Sedimentary evidence of Late Holocene human activity in the Pearl River delta, China

Abstract

This study examines the sedimentary evidence of human activities during the last 4000 years in the Pearl River deltaic area. The analyses are focused on indentifying agricultural signatures present in the sedimentary record and establishing the timing of a change from a simple, rice-based agriculture to a more advanced, diverse agriculture. The examination is based on modern sediment and plant samples and a sediment core collected from the deltaic area. The analyses include particle size and diatom analysis to determine the environmental conditions that were associated with the period of human activities. Organic carbon isotope ratios and major metal elements reveal an expansion in commercial crop production and metal smelting in the Pearl River delta area about 2000 years ago. The input of organic matter from introduced sugarcane, a C4 plant, elevates the bulk organic carbon isotope values in the estuarine sediments above that represented by other common agricultural crops in the study area, including rice, banana and lotus, which are all C3 plants. The increase in bulk organic isotopic value coincides with the rise in the concentration of copper, iron and lead in the sedimentary sequence, suggesting a wider use of metal tools. These results indicate that advanced agriculture started about 2000 years ago as an expansion in human population took place in the area. This record also provides sedimentary evidence that help ascertain the timing and type of human activities that are linked to subsequent land reclamation on the deltaic plain, resulting in rapid shoreline advancement in the last 2000 years.

Mid-Holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

“…The radiocarbon date from 0.52 m produced a modern age (108 cal yr BP), while the date from 1.33 m (immediately below the boundary between zones 1 and 2) provided an age of 2337 -2162 cal yr BP. Based on the chronology and clear change in character of the sediments the change from Zone 1 to Zone 2 most likely relates to enhanced human activity in this area as discussed by Zong et al (2010c). In this paper we concentrate on the mid-Holocene section preserved in Zone 1.…”

“…The sedimentation environment was stable because particle size analysis shows no major change in sand, silt or clay fractions (Zong et al, 2010c), and there is no bioclastic storm bed found in this sediment section (eg Huang and Yim, 2001). The only thin sandy layer found in the core is located at 1.0 m (Zong et al, 2010c). Diatom assemblages from the section containing the age inversion show no significant change either (Zong et al, 2010b).…”

A new regional, mid-Holocene palaeoprecipitation signal of the Asian Summer Monsoon

“…Liu and Huang, 2005), cave speleothems (e.g. Dong et al, 2010;Wang et al, 2005;Zhang et al, 2004) and organic matter flux (Yu et al, 2012;Zong et al, 2006;Zong et al, 2010). Overall, these datasets indicate a general decline in precipitation across Asia from 6.5 ka to present.…”

“…This sample is from a region of the core that has been previously attributed to a marine storm event associated with significant marine deposition (Yu, 2009;Zong et al, 2010).…”

“…Previous reconstructions of relative terrestrial sediment transport to the Pearl River Estuary using bulk organic carbon isotopes (Yu et al, 2012;Yu, 2009;Zong et al, 2006;Zong et al, 2010) have attempted to use this approach to provide a regional signal. These  13 C org records show a general increasing trend with time ( Fig.…”