Relative sea level rise,site distributions,and Neolithic settlement in the early to middle Holocene,Jiangsu Province,China

Abstract

This study details the chronology and the human consequences of early- to mid-Holocene sea level rise and the related marine transgression and regression along the east coast of China. We use archaeological and environmental data to show that there was a significant marine transgressive event that began before 9000 cal. BP. This event reached its maximum extent inland and had the greatest impact on the Jiangsu region between 9000 and 8000 cal. BP. Because of this transgression, most of the low-lying parts of modern Jiangsu Province were either covered by seawater or were converted to a wetland environment that was unsuitable for long-term human settlements until ca. 7000 cal. BP. Between 7000 and 6000 cal. BP, the sea retreated and new lands became available for colonization. Humans rapidly moved into the newly emerged lands, which were ecologically rich with diverse and abundant plants, animals, fish, and shellfish. Evidence that human settlement were earliest in the northwest and generally expanded south and east. The Taihu Plain was rapidly occupied, but because of variations in topography, hydrology, and sea level changes, the Lixiahe Plain remained a coastal lagoon until 6000–5500 cal. BP.

Keywords

China early Holocene middle Holocene neolithic settlement relative sea level rise site distributions

Introduction

Global climates changed considerably at the end of the Pleistocene and into the early and middle Holocene; these climate changes and the associated ice-sheet decay, coupled with local tectonic transformations and subsidence (Chen and Stanley, 1998) as well as geoidal deformation (Mörner, 1976), resulted in a complicated pattern of rising and falling sea levels with multiple, reciprocating changes to coastlines (Lambeck et al., 2014; Smith et al., 2011; Törnqvist and Hijma, 2012). Numerous studies have found that a large-scale transgressive event associated with rising sea levels occurred along the eastern coast of China during the early to middle Holocene (Wang et al., 2013). These events had a profound effect on early human settlement. However, the specific timing of the highest transgression in early Holocene is debated. Different datasets produce different chronologies of rising sea level. Using geological and sedimentological data, Shao (1987) proposed that the maximum transgression in the Yangtze River Delta region occurred approximately at 6900 cal. BP, while Yang and Xie (1984) argued that it may have occurred between 7000 and 6500 cal. BP. However, based on an analysis of microfossils in natural strata, Gou et al. (1999) suggested that the highest sea level in the Holocene occurred between 6500 and 4500 cal. BP. Using pollen data from archaeological sites, Xiao (1990, 1995) indicated that high sea levels appeared before 6000 cal. BP. In a study of archaeological site settlement patterns, Wu (1990) suggested that the transgressive event occurred during the Songze Culture period while studies of the distribution of archaeological sites in the Yangtze River Delta indicate that this event may have occurred before 7000 cal. BP (Wang and Chen, 2004; Zhu et al., 2003).

It is evident that there is still controversy over when the highest transgression along the eastern coast of China occurred. In addition, it is not clear what effects sea level rises and falls had on the development of Neolithic societies in these regions. For example, Wang et al. (2012) argue that as a consequence of wide-scale marine inundation in the early–middle Holocene, ‘the freshwater-dominated environment necessary for the development of agriculture was not sufficiently widespread to support human settlements on the southern Yangtze delta until 6500–6000 cal BP when the end of sea level rise caused rapid delta progradation’. In this paper, we focus on exploring the consequences of sea level transgression and regression and its timing on the development of human cultures in the coastal regions of Jiangsu Province.

Jiangsu has a coastline of over 1000 km along the Yellow Sea and East Sea. Investigations and archaeological excavations over many years in Jiangsu area have found that the human settlement and distributions have been related to the fluctuation of water resources, especially sea level changes. Jiangsu also plays an important role in the origin and evolution of early Neolithic civilization and agriculture intensification. The Neolithic cultures in this area can be divided into three periods: Majiabang Culture (7000–5800 cal. BP), Songze Culture (5800–5300 cal. BP), and Liangzhu Culture (5300–4200 cal. BP). In the late stage of the Neolithic, the archaeological culture throughout the Jiangsu shows a high degree of cultural similarity, but during the early stages the cultures of this region are diverse and heterogeneous. To date, no Neolithic sites before 7000 cal. BP have been found in the low-lying regions of Jiangsu region.

