Middle-Holocene Sea-Level Fluctuations Interrupted The

Quaternary Science Reviews 188 (2018) 90e103

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Quaternary Science Reviews

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Middle-Holocene sea-level ﬂuctuations interrupted the developing Hemudu culture in the lower Yangtze River, China

* ** Keyang He a, c, , Houyuan Lu a, b, c, , Yunfei Zheng d, Jianping Zhang a, b, Deke Xu a, b, Xiujia Huan a, c, Jiehua Wang e, Shao Lei e a Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China b Centre for Excellence in Tibetan Plateau Earth Science, Chinese Academy of Sciences, Beijing 100101, China c University of Chinese Academy of Sciences, Beijing 100049, China d Zhejiang Provincial Institute of Cultural Relics and Archaeology, 310014, Hangzhou, China e Ningbo Municipal Institute of Cultural Relics and Archaeology, 315012, Ningbo, China article info abstract

Article history: The eastern coastal zone of China is densely populated and widely recognized as a center of rice Received 6 February 2018 domestication, which has undergone dramatic sea-level fluctuation during the Holocene epoch. Hemudu Received in revised form culture is distributed mainly in the eastern coastal area and was once presumed as a mature agricultural 26 March 2018 economy based on rice, making it an ideal case for examining the remarkable human-environment Accepted 26 March 2018 interaction in the Lower Yangtze River. Though numerous studies have been conducted on the cultural evolution, ecological environment, and rice domestication of Hemudu culture, the impact of sea-level fluctuation on human settlement and food production remains controversial. In this study, we report Keywords: Cultural interruptions high-resolution pollen, phytolith, and diatom records, and accurately measured elevation from the Sea-level fluctuations Yushan site, which is the closest site of Hemudu culture to the modern coastline. Based on the data Rice domestication gathered, we suggest that the Hemudu culture and subsequent Liangzhu culture developed in the Middle-Holocene context of regression and were interrupted by two transgressions that occurred during 6300-5600 BP Hemudu culture and 5000-4500 BP. The regional ecological environment of the Yushan site alternated between intertidal Lower Yangtze river mudflat and freshwater wetlands induced by sea-level fluctuations in the mid-late Holocene. Though rice was cultivated in the wetland as early as 6700 BP, this cultivation was subsequently discontinued due to the transgression; thus, full domestication of rice did not occur until 5600 BP in this region. Compre- hensive analysis of multiple proxies in this study promote the understanding of the relationship between environmental evolution, cultural interruption, and rice domestication. © 2018 Elsevier Ltd. All rights reserved.

1. Introduction River sits in the interface zone between marine and terrestrial areas that has experienced a dramatic evolution of sea level and climate Though low-elevation coastal zones (below 10 m in elevation) during the Holocene (Chen and Stanley, 1998; Qin et al., 2011; Song currently contain more than 10 percent of the world population et al., 2013; Yi et al., 2003). Accordingly, this area serves as an ideal (McGranahan et al., 2007; Small and Nicholls, 2003), these regions place for studying human-environment interaction (Zong et al., are highly vulnerable to risks resulting from sea-level rise and 2011b, 2012). climate change (FitzGerald et al., 2008; Nicholls and Cazenave, The Lower Yangtze River is densely distributed with Neolithic 2010; Nicholls et al., 2007; PAGES, 2009). The Lower Yangtze sites and is widely regarded as a core area where rice agriculture originated (Fuller, 2011; Silva et al., 2015; Stanley and Chen, 1996; Wu et al., 2014b). These cultural sequences comprise the Shang-

* Corresponding author. Institute of Geology and Geophysics, Chinese Academy of shan (11,000-8500 BP), Kuhuqiao (8000-7400 BP), Majiabang Sciences, Beijing 100029, China. (7000-6000 BP), and Hemudu Culture (7000-5000 BP) during the ** Corresponding author. Institute of Geology and Geophysics, Chinese Academy early to middle Holocene (Fig. 1a) (Liu and Chen, 2012; The Institute of Sciences, Beijing 100029, China. of Archaeology and China Academy of Social Sciences, 2010; E-mail addresses: [email protected], [email protected] (K. He), Underhill, 2013). The Hemudu culture is the most signiﬁcant [email protected] (H. Lu). https://doi.org/10.1016/j.quascirev.2018.03.034 0277-3791/© 2018 Elsevier Ltd. All rights reserved. K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 91

Fig. 1. Location and photographs of the Yushan site. (a) Location of Yushan site and the distribution of archaeological sites of Shangshan (11,000-8500 BP), Kuhuqiao (8000-7400 BP), Majiabang (7000-6000 BP) and Hemudu Culture (7000-5000 BP). (b) Aerial photographs of the Yushan site excavated in 2013 and the trench T0213 were circled by a red square. (c) Photograph of the proﬁle sampled and sediment stratigraphy. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the Web version of this article.)

