Datong native forest

Earth forest

synonym

The earth forest in Datong generally refers to the earth forest

Soil forest is a loose accumulation of clay, sand and gravel in Quaternary lacustrine and fluvial facies, which is eroded and washed by seasonal rain in dry climate. This kind of deposit has a gentle occurrence and is cut into thousands of ravines under the erosion of surface water. In some horizons, due to the enrichment of iron cement, the hard iron cap is formed after weathering, which protects the clay and gravel layer at the lower part and weakens the rain erosion force, thus forming a tower like Earth forest, especially the remains of an ancient castle. The image of personification is vivid. Soil forests are generally distributed in small basins with lacustrine deposits, especially in Banguo and Waipu of Yuanmou Basin, Yunnan Province. In addition, they are also distributed in Jiangchuan and Nanjian of Yunnan Province, Xichang of Sichuan Province and Tianshui of Gansu Province.

Quick navigation

Panorama

Cause of formation

Geographical factors

A group of columnar landforms shaped by earthy deposits. It's named after the forest of distant vision. In the dry and hot climate and the relatively uplifting environment of the ground, the rainstorm runoff strongly erodes and cuts the deep loose clastic sediments on the surface to form a fragmented terrain. Because of the iron weathering crust on the top of the sediment, or the intercalation of iron and calcareous cemented gravel layer, it acts as a protective umbrella for the lower soil layer. In addition, the vertical joints of the sediment are developed, so that the side slope of the raised residual body remains steep. Generally, the height is about 20 meters or even up to 40 meters. The top of each column is the original sedimentary surface. Soil forest generally occurs in basins or valleys, especially in Yuanmou, Yunnan, China. It is also found in huanglianguan, Xichang, Sichuan, Zada, Tibet, Tianshui, Gansu and Zhangye. It is mainly distributed on the high terrace of different times and formed in many stages, reflecting the evolution of paleogeography and geomorphology.

environmental factor

Soil forest is the result of special lithologic association, tectonic movement, wind and rain dynamics and ecological environment. There are 13 soil forests in Yuanmou Basin, with a total area of 42.9 square kilometers, accounting for about 2.1% of the total land area of the county. The most spectacular ones are xinhuatulin, banguotulin and hutiaotan tulin, which have been developed into scenic spots. Together with other small area tulin, they form a rare tulin community in Yuanmou Basin at home and abroad.

Geological structure

Geological experts say that the formation of earth forest can be traced back to the ice age of 80 million to 100 million years. During the period of ice water deposition, debris was brought by ice water flow, and sand gravel layer was formed. After diagenesis and hardening of sand gravel layer, cracks or fissures (called cracks in Geology) appear under the influence of new crustal movement. The surface water (mainly rain water) seeps and penetrates downward along the cracks. Over time, the cracks gradually expanded and deepened due to erosion, and finally split into mounds and columns, becoming today's soil forest. The Sandy Rock at the top of the tulin is a kind of colloidal calcium structure, which is not easy to be weathered and washed, so it is mostly mushroom shaped.

Yuanmou Basin is located in the middle of the North-South structural belt of Sichuan Yunnan. It is a faulted basin controlled by the North-South fault. In the East, there are eroded mountains composed of Jurassic and Baili feldspar quartz sandstone, conglomerate and mudstone, with a relative elevation difference of 1000-1500 m; in the west, there are low Hills composed of gneiss, quartzite, schist, phyllite and Jinning granite of the Yuangu Julin group The late Cenozoic strata of Pliocene Holocene are widely distributed in the area, and tulin is developed in Pliocene early Pleistocene. The basement of the basin is mainly the Ailin group and Jinningian granite.

Formation conditions

1. The semi cemented and high diagenetic gravel layer is one of the internal reasons for the formation of soil forest;

2. The neotectonic movement not only provided the potential energy of water erosion, but also controlled the development trend of soil forest;

3. The iron weathering crust and iron cemented sand gravel layer protect the soil forest in multiple layers;

4. Dry climate and less rainfall are important conditions for soil forest development;

5. Ecological deterioration accelerated the development of soil forest.

Developmental stage

The development of soil forest can be divided into five stages: sheet erosion, furrow and rill stage; gully cutting stage; gully and erosion basin stage; wide gully stage; residual Hill leveling stage. Types of soil forest:

According to the color: Red Soil forest, loess forest, white soil forest, color soil forest.

According to the geomorphological form and its combination and development stage, it can be divided into three types: rill soil bud type, round basin soil column type, wide ditch Castle type and remnant slope column type.

According to the shape: cone column shape, Castle shape, peak cluster shape, city wall shape, slow shape, snow peak shape.

