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Quaternary Geochronology 30 (2015) 398e404

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Quaternary Geochronology

journal homepage: www.elsevier .com/locate/quageo

OSL and radiocarbon dating of flood deposits and its paleoclimatic andarchaeological implications in the Yihe River Basin, East China

HongYuan Shen a, LuPeng Yu a, b, *, HongMei Zhang a, Min Zhao a, ZhongPing Lai c, d, **

a College of Resources and Environment, Linyi University, Linyi 276000, Chinab Key Laboratory of Geological Processes and Mineral Resources of Northern Qinghai-Tibetan Plateau, Qinghai Geological Survey Institute, Xining 810012,Chinac State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, Chinad State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences,Lanzhou 730000, China

a r t i c l e i n f o

Article history:Received 30 October 2014Received in revised form5 March 2015Accepted 14 March 2015Available online 16 March 2015

Keywords:Luminescence datingFlood depositsLate Neolithic ruinsLate HoloceneLongshan CultureEnvironmental archaeology

* Corresponding author. Key Laboratory of GeoloResources of Northern Qinghai-Tibetan Plateau, QinghXining 810012, China.** Corresponding author. State Key Laboratory of BiGeology, China University of Geosciences, Wuhan 430

E-mail addresses: yulupeng319@126.com (L. Yu(Z. Lai).

http://dx.doi.org/10.1016/j.quageo.2015.03.0051871-1014/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

Flood is a kind of serious nature disaster, so studies on the palaeofloods are the keys to understand themechanisms and their relationships with climatic change, geomorphologic evolution and civilizationevolution are of great importance. The floods happened frequently in the Yihe-Shuhe River Basin inhistory, forming the alluvial plain and affecting the evolution of the ancient civilization. However, thecomplex sediment sources and depositional processes make the flood deposits difficult to be dated andconsequently hinder our understanding to the palaeofloods. In this study, we present twelve OpticallyStimulated Luminescence (OSL) ages and four AMS 14C ages of flood deposits to study the palaeofloodactivities in the Yihe River Basin and its palaeoclimatic and archaeological implications. The youngestOSL age of 0.19 ± 0.02 ka at the depth of 0.5 m shows that the residual OSL age, if any, must be muchsmaller than this amount, and the well comparison between OSL ages and AMS 14C ages further confirmthat the flood deposits could be well bleached before buried and consequently the OSL ages are notoverestimated. The source of sediments from ground surface in the mountain regions in the upperstream and the special characteristic of quartz might have contributed to the sufficiently bleaching.Consequently, OSL dating has the potential to offer reliable chronology for the flood deposits. Theextraordinary floods happened at 4.1e3.8 ka, 3.3e3.0 ka and 0.9e0.1 ka correspond to the global abruptclimatic events, demonstrating that the extreme floods might be caused by or be parts of these climaticinstabilities in monsoonal China. The flood happened at 4.1e3.8 ka might have directly caused thedecline of the highly developed late Neolithic civilization (Longshan Culture) in the Yihe-Shuhe RiverBasin.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The study of palaeofloods enables linkages between global cli-matic change and extreme events in river systems to be establishedover a long time-scale (Huang et al., 2010). As a kind of fluvialprocess, overbank floods have often left their sedimentary recordsover the inundated areas in their paths. Optically Stimulated

gical Processes and Mineralai Geological Survey Institute,

ogeology and Environmental074, China.), zhongping.lai@cug.edu.cn

Luminescence (OSL) dating could be applied to the fluvial deposits,because the sediments could be bleached during the transportationin the flows. The main question for its application on flood depositsis whether the sediments could be sufficiently bleached in thehyperconcentrated flows during the floods. Huang et al. (2011)dated the flood deposits in the Qishuihe River, middle reach ofthe Yellow River, on the Chinese Loess Plateau (CLP), and the OSLages of the flood sediments could be well compared with those inthe underlying aeolian deposits and an overlying pottery shard. Liuet al. (2014) studied the palaeofloods in the Jin-Shaan Gorge alongthe middle Yellow River, CLP, and the four palaeofloods were alldated to 1.8e1.6 ka. These are successful applications of OSL datingon flood deposits, however, if the cross-checking between OSL and

Fig. 2. Comparison of archaeologic site distribution during Longshan Culture (4.6e4.0ka) and Yueshi Culture (4.0e3.5 ka) in the Yihe-Shuhe River Basin. The gray regionsshow the mountain regions, while the white regions display the plains. (modified fromState administration of culture heritage (2008)).

