【摘要】 晚中新世-上新世古生态演化是探讨构造-气候-生态环境相互耦合作用的热点议题,该时段不同区域C₄植物是否发生大规模扩张及其在时空维度上如何演化等问题尚存争议。以青藏高原东北缘小水子红黏土为研究对象,基于总有机碳同位素重建了小水子地区晚中新世-上新世（6.7～3.6Ma）的植物生态型,并结合周边结果对C₃/C₄植被时空演化进行综合对比研究。研究表明:小水子地区晚中新世-上新世以C₃植被为主（平均丰度95%）,伴生小部分C₄植被;C₄植被在空间上以六盘山为界呈现东多西少模式,南北方向上在37°～38°N范围内达到峰值;从时间演化序列上来看,4Ma前小水子地区生态演化与黄土高原大致相同,晚中新世C₄植被含量较高、C₃植被含量较低,上新世早期C₄植被减少、C₃植被增多,大气CO₂浓度与区域降水变化可能是植被演化的主要影响因素;4Ma左右夷平面区域构造活动可能导致了小水子地区C₄植被差异性演化。更多还原

【Abstract】 The late Miocene-Pliocene ecological evolution has been a hot topic in discussing the interaction of tectonic,climate and ecological environment. However,whether the C₄ plants in middle and low latitudes expanded on a large scale and how the ecology evolved on the time-space dimension are still debated. In this paper,based on the organic carbon isotope,the plant ecotype during the interval of 6.7～3.6 Ma covered on Xiaoshuizi area in the northeastern Tibetan Plateau were reconstructed and combined with the surrounding regions,the ecotype and its evolution were discussed. Our results show that the Xiaoshuizi area is dominated by C₃ vegetation during the late Miocene-Pliocene（with an average abundance of95%）,accompanied by a small part of C₄ vegetation. In space,the abundance of C₄ vegetation in the eastern Liupan mountain is higher than that in the western,and in the north-south direction the C₄ plant abundance reached the at about37°～38° N. In terms of time series,ecological evolution of Xiaoshuizi planation surface is roughly consistent with that of the Chinese Loess Plateau before 4 Ma. It shows during the late Miocene C₄ vegetation content is relatively high and C₃ vegetation content is low,while C₄ vegetation reduced and C₃ vegetation increased in early Pliocene. The variations of atmospheric CO₂ concentration and regional aridification may be the main influence factor for the vegetation evolution. The tectonic activities in the planation surface area may lead to the differential evolution of C₄ vegetation in the Xiaoshuizi area.更多还原