Oyster beach

Oyster beach

It is the largest, most widely distributed and most clearly sequenced ancient coastal relic discovered so far in the world. It is formed by the accumulation of oyster shells, which can reflect the changes of the ancient Bay. Oyster beaches in Tianjin are rare in both area and thickness. For example, the river course from shizhuangzi to jiangzhuangzi in dongjituo Township in the west of Ninghe County, and peizhuang in the east of Ninghe County near Jingshan railway. The scale, profile thickness, clarity and shell length of oyster beaches in these two places are rare in the world. They are of great significance to the study of marine ecology and sea land changes Your value.

brief introduction

Oyster beach is distributed in the southern part of Baodi County and the central and eastern part of Ninghe county. It is composed of the corpse and burial groups of changchong oyster and Jinjiang oyster in the bay environment. It is the product of 5800-2200 years ago. Oysters grow in the lower part of intertidal zone and under the surface of subtidal zone, so the top surface of oyster layer is regarded as one of the indicators to determine the sea level at that time. The oyster beach in Ninghe county is distributed in zonal east-west direction, which indicates that the tide direction at that time was north-south direction, which is similar to that in modern times. Oyster beach, with the largest area, is located in the river course between shizhuangzi and jiangzhuangzi in dongjituo Township in the west of Ninghe county. It is 1000 meters long from east to west and 730 meters wide from north to south, covering an area of 73 hectares. The thickest oyster beach is located in peizhuang, east of Ninghe County, near Jingshan railway. The thickness of oyster layer is more than 5 meters. Oyster shell accounts for more than 90% of oyster beach. The largest diameter of oyster shell is 50 cm and the smallest is a few cm, which is related to the growth rate. The sedentary group is mainly in sitting position, while the burial group is characterized by lying position and petal shell, reflecting that the Bay was relatively quiet and the sea water was clear at that time. 2200 years ago, the sea level was about one meter higher than today.

Tianjin Ancient coast and Wetland Nature Reserve, approved as a National Nature Reserve in 1992, is composed of oyster beach, Qilihai and shell dike, with a total area of nearly 1000 square kilometers. According to the research of experts at home and abroad, its integrity, clarity and typicality are rare in the world. It is a precious and non renewable natural heritage left by nature. The scale, thickness, clarity and shell length of oyster beach can be regarded as a wonder in the world.

features

Fabric characteristics

The main species was Crassostrea rivieri, followed by Crassostrea Sangha. The bottom is mainly attached to the mixed granite and its weathered soil, variegated or maroon. It grows on gravelly sand clay, and the oyster shell is slightly rounded. Round gravel, mostly mixed granite or migmatite. From the attachment layer to the top, oyster shells are enriched, and the individuals are large and generally long. From the bottom to the middle of the section, almost all oyster shells are mixed with a very small amount of sand. The sand is gray black and gray green, and occasionally carbonated plant debris is seen, which indicates that the oyster beach was exposed to land and buried by sand. There is a layer of modern oysters growing on the top. The oysters and the sand in the upper part are cemented to form a solid oyster shell beach rock.

Primary characteristics

Most of the oyster shells in Qilihai show their original characteristics, such as upright individuals, head upward, double valves coexisting, some closed, some slightly open, overlapping growth and flaky distribution.

Disturbed characteristics: some oysters are mixed, flat and inclined, and wrapped with gray black sand. For example, two ancient oyster shells in the southern edge zone are disturbed, and the shoal in the north of the middle paleoforest also contains two oyster shell enrichment layers which have been disturbed and cemented with sediment.

form

Due to the oscillatory movement of the crust and the different amount of mud and sand transported by waves under different climatic conditions, the exposed thickness and distribution area of the ancient oyster beach are also different, so the degree of erosion is also different. Due to the serious erosion of sea waves, oyster shell beach rocks are broken and stacked in plate-shaped blocks. Some parts of the broken shells form scattered shell accumulation. Some oyster shells and the weathered soil of mixed granite attached to the bottom are eroded and hollowed out by sea water, forming umbrella shaped, mushroom shaped, cave shaped and bridge shaped. Oyster shoals are distributed in discontinuous flakes, and some oyster shells are pushed to different high tide lines by waves. In addition, a large number of rounded gravels underlying oyster shells were eroded by waves, and transported to the shoal near the shore to form gravel shoal with sparse gravel distribution. In the upper part of the near tidal zone, the oyster shells were eroded and transported, leaving upright native oysters, forming a native oyster beach with only the tip of the oyster head exposed, which is flush with the beach surface or slightly higher than the beach surface.