H. Shen et al. / Quaternary Geochronology 30 (2015) 398e404 399

14C dating were applied, the results would be more convincing.The Yihe-Shuhe River Plain (Fig. 1) is mainly composed of flood

deposits (Fig. S1A and B), demonstrating frequent influence fromfloods in history. Ancient trunks (Fig. S1C) and human remains, e.g.,potteries and bronze wares, could be frequently found in thechannels due to the intensive lateral erosion from the Yihe Riverduring the rainstorms, revealing the large-scale palaeofloods inhistory. The Longshan Culture (4.6e4.0 ka) in Shandong region(Fig. 1) was the most advanced Neolithic culture in China in that era(Yu, 1995), and naturally, it should develop to civilization firstly,however, it declined suddenly at around 4.0 ka and was replaced bythe outdated Yueshi Culture (4.0e3.5 ka). The decline was dis-played by the decrease of sites (from 473 to 53 in the Yihe-ShuheRiver Basin; Fig. 2) and backset in quality of potteries and agricul-tural technique. This decline of the Neolithic civilization at 4 ka is acrucial archaeological question in China, and the decline of Long-shan culture in the Yihe-Shuhe River Basin at ca. 4 ka was proposedto be caused by the decrease in temperature (Gao et al., 2006). Gaoet al. (2006) discovered two layers of flood deposits at 4.26 ka and3.94 ka in the Shuhe River Basin (Fig. 1). Taking into account thatthe sites of Longshan Culture mainly distributed on the fluvialplains around the mountain regions (Figs. 1 and 2), the influencefrom the palaeoflood should not be ignored.

In this study, both OSL and AMS14C dating are applied toestablish the chronology of the palaeofloods in the Yihe River Basinand further to discuss its palaeoclimatic and archaeologicalimplications.

2. Study region, sections and samples

The Yihe River, with a length of 574 km and drainage area of17,325 km2, origins from the Lushan Mountain, and flows into theYellow Sea (Fig. 1). The Shuhe River, paralleling to the Yihe River, isanother important river in the Yihe-Shuhe River Basin (Fig. 1).Controlling by the temperate monsoonal climate, the Yihe-ShuheRiver Basin has a mean annual precipitation of 850 mm andmean annual temperature of 17 �C. However, 65% of the precipi-tation is received in summer, so the floods are frequent in summerduring the rainstorms.

Fig. 1. Distribution of Longshan Cluture in Shandong region (modified from State administration of culture heritage (2008)) and locations of the Yihe-Shuhe River Basin and thesections in this study (Beizhai and Lizhuang) and in Gao et al. (2006).

H. Shen et al. / Quaternary Geochronology 30 (2015) 398e404400

The Beizhai (BZ) section locates besides the Wenhe River, abranch of the Yihe River (Figs.1 and 3), and is ca. 8m above the riverlevel. The sediments in the upper part of the section could bedivided into five units, with aeolian deposits in the 1st, 3rd, and 5thlayers and flood deposits in the 2nd and 4th layers (Fig. 2). Thesediments in the upper flood layer are relative coarser, with largeportion of gravels, demonstrating a period with large-scale floods.More than 20 sub-layers could be indentified within the lowerflood layer, displaying a period with frequent overbank floods. Eachof these sub-layers is composed of a coarser sand layer and a finersand layer, demonstrating the change of hydrodynamic force dur-ing each flood event. Eight OSL samples were taken from the floodand aeolian deposits, and four bulk samples for 14C dating weretaken from the aeolian sediments to compare with the OSL ages.The Lizhuang (LZ) flood section (Figs. 1 and 3) is 5 m above the YiheRiver. The section is composed of consistent flood sediments,demonstrating that this region is frequently affected by floods. FourOSL samples were collected in this section.

