The formation of geological relic landscape in Shenzhen has experienced three geological historical stages: Mesoproterozoic to Mesozoic, Early Cenozoic and Late Cenozoic. From Mesoproterozoic to Mesozoic, it is mainly the formation of various rocks and the development and evolution of structural characteristics. The early Cenozoic is mainly the erosion stage of early rocks and structural features formed by structural uplift, and the late Cenozoic is an important stage in the formation, development and evolution of geological landscapes seen today.
(1) Evolution stage from Mesoproterozoic to Mesozoic
This stage experienced a long geological history from Mesoproterozoic to Cretaceous (181400 million to 650 million years ago), and after many tectonic movements in pre-Caledonian, Hercynian, Indosinian and Yanshan periods, marine, continental sedimentary rocks, intrusive rocks, volcanic rocks and metamorphic rocks (including mixed rocks) were formed. Especially during the Yanshan Movement (208 million to 65 million years ago), the intense activity of fault structures led to the upward emplacement, ejection and metamorphism of molten magma in the deep crust, forming intrusive rocks, volcanic rocks and metamorphic rocks all over the city, which laid a broad material foundation for the formation of granite and ancient volcanic landforms and formed the basic structural framework in Shenzhen.
(2) Early Cenozoic evolution stage
This stage mainly refers to the Himalayan movement stage from Paleocene to early Pliocene (65 million years to12 million years ago), during which the eastern continental margin of China changed from Andes to island arc-marginal sea. Himalayan movement is a very obvious tectonic uplift and orogeny, which exposed all kinds of rocks and structural features before Yanshan period to the surface and suffered strong erosion, which made the two functions of tectonic uplift and erosion decrease for a long time, thus forming the embryonic form of Shenzhen geological and geomorphological outline. Wutongshan, Baguang Bijiashan and Qiniang Mountain volcanic rocks are the main structural belts in Northeast China, and Yanshanian granite and coastal mountains developed on this basis. In the east-west structural belt, the circular structure of Baimang granite with Yang Taishan as the center, and the Phoenix Mountain-Dayan Moutain arc mountain developed on this basis, have been exposed continuously through the tectonic uplift of Himalayan movement and the erosion of external forces, forming the basic distribution pattern of ancient volcanic landscape, granite landscape and coastal landscape in Shenzhen.
(3) Late Cenozoic evolution stage
This stage is a new tectonic movement stage since Pliocene (654.38 million +0.2 billion years to modern times). Intermittent and oscillatory uplift of neotectonics is the dominant internal force to form regional geological landscape, while weathering (including physical weathering, chemical weathering and biological weathering, etc. ), the mechanical erosion of running water and the erosion and accumulation of waves are important external forces to shape the landscape of geological relics. The interaction of these internal forces and external forces in the process of landform evolution forms a layered landform landscape developed from multi-stage platforms and terraces in this area. Wutongshan, Qiniang Mountain, Dayanding, Meishajian, Baguang Bijia Mountain and Paiya Mountain are the highest first-class landforms in eastern Shenzhen, while the mountains with an altitude of 460-530 m such as Yang Taishan are the highest first-class landforms in western Shenzhen. After their formation, they have been eroded beyond recognition for a long time, leaving only sporadic peaks and narrow ridges. However, the hills and mountains around it, as a four-dimensional continuum of landform evolution, have been in constant development and change since its formation. The old landform disappears and the new landform appears, which makes the formation and development of volcanic landform and granite landform landscape multi-stage, overlapping, inheritance and regeneration.
The second is the formation, development and evolution of various geological relic landscapes.
(A) the formation and evolution of ancient volcanic landforms
The ancient volcanic landform of Shenzhen was formed on the basis of volcanic rock series and volcanic mechanism from late Jurassic to early Cretaceous, after structural uplift and strong denudation of external forces since late Cenozoic.
