(Jiangsu Geological Survey and Research Institute, Nanjing 2 100 18)

The coastal zone in eastern Jiangsu Province has experienced a complicated land-sea evolution process since Quaternary. The vast coastal plain was formed after the coastline moved eastward, the Yangtze River estuary moved eastward and the sandbars merged into the land for thousands of years, and it is still in constant change. Coastal changes directly affect the development and utilization of coastal beach resources and port production and construction. By using the methods of Quaternary transgression, traces of human activities, historical records and interpretation of remote sensing images, the author analyzes the changes and evolution of the coastal zone in eastern Jiangsu since Quaternary.

Keywords: East Jiangsu; Quaternary; Coastal areas; change

Eastern Jiangsu includes Dongtai under Yancheng, Taixing, Jingjiang and Jiangyan under Taizhou, and Hai 'an, Rudong and Qidong under Nantong. Since the Quaternary, especially since the Middle Holocene, this area has experienced a complex process of land and sea evolution. The coastal plain in eastern Jiangsu Province was formed after thousands of years of coastline moving eastward, Yangtze River estuary moving eastward and sandbars merging into land. With the change of sea level, the rise and fall of new structures and the deposition of sediment, the coastline of eastern Jiangsu is still in constant change, which directly affects the development and utilization of coastal beach resources and the production and construction of ports. It is of great practical significance to study the changes of coastal zone. This paper mainly discusses the coastal changes and shoreline siltation dynamics in eastern Jiangsu since Holocene from the aspects of Quaternary transgression, ancient sandbanks, human activity relics, historical records and interpretation of remote sensing images.

1 transgression and coastline in geological history.

Since Quaternary, due to frequent crustal movement and paleoclimate changes, sea level has risen and fallen, leading to many transgressions and regressions in coastal areas. Based on the analysis of Quaternary sedimentary facies, microfossils and paleomagnetism of more than 100 boreholes, it is found that there were five transgressions in Quaternary strata in the eastern coastal areas of central Jiangsu [1], which reflects that this area experienced at least five large-scale transgressions from morning till night, namely Rugao transgression, Shanghai transgression, Taihu transgression, Gehu transgression and Zhenjiang transgression [. According to the distribution range of transgressive layers, the coastline position in this period can be roughly inferred.

1. 1 Middle Early Pleistocene

This is the first transgression in this area since Quaternary. The transgressive layer is only distributed in the east of Rugao, and it is found in Rugao, Dongbeikan and Qidong Nanyang. It is rich in foraminifera. According to the analysis of sedimentary facies, it was formed in the estuary environment. Judging from its invasion scope, it is the smallest transgression in the Quaternary in this area, and it is inferred that the coastline is roughly on the line of Xiaoyanggang-Rugao-Rudong-Qidong, and turns south to Shanghai [2]. According to paleomagnetic data, the transgressive layer is located between Jia Lamirault polar sub-time and Aoduwei polar sub-time, about 654.38+0.8 million ~ 654.38+0.0 million years ago.

1.2 Early Middle Pleistocene

It was the second deviant, and the scope was slightly larger than the last one. In addition to foraminifera found in Rugao area, glauconite was also found in Jingjiang area, indicating that seawater has spread. It is inferred that the coastline bends from Xiaoyanggang to Rugao slightly from west to east to Haimen line. According to paleomagnetic data, the transgression layer is located at the boundary between the positive polarity time of Bouon and the negative polarity time of Songshan, about 780,000 years ago.

1.3 Early Late Pleistocene

The third transgression occurred in the early late Pleistocene, and invaded to Zhenjiang and eastern Yangzhou westward. The eastern part of central Jiangsu was submerged by seawater, and the coastline was Gaoyou East-Taizhou West-Changzhou-Jintan. The transgressive layer was located near the Black polar secondary step about 654.38 million years ago.

1.4 Early Late Pleistocene

The fourth transgression occurred in the late Late Pleistocene, which was the most extensive transgression in the Quaternary in Jiangsu Province. Its westward invasion position has reached the western hilly area, and it is speculated that the coastline is roughly from Gaoyou-Zhenjiang-Jintan west to Yixing. According to the dating data, the age is about 25000 ~ 50000 years ago.