A total of twelve OSL and four 14C samples were taken from theBZ and LZ sections. All the OSL samples were collected byhammering steel tubes (~22 cm long cylinder with a diameter of~5 cm) into freshly cleaned vertical sections. The ends of tubes werethen wrapped to avoid light exposure. Bulk samples were alsocollected in each sample location for dose rate and water contentanalysis. The 14C samples were bagged with aluminum foil to avoidthe contamination from modern carbon.

3. OSL and AMS 14C dating

3.1. OSL sample preparation and measurement techniques

In the luminescence dating laboratory of Qinghai Institute of SaltLakes, CAS, unexposed middle part of the tube was used to extractminerals for equivalent dose (De) determination. The samples weretreated first with 10% HCl and 30% H2O2 to remove carbonates andorganic matter, respectively. The fractions of 38e63 mm and90e125 mm were then extracted by wet sieving. To purify thequartz, the mixed samples of 38e63 mm were etched with 35%H2SiF6 for about two weeks to dissolve feldspars (Lai et al., 2007;

Fig. 3. Flood deposits and the OSL and AMS 14C ag

Roberts, 2007; Lai, 2010), and the mixed samples of 90e125 mmwere etched with 40% HF for 40 min to dissolve feldspars and thealpha-irradiated outer layer (~10 mm), respectively. Then samples ofboth the two fractions were treated with 10% HCl to remove fluo-ride precipitates. The purity of quartz grains was checked byinfrared (IR, l ¼ 830 nm) stimulation, and any samples withobvious IRSL signals were treated with H2SiF6 again to avoid Deunderestimation (Lai and Brückner, 2008). The well pretreatedgrains were then mounted on the center part (with a diameter of~4 mm) of stainless steel discs (with a diameter of 10 mm) usingsilicone oil.

The luminescence was stimulated by blue LEDs(l ¼ 470 ± 20 nm) at 130 �C for 40 s using a Risø TL/OSL-DA-20reader with 90% diode power, and detected using a 7.5 mm thickU-340 filter (detection window 275e390 nm) in front of the pho-tomultiplier tube. Irradiations were carried out using a 90Sr/90Ybeta source in the reader. A preheat plateau test and dose recoverytest were conducted on sample BZ-1 to select a proper preheattemperature. The Des were tested under different preheat tem-peratures of 220, 240, 260, 280 and 300 �C, and the result shows aDe plateau at 240e280 �C (Fig. 4A). A dose recovery test (Murrayand Wintle, 2003) were conducted with different preheat tem-peratures, and the ratios of recovered dose to given dose (16 Gy)showed the preheat temperature of 260 and 280 �C are better(Fig. 4B). The stable recycling ratio (Fig. 4C) and relative lowerthermo transfer ratio (Fig. 4D) of 260 �C further suggested thepreheat temperature of 260 �C for 10 s for natural and regenerativedoses, and cut-heat at 220 �C for 10 s for test doses for quartz. Theextremely low thermo transfer ratio (0.2e2%) for all the twelvesamples proved the preheat temperature of 260 �C is also suitablefor the relative younger samples in LZ section. Signals of the first0.64 s stimulation (Fig. 5B) were integrated for growth curve con-struction after background (last 10 s) subtraction.

The concentrations of U, Th and K were measured by neutronactivation analysis. For the 38e63 mm quartz grains, the alpha ef-ficiency value was taken as 0.035 ± 0.003 (Lai et al., 2008). Thecosmic-ray dose rate was estimated for each sample as a function ofdepth, altitude and geomagnetic latitude (Prescott and Hutton,1994). The long term water content for each sample was

es in Beizhai (BZ) and Lizhuang (LZ) sections.

Fig. 4. Preheat plateau tests (A), dose recovery test (B), recycling ratio (C), and thermo transfer ratio (D) under different preheat temperature of sample BZ-1.

H. Shen et al. / Quaternary Geochronology 30 (2015) 398e404 401

estimated based on measured modern water contents, depth, andgrain size. The dose rates are shown in Table S1.

