阶段及其中含化石的沉积层位堆积年代。结果显示,区域曾在S₁₄、L₉、L₆、S₂、L₂和L_1SS发育或堆积时期发生过数次古湖湖退或河流下切;含大荔人化石的沉积层是在区域发生于L₆晚期的一次湖退后,洛河于出露至气下的古湖湖底上堆积而成的,其堆积时代与S₅古土壤发育时代相当,平均年龄约0.55 Ma BP。由该研究结果推论,学界对北京猿人年龄估计的老的年龄框架可能偏年轻。

The deduction of the age of the fossil Dali Man from the history of the regional geomorphic-sedimentary evolution

Dali Man, an archaic type of early Homo sapiens, is of great significance to the origin of Homo sapiens. However, there still exists a debate about the age of the fossil. There were a series of lacustrine or alluvial terraces in the northeast part of the Weihe Basin and in the Luohe River near the Dali Man site, and the paper adapted loess-paleosol sequence dating method to determine their ages and make clear the history of the regional paleolake regression-transgression evolution. In combination with the characteristics of the geomorphic-sedimentary body which contains the fossil Dali Man, the paper analyzed the regional paleolake regression-transgression stage during which the body formed. In the light of the particle size evidence and pollen one of the geomorphic-sedimentary body, the paper further analyzed the age of the alluvial sediment in which the fossil human skull was discovered. The result shows that there occurred several paleolake regressions and river down-cutting when S₁₄, L₉, L₆, S₂, L₂ and L_1SS developed or accumulated respectively, and that the sandy-gravel sediment with the fossil was deposited after the paleolake regression at the late stage of the deposition of L₆. This lake regression made some of the paleolake bottom emerge subaerially and Luohe River flowed on it to erode the former lacustrine sediment and deposit the alluvial one. Therefore, the deposition of the alluvial sediment is probably synchronous with the formation of S₅, with an average age of 0.55 Ma BP. Because of more development of the Dali Man than the Homo erectus pekinensis, the result indicates that the age of the Homo erectus pekinensis is probably more than 0.55 Ma BP.