Neolithic culture and is identified by its distinct style of pile- Cultural interruptions are identified by barren layers of soil (i.e., dwellings and rice remains in southern China (Sun, 2013), which layers that lack relics) that are situated between two cultural layers are distributed primarily in the eastern coastal area and divided common in the Lower Yangtze River (Wu et al., 2014a; Yu et al., into two main periods with a remarkable interruption and dispersal 2000; Zhang et al., 2005). Results of pollen, phytolith, diatom, around 6000 BP (Wang and Liu, 2005). seed, and geochemistry from the Tianluoshan site reveal several The interruption and dispersal of Hemudu culture are closely cultural interruptions during and after Hemudu Culture that were related to the change in the hydrologic environment induced by induced by the two largest transgressions during 6400-6300 BP sea-level fluctuation. The core dispute of sea-level curves proposed and 4600-2100 BP (Li et al., 2012; Patalano et al., 2015; Wang et al., previously for the east coast of China lies in whether or not a mid- 2010; Zheng et al., 2011). However, based on the analysis of pollen Holocene sea-level highstand exists (Chen and Stanley, 1998; Hori and foraminifera from the Hemudu site, some scholars argue that et al., 2001; Liu et al., 2004; Song et al., 2013; Zhao et al., 1994; the sludge layers that lie within and above the Hemudu culture Zong, 2004). Divergent views of sea-level change significantly affect layer are both freshwater swamp sediments (Wang, 2006; Zhu the explanation of the palaeoenvironment and the subsistence of et al., 2003), implying an expanded waterbody associated with Hemudu culture in Hemudu and Tianluo sites (Li et al., 2012; Liu the migration of the Yaojiang River (Liu et al., 2016; Wang and Liu, et al., 2016; Qin et al., 2006; Zhu et al., 2003). Nevertheless, 2005; Wu, 1985). Whether the cultural interruptions were caused whether the phenomenon of cultural interruption is a special case by marine transgression or land floods is still in dispute. or universal experience, what environmental changes potentially The discovery of the Hemudu site marks a milestone in Chinese caused the interruption and how the interruption affects the pro- agricultural archaeology with excellent preservation of organic cess of rice domestication remains controversial. materials in waterlogged conditions, especially abundant remains 92 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 of rice (Zhao, 2010; Zhejiang Provincial Institute of Relics and clayey silt and belonged to the early Hemudu Culture Period. Archaeology, 2003). Several intense debates on the characteristics Numerous excavated pottery sherds were tempered with charred of rice and subsistence of the Hemudu culture have been ongoing plants and sand. Unit 8 (215-180 cm) was mainly composed of since the 1970s, and the core dispute lies in whether or not the rice yellow gray clay with no artificial remains excavated. Unit 7 (180- is domesticated and rice farming is established (Fuller et al., 2007, 150 cm) consisted of dark gray silt with fine sand that belonged to 2009; Liu et al., 2007; Zheng et al., 2007). Though most scholars the late Hemudu Culture Period. Artificial remains were composed agree that rice domestication was a protracted evolutionary process primarily of sand pottery and red clay pottery. Unit 6 (150-120 cm) that took at least 2000 years (Allaby et al., 2008; Fuller et al., 2014; was dark black peat and contained rich humus and plant debris. A Gross and Zhao, 2014), scholarly focus on how the cultural inter- few sand pottery sherds belonging to Liangzhu Culture were ruption affected the development of rice domestication is sparse. excavated in this layer. Unit 5 (120-100 cm) consisted of gray-green In the present study, a high-resolution AMS14C dated profile is clay and in it, no artificial remains were found. Unit 4 (100-60 cm) taken from the Yushan site, which is the closest site of Hemudu was composed of yellowish silt; numerous streaks of brown rust culture to the modern coastline. Through synchronized analyses of were distributed in this layer. sporopollen, phytolith, and diatoms integrated with sedimentological information from the Yushan profile, we attempted to: 1) 3.2. Radiocarbon dating explain the possible cause of cultural interruption, 2) reconstruct the evolution of the local environment, and 3) trace the process of Nine soil samples were collected in the boundaries of each layer rice domestication. (Fig. 2) and were screened to retrieve dating materials. Most of the dating materials were charred seeds, except for one plant fragment. 