1. Formation conditions of ancient volcanic landscape
Ancient volcanic landforms are different from other geological relics, and are basically formed when volcanic eruptions form various volcanic structures. The Mesozoic volcanic activity in Shenzhen is an integral part of the entire Pacific Rim volcanic activity zone, belonging to the Lianhuashan volcanic eruption zone in the Zhejiang, Fujian, Guangdong and eastern Guangdong volcanic activity zones. It began in the late Middle Jurassic, reached its peak in the late Jurassic, ended in the early Cretaceous, and migrated from northwest to southeast from morning till night. Eruption mainly occurred in Wu Tongshan-Hongkong New Territories volcanic eruption fault basin, Banzhangling-Baguang volcanic eruption basin and Qiniang Mountain volcanic eruption basin. First of all (probably in the late Middle Jurassic), a large number of volatile and high-viscosity neutral-intermediate-acid magma broke out in the northwest side of Shenzhen fault zone in the form of multiple craters (at a low altitude, about below 200m), and with the collapse of surrounding rocks, neutral-intermediate-acid volcanic rocks with various special granularity and various origins were formed. Due to the high concentration of magma, the channel is gradually blocked, and the volcanic dome appears in Wu Tongshan Basin. Volcanic activity can only erupt linearly along some areas of the fault zone, and the eruption activity begins to migrate to the southeast. In Bijiashan and Qiniang Mountain areas of Baguang, the compound lava overflow with stone bubble structure, flow structure, pore structure and spherulite structure and explosive volcanic material accumulation form primitive, low-level, multi-level, multi-site, different heights and isolated volcanic cones, and also form rhythmic layers of various causes. At this time, all the volcanic passages in Wu Tongshan Mountain were blocked, and the thick magma continued to rise and invade under the impetus of the lower magma, forming the city's first volcanic dome, which stood high in the Wu Tongshan volcanic basin, and the volcanic activity was the first to stop. There are pre-formed craters and volcanic domes on the dome. At the end of the late Jurassic, a volcanic dome was formed in Bijiashan area of Baguang, and volcanic activity stopped. There were volcanic cones and volcanic passages formed in advance on the dome. Volcanic activity continues to migrate to the southeast. In the early Early Cretaceous, only Qiniang Mountain volcanic eruption basin continued to move, and the erupting volcanic materials covered the ancient volcanic rock series with eruptive unconformity. At the end of the early Cretaceous, the volcanic passage was blocked by more viscous magma, and the magma lost its eruptive ability. It was pushed up and squeezed out of the original volcanic passage or side passage to form a volcanic dome (Qiniang Mountain Volcano Dome and Dayanding Volcano Dome), accompanied by the formation of an intrusive volcanic column (Dayanding Volcano Dome). So far, the ancient volcanic landforms in Shenzhen have been basically established.
2. Evolution and development process of ancient volcanic landscape.
In the stage of structural stability during the intermittent uplift of Late Cenozoic structure, the external force was mainly denudation and leveling, which was controlled by crater structure and eruptive lithofacies, and it was "repaired" into ancient crater and volcanic passage when the volcano erupted. During the intermittent uplift period of neotectonics, external forces are mainly erosion and cutting. Erosion cuts rapidly along the volcanic structure, which makes it "restore" into dome, cone and column landforms during volcanic eruption, and "restore" tall ancient volcanic domes, volcanic domes, ancient volcanic cones and ancient volcanic pillars (needles). Later, the neotectonic movement continued to uplift, so that the ancient volcanic dome, ancient crater, ancient volcanic dome, ancient volcanic cone and ancient volcanic column (needle) in the area were lifted to the present height.
(2) Formation and evolution of granite (mixed granite) landscape.
Through field observation, it is not difficult to find that the formation of spherical weathering micro-geomorphological landscape of granite (mixed granite) dominated by stone eggs can be divided into two stages: one is the weathering stage within a certain depth below the surface, that is, physical and chemical weathering first divides granite into spheres by using three groups of primary joint surfaces of granite, forming stone eggs "embryos". If buried underground for a long time, these "embryos" of stone eggs will be further weathered to form strong weathering. The second is the stage when the "embryo" of the stone egg is exposed and exposed, so that the earth-like inclusions on the surface of the "embryo" of the stone egg are washed up at this stage, and finally the stone egg is formed. Since the late Cenozoic, the intermittent uplift of new structures and the formation and disintegration of multi-level detachment planes not only created the necessary conditions for the formation of stone eggs "embryos", but also fully met the geological environment requirements for the formation of stone eggs, so the granite (mixed granite) micro-geomorphic landscape dominated by stone eggs developed in this area; Many granite (mixed granite) geological relic landscapes with important ornamental value are concentrated on the residual ridges or ridges of various stripping surfaces. For example, the high-grade granite geological heritage landscapes such as the main mountain landscape of Mount Yang, the landscape of Phoenix Mountain, the landscape of Apoji and the landscape of Meishajian, as well as the mixed granite, granite stone eggs and stone mushrooms of Jianfeng Mountain in Neilingding Island, all of which are located on the high mountains or ridges, have experienced hundreds of thousands to millions of years of development and evolution, and are very precious geological heritage resources.