1.5 Holocene

The fifth large-scale transgression happened. Around 8500, seawater spread to the eastern part of the province, and the transgression reached its maximum around 7000. The east of central Jiangsu is in the sea. At this time, the coastline of Jiangsu is roughly from Ganyu and Shuyang in the north, passing through Siyang and Jiangba, along the eastern edge of the hilly area, reaching Yangzhou and then turning to Yizheng. The high sea level makes the Yangtze estuary retreat to Zhenjiang and Yangzhou, and the influence of waves and tides reaches the dredging port of Yangzhou and the Beigushan and Xiangshan in Zhenjiang [3]. Then the sea level fluctuated and the coastline began to retreat [4]. In the following thousands of years, due to the increase of sediment in the Yangtze River basin and the decline of sea level, the Yangtze River port line gradually moved eastward, and at the same time, the estuary sandbars began to develop in the Yangtze River estuary, and the Yangtze River Delta entered a development period, which had a far-reaching impact on the land and sea changes in this area.

2 Neolithic coastal changes (about 6000 years ago)

The earliest documented coast in central and eastern Jiangsu can be traced back to the Neolithic Age. About 6,000 years ago, it landed north of the Hai 'an-Jiangyan line. Animals lived here soon after landing, and then the ancestors lived here. According to the animal fossils unearthed in Shuanglou, Qingdun, Zheng Long and other places in Hai 'an, and the dating data of Neolithic cultural site 14C [5,6], compared with the cultural layer, its formation age is 5000 ~ 6500 years, which is equivalent to the formation age of shell dike in the west port of Yancheng Dagang [7]. Other areas in eastern Jiangsu have not yet landed. From this, it can be determined that the coastline is on the west side of Hai 'an, turning northward to Dongtai and Yancheng Dagang, and connecting with the ancient seawall in northern Jiangsu (Figure 1). To the west, roughly along the Toarey Yang Canal and the ancient Yangzhou-Shagang in Thailand [8]. Connect. The coastline represented by Yangtai Gushagang was the north bank of the Yangtze River estuary at that time. The south bank line of the Yangtze River estuary extends southward from the eastern foot of Maoshan Mountain near Jiajiang River in Yangzhong to Changdang Lake [2], and the sandbar of Taixing Huangqiao Yangtze River estuary begins to form. Dongtai, East of Hai 'an, Rudong, Nantong, Qidong and other places in central and eastern Jiangsu are still waters.

3 coastal changes in the historical period

3. 1 Xia Shang

About 4000 years ago, during the Xia and Shang Dynasties, the sea level began to gradually decline, the coastline moved eastward, and then stabilized, and a new coastal sandbar (Donggang) developed along the coast. The eastern coastline of Central Jiangsu is located in Dongtai-Haian West Field, with Donggang in the north and little distance in the east. The southern coastline, that is, the north bank of the Yangtze River estuary, changes greatly, generally turning westward from Xichang, Hai 'an, extending along Anren Bridge and Jiangyan Gugaozhuang, and moving southward and eastward from the previous coastline 10 ~ 20km. With the continuous development of the Yangtze River Delta, the sandbars in the Yangtze River estuary in Huangqiao area gradually emerge from the water surface to form sandbars, with tributaries on both sides of the sandbars. Fu Haizhou is recorded in the historical material "The History of the Later Han Dynasty and the Records of Counties and Countries". "Jiangnan Tongzhi" records: "Fuzhou is Tongzhou, and the Han Dynasty is Fuzhou." Zhou Fuhai should have been a sandbar at the mouth of the Yangtze River [9]. Geographically, the southwest area of Rugao today, that is, the position of Huangqiao sandbar, belongs to paleobranch deposition according to the analysis of drilling data [5]. The south side is low-lying, with lakes and swamps, which is where the south branch of Huangqiao sandbar is located. Nantong and Hai 'an are located in coastal-shallow sea environment.

