This stone forest is a bit strange: Three Ordovician stone forests in my country

In the Karst Grand View Garden, Stone Forest is a common landform, named because the rocks are in the shapes of cones, columns, and swords that stand on the surface and are as dense as a forest.

The Lunan Stone Forest in Yunnan is a classic example of this type of landform. Although the stone forests all look the same, they are actually very different. The differences mainly come from the material composition, the degree of development of structural fissures, as well as the terrain, climate, and hydrodynamic conditions.

In my country's stone forest kingdom, there is a kind of stone forest that can be called a "wonderful" among stone forests. This is the stone forest formed by the "Ordovician Pagoda Formation Turtle Crack Limestone".

▲ Yunnan Lunan Stone Forest (@李忠东)

The Ordovician is the second period of the Paleozoic Era, 443-485 million years ago. During that period, most of the Earth was covered by oceans, and the day lasted only 21 hours instead of 24.

The warm climate of the Ordovician period allowed marine life to flourish. When trilobites, graptolites, nautiluses, and crinoids swam freely in the sea, familiar fish also began to appear, marking the beginning of the vertebrate age.

▲ Paleogeographic map of the Yangtze region and distribution map of the limestone of the Pagoda Formation (according to data)

In the middle of the Ordovician period, a set of limestone was deposited in Yunnan, Guizhou, Sichuan, Hunan and Hubei in southern my country. This set of limestone was named "Pagoda Formation Limestone" because it contained "pagoda-shaped cephalopod Sinian hornstones".

After hundreds of millions of years of sea-land changes, the limestone of the Pagoda Formation rose from the seabed to the land, and then under the erosion and dissolution of flowing water over the years, it formed the stone forest we see today. So what is so strange about this stone forest?

▲Rectangular stones in the Pagoda Formation limestone, photographed in Wansheng Stone Forest (@李忠东)

Stone Forest is a unique karst landform in southern my country. Most of the rocks that form the Stone Forest are carbonate rocks formed in the Permian period about 299-250 million years ago. They are the main strata that formed the Stone Forest landform.

The "Pagoda Formation Limestone" was formed in the Ordovician period about 460 million years ago, which is nearly 200 million years older than the common Permian stone forest. It is truly the "oldest stone forest".

It should be emphasized that the so-called oldest stone forest here refers to the rocks that formed the stone forest, not the time when the stone forest was formed. According to research, the stone forests on the earth basically began to form gradually after entering the Paleogene (about 65 million years ago). However, more scholars tend to believe that the Quaternary Period (more than 2.6 million years ago to the present) is the beginning of the evolution of the stone forest landform.

▲ Meidong Stone Forest (@林卡)

The most notable feature of the "Pagoda Formation Limestone" is the development of tortoise crack structures. That is, the surface of the rock develops a network structure dominated by quadrilaterals and pentagons, which looks like a tortoise shell. Therefore, this kind of limestone is also called "turtle crack limestone", and the famous geologist Ding Wenjiang also called it "horseshoe pattern limestone".

▲ Sketch of the cracked limestone and suture lines (drawn by Yang Jinshan)

There are many different theories about the formation of this limestone, and it is difficult to reach a unified understanding. Some people think that it is caused by "shrinkage and cracking" when the rock is exposed to the air, some people think it is caused by "underwater colloid condensation", and some experts believe that "pressure solution under the control of special structures" is the key.

This kind of limestone is distributed in the Upper Yangtze Platform from southern Shaanxi in the north to northern Guizhou in the south, from eastern Hubei in the east to central Sichuan in the west, with an area of ​​500,000 to 600,000 square kilometers, but it is generally thin, with a thickness of tens of meters. The stone forest formed by "turtle crack limestone" has stone patterns on the surface that are like carvings and paintings, as if the stone forest is covered with dragon scales and leopard clothes, which is very decorative and ornamental, and has become the unique personality and significant identification code of this kind of stone forest.

▲ One of the causes of the formation of the tortoise-crack limestone: the pressure solution theory under the control of special structures (cited from the data)

The dragon-scale-shaped rocks have developed a large number of cracks and joints under tectonic action. The abundant rainfall seeped and dissolved along these cracks, forming the stone forest we see today.

There are stone formations formed by karst gullies controlled by multi-directional joints, and there are also stone forest landscapes as dense as swords. Compared with pure and thick limestone, the karst marks on the weathering surface of this limestone are mainly knife-like and wrinkle-like.

▲The stone patterns are like carvings or paintings, as if the stone forest is covered with dragon scales and leopard clothes (@李忠东)

Due to the effect of differential dissolution, the middle and lower parts of the stone forest have developed belt-shaped dissolution marks and dissolution grooves parallel to the bedding. Some belt-shaped dissolution grooves are wide and deep, forming isolated rocks that are large at the top and small at the bottom. Some dissolution grooves are even completely connected, causing the upper rocks to be suspended, tilted, or formed wind-blown rocks.

