泥河湾盆地磁性地层定年与早期人类演化

MAGNETOCHRONOLOGY OF THE FLUVIO-LACUSTRINE SEQUENCES IN THE NIHEWAN BASIN AND ITS IMPLICATIONS FOR EARLY HUMAN COLONIZATION OF NORTHEAST ASIA

主要评述了近年来泥河湾盆地磁性地层学的研究进展，包括建立泥河湾组的磁性地层年代格架、厘定泥河湾动物群的时代和确定华北地区早期人类活动年代序列。研究表明：第一，泥河湾组河湖相沉积序列记录了高斯正极性时末期以来的地磁极性特征（松山和布容极性时），即沉积时代始于约2．6Ma。早期人类至少在1．66～0．78Ma期间的大约90万年的时间内长期持续地占据高纬度的泥河湾盆地。泥河湾动物群（包括广义和狭义）的时代为2．0—0．8Ma。第二，华北地区早期人类已经能够适应东亚高纬度地区冬季风增强、夏季风减弱和干旱化趋势增强的复杂环境变化，尤其能适应中更新世气候转型前后中国北方多变而且不稳定气候条件和生态环境。因此，气候和生态环境的多变性与不稳定性是促进人类进化的重要因素。第三，早期人类走出非洲以后，可能沿不同的路径并以较快的速度扩散到东亚地区。向南越过印度尼西亚的赤道地区，向北至少扩散到40°N的泥河湾盆地。

The Nihewan Basin is located in the transition zone between the North China Plain and the Inner Mongolian Plateau. The basin is filled with Late Pliocene to Holocene lacustrine, fluvial, and wind-blown deposits. The Nihewan Formation comprises the whole fluvio-lacustrine sequence in the Nihewan Basin, which is overlain by the wind-blown loess sediments of the Holocene, and/or the last glacial period, and/or the interglacial period, and underlain by the Late Pliocene red clay of eolian origin. The timing of the Nihewan Formation rich in mammalian faunas and Paleolithic sites in the Nihewan Basin is critical to our understanding of a series of important issues, such as early human adaptability to the hostile environments in high northern latitudes, infilling process of the Nihewan Basin, and chronological sequence of the Nihewan faunas. This review focuses on recent developments in magnetic stratigraphy of the Nihewan Formation, which has significantly refined the chronology of early human colonization of the high-latitude East Asia, and of the terrestrial Nihewan Formation and faunas. High-resolution magnetostratigraphic investigations suggest that the Nihewan Formation records the tectonosedimentary processes of the Plio-Pleistocene Nihewan Basin and that the Nihewan faunas can be placed between the Matuyama-Brunhes geomagnetic reversal and the onset of the Olduvai subchron （0.78- 1.95Ma）. Specifically, the onset and termination of basin deposition occur just prior to ＇the Gauss-Matuyama geomagnetic reversal and during the period from the last interglacial to the late last glacial, respectively. The Nihewan faunas （ sensu lato ）, which comprises a series of mammalian faunas （ such as Maliang, Donggutuo, Xiaochangliang, Banshan, Majuangou, Huabaogou, Xiashagou, Danangou, and Dongyaozitou）, are placed between the Matuyama- Brunhes geomagnetic reversal and the onset of the Olduvai subchron（0.78 - 1.95Ma） , thus are suggested to span a time range of about 0.8 -2. OMa. In addition, the Xiashagou fauna, which was called the Nihewan Fauna（ sensu stricto） is estimated to span a period of about 0.8-2.0Ma based on faunal similarity. The integration of biostratigraphy, lithostratigraphy, and rock-magnetic stratigraphy with traditional magnetic polarity stratigraphy has resulted in reliable age determinations for a series of stone tool-containing layers of lacustrine sediments in the Nihewan Basin, such as Maliang（0.78Ma）, Donggutuo and Cenjiawan （1.1Ma）, Feiliang（ 1.2Ma）, Banshan （ 1.32Ma）, Xiaochangliang and Dachangliang （ 1.36Ma）, Majuangou （ MJG ）- Ⅰ （1.55Ma） , MJG- Ⅱ （1.64Ma） , and MJG-Ⅲ （1.66Ma）. Together with age determinations of Paleolithic/hominin sites in the southern Loess Plateau, it is concluded that during the Early Pleistocene there is a prominent early human flourishing in the high northern latitudes of East Asia and geographic expansion from middle to high northern latitudes of this area, and that the earliest populations to reach the hostile northeast Asia were able to survive for at least 0.5Ma prior to the Mid-Pleistocene onset of high-amplitude climate oscillation. Early Pleistocene humans of North China have met the long-term climate variability and some of the episodic environmental shifts, such as stepwise southerly migrations of the Mu Us desert lying to the north of the Chinese Loess Plateau, stepwise drying in the central Loess Plateau, and C4 plant expansions in the Loess Plateau region. Apparently, hominins prior to Homo sapiens were also quite adaptable to environmental change. To sum up, early humans were able to survive in the hostile environment of North China, especially of the high-latitude Nihewan Basin during the Early Pleistocene, when that area was characterized by increased environment and climate fluctuation. In particular, during or just prior to the Mid-Pleistocene climate transition, the prominent early human flourishing in the high northern latitude of East Asia and geographic expansion from middle to high northern latitudes of the area were largely due to the increasing fluctuation of global, regional, and local climates and environments over that period and to the innovation of diet, e.g., animal tissues.