基于区域地貌沉积演化的陕山地堑盆地古人类遗址年代研究

There exist many Paleolithic sites in Shaanxi-Shanxi Graben Basin. Some researchers relied on the characteristics of the fossil mammals in the sediment bearing the hominin evidences to evaluate their ages, while other researchers used physical dating methods to analyze their ages. Although many research results had been got, the serious controversy also remains. For the need of living, the hominins around this region normally selected the places near rivers of lakes to dwell in order to get fresh water and stone materials easily. Because of the regional paleolake regression/transgressions during the Quaternary, the hominins often changed their living places, which made alluvial-lacustrine sediments with different ages probably bear stone artifacts and/or skeletal evidence for hominins. For reevaluating the ages of some Paleolithic sites in the region, we planned to do the research as follows. Firstly, we will further investigate the cyclic history of the paleolake regression/transgressions in the region. Secondly, analyzing the characteristics of the geomorphic-sedimentary bodies which bear hominin leaves, we are attempted to decide in which cycle it formed and make clear when it developed and ended. Thirdly, on the basis of the former result, we will do more detailed analysis on rhythm of the geomorphic-sedimentary bodies to confirm the constraint ages of hominin layers in the geomorphic-sedimentary bodies in these Paleolithic sites.

陕山地堑盆地是东亚地区古人类遗址分布比较集中的一个区域。基于哺乳动物化石组合特征和物理测年手段的遗址年代研究，成果丰硕，但争议仍然很大。为了生活之需，栖居在该区域的古人类一般都会选择临水而居（河或湖），地貌上为河岸或湖滨之地。而在盆地湖退-湖侵循环变化背景下，区域内入湖的或连接相邻湖泊的河流段及湖滨之地常会被淹没或又重新露出水面，从而引起古人类生活空间在地貌微区位上的变迁。这使得沉积于不同演化阶段的河湖相地层都有可能保存有古人类遗迹。项目首先拟进一步探明区域湖退-湖侵地貌沉积环境的变化历史；然后，依据保存有古人类遗迹的地貌沉积体的特征判断其沉积所处的历史阶段，并确定其形成的起止时间范围；再次，在已确定该地貌沉积体形成的起止时间范围前提下，对保存古人类遗迹的沉积层序列进行系列沉积特征分析，对含古人类遗迹的文化层层位堆积年代进行确定。研究结论将为进一步研究区域古人类其他方面的问题提供基础铺垫。

本研究从区域地貌演化的视角对陕-山地堑盆地内古人类遗址的形成年代进行探索。基本思路是首先厘清遗址所在区域的湖退-湖侵演化历史与地貌发育的对应关系，分析含有古人类遗迹沉积体的地貌和沉积特征，以湖退-湖侵历史为标尺框定沉积体形成的年代范围。再对遗迹文化层进行沉积特征分析，结合孢粉古气候重建和物理测年进行综合判断，进而确定遗迹文化层的形成年代。采用这样的方法和流程，对陕-山地堑盆地内的四处古人类遗址年代进行了研究。确定了丁村人遗址79:01、54:102、54:100地点文化层分别形成于~0.77Ma-0.47Ma、~0.56Ma-0.20Ma和地~0.25Ma-0.07Ma。厘清了西侯度遗址上方黄土-古土壤序列，古地磁数据说明文化层形成年代上限~1.16Ma；孢粉所反应的古气候特征和三门古湖湖退时间推断西侯度文化层形成年代下限约在1.45~1.77Ma。洛河两岸阶地所记录的区域湖退-湖进发生年代框定了包含大荔人遗址沉积体的年代形成于0.205~0.62Ma，根据文化层上方沉积特征和古气候变化判断遗址形成的年代~0.55Ma。许家窑遗址（74093地点）所在梨益沟沉积物中记录了三次火山活动活跃期，通过大同火山群活动-古湖湖退湖侵演化历史框定遗址文化层形成年代0.09Ma~0.31Ma，光释光测年、孢粉古气候重建进一步确认遗址文化层的形成年代与L2发育的后期相当~0.14Ma。