2. Geographical background and site description These materials were submitted to the Radiocarbon Dating Labo- ratory of Peking University. These ages were calibrated using the The study area is located in the subtropical region of southeast IntCal13 dataset (Reimer et al., 2013) by OxCal v4.2.4 program China under the influence of the East Asian Monsoon. The mean (Ramsey, 2009). Full details of the nine ages in the present study are temperature is ~4 C in January and ~28 C in July, and the average displayed in Table 1. annual precipitation is ca. 1100 mm (Ningbo Chorography A total of nine AMS radiocarbon ages were obtained, and most of Codification Committee, 1995). Regional vegetation is character- the ages calibrated followed a consistent stratigraphic order with ized by subtropical mixed forests of evergreen and deciduous trees. depth ranges, except for the YS21 sample. The dating age corre- The region's most common evergreen trees are Lithocarpus, Cyclo- sponded well to the three cultural periods determined by the balanopsis, Quercus, while its most common deciduous trees are pottery sherds excavated from the site. An age-depth model was Liquidambar, Castanea, Celtis, and Ulmus. constructed using the Bacon model (Blaauw, 2010) and applied to The Yushan site (30020N, 121330E) is located on the southeast the diagram of pollen. This chronology indicated that the Yushan slope of Yushan hill, Ningshao coastal plain of the south Hangzhou profile spanned the last 7300 years. Bay in eastern China (Fig. 1a). The site is about 2 m above local mean sea level (the Yellow Sea datum) and 7.3 km west to the present-day 3.3. Pollen analysis coastline. The Yushan site was excavated by Ningbo Municipal Institution of Cultural Relics and Archaeology and divided into four Samples were treated according to the following standard pro- cultural periods of Hemudu Culture, Liangzhu-Qianshanyang Cul- cedure developed by Moore et al. (1991). First, a tablet of exotic ture, Shangzhou Dynasty, and Tangsong Dynasty. Sediment cores Lycopodium spores (27,637 N/tablet) was added to each sample to indicated that the occupied site was approximately 16,500 m2 in calculate the palynological concentrations. Second, 10% HCl and area, and 1500 m2 were excavated during stage I in 2013 (Ningbo 40% HF were added to remove carbonates and silicates, respec- Municipal Institution of Cultural Relics and Archaeology and tively. Third, the samples were heated with 10% KOH to dissolve Zhenhai Administration, 2016). humic matters. Fourth, an acetolysis solution, made by mixing 10 ml of H2SO4 with 90 ml of acetic anhydride, was added to 3. Material and method remove cellulose. Fifth, the materials remaining after the acid- ealkaline reactions were sieved through a 7 mm mesh in an ultra- 3.1. Sediment and sampling sonic instrument in order to concentrate the pollen. Finally, the residue was suspended in glycerine and mounted on slides for The Yushan profile analyzed in this study was in the south microscopic examination at 400 magnifications. section of trench T0213 (Fig. 1b and c), and the surface elevation of Each sample was counted for pollen and spores over 500 grains the section ranged from 1.98 m to 2.03 m, as measured by the (average 608 grains). A total of 26,169 grains of pollen and spores Zhenhai Urban Planning and Survey Research Institute of Ningbo. had been obtained from the 43 samples. Identification of pollen and The thickness of the Yushan profile was approximately 275 cm and spores were made with reference to modern and Quaternary atlas had been divided into 10 layers according to the sediment and in- (Institute of Botany and South China Institute of Botany, 1982; Tang clusion (Fig. 2)(Ningbo Municipal Institution of Cultural Relics and et al., 2016; Wang et al., 1995). Poaceae pollen was divided into Archaeology and Zhenhai Administration, 2016). The upper 60 cm three size categories (<35 mm, 35e40 mm, >40 mm), and the Poaceae of the profile encompassed historic and modern sediment, which grains (>40 mm) from the sediment of eastern China had been included layers 1 to 3, and was not sampled. The lower 215 cm identified as domesticated rice pollen (Chaturvedi et al., 1998; encompassed prehistoric and natural layers, which included layers Wang et al., 1995). Quercus pollen was separated into two cate- 4 to 10, and was subsampled at 5 cm intervals for the microfossil gories, Quercus (deciduous) and Quercus (evergreen), based on the analyses. A total of 43 samples were collected, and 2 g of each surface, tricolporoidate, and size that were thought to have sample was used for pollen, phytolith, and diatom analysis. ecological significance (Cao and Zhou, 2002; Wang and Pu, 2004). The lower 215 cm of the Yushan profile was divided into seven units from the bottom to the top (Fig. 2). Unit 10 (275-250 cm) was 3.4. Phytolith analysis composed of pure dark green clay, which was widely distributed in the Ningshao Plain. Unit 9 (250-215 cm) consisted of dark gray Phytoliths were extracted using the conventional wet digestion K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 93