3.2. Equivalent dose determination of OSL dating

In the current study, the combination of the Single AliquotRegeneration (SAR) protocol (Murray and Wintle, 2000) and theStandard Growth Curve (SGC) method (Roberts and Duller, 2004;Lai, 2006; Lai et al., 2007; Yu and Lai, 2012, 2014), named as SAR-SGC method (Lai and Ou, 2013), was employed for De determina-tion. In this method, for each sample, 6e12 aliquots were measured

Fig. 5. Growth curves and SGC (red) of BZ-1 (A), decay curves (B), CW-OSL decay curves (Clegend, the reader is referred to the web version of this article.)

using SAR protocol to get 6-12 growth curves, which were thenaveraged to construct an SGC for this individual sample, e.g., theSGC of sample BZ-1 (Fig. 5A); then more aliquots were measured toobtain the values of test-dose corrected natural signals only, andeach of the values could be matched in the SGC to obtain a De. Foreach sample, the final De is average of the SAR Des and SGC Des. TheOSL decay curves (Fig. 5B) decaying to the level of the backgroundwithin ca. 1 s and CW-OSL curves (Fig. 5C) of a random aliquot ofBZ-2 demonstrate that these signals were mainly from the fastcomponents. Fig. 5D shows the De (t) plots of sample BZ-2, inwhichthe De calculated based on OSL signals from different measurement

), and De (t) plots of BZ-2. (For interpretation of the references to colour in this figure

H. Shen et al. / Quaternary Geochronology 30 (2015) 398e404402

channels (per 0.16 s) don't increase with the stimulating time,demonstrating that the OSL signals were well bleached.

3.3. AMS 14C dating

The materials used for radiocarbon dating are bulk sample ofaeolian deposits in the BZ section. To make a cross-checking withthe OSL ages, these 14C samples were mainly taken close to the OSLsamples in the BZ section. The 14C samples were tested by the AMSradiocarbon method in the Acceleration Mass Spectrometry Labo-ratory of Peking University. These samples were sieved and thenthe base soluble humic fraction was collected to be dated. Theradiocarbon ages were finally calibrated by the tree-ring curve ofInCal104 (Reimer et al., 2004) with the procedural of OxCal v3.10(Bronk Ramsey, 2005). The AMS 14C dating results are shown inTable S2.

4. Dating results

All these ages range from 4460e4520 cal BP (14C) to 0.19 ± 0.02ka (OSL) andmost of them follow the stratigraphic sequence exceptthe sample BZ-2 (Fig. 3 and Table S1). The underestimation of thissample is mainly due to the anonymous high annual dose rate(4.26 Gy/ka). If replace it with the dose rate calculated based on theaverage concentration of K, Th, and U elements of the other sevensamples in the BZ section (3.83 Gy/ka), the age will be 4.18 ± 0.27ka, which could be well compared with the other OSL and 14C agesin the lower clay layer. The anonymous dose rate might be cause bythe elements migration resulting from the soak during the frequentfloods. The LZ flood section is mainly formed since 0.87 ± 0.06 ka,offering the flood records in the recent millennium. These OSL agesalso demonstrate that the sediments in the river channel are rela-tive young. The BZ and LZ sections are mainly continuous except apossible hiatus between the flood and aeolian sediments at thedepth of 0.6 m during 3.3e2.2 ka in the BZ section. This should dueto erosion from the large-scale floods during ca. 3.3e3.0 ka. Basedon the OSL and 14C chronology of the flood sediments, twoextraordinary floods could be indentified at ca. 4.1e3.8 ka and ca.3.3e3.0 ka from the BZ section; the floods were also frequent but ofsmaller-scale during the 0.9e0.2 ka.

