上新世/早更新世转型期泥河湾盆地植被演替和气候演变特征与机制

With the formal ratification of the Quaternary system, the terrestrial Global Boundary Stratotype Sections and Points of Plio-Pleistocene boundary become a new international research hotspot. Nihewan strata in the Yanyuan Basin is identified as one of the standard strata of early Pleistocene in northern China, where several late Pliocene stratigraphic sections are also exposed at multiple locations, and these sedimentary sequences of Late Pliocene to Early Pleistocene,can supply the precious geological records in the establishment of terrestrial boundary Quaternary stratotype sections and points. In the project, late Pliocene to early Pleistocene exposed stratigraphic sections with detail paleomagnetic data will be selected as the research object in the lacustrine terraces on both sides of Huliu River from Datianwa to Dagouleng. Through high density pollen sampling (with 10-20 cm intervals), create a high resolution pollen assemblage sequences, restore the vegetation ecological change history and reveal the ecological transformation characteristics from Pliocene to Pleistocene in the Nihewan Basin. Combined with modern pollen process data, quantitative establish the climate change amplitude and cycle from late Pliocene to early Pleistocene and summarizes the characteristics of climate transition event from Pliocene to Pleistocene. By contrast with the proxy records in the key area, explore the dynamic relevance between the ecological transformation and climate change with global change. This project will provide scientific basis and lay a solid research foundation to make it become candidate continental Quaternary Global Boundary Stratotype Section and Point (GSSP). At the same time, this project will also lay the theoretical foundation for deeply understanding the Nihewan hominid living history in the early Pleistocene.

随着第四纪地质年代地位的确立，陆相上新统／更新统界线层型剖面成为国际第四纪研究的热点。阳原盆地泥河湾层沉积序列是我国北方早更新世标准地层，其下伏晚上新世地层在盆地内多个地点亦有出露，这些晚上新世－早更新世沉积序列为建立陆相上新统／更新统界线层型剖面提供了珍贵的地质记录。本项目拟选择大田洼－大沟楞壶流河两岸出露的具有精确古地磁年龄的晚上新世－早更新世地层剖面为研究对象，通过高密度采样（间距为20-10 cm）的孢粉分析，建立高分辨率孢粉组合变化序列，恢复植被演替详细历史，揭示上新世／更新世界线生态转型特征；结合现代花粉过程，定量估算上新世／更新世界线气候转变的速率和幅度；通过与关键区域代用记录对比，探讨该生态转型和气候转变与全球变化的动力关联。本项目的实施不仅将为建立国际陆相上新统／更新统界线层型剖面提供我国的候选剖面，而且将为深入认识泥河湾早更新世古人类生存环境奠定理论基础。

陆相第四系下界线层型剖面的研究是国际第四纪研究的新热点。阳原盆地泥河湾层沉积序列是我国北方早更新世标准地层，也有晚上新统地层出露。高分辨的定量重建泥河湾层底部上新世-更新世过渡期古植被变化和古气候转型过程是建立层型剖面的基础。本项目通过3个剖面1个钻孔近1000个样品的孢粉分析、沉积物粒度、磁化率、及化学元素分析等，结合2116个表土孢粉数据库，75个表土样品花粉产量研究，高分辨率揭示了泥河湾地区上新世末期至早更新世时期（3.3-1.8Ma）的植被与气候变化序列。研究结果显示，上新世/更新世过渡时期泥河湾盆地郝家台地区以湖相沉积为主，沉积物连续性好，孢粉组合总体以乔木花粉为主，含量多高于70%，草本植物花粉含量多低于25%，显示泥河湾地区植被总体以森林植被为主，气候相对湿润。在上新世至早更新世转型期（2.93-2.33Ma）气候变化趋势表现为在波动旋回中由温暖湿润向寒冷干旱方向转化。至少存在4次以云杉花粉为主（多高于40%）或以蒿属、藜科花粉占较高比例（高于60%）的冷期，和4次以松（高于60%）和阔叶树花粉为主（高于5-10%）的暖期。并且冷期持续时间总体长于暖期，特别是进入更新世之后，冷期持续时间明显加长。该时段的全球深海氧同位素的多数冷事件在该地区多有明显体现。定量重建结果显示，过渡期不同时段温度及降水变幅较大。暖期通常年均温多高于7℃，最高可达10℃以上，年降水多高于500mm，最高700mm。冷期年均降水量多低于450mm，年均温多低于6℃。不同时段，森林植被的生物多样性及优势种存在明显差异。植被的重大变化出现于2.83Ma左右，之前，阔叶树花粉含量较高，以较喜暖的榆属、栎属为主，可见山核桃属、楝科、常绿栎等亚热带及暖温带南部树种花粉，之后，亚热带成分消失，阔叶乔木花粉含量迅速下降且以桦属等温带树种为主。频谱及小波分析结果显示气候变化存在4万年和2万年左右周期，以2万年周期最为显著。本项目的实施为建立陆相上新统／更新统层型剖面及深入认识泥河湾古人类生存环境奠定了理论基础。