Fig. 2. The sampled proﬁle in the south section of the trench T0213. Stratigraphically, it is divided into ten sediment units and representative potteries were shown in the cultural layer. Samples from units ④ to ⑩ were analyzed. Locations of the dating samples are shown in the scale of depth on the left side by a red rectangle. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the Web version of this article.)

Table 1 AMS 14C dates for Yushan site.

Sample no. Depth (cm) Material Conventional 14C age Calibrated 14C age Dating ID (14C yr BP) (14C yr BP)

2s (95.4%)

YS14 65e70 plant fragment 4040 ± 30 4782-4771 (2.0%) BA151803 4581-4424 (93.4%) YS21 100e105 seed 4365 ± 25 5032-5018 (3.8%) BA151804 4976-4859 (91.6%) YS26 125e130 seed 4300 ± 25 4960-4934 (4.3%) BA151805 4888-4831 (91.1%) YS31 150e155 seed 4525 ± 25 5307-5214 (29.8%) BA151806 5191-5054 (65.6%) YS37 180e185 seed 4785 ± 25 5591-5571 (14.6%) BA151807 5557-5472 (80.8%) YS44 215e220 seed 5495 ± 25 6394-6372 (3.6%) BA151808 6323-6272 (85.7%) 6240-6217 (6.1%) YS47 230e235 seed 5665 ± 25 6529-6521 (0.6%) BA151809 6511-6397 (93.2%) 6368-6352 (1.6%) YS50 245e250 seed 5860 ± 25 6744-6637 (95.4%) BA1518010 YS53 260e265 seed 6225 ± 25 7253-7146 (49.3%) BA1518011 7130-7013 (46.1%) 94 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 method as follows (Piperno, 1988; Runge, 1999). First, the organic increased gradually from 4% to 18%. Typha rose to 2%, and Myr- matter was oxidized by H2O2 (30%). Second, a tablet of exotic iophyllum reached the peak of 4%. Lycopodium spores (27,637 N/tablet) was added. Third, carbonates were removed by HCl (10%). Fourth, the phytoliths were extracted 4.1.3. Zone III (215-180 cm, 6300-5600 BP) by heavy liquid (ZnBr , 2.35 g/cm ). Finally, the recovered phyto- 2 3 There was a slight decrease in the percentage of trees and liths were permanently mounted on glass microscopic slides with shrubs, from 73% to 65%. Evergreen Quercus declined to a low of Canada balsam. Identification and counting of phytoliths were 24%, whereas Pinus rose to a high average of 8%. Poaceae (<35 mm) carried out using a Leica DM 750 microscope at 400 magnifica- declined rapidly and then remained at a low value of 12%. Poaceae tion. At least 400 phytoliths (average 468 grains) were counted for (>35 mm) rose fast from the middle of this zone, especially the each sample. Poaceae (>40 mm) that increased from 0.8% to 8%. Typha increased Phytoliths were classified according to the system proposed by from 3% to 9%, while Myriophyllum nearly disappeared. Lu et al. (2006) and described according to the International Code for Phytolith Nomenclature (ICPN1.0) (Madella et al., 2005). Rice was the only cereal identified in this study that included three 4.1.4. Zone IV (180-120 cm, 5600-5000 BP): Hemudu Culture Period distinctive phytolith types: (1) Rice bulliform produced in the leaf III and Liangzhu Culture bulliform cells; (2) Paralleled bilobates produced in leaf cells; (3) The percentage of Cyperaceae and Typha all exhibited a Double-peaked glume phytoliths produced in the epidermis of the remarkable increase, reaching peaks of 28% and 31%, respectively. rice husk (Gu et al., 2013). The morphological characteristics of rice Pinus and Chenopodiaceae decreased and remained at a low con- bulliforms and double-peaked phytoliths were measured for tent of 2% and 0.9%, respectively. Poaceae (<35 mm) showed a further discrimination of wild and domesticated rice (Lu et al., declining trend from 21% to 9%, whereas Poaceae (35e40 mm) and 2002; Zhao et al., 1998; Zheng et al., 2003). Poaceae (>40 mm) retained relatively high values of 4% and 7%, respectively. 3.5. Diatom analysis 4.1.5. Zone V (120-60 cm, 5000-4500 BP) fi Diatoms were extracted and identi ed simultaneously with There was a remarkable recovery in the percentages of Pinus, phytoliths. Twenty-two samples at 10 cm intervals were selected Pterocarya, and Chenopodiaceae that reached 4%, 2%, and 2%, for analysis, and no additional extraction processes were required. respectively. Both evergreen and deciduous Quercus increased fi Diatoms were identi ed with reference to modern and archaeo- rapidly, reaching peaks of 37% and 18%, respectively. Cyperaceae logical studies in this region (Liu et al., 2011; Wang et al., 1987, decreased from 14% to 0.2%, and Typha kept a stable level of 10%. fi 2010; Zheng et al., 2011). Diatoms were classi ed into three types of Poaceae (35e40 mm) and Poaceae (>40 mm) reached peaks of 8% freshwater species, brackish species, and marine species. At least and 14%, respectively, and then decreased afterward. 300 diatoms (average 290 grains) were counted for each sample, except for three samples in which diatoms were rare, counting was less than 50 grains. 4.2. Phytolith assemblages

fi 4. Results Thirty-three phytolith morphotypes were identi ed from the Yushan profile, and the major phytoliths are shown in Appendix 4.1. Pollen assemblages Fig.A1. The stratigraphic diagrams of phytolith percentages of the Yushan profile were constructed by C2 version 1.7.4 software fi A total of 78 pollen types were identified including 43 arboreal (Juggins, 2007) and divided into ve phytolith assemblage zones taxa, 18 herbaceous taxa, 7 aquatic taxa, 7 fern taxa, and 3 algae according to the sediment facies (Fig. 4). taxa, of which the major pollens are shown in Appendix Fig.A1. Pollen assemblages of the Yushan profile can be divided into five 4.2.1. Zone I (275-250 cm, 7300-6700 BP) pollen zones from bottom to top according to the sediment and The phytolith assemblage zone I was characterized by high cluster analysis of pollen using CONISS (Grimm, 1987) by Tilia proportions of smooth elongate (27%) and bilobate (19%). The software (Grimm, 1991)(Fig. 3). percentage of short saddle (6%) and tower (10%) exhibited an increasing trend, while that of point (9%) decreased gradually. No 4.1.1. Zone I (275-250 cm, 7300-6700 BP) phytoliths of rice were recovered from this zone. This zone was characterized primarily by a high proportion (approximately 64%) of trees and shrubs, which was dominated by 4.2.2. Zone II (250-215 cm, 6700-6300 BP): Hemudu Culture Period evergreen and deciduous Quercus (28% and 8%, respectively), Pinus II (12%), and Liquidambar (5%). The proportion of upland herbs was The proportions of reed phytoliths (plateau saddle and reed approximately 35% and composed mostly of Poaceae (<35 mm) bulliform) appeared and reached peaks of 9% and 2%, respectively. (13%) and Chenopodiaceae (19%). Pinus and Chenopodiaceae The percentage of short saddle (14%), hat (5%), and tower (19%) exhibited a declining trend from 21% to 5% and 30% to 6%, respec- increased to higher levels, while that of bilobate (11%), smooth tively. In contrast, Poaceae (<35 mm) increased rapidly from 3% to elongate (13%), and point (3%) decreased to lower levels. Rice bul- 33%. liform first appeared and reached a peak of 0.7%. 4.1.2. Zone II (250-215 cm, 6700-6300 BP): Hemudu Culture Period II 4.2.3. Zone III (215-180 cm, 6300-5600 BP) Pollen zone II showed a gradual increase in trees and shrubs Phytolith zone III was characterized by a high proportion of from 58% to 64%. The content of evergreen Quercus increased smooth elongate (27%), square (14%), and point (9%), while the slightly from 32% to 36%. Poaceae (<35 mm) reached the peak and percentage of short saddle (4%), plateau saddle (0.5%), hat (1%), and decreased from 29% to 14%. The percentage of Pinus and Cheno- tower (9%) decreased to lower levels. Rice bulliform nearly dis- podiaceae remained low at 3% and 3%, respectively. Cyperaceae appeared and was only found in a few samples. K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 95

Fig. 3. Simpliﬁed pollen percentage diagram of the Yushan site. Calibrated radiocarbon age ranges before present (cal BP) are shown on the left of the diagram. Five main pollen zones are obtained from a constrained cluster analysis and shown on the right of the diagram.