5. Discussions

5.1. Comparison of OSL and AMS 14C ages of flood deposits

The 14C sample aremainly taken from the aeolian sediments andcould bewell compared with the OSL ages of the aeolian sediments,so both the OSL and 14C ages of the aeolian sediment in the BZsection should be reliable. Generally, the bulk sample of sedimentscould be affected by the penetration of pedogenesis (Lai andWintle, 2006), e.g., the contamination of roots, however, the 14Cages in this study seem not be underestimated. This might be resultfrom the relative high depositional rate of aeolian sediments, whichcan reduce the affect of pedogenesis penetration (Yu and Lai, 2014).The OSL ages of flood deposits in the BZ section could be wellcompared with the AMS 14C ages, e.g., the OSL age of 3.82 ± 0.22 kaat 2.3m is the samewith the 14C age of 3730e3830 cal. BP at 2.2 cm,and the OSL age of 4.03 ± 0.23 ka at 2.5 cm is the same with the 14Cage of 3980e4050 cal. BP at 2.65 m, as a result, the OSL ages of theflood deposits should be convincible.

5.2. Whether the flood deposits could be well bleached?

The OSL age of the flood deposits at the depth of 0.5 m is only0.19 ± 0.02 ka, demonstrating the deposits at the surface might be

modern. That is the residual age, if any, should be negligible for theflood deposits. The good comparison between OSL and 14C ages ofthe flood deposits further confirms the sufficient reset of the OSLsignals before burial. The De (t) plots (Fig. 5D) displays that the Descalculated based on each individual stimulation channel (0.16 s) notincreasewith the stimulating time, demonstrating that the sampleswere well bleached.

Zhang et al. (2009) dated the fluvial sediments of the YellowRiver on the CLP and found the Des from the fine grains were muchhigher than those from the coarse grains, because the coarse grainsare mainly derived from the well bleached surface material, whilethe fine grains were manly from the newly eroded loess-paleosolstratigraphy and poorly bleached. This demonstrates the signifi-cance of origin of the sediments for the OSL dating. In the Yihe RiverBasin, the flood deposits are mainly from the well bleached surfacesediments in themountains in the upper stream. The flood depositsmight also from fluvial sediments in the channels, which might berelative young according to the newly built chronology. Conse-quently, even if some portions of these flood deposits are from thereworked fluvial sediments in the channel, the resulting insuffi-cient bleaching won't cause obvious overestimation of the OSLages.

Additionally, the sediments in this region seem special, withvery low feldspar concentration and extremely bright OSL signals ofthe quartz, e.g., for an aliquot with the diameter of 4 mm of90e125 mm quartz, the signals stimulated in the first 0.16 s are ashigh as 10,000e35,000 after the irradiation (test dose) of 6 Gy. TheOSL signals could decay to the background within ca. 1 s (Fig. 5B),demonstrating that the signals are mainly from the fast component(Fig. 5C). Consequently, the OSL signals could be sufficientlybleached in a very short time.

5.3. Climatic and archaeological implications of the flood record inthe Yihe-Shuhe River Basin

The extraordinary floods happened at 4.1e3.8 ka, 3.3e3.0 ka,and 0.9e0.2 ka in the Yihe River Basin. These periods correspond tothe cold-arid climatic event at 4.2 ka, the climatic decline at ca. 3.0ka, and the cold event of Little Ice Age at 0.7e0.1 ka, respectively,according to the stalagmite record in the Dongge Cave (Wang et al.,2005) and Wanxiang Cave (Zhang et al., 2008) in monsoonal china.Gao et al. (2006) proposed that the temperature decreased during4.26e3.88 ka, and found two flood events at 4.26 ka and 3.94 ka inthe Shuhe River Basin (Fig. 1). Huang et al. (2011) also found theflood record at 4.3e4.0 ka and 3.2e3.0 ka, the arid climatic tran-sitional period, on the CLP. The flood records in this work furtherdemonstrate that both severe droughts and extreme floods mightbe characteristics of the abrupt climatic events in the monsoonalchina.

