Tianjin Shell Dike

　　       Introduction        It is a dike-like landform accumulation composed of marine shellfish and their fragments, along with layers of fine sand, silt, peat, and muddy clay. It is roughly parallel to or has a very small angle with the coastline. Formed near the high-tide line, it serves as a reliable indicator of ancient coastlines in terms of geomorphology. Within Tianjin’s land accumulation plain, there are four shell dikes—No. I, II, III, and IV—arranged from inland toward the sea. These dikes are roughly parallel to the modern coastline and are distributed discontinuously in a ridge-like pattern, representing the positions of the coastline during four different periods. The marine transgression that occurred between 10,000 and 5,000 years ago submerged most of the Tianjin Plain. Later, as sea levels dropped and rivers deposited sediments, the area gradually became land. The shell dikes consist of marine shellfish and their fragments, along with layers of fine sand, silt, peat, and muddy clay, and form dike-like landform accumulations that are roughly parallel to or have a very small angle with the coastline. Formed near the high-tide line, they serve as reliable indicators of ancient coastlines in terms of geomorphology. Within Tianjin’s land accumulation plain, there are naturally four shell dikes—No. I, II, III, and IV—arranged from inland toward the sea. These dikes are roughly parallel to the modern coastline and are...

　　 Tianjin Tanggu District