Fig. 4. Selected phytolith assemblages of the Yushan site. Samples selected for a detailed check of rice bulliform are shown on the left side with red rectangles. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the Web version of this article.)

4.2.4. Zone IV (180-120 cm, 5600-5000 BP): Hemudu Culture Period 4.3. Diatom assemblages III and Liangzhu Culture The percentage of bilobate (24%) and cross (6%) increased to Diatoms were recovered in abundance in nearly all samples high levels, while that of smooth elongate (16%), square (5%), and studied; 24 major morphotypes were identified, as shown in point (2%) decreased to low levels. Cyperaceae phytoliths of Appendix Fig.A1, including marine, brackish, and freshwater spe- polygonal cones were widely recovered and increased to the peak cies. The stratigraphic diagrams of diatom percentages of the of 3%. Rice bulliform reached the peak of 1% and decreased after- Yushan profile were constructed by C2 version 1.7.4 software ward. Double-peaked glume cells appeared for the first time, ac- (Juggins, 2007) and divided into five zones according to the sedi- counting for 0.2%. ment facies and diatom assemblage (Fig. 5).

4.2.5. Zone V (120-60 cm, 5000-4500 BP) The percentage of smooth elongate (21%), long saddle (7%), and 4.3.1. Zone I (275-250 cm, 7300-6700 BP) point (6%) increased to high levels, while that of bilobate (19%), Diatom assemblages in zone I were dominated by marine spe- cross (1%), and sinuate elongate (2%) decreased. Rice phytoliths cies of Campylodiscus spp (26%), Conscinodiscus spp (46%), Tricera- were still recovered from a few samples. Bilobates parallel was tium favus (1%), Cyclotella stylorum (5%), and Diploneis smithii (4%). widely recovered in this zone and increased to the peak of 0.9%. No freshwater diatom was recovered from this zone. 96 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103

Fig. 5. Diagram showing the percentage of selected diatom taxa that were categorized into three types of marine, brackish, and freshwater species.

4.3.2. Zone II (250-215 cm, 6700-6300 BP): Hemudu Culture Period bulliform (Fig. 4). In total, 389 rice bulliform phytoliths were II identified. Fish scale decorations of most rice bulliforms were Marine diatoms decreased sharply and nearly disappeared in weathered and unable to be counted (Lu et al., 2002). Morpho- Zone II. In contrast, this zone was dominated by brackish diatoms of logical characteristics of each individual bulliform were also Nitzschia scalaris (39%) and Pinnularia yarrensis (21%), and fresh- measured (Zheng et al., 2003). The average vertical length (VL) and water diatoms of Amphora ovalis (20%), as well as Navicula cuspidata horizontal length (HL) of rice bulliform were 42.9 ± 7 mm and & radiosa (8%). 34.7 ± 5.1 mm, 45.3 ± 7.9 mm and 37.2 ± 6.1 mm, 42.3 ± 7.9 mm and 36 ± 6.4 mm from the bottom up, respectively. Only one sample of 4.3.3. Zone III (215-180 cm, 6300-5600 BP) double-peaked glume cells was suitable for discriminant analysis Marine diatoms of Campylodiscus spp (18%), Conscinodiscus spp (Zhao et al., 1998) and classified as domestic rice. (40%), T. favus (0.8%), C. stylorum (7%), and D. smithii (4%) increased The percentage of Poaceae fluctuated significantly between again and played leading roles. In addition, brackish diatoms of P. different zones with several peak values of approximate 34.5%. yarrensis (22%) also accounted for a high proportion. However, the composition of the Poaceae pollen changed radically. The first peak, which occurred in zone II, was composed almost 4.3.4. Zone IV (180-120 cm, 5600-5000 BP): Hemudu Culture Period entirely of Poaceae (<35 mm), whereas the peaks in zone IV were III and Liangzhu Culture mainly promoted by the rise of Poaceae pollen (>40 mm). The per- This zone was dominated by brackish diatoms of N. scalaris centage of rice pollen (>40 mm) to Poaceae pollen was as low as 1.1% (43%), and freshwater diatoms of Pinnularia major (28%), N. cuspi- in zones I and II, rose rapidly to a high value of 28% in zone III, and data & radiosa (11%), Cymbella minuta & asper (4%), and Eunotia remained at that percentage until it peaked again to 37% in zone V. praerupta & pectinalia (6%). Several samples revealed only a few marine diatoms. 5. Discussion

