摘要： 综合钱塘江下切河谷SE4孔岩心观察和描述及粒度、孢粉、测年等分析数据,探讨了钱塘江下切河谷晚第四纪沉积环境和古气候演化,揭示了其气候变化机制下沉积响应的具体过程。研究表明SE4孔晚第四纪沉积物自下而上包括河床亚相、河漫滩亚相、古河口湾相、浅海亚相和现代河口湾相5套沉积。研究区晚第四纪以来古植被和古气候演化分为6个阶段:第一阶段植被类型为阔叶树为主的针阔混交林—草原,气候温和偏湿,沉积了河床和河漫滩亚相;第二阶段为落叶栎稍多的针阔混交林,气候温和湿润,沉积了古河口湾相和浅海亚相;第三阶段为针阔混交林,气候温暖湿润,浅海亚相沉积发育;第四至第六阶段植被类型经历了针阔混交林—草原、针阔混交林、针阔混交林—草原的交替,气候经历了温和偏干、温和偏湿、温和偏干的变化,现代河口湾相沉积发育。

关键词: 钱塘江, 下切河谷, 环境演化, 古气候, 晚第四纪, 杭州湾

Abstract: Based on the analyses of grain size,pollen,AMS ¹⁴C ages etc.,the sedimentary environment and palaeoclimate of the late Quaternary sediments from core SE4 in the Qiantang River incised valley are discussed,and the specific process of sedimentary response to climate change mechanism is revealed. The results show that the late Quaternary sediments in core SE4 consist of five sets of depositional units from bottom to top,including fluvial channel,floodplain,palaeo-estuary,neritic deposits,and modern estuary. The palaeovegetation and palaeoclimate evoluiton of the study area since late Quaternary can be divided into six stages. The first stage is characterized by a mixture of coniferous and broadleaf forest-grassland dominated by broadleaf trees,indicating a mild-humid climatic phase,during which the fluvial channel and floodplain deposits were deposited. The second stage is also represented by a mixture of coniferous and broadleaf forest,but with slightly more deciduous vegetation,suggesting a mild and humid climatic phase,during which palaeo-estuarine and part of shallow marine deposits were deposited. The third stage is dominated by a mixture of coniferous and broadleaf forest,indicating a warm and humid climatic phase when some other shallow marine deposits were formed. From the fourth to sixth stage when modern estuary developed,the vegetation types experienced a transition from coniferous and broadleaf forest-grassland,through coniferous and broadleaf forest,to coniferous and broadleaf forest-grassland,suggestive of a palaeoclimatic shift from mild-dry,through mild-humid,back to mild-dry conditions.

Key words: Qiantang River, incised valley, environmental evolution, palaeoclimate, late Quaternary, Hangzhou Bay

中图分类号: 

• P534