Why was the Pearl River Delta established? Can anyone tell me? I need to know urgently

Due to its shallow bedrock and large amount of sand, the Pearl River Delta spreads rapidly toward the sea, causing Panyu, Zhuhai, and Doumen to become counties and cities with increased fields. The coastline continues to stretch toward the sea. The delta was roughly formed during the Atlantic period about 6,000 years ago. At that time, the coastline could be determined by the coastal topography at the foot of the hills and slopes of the delta, such as sea cliffs, sea caves, sea erosion platforms, and sand banks. Today, these coastal landforms can often be seen at the foot of the delta plain hills, such as the Qixinggang sea cliffs and sea erosion platforms in Guangzhou. Therefore, the coastline of Guangzhou's Drowning Valley Bay can basically be determined by the contact line between hills and plains. Deltas began to develop at the front edges of these coastal landforms. For example, the plains in the lower reaches of the Xijiang River have extended to the vicinity of Guangli. The lower age of the shell mounds and the Qulim Burial Neolithic site there is 7170±140 years ago, while the pottery sherds are 5680 years old. In ±284 years (thermoluminescence), the Boluo Hulu Mountain shell mounds are also on the plains, which means that deltas have developed in the lower reaches of each river. According to the distribution of marine diatoms (saltwater species), foraminifera and silt layers, the delta areas in the lower reaches of each river basically reflect the range of transgression in the Atlantic period, that is, the coastline 6,000 years ago reaches the Qingyuan Basin in the north and the Zhaoqing Basin in the west (Zhao Huanting, 1990), east to the Boluo Basin and Tonghu Lake.

From the perspective of Neolithic sites, the scope of the delta in the Dongjiang Delta area can basically be regarded as the coastline. Since there are no rocky islands in the middle of the Dongjiang Delta, most of it is still sea surface, so the surrounding areas of the Dongjiang Delta are 4000 years old. Upper and lower Neolithic shoreline. The top of the Xibei River Delta has also begun to form, because the Jinli Maogang Water Ganlan Site is 4140±90 years old (C14 dating), the rotten wood layer is 3970±110 years old (South China Normal University Geomorphology Office, 1988), and the Xiqiao Mountain Shell Mounds The age ranges from 6120±130 years (ibid.) to 4905±100 years, and more than 53,000 stone tools have been unearthed (Zeng Qi, 1991), which shows that there is a large area of ??land nearby. The age of the blue clams growing under the erosion cliffs of Shijie in the South China Sea is also 4640±280 years. That is to say, the Northwest River Delta has reached south of Xiqiao Mountain and Foshan line in the south (Shuiteng Silt is 3997±190 years old).

2000 years ago (Qin and Han Dynasties), the Dongjiang Delta merged from the Dongjiang and Zengjiang deltas, extending down to Zhongtang (where there is the Yingtang Temple of the Han Dynasty), and the south is still the sea. The Northwest River Delta extends northeastward to the north of the Nanhua Waterway (i.e. the East China Sea Channel). Han Dynasty pottery pieces and other cultural relics have been discovered in Xingtan, buried 2 meters deep (Fengjian Village). Freshwater Malayan crocodiles have grown in Leliu, and the age is 2540±120 years. Shiyong is the hometown of Lu Jia, Prime Minister of South Vietnam, so the surrounding area should be a plain. Chencun also became a land in the Han Dynasty.

1000 years ago (Tang Dynasty), the Dongjiang River reached Dongguan City, that is, the top of the Dongjiang Delta had developed. But most of it is still a pearl pond. The top of Panyu's thrust delta has developed, because "Yuanhe County Chronicles" says "it's seventy miles from the south of Guangzhou to the sea", so it can be seen that the land is right on the shore between present-day Shawan and Shunde. The top of the Zhongshan outburst delta has also developed. Because Huangchao has already stationed troops and fed in places such as Rongqi, Guizhou, and Maqi today, it can be seen that the nearby area is already home to large paddy fields. The Xinhui outburst delta also has a top plain developed. For example, Xinhui was the state seat of the Sui Dynasty, indicating that a large plain was formed at that time. Most of the formations of the Tang Dynasty buried the formations of the Han Dynasty. The delta coastline did not advance much during the millennium of the Han and Tang Dynasties, which may be related to the period of sea level rise during this period.

