杭嘉湖平原 ZK3 钻孔沉积物粒度端元分析及其气候-海平面响应

杭嘉湖平原位于海陆交互的长江三角洲地区，极易受到海平面升降和极端气候事件的影响，对全球环境变化十分敏感。应用非参数化粒度端元分析模型提取杭嘉湖平原ZK3岩芯沉积物的端元组分，分析其物质来源；并结合植物藻类和磁化率指标全面揭示各端元组分对区域全新世气候-海平面变化响应。结果表明：（1）EM1（16.4 μm）主要为洪泛沉积物，EM2（35.3 μm）主要为湖相沉积物，EM3（58.9 μm）则为海相沉积物；（2）杭嘉湖平原8000 a BP以来的气候-海平面变化大致可分为四个阶段：约8000—6200 a BP，受东亚夏季风影响，气候温暖湿润，海平面上升并趋于稳定，区域内同时受到海洋和陆源输入影响，发育海陆过渡相沉积；约6200—4800 a BP，气候趋于干凉化，陆地面积扩大，沉积环境转变为河流为主的洪泛沉积；至4800—3100 a BP，气候回暖，海平面略有回升，发育为湖相沉积；3100—140 a BP，气候趋冷干化，海平面下降，广泛发育为泛滥平原沉积环境。

Grain size end-member analysis in sediments from ZK3 borehole and its responses to climate-sea level in Hang jiahu Plain, China

Background, aim, and scope The Hangjiahu Plain, situated in the Yangtze River Delta region, experiences intense sea-land interactions. Consequently, it is highly vulnerable to fluctuations in sea levels, extreme climatic events, and global environmental changes. The grain size end-member analysis method facilitates the understanding of the relationships among various sediment sources, depositional mechanisms, and pathways, as recorded in the particle size data of the sediments. In this study, we employ a non-parametric grain size end-member analysis model to extract the end-member components of sediments from core ZK3 in the Hangjiahu Plain and analyze their material sources. By utilizing plant algae and magnetic susceptibility, we comprehensively reveal the response of end-member components to regional Holocene climate and sea-level changes. Materials and methods Particle size, magnetic susceptibility, plant algae, and optically stimulated luminescence (OSL) sediment samples have been analyzed using MATLAB R2022 software for non-parametric decomposition of the particle size data into end-member components. Results indicate that borehole ZK3 recorded environmental changes in the Hangjiahu Plain since 8000 a BP. The non-parametric method decomposed the particle size data into three end-members: EM1=16.4 μm, EM2=35.3 μm, and EM3=58.9 μm. The abundances of Concentricystes and Spiniferites varied significantly with core depth, with a lower algal content between 1000—500 cm and a significant increase in the 500—0 cm range. The trends of magnetic susceptibility decreased in a fluctuating manner with depth. Discussion The sources of the three grain size end-members in the ZK3 borehole are identified as follows: EM1 (16.4 μm) is the finest fraction, representing flood deposits from the river. EM2 (35.3 μm) is the most abundant fraction, indicating lacustrine sedimentation. EM3 (58.9 μm) is the coarsest fraction, suggesting marine sediments associated with the high sea level in the Yangtze River Delta region during the Holocene. The climate-sea level changes in the Hangjiahu Plain since 8000 a BP can be roughly divided into four stages: from 8000 a BP to 6200 a BP, the climate was warm and humid due to the influence of the East Asian summer winds, and the sea level rose and stabilized. The region experienced sea-land transition phase deposition influenced by both marine and terrestrial inputs. From 6200 a BP to 4800 a BP, the climate became drier and cooler, the land area expanded, and the depositional environment shifted to river-dominated flood deposition. From 4800 a BP to 3100 a BP, the climate warmed, sea level rose slightly, and lake deposition developed. From 3100 a BP to 140 a BP, the climate became cooler and drier, and the sedimentary environment changed to river-dominated river floodplain. Conclusions EM1 represents river floodplain deposits, EM2 corresponds to lacustrine deposits from the plain, and EM3 denotes marine sediments. The sedimentary environment in the Hangjiahu Plain has undergone four stages since the Holocene: sea-land transition phase, flooded deposits, lacustrine, and river floodplain. Recommendations and perspectives In this study, we have reconstructed the climate-sea level evolution history of the Hangjiahu Plain since the Holocene, dating back to 8000 a BP. Understanding the environmental evolution of the region in response to climate-sea level changes is also of great practical significance for predicting and responding to future shifts in climate and sea levels.