(C) the formation and evolution of coastal landscape
The part of the transition zone between ocean and land affected by ocean dynamic action is called coastal zone, and the unique landform formed by coastal hydrodynamic action in coastal zone is called coastal landform. The evolution of the coast is influenced by many factors, including the original geomorphological characteristics of the coast, the lithologic and geological structural characteristics of the coast, and the characteristics of various external forces (waves, tides and currents) acting on the coast. In addition, the characteristics of non-wave factors such as rivers, climate and biology, as well as the changing characteristics of sea surface, also have an impact on coastal development. The formation of various coastal landforms is controlled by different functions. Since the Late Cenozoic, especially since the Quaternary, the differential activity of the NE-trending fault in Shenzhen has led to the subsidence (or detachment) of the NW-trending fault (or transform fault) on the southeast side of the fault, and seawater intruded into the subsidence zone, forming the coastal landforms of Daya Bay, Dapeng Peninsula and Dapeng Bay. The formation of Neilingding Island and its coastal landforms is closely related to the differential uplift of fault blocks.
1. Formation and evolution of marine landscape
The original barrier coast, a large amount of detrital materials brought into the sea by rivers and erosive materials of sea cliffs, were washed by waves and began to accumulate in the bay, forming the original beach, which can be divided into gravel beach, sandy beach and muddy beach according to different sediments. Then a sandbar is formed at the rear edge of the beach to separate the inland seawater from the offshore seawater (there is a tidal channel on one side as a channel for advancing and retreating tides), and a lagoon is formed at the rear edge of the sandbar.
2. Formation and evolution of marine erosion landscape
Under the erosion of waves, there are many types of marine erosion landforms on the rocky coast: first, waves and entrained stones erode the bottom of the rocky coast, forming grooves and caves (ocean caves); Furthermore, under the continuous action of waves, the cave collapses, and the rocks on it lose their support, and collapse under the action of gravity, forming a steep cliff, and a rockfill pile composed of collapsed boulders appears at the foot of the cliff; The sea waves continue to act, and the sea cliffs retreat, forming a platform inclined to the sea (sea erosion platform), and hard rocks remain on the platform, forming a sea erosion column; The sea waves are eroding the cave, and the upward jet compresses the air in the cave, expanding the cracks at the top of the cave, and finally penetrating the top of the cave, forming a connected vertical cave (sea eclipse skylight); Under the action of wave erosion, the sea caves on both sides of the headland are interconnected, forming a sea erosion arch bridge. Different rock types form different marine erosion landforms and landscape combinations under the action of waves;
1) The Lower Cretaceous Guancaohu Group is a set of non-marine red coarse-grained glutenite series, which often forms a combination of marine cliffs and platforms under the action of waves. A steep cliff was born with a platform slightly inclined to the sea, and sea caves are common at the rear edge of the platform. In this lithology, sea caves are rare, and sea pillars, sea arch bridges and sea skylights are basically invisible. The reason for this landform may be related to the compactness and weak weathering resistance of glutenite. The marine erosion landscape in Jiaotoujiao and the western corner of Dalajia Island is its typical representative.
2) Most Mesozoic granites and pre-Sinian mixed granites form coastal hills. Spherical weathered granite (mixed granite) is further eroded by sea waves, forming various marine caves and troughs, which are carved into various marine stone eggs and low marine pillars by the axe of nature. Both stone eggs and low sea pillars have traces of spherical weathering of granite, which is circular and develops very rapidly. Ren Xian Stone Ocean Landscape in Xinxu and Shidantan Ocean Landscape in the East Back Corner of Neilingding Island are the representatives of granite (mixed granite) ocean landscape.
3) There are various types of marine landforms formed by hard volcanic rocks and seasonal sandstone, including steep marine cliffs and platforms with gentle slopes facing the sea, as well as tall marine pillars, marine caves and their marine arch bridges and windows. Of the three marine arch bridges discovered, two are located in rhyolite, and 1 is located in timely sandstone. The reason for this landform may be related to the hardness and strong weathering resistance of rocks. The marine erosion landforms in Gaopai, Shuangpengzhou and the south of Dalajia Island can be represented.
4) Middle Devonian Dinghushan Group timely sandstone mixed with silty mudstone and argillaceous siltstone. This kind of soft and hard rock forms reef (sea pillar), which is the product of weathering, denudation and sea erosion. The pimple stone, moonstone and sawtooth stone near Xichong are typical of this landscape.
(D) The formation and evolution of waterscape structure
Since Miocene, the tectonic activities in Shenzhen have been quite frequent. Under the joint control of Shenzhen fault zone and NW-trending faults, fault mountains, fault cliffs, triangular surfaces and fault valleys extending in a straight line have formed in Pingshan area and Nanshan and Yangliugang areas.
After Cretaceous, with the intermittent rise of the earth's crust, the deep action of various streams was recognized and played a great role. In the process of crust rising and river deepening, canyons and river banks collapsed, resulting in waterfalls, boulders and rocks.
The rise of the earth's crust exposes many geological landscape resources.