4.3.5. Zone V (120-60 cm, 5000-4500 BP) 5.1. Reconstruction of the ecological environment Marine diatoms of Campylodiscus spp (62%) and Conscinodiscus spp (17%) increased and played a leading role. Freshwater diatoms According to the analysis of sediment, pollen, phytoliths, and of P. major (14%) decreased sharply and only accounted for a minor diatoms, the Yushan site experienced environmental alternations proportion. between intertidal mudflats and freshwater wetlands controlled by the fluctuation of relative sea level (RSL) (Fig. 6)(Zheng et al., 2011). 4.4. Identification of rice pollen and phytolith Diatom assemblages of zones I, III, and V were composed primarily of marine diatoms Campylodiscus spp and Conscinodiscus spp, Rice bulliform phytoliths were recovered from 20 samples with which are common in offshore, coastal, and intertidal zones in the concentrations ranging from 1151 to 27,637 grains/g; concentra- Lower Yangtze River (Liu et al., 2011; Wang et al., 1987; Zhuang tions of 11 of these samples exceeded 5000 grains/g. Two samples et al., 2014), indicating seawater environments and marine trans- for each cultural period were selected for a detailed check of rice gression. In contrast, diatom assemblages of zones II and IV were K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 97 dominated by freshwater diatoms A. ovalis and P. major and triqueter community, Suaeda spp community, Typha spp commu- brackish diatoms N. scalaris and P. yarrensis, which are commonly nity, and Phragmites australis community (Fig. 6b) (Gao and Zhang, recovered from shallow lakes, freshwater marshes/swamps, and 2006; Tang and Lu, 2003; Wu et al., 2008). The zones I, III, and V coastal lagoons (Yang et al., 2008; Zong and Horton, 1998; Zong were characterized by a high proportion of Chenopodiaceae, which et al., 2011a), indicating freshwater wetland environments and indicated Suaeda spp widespread on the supratidal zone of the regressive events (Fig. 6a). marine layer (Fig. 6a) (Xiao et al., 2014). Zones II and IV were Based on the survey of modern plants along southeastern China, characterized by a high proportion of aquatic sporopollen of Typha coastal mudflats can be divided into several plant communities and Myriophyllum that indicated the existence of a freshwater according to elevation and inundation time. From the low tide line wetland (Fig. 6a) (Ma et al., 2010). to the high tide line are bare flat, Scirpus mariqueter & Scirpus In addition, the pollen and phytolith results corresponded well