Study area

Jiangsu Province is in the eastern-central coastal part of China (Figure 1). Jiangsu borders Shandong to the north, Anhui to the west, and Zhejiang and Shanghai to the south. The Yangtze River cuts through the province in the south and reaches the East China Sea, while the Huai River flowed through north Jiangsu to reach the Yellow Sea before 800 cal. BP. Large lakes in Jiangsu include Lake Tai (the third largest freshwater lake in China), Lake Hongze, Lake Gaoyou, Lake Luoma, and Lake Yangcheng.

Figure 1.

A sketch map showing the location of Jiangsu, China.

Jiangsu is mostly flat, with low-lying coastal plains composing 68% of its total area. The Taihu Plain is found in the south and the Lixiahe Plain is located in the middle of Jiangsu. Most of the province stands no more than 50 m above sea level, but the northern and southwestern margins are made up of hills and mountains. Today, Jiangsu Province is situated in the climatic transition belt between the warm-temperate and subtropical zones, with a distinctive humid monsoon climate. The annual average temperature is 13–16°C, with cool, wet winters and warm, humid summers. The average is rainfall is 800–1200 mm, with ~60% of the rainfall concentrated in the summer during the southeast monsoon.

Materials and methods

Almost 1000 Neolithic sites have been surveyed in Jiangsu (State Administration of Cultural Heritage (SACH), 2008; Zhou, 2000). Nearly 100 of these sites date before 6000 cal. BP. However, modern development has destroyed some sites before they could be dated. In addition, many of these sites are dated solely on diagnostic pottery remains, so the chronological position of some sites is still in question (Zhou, 2000). In this article, we use published and unpublished data from 53 archaeological sites with well-dated contexts to investigate the chronology and ecological implications of human occupation of the low-lying portions of Jiangsu.

This paper aims to re-examine human–environmental interaction in the early to middle Holocene by combining the spatial distribution of archaeological sites with contemporary geological and stratigraphic data. Archaeological sites were analyzed in terms of their spatiotemporal distribution patterns, stratigraphic deposits, and material culture remains. Furthermore, to contextualize data from Jiangsu, we also investigated similar data from the Yangtze Delta region (e.g. northern Zhejiang and Shanghai).

Results and interpretations

Temporal and spatial distribution of archaeological sites

Only two Neolithic sites dating from 10,000 to 7000 cal. BP have been found in northwestern Jiangsu (Table 1). These sites, Shunshanji (Figure 2-1) and Hanjing (Figure 2-2), are found on small hills with an elevation of 30 m. Other early sites, such as Luotuodun (Figure 2-8), Xixi (Figure 2-7) (Tian et al., 2009), and Shendun (Figure 2-6) (Tian et al., 2009), may date to approximately 7000 cal. BP. These early period archaeological sites are located in the hilly highlands of western Jiangsu. There are no archaeological sites that are dated before 7000 cal. BP that have been found in low-lying parts of Jiangsu, such as the Lixiahe and Taihu plains.

Table 1.

AMS ¹⁴C chronosequences and Calib 7.10 calibration results of the archaeological sites in Jiangsu area.

