The origin of the Pearl River Delta

C Due to shallow bedrock and large amount of incoming sand, the Pearl River Delta rapidly extends to the sea, making Panyu, Zhuhai and Doumen become zengtian counties and cities. The coastline extends all the way to the seaside. The delta was formed in the Atlantic period about 6000 years ago. The coastline at that time can be determined by the coastal topography at the foot of hills and slopes in the delta, such as sea cliffs, sea caves, sea terraces and sand dikes. Today, these coastal landforms can be seen at the foot of the hills in the delta plain, such as the ocean cliffs and platforms in Qixinggang, Guangzhou. Therefore, the coastline of Shui Gu Bay can be basically determined by the contact line between hills and plains. Delta began to develop at the front of these coastal landforms, such as the plain in the lower reaches of Xijiang River, and extended to Guangli, because the time when the Neolithic site was buried in Beiqiu of Shell Island and Qulinbu was 7 170 140, while the pottery piece was 5680 284 (thermoluminescence), and the Beiqiu of Boluo Hulu Mountain was also on the plain, indicating that the delta in the lower reaches of the river had developed. According to the distribution of marine diatoms (brackish water species), foraminifera and silt layers, the delta areas in the lower reaches of rivers basically reflect the transgression scope in the Atlantic period, that is, the coastline 6000 years ago reached Qingyuan Basin in the north, Zhaoqing Basin in the west (Zhao Huanting, 1990) and Dabulo Basin and Tonghu Lake in the east.

Judging from Neolithic sites, Neolithic sites can basically be used as the coastline of Dongjiang Delta. Because there are no stone islands in the middle of the Dongjiang Delta, most of them are still on the sea, so the Dongjiang Delta is surrounded by the Neolithic coastline of 4,000 years. The top of the northwest river delta has also begun to take shape, because the fence site of Jinlimaogang water trunk line is 4 140 90 (measured by C 14) and the rotten wood layer is 3970110 (Geomorphology Room of South China Normal University,/kloc-0) The age of the epiphytic blue clam under the cliff in Shijie, South China Sea is also 4640 280 years old. That is, the northwest river delta reaches the south of Xiqiao Mountain and Foshan Line (the silt of rattan is 3997 190).

Before 2000 (Qin and Han Dynasties), the Dongjiang Delta was formed by the merger of Dongjiang Delta and Zengjiang Delta, extending down to nave (there was Tang Ying Temple in Han Dynasty), and the south was still a sea area. The northwest river delta extends northeast to the north of the South China Sea Waterway (namely the East China Sea Waterway). Because of the discovery of Han Dynasty pottery pieces and other cultural relics in Xingtan, the burial depth is 2m (Feng Jian Village). Freshwater Malay crocodile grows in Liu Le, and its age is 2540 120. Shi Chong is the hometown of Lv Jia, South Vietnam, so it should be a plain nearby. Chencun also became the land of the Han Dynasty.

/kloc-On the coastline 0/000 years ago (Tang Dynasty), Dongjiang had reached the downtown area of Dongguan, that is, the top of Dongjiang Delta had developed. But most of them are still pearl ponds. The top of Panyu thrust delta has developed, because "Guangzhou is 70 miles south to the sea" in Yuanhe County Records, indicating that this land is between Shawan and Shunde. The top of Zhongshan thrust delta has also developed, because Huang Chao has troops in today's Rongqi, Guizhou and Ma Qi, so it can be seen that the nearby area has become the hometown of big paddy fields. Xinhui thrust delta also has a top plain, such as Xinhui, which is the seat of the Sui Dynasty, indicating that a large plain had been formed at that time. The strata in the Tang Dynasty mostly covered the strata in the Han Dynasty, and the delta coastline did not advance much during the Millennium of the Han and Tang Dynasties, which may be related to the sea level rise during this period.

700 years ago (at the end of Song Dynasty), the coastline went south to the middle of thrust deltas, and Dongjiang reached the line of Mayong, Dafen and Daojiao (according to genealogy); Panyu has reached the first line of nuclear fish vortex and Xiqiaoyong has been recorded (1233); Zhongshan coastline is on the first line of Henglan, Fu Wei (now named Fusha), Huangpu and Tanzhou (according to records); Near Xinhui, the Song Dynasty has become a tidal field, and ritual music has become a sand in the open sea. During this period, Tanjiang River developed rapidly, with Gemini and Huangchong as the first line, which was the result of Zhuji port immigrants pouring into the delta to build dikes in the Song Dynasty. Turning tidal fields into flat land also has an impact on sea level decline. Jiaowei is a waterway connecting the two rivers.

400 years ago (late Ming Dynasty), due to the dike construction in Song Dynasty, water flowed into the trough, and the alluvial delta accelerated sand deposition. For example, Zhongshan belonged to Dongguan in the early Song Dynasty and entered Guangzhou in the Southern Song Dynasty. Because Xiangshan and Panyu were three hundred miles across the sea in the Northern Song Dynasty, it is not as convenient as going to Dongguan. This shows that in the Southern Song Dynasty, the Zhongshan thrust delta has been extended to Shi Qi and ports, that is, 16 sands in the East China Sea and 18 sands in the West China Sea have been formed. Panyu thrust delta has reached Xiahengli (Sha Yi), and Hongqi Likoumen has begun to take shape. Xinhui thrust the delta to Jiuzisha in the southern margin, and the coastline moved from Li Le to Xiongzishan (Xiongzhou). Most of the Dongjiang Delta was formed in the late Song Dynasty. In the late Ming Dynasty, it extended to the east of Zhang Peng, and the south tributary also extended to the north of Houjie. In the Ming dynasty, the acceleration of the delta coastline was also artificially influenced. Unlike the Song Dynasty, the Ming Dynasty did not build dikes to protect fields, but built dikes into fields and planted reeds and grass on the beach to promote siltation. The top of Doumen Delta has begun to develop, that is, the big Aosha has been formed, and Zhou Mu and Sanjiangkou have also risen. Yellow cloth sand has been formed, and it only enters the southern islands of Zhuzhou and Fenzhou.

100 (late Qing dynasty), the front coastline was further advanced, and the outer edge of the delta was cut off at Doumen, that is, bamboo was used to drive sand, and the east and west sides of Denglangsha were used; Xinhui will go to the Yinzhou Lake in the west of Sanjiang River, and the coastline of Panyu will fill up the Wuzhuyang Ocean, with thousands of hectares of sand reaching ten surges. Dongjiang is progressing slowly, because the lion ocean tide is very strong.

In short, the coastline of the Pearl River Delta is constantly moving towards the sea, with periods of fast and slow. Natural factors are related to the fluctuation of sea level. At high sea level, the coastline advances slowly, but it is faster at low sea level. Man-made factors are dike construction, such as dike protection in Song Dynasty, which accelerated the sedimentation in Shatian downstream, and planting reed mud in Ming Dynasty, which accelerated the sedimentation. Tidal action and upstream sediment and water also have influence, such as slow sedimentation in Humen and Yamen waterways, which is the reason for strong tidal current. Between Humen and Yamen