扬子浅滩MIS6阶段以来沉积地层及环境演变

Characteristics of sedimentary strata and environmental evolution of the Yangtze Shoal since Marine Isotope Stage 6

通过对扬子浅滩钻孔岩性、沉积结构和构造以及微体古生物组合的综合分析,划分出5个沉积单元,同时结合沉积物定年数据和邻区若干钻孔的地层对比研究,将MIS6阶段以来扬子浅滩的环境演化划分为5个阶段,先后发育河流(MIS6),浅海,近岸浅海,浅海(MIS5),河口湾(MIS3)和浅海(潮流沙席)(MIS1).研究认为MIS6阶段低海面泥沙堆积的河流高地是扬子浅滩形成的古地形基础;MIS3阶段形成的河口湾沉积为扬子浅滩提供了大量的物源,加速了扬子浅滩在地形上的崛起,10ka^6ka逐渐建立的辐聚辐散潮流场,以及强潮流的改造为扬子浅滩的形成提供了动力条件.潮流作用形成的砂质沉积概率累积曲线是以滚动总体为主的三段式,频率曲线呈双峰式,与潮流期的粗颗粒搬运堆积和歇流期的细颗粒悬浮物落淤有关.

Abstract：Based on comprehensive analysis of lithology, sedimentary structure and micro-fossils assemblage of core YZ05 from the Yangtze Shoal, five sedimentary units were identified. At the same time, combined with several sediment dating results and stratigraphic correlation of some cores in the adjacent region, we divided the environmental evolution of the Yangtze Shoal into five stages since MIS6. River（MIS6）, shallow sea to nearshore to shallow sea（MISS）, estuary front to estuary（MIS3）and shallow sea（tidal sand sheet, MIS1 ）have been developed suc- cessively in the study area. Research also reveals that the river highland formed during the low-sea-level period in MIS6 is the ancient topographic foundation of the Yangtze Shoal. Estuarine deposits formed during MIS3 provided a large amount of sediment sources,and this contributed to the quickly topographic rise of the shoal. The convergent and divergent tidal current field established from 10ka to 6 ka BP and transformation of strong tidal current provided the dynamic conditions for the formation of the Yangtze Shoal. The sandy sediments formed by tidal current had probablity accumulation curves as three-segments type with a high quantity of rolling component, and their frequency curves were bimodal type. This is related to the accumulation of coarse particles in the tidal period and the accumulation of fine particles in the intermittent period. Key words Yangtze Shoal, characteristics of sedimentary strata, environmental evolution, formation mechanism