Region site	Radiocarbon lab no.	Material	Conventional ¹⁴C (age BP)	Calibrated age, cal. BC (±2σ)	Median (cal. BP)	Reference
West highlands
Luotuodun-8	KF071204	Muddy peat	5281 ± 175	4449 (100%) 3712	6059	Li et al. (2009)
Luotuodun-9	KF071205	Turf	5464 ± 165	4624 (97.9%) 3962	6244	Li et al. (2009)
Luotuodun-10	KF071206	Turf	6016 ± 200	5363 (100%) 4462	6877	Li et al. (2009)
Luotuodun-10	KF071202	Turf	8036 ± 190	7477 (99%) 6563	8922	Li et al. (2009)
Northwest
Shunshanji	BA111867	Carboned rice	7035 ± 35	5994 (100%) 5845	7881	Lin et al. (2013)
Shunshanji	ZK-3447	Charcoal	7427 ± 31	6382 (100%) 6234	8261	Lin et al. (2013)
Shunshanji	ZK-3448	Charcoal	7237 ± 35	6210 (100%) 6030	8052	Lin et al. (2013)
Hanjing	BA111868	Carboned rice	7470 ± 40	6423 (100%) 6247	8292	Lin et al. (2013)
Hanjing	BA111869	Carboned rice	7325 ± 40	6252 (99.4%) 6070	8117	Lin et al. (2013)
Dadunzi	ZK-0090	Charcoal	5785 ± 105	4850 (95.9%) 4443	6588	Institute of Archaeology (IA), CASS (1992)
Wanbei	ZK-2264	Charcoal	5770 ± 100	4840 (96.8%) 4442	6573	IA, CASS (1992)
Wanbei	ZK-2265	Charcoal	5775 ± 85	4808 (98.9%) 4450	6576	IA, CASS (1992)
Wanbei		Shell	5800 ± 90	4849 (99.4%) 4454	6602	Tang et al. (1991)
Taihu Plain
Dongshancun	BK90148	Wood	6060 ± 130	5306 (100%) 4689	6931	Zhang and Yao (1999)
Dongshancun	BK90147	Charcoal	5590 ± 120	4721 (98.4%) 4227	6391	Zhang and Yao (1999)
Dongshancun	BK90146	Charcoal	5240 ± 60	4234 (100%) 3959	6016	Zhang and Yao (1999)
Dongshancun	BK90150	Charcoal	5320 ± 60	4269 (88.7%) 4036	6102	Zhang and Yao (1999)
Guangfucun	BK94092	Charcoal	5410 ± 80	4374 (97.8%) 4042	6201	Ding et al. (2001)
Caoxieshan	BK76022	Wood	5370 ± 110	4374 (97.7%) 3969	6141	IA, CASS (1992)
Caoxieshan	ZK-0201	Wood	5620 ± 115	4721 (100%) 4246	6421	IA, CASS (1992)
Caoxieshan	ZK-0202	Charcoal	5365 ± 105	4371 (99.1%) 3968	6140	IA, CASS (1992)
Sanxingcun	ZK-2880	Charcoal	4995 ± 75	3950 (100%) 3655	5740	Center for Science and Techniques in Archaeology (CSTA) of IA, CASS (1997)
Sanxingcun	ZK-2881	Charcoal	4951 ± 86	3958 (98.3%) 3632	5701	CSTA of IA, CASS (1997)
Sanxingcun	ZK-2882	Charcoal	5037 ± 90	3987 (100%) 3650	578	CSTA of IA, CASS (1997)
Weidun	ZK-716	Charcoal	5480 ± 200	4770 (98.4%) 3937	6264	IA, CASS (1992)
Weidun	ZK-717	Charcoal	5555 ± 150	4718 (100%) 4045	6355	Lab in IA, CASS (1981)
Weidun	ZK-316	Wood	5020 ± 120	4055 (97%) 3627	5772	Lab in IA, CASS (1978)
Weidun	ZK-315	Wood	5000 ± 120	4045 (96%) 3624	5752	Lab in IA, CASS (1978)
Lixiahe Plain
Qingdun		Charcoal	5035 ± 35	3949 (94.4%) 3760	5813	Ji (1983)
Qingdun-6	GZ6766	Muddy peat	5055 ± 35	3957 (100%) 3773	5820	Zhu et al. (2016)
Qingdun-7	GZ6771	Muddy peat	7780 ± 35	6660 (98.8%) 6506	8563	Zhu et al. (2016)
Qingdun-8	GZ6770	Muddy peat	8135 ± 40	7191 (90.5%) 7049	9074	Zhu et al. (2016)
Taozhuang-4	GZ5405	Muddy peat	5105 ± 30	3880 (59.4%) 3800	5816	Zhu et al. (2016)
Taozhuang-6	GZ6743	Muddy peat	8225 ± 40	7357 (99.1%) 7081	9193	Zhu et al. (2016)
Taozhuang-6	GZ6745	Muddy peat	8330 ± 30	7496 (100%) 7324	9360	Zhu et al. (2016)
Taozhuang-6	GZ6748	Muddy peat	8470 ± 45	7587 (100%) 7483	9493	Zhu et al. (2016)
Kaizhuang-3		Muddy peat	4045 ± 20	2540 (50.1%) 2488	4500	Zhu et al. (2016)
Kaizhuang-3		Muddy peat	4470 ± 25	3336 (58.8%) 3210	5182	Zhu et al. (2016)
Kaizhuang-4		Muddy peat	7010 ± 45	5992 (100%) 5783	7851	Zhu et al. (2016)
Kaizhuang-4		Muddy peat	7935 ± 35	6865 (59%) 6688	8777	Zhu et al. (2016)
Tingchigang	GZ3417	Muddy peat	2522 ± 29	653 (52.1%) 542	2598	Jia et al. (2012)
Tingchigang	GZ3418	Muddy peat	2733 ± 27	925 (100%) 817	2822	Jia et al. (2012)
Tingchigang	GZ3421	Muddy peat	4776 ± 32	3643 (98.1%) 3516	5520	Jia et al. (2012)
Tingchigang	GZ3419	Muddy peat	4918 ± 30	3716 (85.3%) 3646	5638	Jia et al. (2012)
Tingchigang	GZ3420	Muddy peat	8704 ± 36	7822 (100%) 7598	9645	Jia et al. (2012)
Dongyuan	ZK-3056	Charcoal	4648 ± 60	3539 (85.3%) 3333	5400	Zhu et al. (2004)
Dongyuan	ZK-3055	Charcoal	4744 ± 60	3642 (68%) 3491	5485	Zhu et al. (2004)