Each stone forest has developed karst grooves, which are fan-shaped or pothole-shaped, narrow at the top and wide at the bottom. The edges of the karst ridges are sharp as knives. The stone forest is thick at the top and bottom, slender at the waist, and graceful in shape. The flowing water dissolves along the vertical joints, forming vertical tubular or well-shaped karst pits. The two-way dissolution of the karst grooves often penetrates the rock wall to form holes.

▲ Bidirectional dissolution of the karst trough often forms holes, taken in Xingwen Taian (@李忠东)

The area where "turtle crack limestone" is distributed has a humid and rainy climate. This climate environment is conducive to karstification and the formation of stone forests. On the other hand, it is also conducive to the reproduction and growth of plants. In particular, this area happens to overlap with the concentrated distribution area of ​​bamboo in my country. Most of the ancient stone forests grow together with bamboo forests, forming a wonderful combination of "stones in bamboo, bamboos in stones, and bamboo and stones coexisting".

Bamboo has joints, stone is firm, the combination of stone and bamboo has always been highly praised by ancient painters, and is also the favorite in ancient Chinese garden design. From a certain perspective, it represents the appreciation tendency and aesthetic taste of ancient literati - the rugged and elegant stone, the upright and elegant bamboo. Here, nature is so magical that it inadvertently combines the elegant artistic conception of classical China.

▲ The combination of bamboo forest and stone forest, taken in Xingwen Tai'an (@李忠东)

The distribution of this kind of stone forest is mainly related to the distribution of the Pagoda Formation limestone, so it is distributed in Yunnan, Guizhou, Sichuan, Hunan and Hubei. The most typical distribution area is located on the southern edge of the Sichuan Basin, because the slope area where the Yunnan-Guizhou Plateau transitions to the basin is more suitable for the development of stone forest.

There are three most typical landscapes, namely Tai'an Stone Forest in Xingwen, Sichuan, Meidong Bamboo and Stone Forest in Changning, Sichuan, and Wansheng Stone Forest in Chongqing.

▲The stone forest landscape as dense as swords (@杨建)

Tai'an Stone Forest, located in Lianglong Township in the northwest of Xingwen County, about 35 kilometers away from the county seat, is an important part of Xingwen World Geopark.

The stone forest is hidden among bamboo, trees, bushes and vines. From a distance, it looks all green and vast. Once you enter the dense forest, the stones hidden in the forest appear before your eyes in various shapes and forms.

Stone forests are usually 2.5 to 4 meters high. They may be piled up in a large area, like castles from a distance; or in groups of two or three, like literati holding wine and singing; or stand alone, like lonely travelers or ascetic monks. Ancient stone forests are scattered throughout the mountains, existing here in a primitive and ecological way, full of "wild interest".

In addition to being hidden among bamboos and trees, stone forests often appear in the fields, and even "grow" in front of and behind villagers' houses, appearing extremely casual.

Leading to these "scenic" spots are country roads where people go out in the morning and return in the evening. The ancient stone forest accompanies the villagers from sunrise to sunset, and the villagers here are used to traveling through the stone forest every day.

Only tourists who come here occasionally will be surprised by their existence and marvel at the silence and beauty of this paradise-like place.

▲ The karst trough in the stone forest dissolves in both directions, eventually dissolving through the rock wall to form a hole (@周江陵)

The Meidong Bamboo and Stone Forest is located in the southern part of Meidong Town, Changning County, on the southern edge of the Sichuan Basin. It covers an area of ​​about 20 square kilometers and is mainly divided into three areas: Bamboo and Stone Forest, Shilongpo and Tianmenzhai.

Gaojian Village in the Zhushilin area is the core distribution area of ​​Meidong Stone Forest. The height of individual stone forests ranges from 2 to 10 meters. They are distributed in patches and are extremely spectacular. The main landscapes include Five Sons Passing the Imperial Examinations and Zhong Kui Catching Ghosts. Tianmenzhai Scenic Area is located in Zhongping Village and Lianghekou Village and consists of Huadong, Husband and Wife Stone, Tianmenzhai Stone Forest Belt, Wujiadong and other landscapes.

The Husband and Wife Rock is the most magnificent. It is 18 meters high, 11 meters wide and 4 meters thick, just like a loving couple.

▲ The iconic landscape of Meidong Stone Forest, Five Sons Passing the Imperial Examination (@林卡)

▲The different dissolution of rocks forms a mushroom shape that is larger on the top and smaller on the bottom (@林卡)

Wansheng Stone Forest is located in Shilin Town, Wansheng District, Chongqing, and is divided into two areas: East and West Stone Forest.

The West Stone Sea is covered with clusters of stone forests, stone walls, stone buds and peaks, which are scattered across the mountains. They look like thousands of teams of cavalry, a chess formation in a stone forest, or a swaying giant fan and a stone drum hanging in the air.

Dongshihai, with an area of ​​less than 1 square kilometer, is dotted with ancient stone forests, peaks, and eroded and denuded cavities and caves. On the stone peaks, there are either hanging ancient vines or independent trees. "There are stones in the forest, trees on the stones, and trees and stones coexist."

▲ Iconic landscape, stone fan (@李忠东

▲ Wansheng Stone Forest and the widely developed solution windows and solution pores on the stone forest (@李忠东)