The Yihe-Shuhe River Basin has the most archaeological sitesof the Neolithic Civilizations (including Dawenkou Culture,Longshan Culture and Yueshi Culture), in Shandong region, eastChina. The Longshan Culture (4.6e4.0 ka) is the most advancedculture in China in that era (Yu, 1995), with 473 sites found in theYihe-Shuhe River Basin (Fig. 2). However, the Longshan Culturedeclined and was replaced by Yueshi Culture (4.0e3.5 ka),another kind of outdated culture demonstrated by the backset ofpottery quality and agriculture techniques. There are only 53sites of Yueshi Culture were found so far, in which only 34 siteswere develop over the former sites of Longshan Culture, i.e., atleast 93.3% sites of Longshan Culture vanished (Stateadministration of culture heritage, 2008; Fig. 2). The decline ofthe highly developed Longshan culture at ca. 4 ka was proposedto be caused by the decrease in temperature (Gao et al., 2006).Besides the decrease of sites, the distribution of sites also

H. Shen et al. / Quaternary Geochronology 30 (2015) 398e404 403

changed (State administration of culture heritage, 2008; Fig. 2),e.g., the sites developed on the alluvial plain decrease from 436(92.2% of Longshan Culture) to 17 (32.1% of Yueshi Culture). Thatis the ancient people abandoned the plain, close to water sources,and migrated into the mountains during a cold and arid period,which seems illogical. The frequent floods happened at 4.1e3.8ka offer a sound interpretation for the decline of the LongshanCulture. During the 4.2 ka cold-arid event, the arid climate driveancient people to the lower plain, especially for the agriculturebased on rice, meanwhile, this increase the danger for sufferingfrom the floods. In regions influenced by Asian summermonsoon, floods mainly happen during the summer, the mainvegetative period for the crops, so one flood can destroy the farmland and largely reduce the grain output of the whole year, andworse still there might be no seeds for the next year. The floodcan also wash away the fertile surface soil; if the floods happenedfrequently the productivity could be largely reduced, furtheraffecting the grain output. The resulting famine could cause massstarvation, wars for resources, pestilences, and emigration,making great impacts to the Longshan Culture living on agri-culture and reducing the population. This should be the bestinterpretation for the emigration from the plain during a coldand arid period, and further imply that the frequent floodsshould be the direct cause for the decline of the Longshan Cul-ture, rather than the decrease in temperature and precipitation.

On the CLP, floods deposits during 4.1e4.0 ka were found onthe culture layer of a Neolithic settlement (4.3e4.0 ka) in theJinghe River, the branch of the Yellow River, which partly resul-ted in settlement abandonment (Huang et al., 2010). Whythe floods happened frequently during the instable climate?Firstly, though the mean annual precipitation decreased, theprecipitation might occur as rainstorms with higher amounts andlower frequency. Secondly, cold and arid climate could destroythe vegetation in the mountain regions, so when rainstormhappened, less water could be conserved within the vegetationand soils and more water flowed into the river in a short time.Finally, in the lower stream, the channels were filled with de-posits due to the decreased hydrodynamic force during thearid climate, which hindered the pass of flood peaks and formingfloods. Consequently, the frequently (more than 20) floods andthe cold-arid climate during 4.1e3.8 ka might have directlycaused the decline of the Longshan Culture in the Yihe-ShuheRiver Basin. Taking into account that the sites of Longshan Cul-ture in Shandong region mainly distribute on the plains aroundthe mountain region (Fig. 1), the decline of the Longshan Culturemight be also result from the frequent floods.

6. Conclusions

(1) The OSL age of flood deposits at the depth of 0.5 m is only0.19 ± 0.02 ka, and OSL ages of the flood deposits could bewell compared with their corresponding AMS 14C ages,demonstrating that the flood sediments could be wellbleached and consequently OSL dating has the potential tooffer reliable chronology for the flood deposits.

(2) The source of the flood deposits, transportation processes,and the special characteristic of quartz decide whether thesediments could be well bleached before burial.

(3) Based on the OSL and 14C chronology, three periods withlarge-scale floods were reconstructed at 4.1e3.8 ka, 3.3e3.0ka, and 0.9e0.2 ka, corresponding to the global abrupt cli-matic variability events. The frequent floods might be part ofor caused by abrupt climatic events in the monsoonal china.

(4) The frequent floods happened during 4.1e3.8 ka might havedirectly caused the decline of the highly developed late

Neolithic Civilization (Longshan Culture) in the Yihe RiverBasin.

Acknowledgments

This study was supported by NSFC (41462006, 41372182,41290252, and 41330526), Natural Science Foundation of ShandongProvince (ZR2012DL02).

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.quageo.2015.03.005.

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