All ¹⁴C dates mentioned in this study were calibrated using Calib 7.10 (Stuiver et al., 2017) based on the original data.

Sites dating from 7000 to 6000 cal. BP are not only numerous but are also more broadly distributed across a variety of landforms. Besides the western highlands of Jiangsu, nearly 50 archaeological sites have been found on the Taihu Plain and in the north highlands of Jiangsu.

In the Taihu Plain, there are at least 28 archaeological sites that have been investigated and excavated (SACH, 2008). The known sites containing late early-Holocene to early mid-Holocene remains are Guangfucun (Figure 2-36), Caoxieshan (Figure 2-30), and Weidun (Figure 2-9). These findings indicate that the archaeological sites appeared in the Taihu Plain generally after 6500 cal. BP (Hu et al., 2015). These sites are identified with the Majiabang Culture. Most Majiabang Culture sites are concentrated on the shore of Lake Tai, especially the northern and eastern parts of the lake. The topography of this area is relatively low and flat, but here the lake is rich in aquatic resources, and it is also a good place for cultivation. Archaeological sites bear evidence that people widely cultivated rice and utilized domestic livestock during Majiabang times. For example, at the Caoxieshan and Chuodun (Figure 2-33) sites, archaeologists excavated paddy fields (Wang and Ding, 2013). However, the remains of fish and shellfish, as well as sika and roe deer bones at some Majiabang Culture sites, show that some inhabitants in areas near the Taihu Plain were not totally reliant on agricultural production. Hunting, shellfish collection, and fishing played an important role in human life before 6000 cal. BP (Chen, 1963; Nanjing Museum, 2016; Zhou et al., 2009).