The rate of soil forest development is estimated as follows

The time needed for the formation of soil forest is as follows

According to the calculation of erosion modulus analogy method, it takes 96-6490 years for soil forest to form. It was first formed in the Atlantic period of the middle Holocene and last formed in the sub Atlantic period. The tall earth forest may be the product of the sub northern period of the Holocene.

Calculation of erosion rate of soil forest development

The average erosion rate of soil forest is 6.16-41.6 mm / year, which is 120-830 times higher than that of karst landform in eastern Yunnan.

It can be seen that the development of soil forest is very fast, but it can not be formed in thousands of years. Therefore, soil forest is not so easy to die out. As a kind of tourism resources and natural protection object of geological landform, this generation of soil forest will not die out in hundreds of years. Even if the old age soil forest is dying out, as long as the crustal movement does not stop, as long as the soil erosion does not stop, a new generation of soil forest will gradually come into being. Human activities can not prevent the development and formation of soil forest, but can only accelerate or delay its expansion.

influence factor

Regional stability

The main factors affecting the stability of the region are active faults, earthquakes and neotectonic movements. Due to the extension of the compressional and torsional large fault zone running through the eastern part of Yuanmou Basin in the North-South phase, many main soil forests, such as hutiaotan soil forest, Banguo soil forest and Xinhua soil forest, are located in the western part of the basin, 10-40 km away from the eastern fault zone, and the influence of the western part is relatively weakened when the fault is active. In Yuanmou Basin, there are few earthquakes with magnitude greater than 4.7. The calculation results show that the force that the soil column can bear per square meter is far greater than the horizontal force produced by the earthquake per square meter. Even if there is an earthquake with magnitude 6-7 in the basin, the soil forest is stable on the premise of considering only the horizontal force of the earthquake. The neotectonic movement in Yunnan Province and central Yunnan is relatively stable, and the regional crustal stability is medium.

Self stability

The soil forest is located in the color air zone above the groundwater, and its foundation is firm and stable; the semi cemented soil of the soil forest plays a decisive role in the stability of the soil forest itself; the multi-layer protective cover enhances the stability of the soil column. Rainfall is the most important external factor affecting soil forest stability.

practical value

Ornamental value

It includes four aspects: beauty, strangeness, richness and organic combination.

1. Gracefulness

(1) Natural modeling beauty: from the perspective of viewing, the earth forest can also be called small foot shape landform. Its natural shape is personified or imitated, lifelike, lifelike, delicate and full of verve. Modeling categories can be divided into people, animals, plants and simulacra, which are the main landscape and key ornamental content of tulin scenic spot. The feedback from tourists who have been open for more than ten years shows that more than 90% of the tourists are deeply shocked by the world's most peculiar landscape and have accepted a baptism of sensory and spiritual art.

(2) Beauty of natural scenery: the native forest scenic spot is primitive, desolate and rugged. The sand ditch, barren mountain and secluded valley constitute a wild ancient world. The natural scenery is unique, giving people a kind of primitive beauty and rugged beauty. It has a strong attraction, attracting many painters to come to paint from life and photographers to capture the flash. The native forest has become the focus of some film and television production teams It is the first choice of scenic base and tourists who pursue and advocate nature. Baisha loess is a unique environment with sparse vegetation, scarce water resources and hot and dry climate. It is another form of natural beauty different from green mountains, green waters and fragrant flowers. It's like going back to the distant past, where the appeal of nature is fully revealed.

(3) Natural beauty: tulin scenery has different charm in different seasons, different times, different climates and different angles. It is an all-weather scenic spot. In the sun, the shape of the earth forest is strong, eye-catching, straight and straight, and you can see it at a glance; in the rain and fog, the landscape of the earth forest seems to be obvious, like dew, like light and dark, like a girl wrapped in soft yarn, hazy and implicit. In winter, the earth forest is warm as spring, and the climate is pleasant. In summer, the scenic spot is hot and hot, like being in the sand sea desert. In addition, the stability of soil columns is poor, and it is easy to drain. Some soil columns are like chickens this year, like dogs next year, and disappear in three or five years, leaving a pile of white sand and loess for people to recall the past. This rare changeable and hazy beauty is full of mystery, which arouses the curiosity of today's tourists and makes tulin a scenic spot with the most "repeat visitors". Here, they taste the changes, look for the extinction, look forward to the rebirth, and integrate themselves into the lifeless earth pillar.

2. Singularity

Singularity refers to the probability of such scenes appearing in China and even all over the world. Soil forest landscape is a new tourism resource discovered in recent decades, which is novel, special and unusual

Chinese PinYin : Da Tong Tu Lin