Fig. 6. Ecological models of plant communities and human activities along the coast of the Lower Yangtze River during regression and transgression (Appendix B. Supplement dataset S1). 98 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 in zones II and V with reference to reeds and sedges (Fig. 6a). In (Ningbo Municipal Institute of Cultural Relics and Archaeology, zone II, the percentage of Poaceae (<35 mm) pollen reached its peak, 2013), and Tianluoshan (Zheng et al., 2011)(Fig. 7a). The estimated possibly due to the expansion of wild rice, weed, or reed. Mean- date of the interruption layer ranged from 6400 to 5600 BP and the while reed phytolith (reed bulliform and plateau saddle) also depth ranged from 2.9 to 1.1 m to the surface (Fig. 7b, Table .2). In the reached its peak. In zones IV and V, the percentage of Cyperaceae present study, accurate elevation and age were measured at the pollen reached its peak, while that of sedge phytolith (polygonal Yushan site and the effects of local subsidence and sediment cones) emerged, accounting for the highest proportion in the consolidation were also considered (Appendix Table. A1)(Zhan and profile. The remarkable coincidence between the pollen and phy- Wang, 2014; Zhang and Liu, 1996; Zong, 2004). Accordingly, we tolith indicated two events of regression and formation of wetland suggest that the RSL was at least 0.4 m above the present during that occurred during 6700-6300 BP and 5600-5000 BP, which 5600 BP. When it comes to the other transgression that ended in provided a rich habitat for the development of Neolithic culture and 4500 BP, the RSL was up to 1.8 m above the present at this site. the cultivation of rice (Zheng, 2012; Zong et al., 2007). Previous studies suggested that settlements in the Yangtze 5.3. Process of rice domestication coastal plain gradually moved seawards over the course of the Neolithic period (Stanley and Chen, 1996; Zong et al., 2012). Newly The concentration of rice bulliform exceeded 5000 grains/g in a emerged marshes and mudflats in the process of regression pro- few samples from zone II and reached the peak of approximately vided rich wild food resources (Yuan et al., 2008; Zheng, 2012) and 27,000 grains/g in samples from zones IV and V, indicating that rice were suitable for rice cultivation, hence may attract people migrate cultivation (Fujiwara, 1976) had already started during the Hemudu following the receding sea. The sedimentary strata in the Yushan Culture Period II in this region. Measurements on rice bulliform site were similar to that of the Tianluoshan site while the beginning phytoliths from zones II and IV fell into the area close to that after of Hemudu culture at the Yushan site was approximate 300 and 700 the Majiabang culture and did not shift towards larger sizes (Fig. 8a) years later than that at Tianluoshan site, respectively (Zheng et al., (Fuller et al., 2007; Qin et al., 2006). Though morphological features 2011). Compared to the Tianluoshan site, the Yushan site was of bulliform from modern Oryza sativa display wide overlaps with located closer to the coastline, which resulted in the regression that of wild species (Fig. 8b) (Gu et al., 2013), previous studies of occurring later than at the Tianluoshan site. In other words, some rice bulliform from archaeological sites show an increasing trend ancient people of Hemudu culture may have migrated with the through the Neolithic Age (Zheng et al., 2000, 2003). Thus, we regression to search for new wetlands suitable for inhabitation. suggest these rice had already been cultivated and was in the process of domestication since 6700 BP. 5.2. Cultural interruption and sea-level fluctuation Although the use of a size threshold to identify rice pollen is still disputed (Mao and Yang, 2015), two main criterions of 35 mm(Li Evidence of pollen and diatoms in the Yushan profile discussed et al., 2015; Shu et al., 2007; Yang et al., 2012) and 40 mm above indicates that the three natural layers of zones I, III, and V (Chaturvedi et al., 1998; Wang et al., 1995; Zong et al., 2007) were all formed by marine transgressions. As for zone I, abundant (Fig. 8d) are widely applied to modern field and ancient sediment. A data from cores revealed that the marine layers were widely great change occurred in the composition of Poaceae in zone IV as distributed before human settlement in Zhejiang province (Fig. 7b) the percentage of rice pollen (>40 mm) rose sharply from 1.1% to and varied from several meters to approximately 45 m in thickness 28% and continued its upward trend (Fig. 8c). In contrast, the peak (Feng and Wang, 1986). Many foraminiferas including the species of Poaceae pollen percentage in zone II was nearly all comprised of Ammonia beccarii were recovered from the layer beneath the cul- Poaceae (<35 mm). The remarkable contrast between these two tural layer at the Hemudu site, illustrating an inner-shelf shallow zones indicated that rice cultivated in the Hemudu Culture Period II sea environment (Zhu et al., 2003). Recent studies on the spatio- was more similar to the wild type, whereas the rice in Hemudu temporal distribution of Neolithic sites indicate that the East Culture Period III was more likely to be fully domesticated. In sum, China coastal plain experienced widespread transgression and we suggest that rice farming have already established in this region turned into a shallow marine environment during 9000e7000 BP at least since 5600 BP. (Li et al., 2018; Zheng et al., 2018), and forming the marine layer of Though modern genetic dataset suggests rice may have origi- zone I in the Yushan profile. nated from the Pearl River basin (Huang et al., 2012), numerous As for zones III and V that interrupted and overlay Hemudu and evidences of genetics, archaeobotany and computational modelling the subsequent Liangzhu cultural layers, some scholars argued that are consistent with the domestication of O. sativa japonica in the these layers were freshwater swamps, with no genera of forami- Yangtze River valley (Fuller et al., 2010b; Gross and Zhao, 2014; nifera found in the Hemudu site (Zhu et al., 2003). Nevertheless, Silva et al., 2015). The process of domestication has been recognized evidence of diatoms and seeds from the Tianluoshan site indicated a protracted and dynamic transition taking thousands of plant that these layers of cultural interruption were likely to be the result generations (Allaby et al., 2008; Fuller et al., 2010a). The rate of of transgression induced by sea-level fluctuation in the mid-late domestication is not a constant, instead it varies along the process Holocene (Wang et al., 2010; Zheng et al., 2011). This dispute may in response to different human behaviors (Fuller et al., 2010a). The derive from different sea-level indicators (Wang, 1989) or varied long process of pre-domestication in the Lower Yangtze River local environment. Diatoms in zones III and V, as discussed above, (Fuller, 2007; Fuller et al., 2010b) may be the result of the unstable indicated the existence of two large-scale marine transgressions. In environment induced by sea-level fluctuations. The accelerated fact, the Hemudu culture developed above the intertidal mudflat accomplishment of rice domestication during the Hemudu Culture formed by the regression beginning around 7500-7000 BP (Zheng Period III may attribute to the formation of the paddy field systems, et al., 2018; Zhu et al., 2003); nevertheless, several transgressive which efficiently separates cultivated rice from other wild plants events induced by sea-level fluctuation still occurred in the process and significantly reduces cross-pollination with free-growing wild of regression (Zheng et al., 2011). rice (Fuller and Qin, 2009; Fuller et al., 2010b). In addition, the interruption layer between the Hemudu periods II and III was also found in several sites distributed along the coast of 6. Conclusion the Ningshao Plain, such as at Loujiaqiao (Zhejiang Provincial Institute of Cultural Relics and Archaeology et al., 2010), Fujiashan Evidence of pollen, phytoliths, and diatoms integrated with K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 99

Fig. 7. The phenomenon of cultural interruption along the coast of Ningshao Plain. (a) Distribution of archaeological sites of Hemudu culture and location of the sites with cultural interruptions (Appendix B. Supplement dataset S2). (b) Schematic diagram of sediment stratigraphy from these archaeological sites. Natural layers that underlie and interrupt the Hemudu cultural layers are displayed in gray. 100 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103

Table 2 Phenomenon of cultural interruptions.

Site Hemudu Culture II Interruption Hemudu Culture III Depth of Interruption Elevation of Surface

Loujiaqiao 6700-6400 BP 6400-6000 BP 6000-5800 BP 2.9e2.7 m 5.5 m Hemudu 6300-6000 BP Unknown 6000-5600 BP 2.7e2.3 m 2.4 m Tianluoshan 7000-6400 BP 6400-6300 BP 6300-4600 BP 2.5e1.8 m 2 m Fujiashan 6300-6000 BP 6000-5700 BP 5700-5300 BP 1.2e1.1 m 2 m Yushan 6700-6300 BP 6300-5600 BP 5600-5200 BP 2.1e1.8 m 2 m