Nearly 20 sites containing cultural layers dating between 7000 and 6000 cal. BP have been found in the north highland of Jiangsu area (Gu and Zhu, 2005). The sites that have been excavated are Erjiancun (Figure 2-37) (Wang and You, 1962), Dayishan (Figure 2-39) (Ji, 1988), Wanbei (Figure 2-49) (Gu and Yin, 1992), Dadunzi (Figure 2-52) (Yin et al., 1962), and Liulin (Figure 2-53). These sites are mainly concentrated in hills and mountains and are also close to lakes and rivers, such as Lake Hongze, Lake Luoma, and the Huai River.

From Figure 2, we can see that the Lixiahe Plain is devoid of archaeological sites. Dated deposits from early Neolithic cultural layers show that the occupants colonized this area after 6000 cal. BP (Table 1). The sites that have been investigated and excavated, such as Qingdun (5820 cal. BP; Figure 2-e), Taozhuang (5816 cal. BP; Figure 2-c), Kaizhuang (5182 cal. BP; Figure 2-d), Tingchigang (5638 cal. BP; Figure 2-a), and Dongyuan (5485 cal. BP; Figure 2-e), all date after 6000 cal. BP. Furthermore, no sites before 6000 cal. BP were found in the northern margin of the Yangtze delta or in the Shanghai area (Wu, 1988).

Figure 2.

Distribution of archaeological sites in Jiangsu province in early Holocene.

In summary, the sites on the hilly and mountainous areas of western Jiangsu are the earliest, followed by sites in the north highland and in the Taihu Plain; sites located in the Lixiahe Plain are most recent.

These data indicate that the pattern of colonization in Jiangsu is from north and south to the middle, from west to east, and from the mountains and hills into the low-lying plains by 6500–5500 cal. BP. In general, this pattern could be read to indicate that the low-lying regions of eastern and southern Jiangsu and the northern portions of the Yangtze Delta were uninhabitable until 6500 cal. BP.

Stratigraphic sediments and special remains

From Figure 3, we can see that the marine microfossils have been recovered from stratigraphic deposits at six archaeological sites in the Jiangsu region (Li et al., 2009; Wang and Zhoa, 1997; Zhu et al., 2016). However, these deposits all appear to pre-date human occupation. All cultural remains are stratigraphically superior to gley mud and sand deposits with marine microfossils that are interpreted to be marine or marine–lacustrine facies. These gley mud and sand facies deposits also exist in other contexts (Li et al., 2008; Yang et al., 1988), suggesting these remains are the result of the final regressive phase of sea level fall that exposed the current land surface.

Figure 3.

Schematic of the marine sediments in the strata of archaeological sites, Jiangsu area.

Accelerator mass spectrometry (AMS) ¹⁴C dating has been conducted on some of these gley mud and sand layers (Table 1). Dates from these contexts reveal that these deposits formed before 9000 cal. BP and ceased to form after 5500 cal. BP. Most of these gley mud and sand layers have been found on the Lixiahe Plain. For example, a gley mud and sand layer at the Qingdun site formed before 9000 cal. BP and ended at ~8500 cal. BP; at the Taozhuang site, this layer is dated from ~ 9500 to 9200 cal. BP. However, at Kaizhuang, this deposit dates between 8700 and 7800 cal. BP. Moreover, the stratigraphic data at Tingchigang and Dongyuan show that the deposition of the gley mud and sand layer may have begun at ~9600 cal. BP and continued until ~5600 cal. BP. Chenier ridges located in the eastern portion of the Lixiahe Plain (Figure 2) were formed before 9500 cal. BP and the terminal date from shells on these ridges is ~6000 cal. BP (Zhao et al., 1992). These chenier ridges mark a paleoshoreline characterized by a low gradient with mostly low wave energy and an abundant sediment supply. Therefore, based on an analysis of marine facies sediments, we concluded that the transgression of the Lixiahe Plain may have begun before 9000 cal. BP and ended by approximately 5500 cal. BP; in some lowlands, these deposits may have continued to be laid down until ~5400 cal. BP.

