摘要
晚上新世至更新世是地质历史时期中十分重要的阶段,2.7Ma之后北半球由温暖湿润的气候进入冰期,水杉叶片化石稳定碳同位素值、叶片面积和叶片长宽比在地质历史时期的变化可以推测该时期内环境的变化趋势、探索植物对环境变化的响应.本研究选取日本中部地区的5个化石点（泉南郡、八王子市、东近江市、十日町市和生驹市）的水杉叶片化石（3.00～0.95Ma）材料.这些化石点的化石叶片稳定碳同位素值在八王子市（2.6～2.7Ma,晚上新世）出现最低值（-29.05‰±0.15‰）,明显低于其他化石点材料的稳定碳同位素值,并且在此期间化石叶片的面积为7.45±1.31mm2,大于其他时期;同时,叶片的长宽比较大,为4.22±0.67.这些结果相互印证共同指示出,上新世与更新世交界时期存在一个间冰期;之后,气候逐渐变冷变于.并且本研究结果与日本古植物群落演替得出的结论相一致.
During the Plio-Pleistocene boundary （2.7~2.4Ma）, the glaciation of the Northern Hemisphere started.Previous research reported the expansion of northern hemispheric continental ice sheet and the climate deterioration began at around 2.7Ma.On the contrary, other studies argued that 2.7Ma was an interglacial period.Therefore, more evidences are necessary to clarify the debate.Here we use organic carbon isotope（δ^13C）, leaf size and leaf length/leaf width ratio of fossil Metasequoia needles as the proxy of paleoenvironment to assess if 2.7Ma ago was an interglacial period or not.
The fossil Metasequoia needles were collected from five localities in central Japan：Sennan, Hachioji, Higashiomi, Tokamachi and Ikoma.The ages of these materials varies from 3.00Ma to 0.95Ma（Late Pliocene to Pleistocene）.For each locality, we prepared 1~5 samples for δ^13C analysis, and 5 leaves for leaf size and leaf length/leaf width ratio measurements.These three characters have been shown to be mainly affected by temperature and precipitation of the growth environment.δ^13C values are negatively correlated with temperature and precipitation whereas leaf size and leaf length/leaf width ratio are positively correlated with temperature and precipitation.
The results of this research show that： the lowest δ^13C value（-29.05 ‰）was measured for the period around 2.6~2.7Ma（Late Pliocene）, indicating a warm and humid environment.The leaf area and leaf length/width ratio of fossil Metasequoia needles during 2.6~2.7Ma（Late Pliocene）are also larger（7.45mm^2 and 4.22 respectively）, supporting that 2.6~2.7Ma is a warm and humid period.Thus, our results indicate that there is an interglacial period at the Plio-Pleistocene boundary（around 2.7Ma）.After that period, the climate deteriorated, as the environment became cooler and dryer.This climate change is corroborated by the mega fossil records, as the succession of floral assemblages during Pliocene to Pleistocene also indicated a similar trend.
出处
《第四纪研究》
CAS
CSCD
北大核心
2015年第3期767-775,共9页
Quaternary Sciences
基金
国家自然科学基金项目（批准号：31300188）、国家重点基础研究发展规划项目（973项目）（批准号：2012CB821901）和中国科学院135项目（批准号：XTBG-F01）共同资助
关键词
水杉
上新世
更新世
古气候
叶化石
碳同位素
Metasequoia, Pliocene, Pleistocene, paleo-climate, fossil leave, carbon isotope