Formation process

The growth and survival process of Qilihai oyster has experienced the following paleoenvironmental changes: Late Pleistocene continental gravelly sand clay, from a certain amount of ground gravel underlying the original oyster, Qilihai was a strong hydrodynamic river environment before the sea immersion. At that time, the crust rose at a rate equivalent to the rate of hydrodynamic sea-level rise, and the depth of the sea was stable. Because of the bay environment where the sea water in Qilihai began to swim up along the early rivers, the hydrodynamic force was weak, the coastal environment was stable, and the coastal environment was stable There are some runoff water into the Bay, which makes the bay rich in nutrient solution. Qilihai grows a large number of ancient oysters, forming a wide late Pleistocene ancient oyster beach. From the fact that there are ancient oyster shell enrichment layers distributed on both sides of the middle area of the submarine ancient forest, it can be seen that the ancient oyster beach at that time was connected together, including the present middle area of the submarine ancient forest. At that time, it was also an oyster beach environment, which was widely distributed There are ancient oysters. In the following period of time, the crust uplifted rapidly at a rate higher than that of the hydrodynamic sea level rise, with strong PALEOEARTHQUAKES, the sea water retreated, the Qilihai sea became a land environment, and the paleooyster beach became a platform. In the process of crustal uplifting, due to the erosion and denudation of loose late Pleistocene sediments by water flow and the collapse of hillock caused by strong uplifting, depressions or depressions about lower than the ancient oyster beach surface were formed everywhere in Shenhu Bay. During this period, the ancient oyster beach platform and ancient oyster shell were also largely eroded, and the ancient oyster beach platform was dismembered and broken. The earth's crust is relatively stable, the depression is easy to accumulate water and nutrients, and the depression faces east to the sun, which makes it possible to grow a large number of ancient forests. After a strong paleoearthquake occurred, the depression where the ancient forest grew quickly sank to the bottom of the intertidal zone, the ancient forest quickly died, part of it was quickly buried by marine sediments, and the remaining ancient oyster beach platform sank to a higher level than the current sea level.

After the earthquake, Qilihai was mainly a lagoon environment, and the ancient forest remains were further buried by the lagoon deposits, resulting in another strong paleoearthquake. The relic of the submarine ancient forest and the buried lagoon in the Shenhu Bay rapidly sank to the deeper sea floor, and the residual ancient oyster beach platform rapidly sank to the subtidal sea floor and intertidal sea area. Due to the oscillatory movement of the earth's crust and the changes of different climatic conditions, the remains of the submarine ancient forest and the late Pleistocene ancient oyster beach in Shenhu Bay are sometimes buried by most of the intertidal sea sand, and sometimes exposed in most of the intertidal sea sand, and eroded and transported by the intertidal waves, finally forming the remains of the submarine ancient forest and the late Pleistocene ancient oyster beach in Shenhu Bay.

Therefore, the reason why oyster beach can appear in today's intertidal zone is that oyster beach has experienced rapid uplift after its formation, which makes oyster beach leave the sea quickly and not be eroded by sea water and buried by marine sediments. In many other places, the late Pleistocene marine sediments were either eroded by seawater due to slow uplift, or due to the subsidence of the crust, or due to the coverage of sediment carried by the slow rise of the hydrodynamic sea level, so that they were mostly buried and could not be exposed. Although the oyster beach was uplifted above the sea surface to form oyster beach platform and was exposed to the land environment, most of it was eroded or denuded, but a considerable part of it was preserved. The two strong PALEOEARTHQUAKES made the crust sink rapidly again and again. After the rapid subsidence of the paleooyster beach platform in the late Holocene, part of the platform quickly sank to the bottom of the subtidal zone and avoided the erosion of high-energy waves in the intertidal zone. If it is not because of rapid subsidence, but because of the slow subsidence of the crust or the steady and slow rise of the hydrodynamic sea level, the oyster beach platform will also be eroded and not be preserved. Although the ancient oyster beach which quickly subsides back to the intertidal zone is often eroded by the intertidal waves, because it is not a long time to return to the intertidal zone and the crust is relatively stable after it returns to the intertidal zone, sometimes the oyster beach will be destroyed Oyster beach is covered by thin layer of sand, so that a considerable part of ancient oyster beach is still preserved in intertidal beach, which is an important reason why oyster beach can be more preserved in intertidal beach today.

Tourism season

Although Tianjin is close to the Bohai Bay, because the Bohai Bay is a semi closed inner Sea bay with a small water body, the impact on Tianjin's climate is relatively small. Therefore, Tianjin's climate is still a temperate semi humid continental monsoon climate. In winter, it is affected by the Mongolian high, which is dry and cold. In summer, it is affected by the subtropical high, which is hot and rainy, warm and windy in spring, and cool in autumn, The temperature is suitable. Therefore, the best travel time of oyster beach in Tianjin is late spring, early summer and autumn.

traffic

From Tanggu to oyster beach in Ninghe, after arriving at Lutai bus station, you can take a bus to Qilihai. There is a bus to Lutai from Dalian Road bus station in Tanggu.

value

Oyster beach, Qilihai and shell dike together form Tianjin Ancient coast and Wetland Nature Reserve, which has been approved as a national nature reserve. Oyster beach in Qilihai is an extremely rare natural relic and a true record of the vicissitudes of life. It is of great value to the study of Oceanography, wetland ecology and other disciplines.

Tianjin oyster beach is brand new

Chinese PinYin : Mu Li Tan