浙江瓶窑BHQ孔全新统孢粉组合特征与气候变化

利用浙江省瓶窑北湖BHQ孔长约14m的岩心,以4个AMS¹⁴C数据为年代依据,对49块样品进行孢粉分析。分析结果发现,样品中孢粉浓度差异较大,植物种类繁多,总计103个科/属。通过对孢粉组合特征的分析,结合岩性特征,划分出3个孢粉带和9个亚带,重建了研究区早—中全新世植被演替和气候冷暖波动的环境序列。19～8.9m沉积时段,对应于早全新世气候回暖期,研究区植被主要是以落叶栎、松、阿丁枫和枫杨为主,混有少量常绿栎和榆等的针叶—落叶阔叶混交林,常绿乔木花粉含量较低,说明研究区经历晚更新世晚期新仙女木事件后进入全新世,气候迅速转暖;8.9～6.7m沉积时段,对应于全新世最适宜期,为研究区水热条件配置最佳阶段,主要发育由落叶栎、常绿栎、松、阿丁枫、枫杨和榆等组成的常绿—落叶阔叶混交林,常绿乔木的种类和含量要远远高于前一阶段,指示气候变化的最适宜阶段;6.7～4.775m沉积时段,对应于中全新世气候波动期,孢粉组合发生明显波动,研究区植被主要以落叶栎、枫香、松、枫杨等落叶阔叶乔木为主,常绿栎花粉的含量急剧萎缩,表明研究区植被类型演替为落叶阔叶林,反映经历了较为剧烈的气候恶化事件,而本段高含量的稻属花粉(≥35μm)可能指示该时段研究区存在一定规模的古人类活动。

Characteristics of pollen assemblage and climate change in the Holocene at Borehole BHQ in Pingyao area,Zhejiang Province

This research was based on a 14 m long core from the Borehole BHQ in Beihu Lake,Pingyao area of Zhejiang Province. With 4 dating data by AMS¹⁴C method,palynological analysis was performed on 49 samples. It showed that the palynological concentrations varied greatly in different samples,and there were a wide variety of plants,i.e., totally 103 pollen types were recorded. Based on characteristics of palynological assemblages and lithology,3 pollen zones and 9 pollen subzones were divided,and the environmental sequence of vegetation succession and climatic temperature change in the Early and Middle Holocene for the study area was reconstructed. In the interval of 19-8.9 m,corresponding to the Early Holocene,vegetation in the study area was mainly conifer-deciduous broad-leaved forest,including Quercus(deciduous),Pinus,Altingiaceae and Pterocarya as well as Quercus(evergreen), Ulmus,etc. There were low content of evergreen trees,indicating that after the “Younger Dryas Event”at the late period of Late Pleistocene,the study area entered into the Holocene,and climate quickly turned warm. In the interval of 8.9～6.7m,corresponding to the Megathermal,this was the best period of hydrothermal condition in all sections. At this period,evergreen and deciduous broad-leaved mixed forest were dominant,including Quercus(deciduous),Quercus(evergreen),Pinus,Altingiaceae,Pterocarya and Ulmus. And the species and quantity of evergreen trees were far more than that of the former period,indicating warm and humid climate. During the 6.7～4.775m sedimentary period,corresponding to the Middle Holocene,there was an apparent fluctuation in palynological assemblages,and the vegetation in the study area mainly contained deciduous broad-leaved forest such as Quercus(deciduous),Altingiaceae,Pinus and Pterocarya. The number of Quercus(evergreen)dwindled rapidly. It showed that the vegetation type in the study area had evolved into deciduous and broad-leaved forests. It reflected that the area experienced a relatively-drastical climatic deterioration event. And the high concentration of Oryza pollen(≥35μm) during this period might indicate a certain scale of ancient human activity in the study area.