【摘要】 主要对泥河湾盆地下沙沟动物群(即狭义的泥河湾动物群)所在剖面河湖相沉积物进行了详细的磁性地层学和岩石磁学研究,揭示出下沙沟剖面记录了高斯正极性时(Gauss normal chron)晚期、松山负极性时(Matuyama reverse chron)及布容正极性时(Brunhes normal chron)。下沙沟动物群的层位跨越留尼旺(Reunion normal subchron)和奥杜威(Olduvai normal subchron)正极性亚时,其年代约为2.2~1.7Ma。上新世/更新世界限(高斯/松山(Gauss/Matuyama)地磁极性倒转界限)位于下沙沟剖面底部。结合前人研究结果,将泥河湾盆地已有磁性地层年代数据的动物群标注在地磁极性年表上,获得了泥河湾动物群的年代序列,结果表明泥河湾动物群位于高斯/松山和松山/布容(Matuyama/Brunhes)两个地磁极性倒转界限之间,因此,泥河湾动物群的年代区间为2.6~0.8Ma,这一研究结果完善了泥河湾盆地的生物地层年代学框架。更多还原

【Abstract】 The Nihewan Basin is one of a series of East Asian Cenozoic basins,which is located in the transition zone between the North China Plain and the Inner Mongolian Plateau.The Nihewan Basin sedimentary sequences are rich in mammalian fossil and Paleolithic sites,which has attracted the attention of geologists,paleontologists and paleoanthropologists,thus providing insights into our understanding of Quaternary land mammal biochronology and early human settlements in East Asia.The Nihewan Fauna(sensu lato) comprises a series of mammalian faunas in the Nihewan Basin.However,the Nihewan Fauna(sensu stricto) represents only the Xiashagou(XSG) Fauna.The XSG section(40°17′03″N,114°42′57″E) lies in the eastern margin of the Nihewan Basin.Here the Nihewan Formation has a thickness of 260 m.The fluvio-lacustrine sequence in the section consists of mainly grayish-yellow clayey silts,silts,sandy silts,conglomeratic silts and conglomerates.A total of 658 block samples oriented by magnetic compass in the field were taken at 20 ~ 50 cm intervals,except for the conglomerate layers.Here we present high-resolution magnetostratigraphic results that place stringent age controls on the XSG Fauna in the Nihewan Basin,Northern China.On the basis of the paleomagnetic,sedimentological and biochronological data,the recognized magnetozones of the XSG section can be correlated with the geomagnetic polarity time scale(GPTS).The detailed magnetostratigraphic results presented in this study place stringent age controls on the XSG Fauna.Fossils of this fauna mainly came from the depth interval of 140 ~ 220 m of the XSG section.Results show that the XSG sequence recorded the Brunhes normal chron,the Matuyama reverse chron and the late Gauss normal chron.The XSG Fauna resides in the Matuyama reverse chron(between the pre-Reunion Matuyama chron and the post-Olduvai Matuyama chron),yielding an estimated age of ca.2.2~ 1.7Ma.The Pliocene-Pleistocene boundary(Gauss/Matuyama boundary) is located in the lower part of the XSG section,ca.l4 m above the eolian red clay formation.Therefore,the basal age of the Nihewan Formation at the XSG section can be constrained just prior to the Gauss/Matuyama geomagnetic reversal.The combined evidence of our study and previously published magnetostratigraphic data documents a magnetochronological sequence of the mammalian faunas in the Nihewan Basin,which have been placed between the Gauss-Matuyama geomagnetic reversal and the Matuyama-Brunhes geomagnetic reversal(between 2.58 Ma and 0.78 Ma).Thus,the age of the Nihewan mammalian faunas can be revised to a time range of ca.2.6~0.8Ma.更多还原