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.