What is the Neogene Period?

The Neogene (English: Neogene, symbol N) refers to the second age of the Cenozoic (formerly called the post-neogene Tertiary, upper Tertiary ^[1] ). The overall appearance of the Neogene biosphere is closer to that of modern times, beginning 23 million years ago and continuing for 21.4 million years. It includes Miocene and Pliocene, and it is also one of the few periods in which large-scale glacial activities have occurred in the history of the earth. It is also an era of highly developed mammals and angiosperms. The emergence of humans is the most prominent event of this era. .

Neogene

Neogene is

Neogene change

In the Paleo-New Century, the Tengchong-Bango and Kuyake-Golmud uplift zones appeared in the Eocene. The West Kunlun uplift zone expanded to the east, the Qilian uplift zone widened, and the Songpan-Ganzi uplift zone shrank to the east. . During the Oligocene, the Gangdise and Himalayan belts were excavated, and the Kunlun-Algin-Qilian further uplifted, resulting in a macro-geomorphological pattern of the entire plateau with a mountain system in the periphery and a basin in the hinterland.

Neogene data

Neogene basalt magma

Observation and research on the primary corundum giant crystals of Neogene alkaline basalt in Changle Fangshan, Shandong found that there is a reaction edge between the corundum giant crystals and basalt. It can be seen that the corundum giant crystals of Neogene alkaline basalt are trapped crystals. Observed under the electronic probe, there are two types of reaction edges: the first type consists of a spinel belt and a titanomagnetite + melt zone, and the second type consists of a spinel belt and a feldspar + titanium magnetite zone. In the type 1 reaction edge, the spinel band is very narrow (<40 m), and the titanomagnetite + melt band is wide (100-120 m). Moreover, the composition of the spinel varies greatly, from close to corundum. From the side (inside) outward, Al2O3 gradually decreased, from 85.08% to 58.94%, and MgO and FeO gradually increased, from 5.14% to 14.82% and 8.08% to 28.24%, respectively. In the second type of reaction edge, the spinel belt is wide and stable (about 100 m); the feldspar + titanium magnetite belt is unstable, especially the titanium magnetite is not only narrow (<40 m), but also intermittently distributed; sharp The composition of the spar is relatively small, ranging from 59.25% to 62.82% for Al2O3, 12.34% to 13.50% for MgO, and 23.25% to 27.37% for FeO. This paper discusses the formation modes of the two types of reaction edges. It is considered that the duration of the reaction time between the corundum giant crystals and basalt magma is the main factor leading to the formation of the two types of reaction edges. Type 2 reaction edges are products of equilibrium or near equilibrium.

Based on the 1: 250000 geological mapping data completed in the plateau and adjacent areas in the past 7 years, a total of 92 Paleogene-Neogene residual basins in the Qinghai-Tibet Plateau and adjacent areas were divided. Basins with large sedimentary ranges and complete sequences are distributed around the plateau periphery and hinterland. In the south, north, and east margins of the plateau, many strike-slip basins are distributed along regional large fault zones. The Paleozoic-Eocene marine strata are only distributed in southern Tibet and Yecheng area, Xinjiang. The semi-deep sea-deep sea sediments in southern Tibet are distributed along the Jiangzi-Saga-Guoyala-Sangmai line. The seawater is shallow to the east and deep to the west, and the west is active, reflecting the time when the New Tethys Ocean closed from east to west. Crustal uplift first begins on the east side. The Late Cretaceous uplift area is mainly distributed in the northeast of the study area, and the overall landform pattern of the plateau is low in the northeast and southwest. The deep water is integrated with the sedimentary physical properties, benthic foraminifera, and isotopes of the ODP stations 1148, 1146, and 1143 in the South China Sea, and the evolution characteristics of deep water in the South China Sea since the Early Miocene. The results show that there are three lithologic units rich in reddish brown clay in the three periods of 21 to 17 Ma, 15 to 10 Ma, and 10 to 5 Ma. The increase in the red parameter indicates an increase in the dissolved oxygen content in the deep water of the South China Sea. The comparison found that the oxygenation of deep water in the first two stages was related to the enhancement of the Antarctic bottom water and the North Atlantic combined water, and the bottom water in the former South China Sea and the field were basically interconnected. After 10 Ma, the dissolved oxygen in the deep water of the South China Sea decreased, while the CaCO3 content between the 1148 station in the lower deep water and the 1146 station in the upper deep water increased, the aerobic benthic foraminifera decreased, and the benthic 13C was ~ The significant decrease in 10 Ma indicates that the deep waters of the South China Sea at that time were weakened by the control of deep ocean waters. It is speculated that after the South China Sea basin stopped expanding, the South China Sea gradually closed and caused the formation of local deep water. A large number of markers of benthic foraminifera in the bottom and deep waters of the Pacific began to appear around 6 Ma. The difference in CaCO3 content between 1148 and 1146 stations during the period of 5 to 3 Ma reached 40%, marking the largest difference in deep waters of the South China Sea period. In addition to the effects of global climate cooling and northern hemisphere icing, which caused deeper water expansion in the Pacific Ocean, further sinking of the South China Sea basin due to a stronger eastward subduction may also be one of the reasons. The deep water evolution of the South China Sea has entered a modern model, and the difference in CaCO3 content between the two stations has stabilized at about 10%, and the abundance of anaerobic benthic species has increased.

The marker species of the bottom and deep waters of the Pacific have been greatly reduced at 1.2Ma and 0.9Ma, and the benthic 13C has also been significantly lightened to the lowest value of the Neogene, indicating that the impact of the bottom Pacific water has basically disappeared, and the impact of the deep Pacific water Greatly weakened. Therefore, it is speculated that the deep waters of the South China Sea in the standard modern model began to form mainly because the sea threshold below the Bus Channel during the "Middle Pleistocene Climate Transition" rose to a depth of nearly 2600 m.