The Cambrian Strata of Tianmen Mountain

1. Geographical Environment

Tianmen Mountain National Geopark is located on the south bank of Lishui River in Zhangjiajie City, with geographical coordinates of 110°26'15"-110°30'45" east longitude and 29°01'30"-29°06'15" north latitude, covering a total area of 68 square kilometers. Its highest peak reaches 1,518.6 meters above sea level. Although not particularly high in absolute altitude, the relative height difference of over 1,300 meters, combined with its towering, steep, and precipitous nature, dominates the southern skyline of the city, presenting a majestic and imposing spectacle.

2. Origin of the Name

Tianmen Mountain was anciently known as Fanghu Mountain, and later as Songliang Mountain. In the sixth year of Yong'an reign of the state of Wu during the Three Kingdoms period (263 AD), the governor of Wuling Prefecture, Zhongli Mu, was suppressing a rebellion by the "Wuling Barbarians" when a cave on Songliang Mountain suddenly "opened up like a door." Upon his return to the capital and report to the Wu emperor Sun Xiu, the emperor considered it an auspicious omen and bestowed upon the mountain the name Tianmen Mountain and the cave Tianmen Cave, signifying the "Gate of Heaven."

3. Geological Formation

3.1 Formation of Tianmen Mountain

Research suggests that the uplift of Tianmen Mountain began during the Yanshanian orogeny and was further shaped by the Himalayan orogeny, which formed the main body of the mountain. Subsequent intense erosion and dissolution processes led to the formation of the present-day karst mountain landform. The summit, due to prolonged weathering, erosion, and faulting, has had its steeper surrounding sections eroded away, leaving behind a relatively flat terrain composed of the core strata. This process has resulted in an isolated mesa landform. Several ridges and valleys extend downwards from the cliffs below the mesa, creating the Tianmen Mountain we see today.

3.2 Formation of Tianmen Cave

There are various explanations regarding the formation of Tianmen Cave. Mythological legends describe it as a gateway to heaven. Some speculate it was formed by a seismic event in 263 AD, while others attribute it to natural mountain collapse or the dissolution and collapse of a cave system.

Investigations reveal that Tianmen Cave was originally an underground cave at the edge of the mesa. The cave roof corresponds to the core of a synclinal structure. Due to compressional forces within the syncline, the rock strata at the core were already fractured and prone to collapse. Coupled with prolonged dissolution and erosion, the rock layers at both the north and south ends eventually crumbled, revealing the opening we know as Tianmen Cave.

4. Geological and Geomorphological Features

Tianmen Mountain belongs to the New Cathaysian System and the Wuling Uplift Belt. It is an eastward extension of the Wuling Mountains into the Dongting Lake Plain. The bedrock in the area primarily consists of Cambrian limestone, dolomite, and shale, with Sinian carbonaceous shale visible in the southern part.

4.1 Main Characteristics:

1. The ancient, magical, and globally unique Tianmen Cave
2. The majestic, steep, and solitary mountain landscape
3. The diverse and scenically distinct karst landforms
4. The spectacular, beautiful, and enchanting waterfalls
5. The ever-changing and magnificent atmospheric and meteorological phenomena combined with the geological landscape

4.2 Main Geological Landscapes:

Karst plateau, karst peak cluster, karst canyon, karst sinkhole, stone buds, stone forest, karst cave, natural bridge and stone gate, spring and waterfall, geological structure, etc. (see diagram).

4.3 Additional Features

Tianmen Mountain also boasts:

• A historical significance as a sacred mountain
• Well-preserved secondary forests
• A rich diversity of rare flora and fauna
• A profound religious and ethnic minority cultural heritage

5. Notable Landscape Features

5.1 Karst Sinkholes

Sinkholes are abundant on the plateau, with dozens of them ranging in diameter from 2 to 70 meters, mostly found on the eastern part of the summit. These sinkholes are mainly formed by karst collapse, and many of them have caves underneath. Notable sinkholes include "Tianchi" (Heavenly Pool), "Wolongtan" (Crouching Dragon Pool), and "Meihuayu Yuan" (Plum Blossom Rain Source) (see photos). The varied shapes and depths of the sinkholes scattered throughout the forest add to the mysterious and profound atmosphere.