700 years ago (at the end of the Song Dynasty), the coastline moved southward to the middle of the flooded deltas. The Dongjiang River reached Mayong, Dafen, and Daokiao (according to genealogy); Panyu reached Lanhe, Yu Along the vortex line, Xiqiao Yong has been recorded (1233); the Zhongshan coastline is along the Henglan, Fuwei (now known as Fusa), Huangpu, and Tanzhou lines (according to records); the vicinity of Xinhui has become a tidal field in the Song Dynasty, and Li The Le and Waihai lines became sand; the Twin and Huangchong lines of the Tanjiang River developed rapidly during this period. This was the result of the influx of immigrants from Zhuji Port southward into the delta during the Song Dynasty to build embankments and develop the tidal fields. The tidal fields were converted into flat fields, and the sea level dropped. It also has an impact. Jiao is the waterway connecting the two rivers.

400 years ago (at the end of the Ming Dynasty), due to the construction of dikes in the Song Dynasty to divert water back into the trough, the coastline was silted up into sand at a faster pace. For example, Zhongshan belonged to Dongguan in the early Song Dynasty, and Guangzhou began to enter the Southern Song Dynasty. Xiangshan and Panyu are three hundred miles apart from each other by the sea, so it is not as convenient as going to Dongguan. This shows that in the Southern Song Dynasty, the Zhongshan outburst delta had extended to Shiqi and the port area, that is, the sixteen sands in the East China Sea and the eighteen sands in the West China Sea had been formed. The Panyu delta has reached Xiahengli (Yisha), and the entrance gate of Hongqili has just been completed. The Xinhui outburst delta has reached the southern edge of Jiuzisha, and the coastline has moved southward from Liyue to Xiongzishan (i.e. Xiongzhou). Most of the Dongjiang Delta became land in the late Song Dynasty. In the late Ming Dynasty, it extended to the east of Zhangpeng, and the southern branch also extended to the north of Houjie. The accelerated advance of the delta coastline in the Ming Dynasty was also due to artificial influence. In the Ming Dynasty, instead of building embankments to protect the fields like the Song Dynasty, embankments were built to form fields, and reeds and grass were planted on the beach to promote siltation. The top of the Doumen Delta has begun to develop, and now Da'aosha has been formed, and Muzhou and Sanjiangkou have also risen. Huangbu and Dasha have been formed, and they only enter the island south of Zhuzhou and Fenzhou.

In the 100th year of the Qing Dynasty (the end of the Qing Dynasty), the front coastline was advanced again, and the outer edge of the Doumen excavated delta was at the grinding gate, namely Bamboo Pavilion Sand, Lantern Sand East Head and West Head Wai; Xinhui then entered the west of Sanjiangwei The shores of Yinzhou Lake and the Panyu coastline have filled up the Wuzhu Ocean, and the tens of thousands of hectares of sand have reached ten peaks. The progress of the Dongjiang River is slow due to the strong tidal force of the Lion Ocean.

In short, the Pearl River Delta coastline continues to advance seaward, with periods of rapidity and slowness. Natural factors are related to changes in sea level rise and fall. During periods of high sea level, the advancement of the coastline slows down, while during periods of low sea level, it advances more slowly. quick.

Man-made factors include building embankments to protect fields. For example, in the Song Dynasty, embankments were built to protect fields, which accelerated the sedimentation of sand fields downstream. In the Ming Dynasty, embankments were built to cultivate fields and reed planting to accumulate mud accelerated sand formation. Tidal action and upstream sand and water also have an impact. For example, the Humen and Yamen waterways accumulate very slowly because of the strong currents.