华北泥河湾盆地铺路哺乳动物群的磁性地层学定年

Magnetostratigraphic dating of the Pulu mammalian fauna in the Nihewan Basin,North China

华北泥河湾盆地的晚新生代河湖相沉积地层,产出了十分丰富的旧石器和哺乳动物化石,记录了早期人类活动以及晚上新世以来哺乳动物群的演化过程.作为广义泥河湾动物群之一,铺路动物群化石点位于盆地内的壶流河东侧,含有晚上新世及早更新世哺乳动物化石.本文结合生物地层学和岩石地层学,对含铺路哺乳动物化石的河湖相沉积物,进行详细的岩石磁学及高分辨率的磁性地层学研究,旨在对铺路哺乳动物群进行精确定年.结果表明,铺路剖面河湖相沉积物的磁性矿物主要为磁铁矿、磁赤铁矿和赤铁矿,平均粒度以准单畴为主.铺路剖面河湖相沉积物记录了布容正极性时(Brunhes normal chron)早期、松山负极性时(Matuyama reverse chron)、高斯正极性时(Gauss normal chron)和吉尔伯特负极性时(Gilbert reverse chron)晚期,铺路动物群产出在留尼旺(Réunion)地磁漂移之前,凯纳(Kaena)负极性亚时之后,年代约为3.0~2.2 Ma.本研究结果将广义泥河湾动物群的年代下限延至约3.0 Ma.此外,结合泥河湾盆地古气候学及古环境学研究结果,表明在上新世与更新世过渡期间,泥河湾动物群的演化受气候环境变化的影响,更适应干旱寒冷的生存环境.

The late Cenozoic fluvio-lacustrine deposits in the Nihewan Basin,North China,have yielded a very rich source of paleolithic sites and mammalian fossils,which recorded early human activities and the evolution of mammalian faunas since the late Pliocene.The Pulu fauna,one of the Nihewan faunas(sensu lato),is located on the eastern bank of the Huliu River in the Nihewan Basin and contains mammalian fauna in the late Pliocene to early Pleistocene.Here,we selected the fluvio-lacustrine deposits containing the Pulu mammalian fauna to conduct detailed rock magnetic and high-resolution magnetostratigraphy studies,combined with biostratigraphic and lithostratigraphic results,to precisely constraint on the Pulu mammalian fauna.The results showed that the magnetic minerals in the fluvio-lacustrine deposits of the Pulu section are mainly magnetite,maghemite and hematite,with predominantly pseudo-single domain.The Pulu fluvio-lacustrine deposits recorded the early Brunhes normal chron,the Matuyama reverse chron,the Gauss normal chron and the late Gilbert reverse chron.The Pulu mammalian fauna was found during the pre-Réunion Matuyama chron and the post-Kaena Gauss chron with the age about 3.0~2.2 Ma.This study has extended the lower age of the Nihewan faunas to about 3.0 Ma.Furthermore,the paleoclimatic and paleoenvironmental studies in the Nihewan Basin suggested that the evolutionary direction of the Nihewan faunas were influenced by changes in climate and environment during the Pliocene and Pleistocene transitions,and Nihewan faunas evolved towards adapting to a cold and arid environment.