Diatom record the holocene marine facies deposition history in inner bay of Pearl River Estuary, South China

Abstract

To understand the evolution of river mouth systems under natural and human being forces is a critical task in coastal and marine science studies. We present a new sedimentary record with diatom, grainsize analysis and radiocarbon age dating, recovered from a drilling core in an inner bay of the Pearl River Estuary, South China, in order to describe marine facies depositional history and to examine relative palaeoclimatic and palaeoenvrionmental changes during the Holocene. The occurrence of marine diatoms at ca. 9,000 cal. yr. BP provides marine facies starting point at this core profile in the shoal area, west of the Pearl River Estuary. Three fossil diatom units were distinguished following the early to late Holocene epoch division. The changed diatom bio-facies before and after ca. 8,200 cal. yr. BP, especially in coastal and neritic species relative abundances contrast, offers a diatom floral response to the "8.2 kyr" event. In middle Holocene, enhanced diatom absolute abundances of tropical open-sea water species and increased neritic species number and relative abundances, with more sand fractions, provide evidences of diatom bio-facies response to higher sea-level and strong hydrodynamic clearly. Following the regression, fossil diatom flora experienced a long-term decline after ca. 5,500 cal. yr. BP, until to ca. 1,400 cal. yr. BP. In the past ca. 1,400 years, there has been a clear increase in the absolute abundances and biodiversity of diatoms, along with a greater presence of coarse granularity fractions. This is a strong signal that human activities influenced local environmental change, combined with natural forces.An interesting phenomenon of higher sedimentation rate was observed in three periods as a millennial-scale pulse, at ca. 9,000–8,000 cal. yr. BP, ca. 6,500 - 5,500 cal. yr. BP, and ca. 1,000 - 0 cal. yr. BP. Meanwhile, two periods of lower sedimentation rate over longer time interval occurred during those pulses. Through regional correlation, this study presents a record of deposition after ca. 9,000 cal. yr. BP in Holocene marine facies, provide improved understanding of the west shoal evolution history in Pearl River Estuary, and natural and human being impact on diatom flora and coastal geo-environment in low latitude river mouth systems in Asian Monsoon realm.