Identifying paleoflood deposits archived in Zhongba Site, the Three Gorges reservoir region of the Yangtze River, China

Abstract

Based on the principle that the present is the key to the past , detailed analyses, such as AMS 14 C dating, grain size, component and morphology of heavy minerals, micro-morphology of zircon, Rb/Sr, magnetic susceptibility and total organic carbon (TOC), were conducted to identify paleoflood sediments archived in Zhongba Site. The results indicate that the plaeoflood sediments bear great similarities with modern flood sediments in the following aspects: (1) probability cumulative curves mainly show a pattern of 3-4 segments; (2) grain-size distribution of suspended matter ranges between 3 and 10Ф; (3) the sediments are well-sorted, most of which are suspended matter (>50%); (4) the same species, quantity and morphology of heavy minerals; (5) scanning electronic microscope images show that shapes of zircon are mainly oval and nearly spheral, rounded due to long-distance transport; (6) higher Rb/Sr values (0.55 -0.66)than those of sediments from cultural layers (0.03-0.26); (7) magnetic susceptibility values (133.73 -433.05 10 -6 m 3 /kg) are lower than those of sediments from cultural layers (959.25 -2442.44 10 −6 m 3 /kg); (8) TOC (0.14% -0.33%) are lower than those of sediments from cultural layers (1.13%-2.95%). Our results demonstrate that, except for the 1981 flood, there are at least six paleoflood events that occurred during the Qing

Holocene Environmental Archaeology of the Yangtze River Valley in China: A Review

“…Combined with the above natural sedimentary records, a comprehensive inte-grated analysis shows that there are eight paleoflood layers in the archaeological site strata during the Holocene climatic optimum of 6.7-4.2 ka BP, i.e., the 4th, 5th, 6th, 7th, 8th, and 10th strata of the Yuxi Site and the 76-2 and 50-1 strata of the Zhongba Site [71,75]. From 3.5 to 0.9 ka BP, when the precipitation dropped, there are only two flood layers in the Zhongba Site, i.e., the 37-1 strata in the Western Zhou Dynasty and the 21 strata in the early Warring States Period.…”

“…Research progress in this area has primarily been made by the environmental archaeology studies contrasting typical Neolithic sites in Zhongba (in Zhongxian Coun-ty), Yuxi (in Fengdu County), Zhangjiawan, and Shuangyantang (in Wushan County) with Dajiuhu peat records of Shennongjia, taking advantage of the rescue archaeologi-cal excavations prior to the Three Gorges Project in the Yangtze River [70][71][72][73][74][75][76][77][78][79]. The most important research focused on the Zhongba Site, where archaeological and cultural layers are almost intact in all historical times during the 5000 years ranging from the Neolithic Age to modern times [71]. Since then, more than 200,000 pieces of artifacts have been unearthed, along with a large number of animal bones (from more than 200 excavation units; in one excavation unit alone more than 200,000 bones were discov-ered from at least 42 species of mammals, fish, birds, amphibians, and reptiles); the Zhongba Site was named one of the nation's top ten archaeological discoveries in 1999 [74].…”

“…If a flood deposit site does not experience subsequent erosion, the later slack-water de-posits would overlie the deposit of the previous event so that a somewhat bigger and longer flooding record might be preserved [81]. Comparing the modern flood sedi-ments in 1981 preserved on the surface of the Zhongba Site with the sedimentary characteristics of natural sediment sources, heavy mineral composition, and zircon micromorphology in strata, Zhu et al [71] explored a set of reliable research methods for judging the paleoflood deposits in archaeological sites and reproduced the process and sequence of paleoflood events since the Neolithic Age. By comparing the strati-graphic sediment of the Yuxi Site with modern flood sediment, AMS (accelerator mass spectrometry) 14C dating, grain size, heavy minerals and zircon micromorphology, magnetic susceptibility, Rb/Sr ratios, and other geochemical indicators, it was learned that since 7.6 ka BP paleofloods with water levels over 147.02 m in Wusong elevation had left at least 16 sedimentary records in the Neolithic strata of the T0403 excavation unit (154.747 m in Wusong elevation) at the Yuxi Site [75].…”

Preliminary identification of palaeofloods with the alkane ratio C31/C17 and their potential link to global climate changes

“…Total organic carbon (TOC) and magnetic susceptibility (MS) have been used as palaeoflood proxies in riverine sediment cores 24 25 . Our analysis showed that the TOC content in the sediment core varied from 0.58% to 1.03% without clear temporal variations and with no indication of any palaeoflood events ( Supplementary Information Fig.…”