Geomorphological Landscape of Marine Granite in Pingtan Island, Fujian Province

Pingtan county is located in the southeast of Fujian province. It consists of 126 islands and 648 famous rocks, and is the largest island county with thousands of reefs in China. Haitan Island, the main island where the county seat is located, is the fifth largest island in China and the largest island in Fujian Province. It is only 68 nautical miles from Taiwan Province Strait and Hsinchu, Taiwan Province Province, and it is the closest place for the mainland to Taiwan Province Province. West of Haitan Strait, facing Changle, Fuqing and Putian counties, it is 28 km away from Fuzhou/KLOC-0 and 300km away from Xiamen, so the geographical position is very important.

Qiandao Reef and hundreds of islands in Pingtan County are mostly made of granite in the late Yanshan period. In the long geological period, they have been eroded by various external forces, especially spherical weathering, which has created many amazing modeling landscapes. To sum up, its granite surface landscape includes: winding harbor and charming beach dominated by Longwangtou; The whole island has its own natural museum of marine erosion and geomorphology. Their concentrated expressions include the world wonder of "semi-sail", the "Stone Man Temple" worshipped by ancestors, the rock forest in Nanzhai, and the 36-foot lake, the largest freshwater lake in Fujian, which evolved from a coastal lagoon.

Figure 4-37 Mushroom Granite Pillars

Figure 4-38 Square Stone Column Group

2. Marine granite landscape

Haitan Island has hundreds of sanitary islands, thousands of reefs criss-crossing, seamounts shining, and the landscape is very strange. Due to the influence of structure and seawater erosion, many magnificent marine erosion landforms have appeared in the whole island. They are huge, unique and magnificent, which can stimulate people's strong interest in exploring strangeness and can be called irreplaceable monopoly landscape. Their outstanding figures include the "semi-sail" known as the wonders of the world, the "South Sea God" worshipped by ancestors-Man Qin, a stone, and Nanzhai Mountain Forest, which is a fantastic spectacle.

Figure 4-39 Circular Stone Pillars

Figure 4-40 Irregular-shaped stone columns

(1) Semi-ocean sail simulation landform

Semi-ocean Fan Shi, also known as Shipaiyang, is located in the northern mouth of Haitan Strait in the northwest of Haitan Island. Here, you can see two granite columns, which are staggered and supported on the towering sea in the form of boat-shaped reef plates. Shaped like Fan Shi, the highest is 33m and the lowest is 15m. It is huge and has a strange image. For more than 400 years, it has been known as the "miracle of the world" and is the largest granite ball in China. This pair of sea pillars consists of homogeneous coarse-grained white granite. In the long geological history, there have been strong spherical columnar weathering and layer-by-layer peeling. Now the two sails are the fresh core parts stripped by spherical columnar weathering. At the column base 1.5m, obvious sea erosion ditches and transverse holes can be seen, indicating that seawater wave erosion is also an important weathering mode involved in its erosion and denudation.

In order to set off the "semi-foreign sail", a series of incredible spherical aeolian fossils are preserved on the gentle granite beach in Aokan Village, such as concentric round stone eggs wrapped layer by layer (Figure 4-42), as well as lifelike frogs facing the sky, double turtle arch bridge, chicken nest stone eggs, porcupines going to the beach (Figure 4-43), ancient armor unloading and Yandunbao.

Figure 4-4 1 Pingtan sea pillar-"semi-sail" (according to Yang Yichou, 2007)

Figure 4-42 Pingtan concentric stone eggs (according to Yang Yichou, 2007)

More interesting is the granite peak here. The red weathering crust with a thickness of 4 ~ 5m is wrapped with many gray fresh spherical weathered fossil cores, some of which roll down, leaving circular pits on the shore wall, which can correspond to each other (Figure 4-44). Some stone cores have not rolled down yet, forming a "sarcophagus", which can be confused. The combination of spherical weathering has also formed a "Maitreya Buddha" with a bald head and a bulging belly. There is a brown embankment around the Buddha statue, just like the golden "Hada" dedicated to the Buddha statue (Figure 4-45).

(2) Granite islands and mountains

There is a granite island mountain in the south of Pingtan, like a huge naked male stone statue lying on his back on the edge of the land and sea. It is composed of gray-white coarse-grained granite, with golden beaches on its head and blue waves in the East China Sea at its feet. It is the world's largest spherical weathering model of natural granite, with its peculiar shape and well-proportioned body parts (length 330m, width 150m, chest height 36m, head length 33m and width 25m). He has a bald head, ears and mouth, his chest bulges, and his lower genitals are impressive. His genitals are firm and inclined, and his image is vivid and lifelike (Figure 4-46). The stone man is actually made up of a huge spherical granite weathering body, and his bald head and ears are made up of stone balls left on the surface of the huge spherical weathering mound. The convex belly bare dome is a spherical weathered convex surface of granite hills, and the genitals of the lower body are the residual parts of the weathered shell eroded by the waves. It looks like an upside-down boot, relatively more than 4 meters high, very vivid. There are many carved stone scenes near the Stone Man, including pneumatic stone (this stone is located on the left side of the human head and constitutes the left ear of the "God of Heaven"), gongs and drums stone, sail stone, Eight Immortals Go stone, Muyu stone, incense burner stone, peach stone, ox nose stone, fisherman fishing alone, double lions playing ball and so on. , forming a sculpture rock group with stone people as the main scene.

