• 责任者：Yu Fengling (Earth Observatory of Singapore ; Nanyang Technological University ; Singapore 639798 ; China) ; Adam D. Switzer
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(6)
• 关键词：冲积层 ; alluvium ; 气候 ; climate ; 广东 ; Guangdong
• 页码：p.1171-1182
• 图表：4 illus., 45 refs.
• 分类号：0200
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

     Chaoshan plain in Southern China experiences seasonal typhoons that commonly result in considerable loss of both human life and infrastructure. This is particularly the case for the low-lying Rongjiang River deha（〈3m above PMSL） in western Chaoshan plain. From 1900 to 2010,there have been a total of 91 typhoons traced within 100km radius from Niutianyang,in the lower reach of the Rongjiang River. Among them,large typhoons, such as Chanchu in2006,Viola in 1969 and an unnamed typhoon in 1922, have caused considerable destruction and basin-wide flooding in the Chaoshan plain. As flooding events in this area are mainly induced by large typhoons,it is important to understand the spatial and temporal distribution of large typhoons as such evidence is key to reducing future losses. However, monitoring data collected only since 1950 are not adequate for investigating the recurrence interval of large typhoons,which are usually one in 50 year events or even one in 100 year events. Sedimentary records have the potential to span millennia and have proved to be very useful archives elsewhere, such as the Yangtze delta and the Yellow River delta in China.  This study was carried out to examine the sedimentary features of the Rongjiang River flood plain, and to explore its applicability as an indicator for palaeo typhoon hazards and as an indicator for recently enhanced human activities. Two sediment cores were collected from Niutianyang at the west of Rongjiang River estuary in September 2011 using a gouge auger. Core 1, 1.9m in length, was collected from the Hudong Village （23~21.376＇N, 116~31.817＇E） ,south of Niutianyang; and Core 2,2.2m in length, was collected from the Tiangang Village （23~22. 537＇N, 116~36. 096＇E）, north of Niutianyang. For both cores ,the chronology was developed using the Zl~Pb dating methods via the CRS（ Constant Rate of Supply）model, suggesting a timeframe of ca. 150 years. To examine the sedimentary features, the two cores were then analyzed for grain size composition and faunal composition （foraminifera） at a 1 -5em sampling interval.  The results of sedimentary analyses show that deposits from both sites are dominated with clayey silt, interrupted by sandy layers of 1 - 20em in thickness. The sedimentary features of south Niutianyang （ Core 1 ） are different from that of the north（Core 2） ,as tide influence is stronger on the south than on the north. Core 1 has a mean grain size value of 7.2~b,poorly sorted,with a near-symmetrical skewness and a mesokurtic kurtosis. Slightly etched foraminifera（Ammonia spp. and Elphidium spp. ）were found in the clayey silt deposits. Core 2 has a mean grain size value of 6.8b, slightly coarser than sediments from the south. Sediments are poorly sorted,with a near- symmetrical skewness and a leptokurtic kurtosis, foraminifera（Ammonia sp. ）were only found in one sample from bottom of the core. For both cores, intercalated among the normal clayey silt deposits are several sandy layers. In Core 1, these sandy layers are dominated by very poorly sorted fine sand that is fine skewed, and exhibits leptokurtic kurtosis. The sand layers also exhibit low 21~Pboxc activity （141.0Bq/kg, lower than the core mean value of 155.2Bq/kg） and large amounts of bivalve debris were found in fine sand layers from bottom and top of the core. In Core 2, sandy layers were dominated with very poorly sorted medium and coarse sand that is fine or strongly fine skewed,and exhibits platykurtic or very leptokurtie kurtosis. The sand layers here exhibit low 21~Pbex~ activity （118.6Bq/kg,lower than the core mean value of 123. 1Bq/kg）and no foraminifera or shell debris were found in these layers. Different sedimentary features for the sandy layers are most likely due to stronger tide influence on the south than on the north.  In these sandy layers,the high proportion of sand and the absence of foraminifera indicate their terrigenous nature. We imply that the terrigenous sediments for these sandy layers were delivered into Niutianyang by strong river runoff during large typhoons, and formed the flood deposits. In return, these flood deposits can be used to indicate big flooding events which mainly induced by large or intense typhoons in this area. Thus, we conclude that flood deposits from the Rongjiang River flood plain can be used to reconstruct palaeo large typhoon events. In order to estimate the recurrence interval of palaeo typhoon events,spectral analysis was applied to particle size parameters of Core 1 ,suggesting four main periodicities as 30 and 80 years by kutosis values,and 50 and 120 years by mean size,sorting and skewness values. By comparing the result of spectral analysis with the chronologically constrained sedimentary record as well as historical records of typhoons,we suggest that the recurrence intervals of 50 and 120 years are more obvious,and we suggest the next 20 years a period with intense large typhoons and probable basin- wide flooding events. Furthermore, this study also suggests that recently enhanced human activity is the main driving mechanism for the significantly increased sedimentary rate since late 1980s of 3.22cm/a,with comparison to 1.36cm/a during 1930 - 1980 and 0.33cm/a in early 20th century.