In the northern end of the Lixiahe Plain, a gley mud and sand layer at the Wanbei site was deposited by 6600 cal. BP (Gu and Yin, 1992). In the western Taihu Plain, marine microfossils found at the Luotuodun site show that the influence of transgression in this part of the Taihu Plain ended at ~7000 cal. BP (Li et al., 2009). Because it is the lowest plain closest to the sea, the Lixiahe Plain was probably where the effect of the transgression first started and last ended. In contrast, the slightly more elevated western margins of the low-lying plains were where the effect of the transgression started latest and ended first. This pattern is consistent with the order of appearance of archaeological sites in Jiangsu area.

Discussion

Highest transgression in Holocene

During the late Pleistocene and early to middle Holocene, relative sea level changed frequently with climatic fluctuations, ice-sheet decay, local tectonics and subsidence, and global eustatic adjustments at the end of the glacial period (Abe-Ouchi, 2013; Kemp et al., 2011; Lambeck et al., 2014; Long et al., 2011; Smith et al., 2011). Various sea level curves have been proposed for the coast of China in the past two decades (Liu et al., 2004: Figure 18). These relative sea level curves indicate a complex history of mid-Holocene sea level changes (Zong, 2004), but they show general agreement in the early Holocene. The reconstructed relative sea level curve implies that sea level rose rapidly during the early Holocene up to 8000 cal. BP. Dutton et al. (2015; see also Liu et al., 2004: Figure 18) suggest that relative sea level rose from −20 to −5 m during the period from 9000 to 8000 cal. BP in the eastern coast of China, which is the largest increase in the coastal regions of the seven continents. A relative sea level rise from approximately −30 to −10 m between 9000 and 8000 cal. BP is reflected by natural deposits at the Qingfeng profile (Zhao and Zhang, 1982). The period from 9000 to 8000 cal. BP also exhibited the fastest and largest Holocene relative sea level rise based on the study of the stratigraphic sediments and sedimentary systems (Li et al., 2014; Yan et al., 1993). By studying foraminifera, ostracods, and mollusks in natural layers, Xue (2002) found that ~7700 cal. BP was when the rapid relative sea level rise ended; these findings are confirmed by subsequent AMS dating of Yangtze Delta sediments (Wang et al., 2013, 2012). The most immediate consequence of early- to mid-Holocene rapid relative sea level rise was a marine transgression. Therefore, based on an analysis of the rate of sea level rise shown by variety datasets, we suggest that the highest transgression in Holocene may have occurred between 9000 and 8000 cal. BP along the eastern coast of China.

Data from archaeological and geological contexts demonstrate that along the eastern coast of China, the marine transgression began before 9000 cal. BP. Between 9000 and 8000 cal. BP, marine inundation reached its maximum extent inland and placed the apex of Yangtze estuary at Zhenjiang, 180 km inland from the apex of the present-day delta (Zong, 2004). After that, there was a general falling trend in the rate of sea level rise. The scale of the transgression gradually decreased, and the coastline slowly receded after 8000 cal. BP. However, due to different distances to the sea and because of the height of the terrain, the transgression ended at different elevations and in different landscapes.

An analysis of the stratigraphic deposits show that the cultural layers in the Jiangsu region appeared after the gley mud and sand deposits that mark the transgression–regression phase (Figure 3). Because the transgression ended at a different time in each area, the pace of colonization was determined by the speed of regression and the appearance of suitable dry land for human occupation. The above analysis of the dates about the archaeological sites in the Jiangsu region reveals that the sites in the western highland were the oldest. The emergence of archaeological sites in most areas of the northern highland occurred between 7000 and 6000 cal. BP, and in the Taihu Plain, human inhabitation began by roughly 6500 cal. BP. No human habitation has been documented in the Lixiahe Plain before 6000 cal. BP. The areas in which archaeological sites appeared earliest were the routes of successive regressions. This fact further proves that the appearance, in time and space, of early human life in the Jiangsu region during the Holocene had a clear relationship with the transgressive and regression event.

