全新世浙闽泥质沉积体物源示踪及其古气候意义

The continental shelf is the most relevant marine environment to human activity. In spite that most of continental shelf is covered by sandy sediments, muddy sediments is also very common. In the mud depocenter, fine-grained sediments deposit continuously with high sedimentation rate, thus, paleoceanographic and paleoclimatic information would have been well preserved. A number of mud depocenters have been developed on the continental shelves of East China Sea since the Holocene sea-level highstand. These muddy sediments provide us valuable materials for the study of the source-sink process of rivers in Asia and the East Asian monsoon evolution. However, the current understanding of Zhejiang-Fujian mud depocenter, especially in terms of sediment provenance and paleoclimatic indicators, is still remains controversial. Thus, this project will use sediments from drilling core in the Zhejiang-Fujian mud depocenter, combined with the sea surface and river sediments, to carry out related research. The project intends to apply the grain size, clay minerals, geochemical composition and Sr-Nd isotope of terrigenous sediments, to evaluate the provenance of fine-grained terrigenous sediments and its implication for climatic changes under the 14C age framework. It aims to explore the influence of ocean currents, continental weathering and fluvial discharge for the development of mud depocenter under the context of the East Asian monsoon, thereby to establish a sedimentological model for mud depocenter developed on the passive continental margin. On the basis of this knowledge, reliable indicators of climate change will be extracted, to reveal the East Asian monsoon evolution and its driving mechanism during the Holocene. The findings of this project will help us to understand the process of shelf muddy sediments; and provide a new case for the study of source-sink process of muddy sediments under the background of the East Asian monsoon.

大陆架泥质区沉积速率较快且连续，能够较好地保存高分辨的古海洋和古气候信息。东海陆架在全新世高水位期发育了若干泥质沉积区，为研究亚洲河流的源-汇过程、东亚季风的演化等科学问题提供了良好的材料。目前对东海陆架浙闽泥质沉积体的研究，特别是沉积物源和古气候指标等方面还有待进一步的研究。本项目以浙闽泥质沉积体的钻孔岩心沉积物为重点，同时对河流沉积物进行沉积学的研究，拟利用粒度、粘土矿物、粘土组分的地球化学和锶-钕同位素等参数，结合14C年龄的地层格架，综合分析评价泥质沉积体粘土级陆源组分的源-汇过程，遴选可靠的物源示踪和气候变化指标。旨在探讨被动大陆边缘背景下，泥质沉积形成过程对海（洋）流循环、化学风化、河流输入等因素的响应。在此基础上，利用高分辨率沉积记录揭示全新世东亚季风的演化及其驱动机制。研究结果将加深对陆架泥质沉积过程的认识，为研究东亚季风背景下泥质沉积的源-汇过程提供新的依据。

东海内陆架泥质沉积物具有沉积连续，分辨率高的特征，是研究沉积环境演化的理想载体，但目前研究，特别是长时间尺度（末次冰期以来）的研究还需要加强。本项目利用东海内陆架获取的ECMZ和EC2005钻孔沉积物以及浙江河流（瓯江、钱塘江、飞云江等）沉积物开展沉积物源-汇过程的的研究。首先，利用放射性C-14定年，建立地层格架，恢复末次冰消期以来东海泥质区的环境演化，并结合粒度特征和潮坪沉积环境的演化，重建了末次冰消期海平面变化曲线。随后，柱状沉积物粘土矿物和重矿物的研究表明长江物质一直主导泥质沉积区内的物质来源，并且自末次冰消期以来基本稳定，直到1.5 ka，区域小河流的贡献才有所增加。在上述物源研究的基础之上，我们提出泥质沉积的粒度能够反映东亚冬季风的演化，特别是7.5 ka以来。沉积物粒度的结果表明，中晚全新世以来，东亚冬季风的演化可能受到低纬度ENSO波动的调控，强调了高纬度和低纬度对东亚季风不同的影响机制。此外，在重矿物的研究过程中，我们发现自生黄铁矿广泛发育，并且首次在该区域报道自生石膏。进一步研究发现自生黄铁矿的硫同位素与沉积速率（受控于沿岸流强度）有关，可能为研究古气候演化提供新的指标。最后，我们发现区域小河流沉积物的地球化学和矿物组成可能受到长江物质的影响，在物源分析的研究中需要注意。总之，通过该项目的研究，并对比其它不同地质背景（例如东非）的泥质沉积，将丰富泥质沉积的源-汇体系，并为研究相关的生物地球化学过程提供了新思路。