3.2 Qin and Han Dynasties (about 2000 years ago)

According to historical records, Yancheng was a sandbar in the Han Dynasty [10]. According to the Han Tomb unearthed in Sanyangdun, Yancheng, it is speculated that the central coast of northern Jiangsu was on the line of Funing, Yancheng and Dongtai at that time, and it was connected to the north shore line of the ancient Yangtze River estuary in southeastern Rugao to the south, and the coastline was only several thousand meters eastward than that in Xia and Shang Dynasties. However, due to the eastward movement of the Yangtze River Delta, the coastline in the eastern part of Central Jiangsu has changed greatly, especially the coastline on the north bank of the Yangtze River estuary has moved to Taixing-Jishi-Shuangdian line, about 30km to the south, and basically maintained at Dingsuo-Fuan-Anfeng Dongtai line to the north. Yu Gong in the Warring States period said, "Huaihai is only Yangzhou". In the tenth year of Chu Huaiwang (the first 39 1), Yangzhou was called Guangling, and only Guangling County was located on the north bank of the Yangtze River. In the Western Han Dynasty, Hailing County (now Taizhou) was relocated due to the growth of its eastern land. In the Eastern Jin Dynasty, Rugao County was located to the east of Hailing. You can see the land moving eastward gradually. By the Western Han Dynasty, Huangqiao sandbar had merged with the shore [9]. At the same time, Huangqiao sandbar is connected with the north shore to form land. At present, a new sandbar has appeared in Pingchao and Jinsha areas of Nantong, namely Hudouzhou, also known as Hudouzhou [1 1], and the road between Hudouzhou and Rugao is Guhengjiang Road. Taixing and Jingjiang are the Yangtze River, and Rudong and Haimen are the front of the delta.

Figure 1 map of coastal changes in eastern Jiangsu since Holocene

3.3 Sui and Tang Dynasties (about 1200 years ago)

Seawall is an artificial symbol built in coastal plain area to resist tides and prevent seawater intrusion. According to textual research [12], Changfeng Weir was built in Tang Dynasty (756 ~ 76 1), with its northern end in Funing Goudun and its southern end in the south of Dafeng Liu Zhuang. It was built in Dongtai and Fuan in the Northern Song Dynasty. The seawall basically represents the position of the coastline at that time. 1973 A Tang Dynasty shipwreck was found in Xishili, Baipu Town, Rugao [13], which proves that the ancient Hengjiang Road in Qin and Han Dynasties still existed in the early Tang Dynasty. By the end of the Tang Dynasty, the coastline south of Hai 'an was obviously advancing toward the sea, and the Hengjiang River was silted up, and Hudouzhou was connected with Rugao, the northern shore [14]. At this time, the western waters of Rudong have all landed, and the coastline has moved eastward to the Fuan-Rudong-Qiandongshe line, which is connected with the coastline on the north bank of the Yangtze River estuary. A large sandbar has been formed in the southern part of Haimen. The coastline of this period reflects the rapid growth of the Yangtze River Delta since the Han Dynasty, with the coastline moving 20 ~ 50 kilometers to the east and about 20 ~ 50 kilometers to the south. It is closely related to the reclamation of mountains in the Yangtze River basin [15].

3.4 Northern Song Dynasty (about 900 years ago)

According to historical records, the defensive seawall built in the Northern Song Dynasty (1023 ~ 1027) is called Gongfan dike, and its northern section is similar to Changfeng weir [16], which is roughly parallel to Tongyu Highway. The south section of the seawall turned to Bao Li and passed through Rudong-Qianlu Port eastward, which roughly represented the coastline position of eastern Jiangsu during this period. Hai' an does not move eastward along the north shore line, and the Hai' an-Rudong section advances eastward by about 5 ~ 10 km. The Sanyuwan in Rudong and Lvsi regions was thus formed. During this period, the eastern waters of Nantong silted up into land, and the northern part of Nantong-Qidong silted up fastest, and the shore of Haimen sandbar merged, and the north bank line of the Yangtze River estuary was pushed to Qidong now.