A similar situation has been found in Zhejiang province and in the Shanghai area. So far, no Neolithic sites earlier than 7000 cal. BP have been found in the Shanghai region (Wu et al., 2014). In northern Zhejiang, the known archaeological sites dating to approximately 7000 cal. BP are Luojiajiao, Qiucheng (IA, CASS, 1992), and Hemudu (Lab in IA, CASS, 1981), which are located on the highlands of small mountains. Two major evapotranspiration events, indicated by the dataset of n-alkane isotope from the sediment samples of Tianluoshan site (at the edge of Ningshao Plain in the Yangtze Delta), have been found around 7000 and 6400 cal. BP (Patalano et al., 2015); these two short drought episodes coincide with the timing of two periods of relative sea level regressions (Zheng et al., 2012). These events are argued to have opened suitable new habitats for expanding rice agriculture in the lower Yangtze Delta (Fuller et al., 2009). The ~6400 cal. BP regression and drought coincide with an episode of global climate change noted in a variety of proxy records (Bond et al., 2001; Fleitmann et al., 2003; Koutavas et al., 2006; Neff et al., 2001).

Environmental evolution

Rapid relative sea level rise at the end of the Pleistocene and in the early to middle Holocene pushed seawater onto the land and inundated the lowland areas of Jiangsu, resulting in the intrusion of seawater along rivers and lakes, which resulted in soil salinization and the emergence of wetlands, as drainage systems became less efficient. Because of the environmental effects of the large-scale transgression prior to 8000 cal. BP, most of the low-lying parts of Jiangsu may have been a wetland environment between 8000 and 7000 cal. BP. There was a black, muddy peat deposit above the gley mud and sand layer at Qingdun site and a yellowish-gray hydric sediment above the gley mud and sand layer at Taozhuang site (Li, 2014). These deposits indicate the existence of wetland environments, while the gley mud and sand layer consisting of salt-affected soils demonstrate the existence of marine deposits associated with the transgression. Moreover, a thick layer of organically enriched black mud was found below the cultural layer at Luotuodun and Dongshancun sites. These data indicate that most of archaeological sites in Jiangsu area were inhabited after a period when wetland environments dominated the lowland landscapes.

Relative sea level rise associated with shoreline transgressions had considerable effects on the lives and economic activities of people living in the region (Zheng et al., 2012). Between 7000 and 6000 cal. BP, the climate of the Jiangsu region improved markedly but remained humid (Chen et al., 2005). Transgression forced people to build settlements on uplands, such as hillsides and topographic rises, but the regression, which followed soon after, opened new habitats. Large-scale progradational deltas on the East China coast were formed during the period of high sea level (Li et al., 2014). Accompanied by regression, the rate of river deposition increased, resulting in the infilling of the accommodation space of what was the Yangtze mouth estuary with a great deal of sediments and the development of the Yangtze delta. This process increased the space available for farming while providing freshwater for human and agricultural use (Li and Fan, 2009; Wang et al., 2013). By approximately 6000 cal. BP, Neolithic farmers were cultivating rice extensively in the Yangtze River Delta region (Zhou, 2000). Paddy fields dating to the Majiabang Culture period have been found at Chuodun, Jiangli, and Caoxieshan sites (Wang and Ding, 2013). Additionally, fishing, hunting, and gathering were still important economic activities among the inhabitants of the Yangtze delta. However, this low-lying area was still susceptible to episodic hydrological events and frequent sea level changes because of poor drainage (a legacy of the former wetland environment), floods, storms, high tides, and ongoing subsidence. In this period, houses were mainly constructed using a pole-railing style, generally with wooden boards as plinths. Living surfaces were paved with the shells of snails and mussels. Drainage facilities around the houses indicate that water- and moisture-proofing were key considerations at the time of construction.