Fig. 8. The process of rice domestication in the Yushan site with reference to evidence of phytoliths and pollen. (a) Measurements of rice bulliform from the Yushan site (Appendix B. Supplement dataset S3) and trend of increasing size in the Lower Yangtze River (Fuller et al., 2007). (b) 3-D scatter plots for morphological parameters of rice bulliform (Gu et al., 2013). (c) Percentage of Poaceae pollen to the total terrestrial pollen and percentage of rice pollen (>40 mm) to the Poaceae pollen. (d) Size distributions of Poaceae pollen inside the rice cultivated fields (Yang et al., 2012). sedimentological information from the Yushan site indicates the financial support for this work that could have influenced its existence of a dynamic interaction between human activity and the outcome. sea-level fluctuation beginning in 6700 BP. Hemudu culture and the This research has not been submitted for publication nor has it subsequent Liangzhu culture developed in the context of regression been published in whole or in part elsewhere. We attest to the fact and were interrupted by two transgressions that occurred during that all authors listed on the title page have contributed signifi- 6300-5600 BP and 5000-4500 BP. The regional ecological envi- cantly to the work, have read the manuscript, attest to the validity ronment of the Yushan site alternated between intertidal mudflats and legitimacy of the data and its interpretation, and agree to its and freshwater wetlands induced by sea-level fluctuation in the submission to the Quaternary Science Reviews. mid-late Holocene. Though rice was first cultivated on wetlands We confirm that we have given due consideration to the pro- beginning in 6700 BP, its cultivation was halted by the subsequent tection of intellectual property associated with this work and that transgression; thus, the full domestication of rice in this region was there are no impediments to publication, including the timing of protracted until 5600 BP. publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property. Declaration of interest We understand that the Corresponding Author is the sole con- tact for the Editorial process. He is responsible for communicating We wish to confirm that there are no known conflicts of interest with the other authors about progress, submissions of revisions and associated with this publication and there has been no significant K. He et al. / Quaternary Science Reviews 188 (2018) 90e103 101

ﬁnal approval of proofs. We conﬁrm that we have provided a cur- “Macroevolutionary Processes and Paleoenvironments of Major rent, correct email address which is accessible by the Corre- Historical Biota” of the Chinese Academy of Sciences (No. sponding Author. XDPB0503), and National Natural Science Foundation of China (No. 41430103).

Acknowledgements Appendix B. Supplementary data We sincerely thank Professor Guoping Sun for the assistance in Supplementary data related to this article can be found at samples collection. We also thank Yafei Zou for helping identify https://doi.org/10.1016/j.quascirev.2018.03.034. diatoms. We are grateful to Can Wang and Xiaoshan Yu for their useful suggestions on the manuscript. We greatly appreciate the valuable comments of anonymous reviewers that improved the Appendix A ﬁnal manuscript. This work was jointly funded by the National Basic Research Program of China (No. 2015CB953801),

Fig. A1. Images of typical microfossils identiﬁed at the Yushan site, including pollen (1e23), phytoliths (24e43), and diatoms (44e55). Pollen (1e23) 1. Pinus;2.Quercus.deciduous; 3. Quercus.evergreen; 4. Carpinus;5.Betula;6.Alnus;7.Liquidambar/Altingia;8.Ulmus/Zelkova;9.Pterocarya;10.Castanopsis/Lithcarpus;11.Castanea; 12. Poaceae (>40 mm); 13. Poaceae (35e40 mm); 14. Poaceae (<35 mm); 15. Artemisia; 16. Chenopodiaceae; 17. Nymphoides;18.Myriophyllum;19.Typha; 20. Typha (tetrad); 21. Cyperaceae (small); 22. Cyperaceae (big); 23. Persicaria. Phytoliths (24e43) 24. Reed bulliform; 25. Long saddle; 26. Plateau saddle; 27. Short saddle; 28. Rectangle; 29. Square; 30. Polygonal cones (Cyperaceae); 31. Smooth elongate; 32. Sinuate elongate; 33. Faceted elongate; 34.wavy-trapezoid; 35.Wavy-narrow-trapezoid; 36. Point; 37. Hat; 38. Tower; 39. Bilobate; 40. Cross. 41. Bilobates parallel; 42. Double-peaked glume cells; 43. Rice bulliform. Diatoms (44e55) 44e45. Campylodiscus echeneis; 46. Coscinodiscus nodulifer;47.Diploneis elliptica;48. Pinnularia yarrensis;49.Nitzschia scalaris; 50. Amphora ovalis;51.Neidium productum; 52. Cymbella cistula; 53. Pinnularia major; 54. Navicula triviali; 55. Eunotia praerupta. 102 K. He et al. / Quaternary Science Reviews 188 (2018) 90e103

Table A1 Correction for sediment compaction settlement for Yushan proﬁle.

Unit Depth Measured (cm) Lithology Porosity (n) Porosity (n0) Thickness Compaction capacity Depth Corrected (h/cm) (△h) (cm)

1e30e60 silt 0.5 0.48 60 2.4 41.4e21 4a 60e100 clayey silt 0.68 0.63 40 6.3 21e67.3 5a 100e120 clay 0.7 0.62 20 5.3 67.3e92.6 6 120e150 clayey silt 0.68 0.63 30 4.7 92.6e127.3 7 150e180 silt 0.5 0.48 30 1.2 127.3e158.5 8a 180e215 clay 0.7 0.62 35 9.3 158.5e202.8 9 215e250 clayey silt 0.68 0.63 35 5.5 202.8e243.3 10 250e275 clay 0.7 0.62 25 6.7 243.3e275

a The Yangtze Delta has experienced a weak subsidence in the Holocene and the small amount of subsidence was not calculated in this study.

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