3.5 Ming and Qing Dynasties (1368 ~1911)

In the early Southern Song Dynasty (1 128), the Yellow River took the Huaihe River south to the sea and returned to the north in 1855, which lasted more than 700 years. It carries a lot of sediment into the sea, which pushes the coastal areas of northern Jiangsu out quickly. In the seventh year of Hongzhi in Ming Dynasty (1494), the Yellow River flooded the Huaihe River into the sea, and by 1582, the estuary began to show a sudden trend. The coastline in the northern part of the eastern part of Central Jiangsu Province obviously advances to the sea, and silts up about 10km. The coastline is roughly on the Dafeng-Shen Zao-Baoli line and the coastline in the south of the Yangtze River Delta, but the speed is slow during this period. During the Guangxu period of the Qing Dynasty (1820), the coastline of Dongtai section in the eastern part of the Soviet Union had been advanced to the east of Sancang-Bao Li, with an advance of about 20 kilometers. Bao Li —— If the eastern coast is weak, the coastline of Sanyuwan will advance eastward by about 10km.

4 Modern coastal changes

During the 50-year period from the return of the Yellow River to the north/KLOC-0, the coastline of Jiangsu Province entered an adjustment period. From 1855 to 1890, the coastline of the Yellow River estuary stopped advancing toward the sea, and the ocean dynamic action began to erode the abandoned Yellow River estuary, and the coastline showed a full-line retreat trend. However, the coastal areas in the east of Central Jiangsu Province continue to deposit, with the fastest deposition speed in the region, such as the southeast coastline, where the average deposition in 35 years is as high as 12.5km, and other coastlines generally do not exceed 10km[ 17]. From 1890 to 192 1 for more than 30 years, the coastline in this area is still silting, and the Qidong sandbar formed before the Yangtze River estuary 1890 has expanded to land, and the Qidong estuary has been formed.

From 1855 ~ 192 1 year, after more than 60 years of adjustment, the shaping of the coast and the redistribution and transportation of huge amounts of sediment have been basically completed. The eastern coast of Central Jiangsu has always followed the siltation state of the historical coast. The lines of Dongling Port-Xinkai Estuary and Yangtze River Port have been silted into the sea for about 12km, and the coastline of Chuanshui Port has reached 65,438.

Since 1970s, the coastline has gradually become straight under the action of ocean hydrodynamic forces, but the advance and retreat characteristics basically follow the evolution law of historical coastline.

5 modern coastal stability and evolution trend

The eastern part of Central Jiangsu belongs to muddy coast. According to the data of four satellite remote sensing images since 1970s, except Dongzaogang-Hao Zhigang coastline, the coastline in this area is in a state of siltation.

5. 1 Chuanshui Port-Dongzao Port Shore Section

Including Dongtai, Hai 'an, Rudong, Tongzhou and Haimen, it is a muddy coast with muddy deposits and different beach widths, in which the width of Xiaoyanggang section of Chuanshui Port is 1000 ~ 5000m, that of Dongling Port-Dongzao Port section is 500 ~ 2500m, and other coastal sections are relatively narrow. The bank has been silted for a long time, but the siltation speed is slow and uneven. The northern shore of Xiaoyang Port and the shore of Dongling Port-Dongzao Port are strongly silted coasts, with an average annual siltation of 360m and 435 m respectively. The shore section of Xiaoyanggang-Dongling Port has a small siltation, with an average annual siltation of about 92m, belonging to a weakly silted coast. 1977 ~ 1984 silted into 120 ~ 4400 m, with an average of17 ~ 733 m; However, in 1984 ~ 1997, the sedimentation rate is 0 ~ 3800 m, with an average annual rate of 0 ~ 292 m, which is obviously slowed down.

From the position of the coast, the coastline of Chuanshui Port-Dongzao Port is located at the intersection of the abandoned Yellow River Delta and the Yangtze River Delta. Due to the erosion and retreat of the northern coast, a large amount of sediment moved southward along the coast, and the sediment from the Yangtze River spread northward, and there is still a large amount of sediment in this section every year. Therefore, the coastline is still silting up and expanding outward in the near future, and will continue to silting up in the future. However, it is worth noting that the hydrodynamic conditions along the coast of Xiaoyanggang-Chuanshuigang are complex, tidal gullies develop on the beach surface, and tidal waterways migrate, which has a strong erosion effect on the beach surface. Since the mid-1980s, the low tide beach has changed from siltation to erosion, and the erosion distance has reached 500 ~ 2000m in recent 20 years.