At the Dongshancun site, the distribution of remains shows obvious functional zonation. Early houses and burials were distributed on high sloping tablelands, whereas areas for agriculture were found in low-lying areas. Additionally, the low-lying areas were composed of a wetland swamp environment (Li et al., 2015). At the Guangfucun site, many rice plant phytoliths were found in the Majiabang Culture strata, but pollen data from the site indicate that the vegetation was dominated by aquatic herbs (Ding et al., 2001). At Jiangli (Xiao et al., 2013), Zhoubeidun (Han and Zhu, 1997), Wanbei (Tang et al., 1991), and Qingdun (Huang and Liang, 1984) sites, the palynological assemblages also showed that herbaceous pollen prevailed in the early strata and that pollen of aquatic plants dominated. These data indicate that there were lakes and large areas of water near these sites during the early stage of cultural development. Animal remains, including deer, buffalo, fish bones, and mussel shells, were found in Dadunzi (Yin et al., 1964), Erjiancun (Wang and You, 1962), Qingliangang (Wu, 1973), and Luotuodun sites (Zhou et al., 2009). Wild pigs were found in Weidun (Huang, 1978) and WanBei Sites (Li, 1991). These findings of plant and animal remains suggest that the Delta region and the northern highland had a subtropical forest–wetland environment between 7000 and 6000 cal. BP.

Conclusion

The varying scientific conclusions about the timing and effects of relative sea level rise on the eastern coast of China in the early to middle Holocene are likely related to the types of datasets available, the number and precision of radiocarbon or other dated archaeological and sedimentary sites, and the nature of the observed sediments. Geological and geoarchaeological analysis of sediments shows that the marine transgression probably began before 9000 cal. BP and may be a consequence of a rapid increase in the rate of relative sea level rise associated with meltwater pulse 1-c (Liu et al., 2004; Wang et al., 2013). The marine transgression reached its maximum extent inland and had the greatest effect on the low-lying portions of the Jiangsu region between 9000 and 8000 cal. BP. After this time, the rate of sea level rise slowed down. The scale of the transgression steadily decreased, and the coastline gradually receded after 8000 cal. BP. However, because of different distances to the sea and heights of terrain, the transgression ended at different times in different locations and landscapes.

The marine transgression had considerable effects on the lives and economic activities of people living in the region. Because of the transgression, most low areas in Jiangsu province may have been converted to wetland environments between 8000 and 7000 cal. BP. These environments were unsuitable for long-term human settlement. Therefore, until approximately 7000 cal. BP, settlements were located on hillsides and mounds to take advantage of higher elevations. Beginning at roughly 7000 cal. BP, inhabitants began to colonize the newly exposed low-lying plains, moving down from the hills and taking advantage of the ecologically rich and highly productive former wetland landscapes. At the same time that the low-lying areas became available for human use, the climate was improving, creating an optimal situation for human settlement and social development. Early inhabitants of the Taihu Plain were quick to develop a diverse economy that incorporated both cultivated plants and domesticated animals but that also relied considerably on wild resources. However, while the Taihu Plain was quickly colonized after 7000 cal. BP, the Lixiahe Plain remained a coastal lagoon.

Relative sea level rise is a complicated process and its geological, geographic and human consequences are often difficult to sort out. With the collapse of the Pleistocene ice sheets, there were rapid and profound changes to coastlines worldwide. However, global eustatic sea level rise cannot be readily translated to every region of the globe. Along the eastern coast of China, we see that rapid relative sea level rise in the early to middle Holocene had major consequences for early human settlement and the development of social systems. Topographic and ecological changes associated with major marine transgressions and regressions, and the long-term hydrological effects they engendered, help us understand the human colonization and use of low-lying portions of modern Jiangsu. These data provide a window into the complexities of human adaptation to changing sea levels and may provide a glimpse of the effects of contemporary and future sea level rise in light of modern climate change.

Footnotes

Acknowledgements

The authors are extremely grateful to the reviewers and the editors whose constructive comments have helped improve the paper greatly.

Funding

This research has been supported by the National Social Science Foundation of China (Grant No. 16CKG001), National Natural Science Foundation of China (Grant No. 41171163), and the China Scholarship Council (File No. 201606245041).

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