近33ka以来辽河口沉积环境演变与生物硅记录

沉积物岩心记录着沉积环境的演变过程,其中生物硅(BSi)记录能反映硅质生物的生产力时间和空间变化,2012年5月在下辽河平原西南缘得到了ZK2钻孔柱状样,通过对其沉积物原位密度、生物硅、碳埋藏、粒度、AMS~(14)C和OSL测年、有孔虫鉴定、孢粉鉴定,将ZK2孔的沉积环境主要划分为上三角洲平原相沉积、海洋主导的沉积、湖相沉积、河道沉积4个沉积单元,其相应的生物硅(BSiO_2)浓度分布依次为(2.85±0.23)%、(1.55±0.10)%、(1.96±0.10)%、(0.92±0.05)%,并且生物硅的波动与颗粒有机碳浓度的波动同步。特别是在17~25 cal ka BP冰期形成的湖沼沉积出现较大的颗粒无机碳(PIC)浓度的波动,推测与当时干冷气候条件下CaCO_3过饱和从湖水中沉淀析出有关。钻孔沉积物生物硅浓度记录对格陵兰冰芯~(18)O同位素值的响应存在大约300 a的滞后现象。

The sedimentary environment evolution and biogenic silica records of the Liaohe Estuary since 33 ka BP

Abstract: Buried biogenic silica (BSi) in sediments is regarded as making up only 3% of the global silica production in surface water, and the abundance of BSi in the sediments can provide unique information for past environmental dynamics in continental settings. ZK2 core was taken from the southwest of the lower Liaohe River plain in May, 2012. The laboratory analysis focused on bulk densities, content of BSi, carbon and other nutrients, sedimentary characteristics, AMS14C and OSL dating, foraminiferas and pollens to document sediment provenance changes and environmental evolution. The sedimentary environments were mainly divided into 4 units, namely upper delta plain environment, marine dominant environment, lacustrine depositional environment and riverine environment, with the corresponding biogenic silica (BSiO2) concentrations being (2.85±0.23)%, (1.55±0.10)%, (1.96±0.47)%, and (0.92±0.05)%, respectively. The concentrations of BSi were positively correlated with particle organic carbon concentrations. Remarkably, at the time span of 17-25 cal ka BP, great fluctuations of inorganic carbon (PIC) concentrations took place in lacustrine depositional sediments formed in the last glacial period. It is inferred that at that time, CaCO3 was precipitated and deposited from the supersaturated lake water due to the dry and cold climate, as indicated by pollen assemblages. Moreover, in responce to 18O fluctuations of Greenland ice core, ZK2 BSi concentrations had a about 300 year lag.