5.2 Dongzao Port-Haozhi Port Shore Section

This is an erosive coast, 24 kilometers long, located along the coast of Haimen and Qidong. The beach outside the breakwater is very narrow, the sediment is thicker than the northern coast, and tidal gullies are developed on the beach surface. Due to the influence of swell in the South Yellow Sea and the action of wind and waves, and the existence of sand ridges outside the breakwater, the wave refraction effect is obvious, which makes the sea surface near Lvsi in the southeast of Dongzao Port a wave convergence area and the waves increase. In addition, the coast is perpendicular to the northeast wind waves, which makes the waves erode the coastline and brush the beach surface deeper. From the 1970s to the mid-1980s, the coastline retreated by an average of 25 meters every year. Since the mid-1980s, due to the construction of seawalls, the invasion and destruction of storm surges have been effectively prevented, and the coastline that has been in the process of erosion and recession for a long time has also been permanently protected. In the future, due to the influence of Xiaomiao Hongshen trough, the strong erosion of this plate will continue, and the brushing amount will continue. The high tide beach in this section is almost eroded, but the coastline will not retreat because of the protection of the seawall.

5.3 Haozhi Port-Lianxing Port Shore Section

This is a stable coast about 45 kilometers long. The beach outside the dike is 3.5 ~ 5.5 kilometers wide. The sediments are silt and silt, which appeared in the 1970s. Recently, due to the limited material sources, the erosion and siltation are basically balanced, and the beach has not changed much. There is no sandbar under the mouth of Lianxinggang in this coastal section, and the seasonal wind and waves from the East China Sea have a strong impact on the coast. Recently, the planting of Spartina has played a good role in promoting siltation and revetment. At the same time, because this coastal section is located at the mouth of the Yangtze River and supplemented by the sediment of the Yangtze River, the beach surface of the coastline has been basically stable recently.

6 concluding remarks

Since the Quaternary, the coastal zone in eastern Jiangsu has experienced five large-scale land-sea changes. Land-sea change is influenced by sea level fluctuation, crustal movement and river sediment transport. The Yellow River's capture of Huainan to the north, the Yangtze River's south swing and the merger of sandbars are two main factors that caused the changes of the eastern coast of Jiangsu in historical period.

Before the Song Dynasty, the coast of Dongtai was relatively stable and changed slowly, while the southern coast moved eastward obviously due to the development of the Yangtze River Delta. In the early Southern Song Dynasty, the Yellow River seized the Huai River and entered the sea, which made Dongtai coastline move eastward rapidly, while the southern coastline moved slowly to the sea. After the return of the Yellow River to the north, the coastal changes entered an adjustment period, but it still showed a siltation state moving eastward, and the siltation speed slowed down obviously.

From the mid-1970s to the present, multi-temporal remote sensing images show that the coastline of eastern Jiangsu is still evolving in the near future, and will continue to evolve in the long term. Except for Dongzao Port-Haozhi Port, which is in weak erosion recession, most of the coastal river sections are in siltation state, and the siltation trend will remain in the future. It is worth noting that the hydrodynamic conditions along the coast of Xiaoyanggang-Chuanshuigang are complex, and the migration of tidal channels has strongly eroded the beach surface, and the low tide beach has changed from siltation to erosion.

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Changes and evolution of the central and eastern coast of Jiangsu Province since Quaternary

Xu Xueqiu, Zhang, Fan, Wu,

(Jiangsu Geological Survey Institute, Nanjing 2 100 18)

Abstract: Complex changes and evolutions have taken place in the coastal areas of central and eastern Jiangsu Province since Quaternary. The coastline and estuary of the Yangtze River moved eastward, alluvial erosion of the mainland, forming a vast coastal plain. Nowadays, the coastal changes are affecting the development and utilization of tidal flat resources and port production. Based on the changes of Quaternary strata, traces of human activities, historical documents and remote sensing images, this paper analyzes the changes and evolution of the coast since Quaternary.

Key words: central to eastern Jiangsu Province; Quaternary; Coastal zone; change