5.2 Cave Landscapes

Tianmen Mountain is riddled with caves, many of which are vertical shafts plunging hundreds of meters deep, some with depths yet unknown. These caves are interconnected through horizontal passages, forming a complex network with multiple levels, caves within caves, and caves above caves. Springs flow through many of the caves, creating the most wondrous subterranean symphony. Notable named caves include Zushi Cave, Yuhuang Cave, Guigu Cave, Qiu'er Cave, Guanyin Cave, among sixteen others. Studies show that these caves are primarily formed along vertical joints and are often connected to the karst sinkholes on the summit. They are characterized by their height, depth, and steepness, making them suitable for exploration by domestic and international professional caving expeditions.

Among the Tianmen Caves, one stands out for its mystery and intrigue: Guigu Cave, also known as "Guiguzi Cave" or "Guigu Immortal Cave." Situated high on a sheer cliff face, the cave is inaccessible by foot. Entry requires descending from the summit via ropes. Inside the cave, one can find a "stone table," "stone bed," "seal script inscriptions," and other features. Legend has it that this was where Guiguzi, a hermit strategist from the Warring States period, cultivated his skills. For centuries, countless adventurers have attempted to unravel the secrets of this cave, but all have failed. In recent decades, a retired soldier organized six expeditions to explore the cave, yet none succeeded. Each attempt, however, yielded peculiar discoveries, most notably a photograph capturing what appears to be an image of Guiguzi meditating on the cave wall, a phenomenon that remains unexplained (see photos).

5.3 Magnificent and Enchanting Waterfalls

There are over a dozen waterfalls scattered throughout the Tianmen Mountain scenic area, with the most famous being the Double Dragon Waterfall, Tiacao Waterfall, Seven-level Waterfall, and Tianmen Divine Waterfall (see photos). All of them are formed by karst springs cascading down the cliffs.

• Double Dragon Waterfall: Located on a sheer cliff above the Yunmengze area, two springs cascade down the cliff from a height of several hundred meters, forming two distinct streams, one yellow and one white. They plunge into the "Shenxianta" (Immortal's Terrace), creating a mist that envelops the area. This natural spectacle of clear and turbid waters merging together offers a metaphorical reflection on life and society, making it one of the most unique sights at Tianmen Mountain.

• Seven-level Waterfall: Situated below the Guihua Bridge, at the lower end of the cable car canyon, this waterfall plunges down from a cliff several hundred meters high in seven distinct stages, resembling a white dragon ascending Tianmen Mountain.

• Tianmen Divine Waterfall: This is an intermittent waterfall. At the top of Tianmen Cave lies a sinkhole that collects rainwater and karst water from the surrounding area. This sinkhole is also the source of the Plum Blossom Fish. When the sinkhole overflows, water spills over the edge and cascades down the cliff, creating the spectacular Tianmen Divine Waterfall (also known as Tianmen Overflow). Legend has it that the clarity and appearance of the Tianmen Divine Waterfall are linked to major events in the human world, adding a layer of mystique to this natural wonder. Whenever the waterfall appears, it draws crowds from the city eager to witness the rare spectacle.

Questions and Answers

Q1: What is the geological age of the rock formations found on Tianmen Mountain?

A1: The primary rock formations on Tianmen Mountain belong to the Cambrian period.

Q2: How did the distinctive Tianmen Cave form?

A2: Tianmen Cave originated as an underground cave at the edge of the mountain's plateau. The collapse of its roof, weakened by geological forces and erosion, created the massive opening visible today.

Q3: What is the significance of the Tianmen Divine Waterfall?

A3: The Tianmen Divine Waterfall is an intermittent waterfall, only appearing when a specific sinkhole overflows. It's believed by some to be a harbinger of significant events, adding to the mountain's mystique.