Figure 4-43 Pingtan porcupine (granite pictogram) (according to Yang Yichou, 2007)

Figure 4-44 Spherical Weathered Fossil Cores in Pingtan Weathered Crust (According to Yang Yichou, 2007)

(3) Other simulated marine erosion landscapes

Wangye Mountain, located in the prominent part of Haitan Island in the northeast, is adjacent to the open sea in the east. The bank slope of bedrock is directly eroded by waves, and different types of marine erosion landforms, such as majestic sea cliffs, caves, stone pillars, terraces and grooves, have developed, which are steep, magical and fascinating. Because the landscape has a strong sense of mystery, it is called "fairyland". Its main marine erosion simulation landscape is Ren Xian Well, with a wellhead diameter of 33 meters and a depth of 43 meters. The cave walls are as steep as knives and axes, and there are patterns on the walls that look like various birds and animals. There are two holes near the bottom that communicate with the sea outside. Ocean currents surge back, beating against the shore wall, splashing waves, blue waves and silver light, echoing the wall, which is thrilling. Therefore, it is called "Jing Xian growl". What's even more amazing is that at low tide, you can drive into Xianjing, and under the reflection of Asahi, you can see the wonderful "Golden Guanyin" in the cave. Its mystery is really unfathomable. Because she must be in a certain weather (sunny day) and at a certain time (from sunrise to 8 am in summer), she is full of great mystery and has stimulated many people to wander through the ages.

Figure 4-45 Pingtan spherical weathering-"Maitreya Buddha" (according to Yang Yichou, 2007)

Figure 4-46 Spherical Weathering in Pingtan-"Stone Man" (according to Yang Yichou, 2007)

Besides, the wall of Ren Xian Valley is steep, and there is a hole in the south wall that can pass through Ren Xian well. Oyster Reef is a hollow valley next to Fairy Well. The wall of the valley stands upright like a door, and there are strange rocks and waterfalls outside the valley. The scenery is excellent.

In the southeast of Li Nan Village, Pingtan City, there is a hill made of granite. The mountains are criss-crossed, and the huge stones are rugged, grotesque, intertwined and mountainous. In addition, there are rugged rocks and beautiful scenery in the area. There are many strange stone scenes, and the scenery is concentrated and within reach. Typical stone scenes can be summarized as five peaks and one valley, namely crocodile peak, immortal peak, sheep peak, eagle peak, frog peak and turtle peak. In particular, all kinds of animal shapes, such as the eagle with wings spread, the clouded leopard with claws, the monkey scratching its head, and the charming pheasant ... all kinds of birds and animals are lifelike, with both form and spirit, and are known as "all animals look at the garden" (Figure 4-47). The formation of carved stone scenes is due to the fact that granite with developed joints experienced sea erosion, then rose, weathered by running water and even blown by the wind, and finally became various magical forms.

Figure 4-47 Spherical Weathering in Pingtan —— "Animal Watching the Garden" (according to Yang Yichou, 2007)

3. Cause analysis

Pingtan Island is located on the east side of the metamorphic rock belt along the southeast coast of Fujian Province, and granite in the late Yanshanian period (about10.30 billion years ago) is widely distributed on the island. In the late Yanshan period, due to strong magmatic activity and fault activity, many acid dikes were interspersed in granite, forming a NNE and NNW rhombic fault structure. In the later geological history, the ups and downs of tectonic activities and the ups and downs of blocks separated by faults formed a horst graben-like structural pattern, which controlled the basic arrangement and structural pattern of thousands of reefs and hundreds of islands in Pingtan County, and controlled the twists and turns of the coastline of Haitan Island and the ups and downs of mountain plains. In particular, many rhombic joint structural systems have destroyed the firmness and impermeability of granite itself. The structural joints in Pingtan Island reef granite are typical cubic crystal system, which creates good basic control conditions for the development of stone egg landform and its modeling landform. However, groundwater, chemical weathering and biological weathering can penetrate into the ground with vertical or horizontal joints, and erosion can go deep, erode laterally and denude downward, forming gullies, shafts, valleys and lateral caves. Almost all canyons, cliffs, natural bridges, shafts and caves along the coast of Pingtan Island are formed by the development of lattice joints. Some landforms such as steep cliffs, cliffs and dangerous reefs in mountainous areas, hills and coastal areas are also mainly the result of vertical combined action (such as freezing and cracking, mechanical weathering, etc.). ).

Pingtan granite island has been in a uplift state since its formation. In the late Cenozoic, influenced by the fluctuation of the world ocean surface (mainly caused by glacial and interglacial periods) and neotectonic movement, it once sank into the sea and suffered seawater erosion, and then rose intermittently. So far, low hills, coastal platforms, terraces, marine plains, beach rocks and other landforms. It has been preserved on the island, forming the island chain landform of the coastal hills in southeastern Fujian.