This section is written by Yuan Baoyin, Xia Zhengkai, and Wei Qi. Yuan Baoyin, Institute of Geology and Geophysics, Chinese Academy of Sciences. Xia Zhengkai, School of Urban and Environmental Studies, Peking University. Wei Qi, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.
1. Biological fossils and burial characteristics of ancient human sites
Many mammal fossil sites and Paleolithic sites have been found in the Nihewan Basin. Their taphonomic characteristics are useful for studying early ancient humans. The living environment provides a wealth of practical materials. However, our country's taphonomic research is relatively weak. Only a few scholars have made some simple discussions on taphonomic issues when studying fossils and Paleolithic tools, and there is a lack of in-depth research. Therefore, this can only be briefly described here.
(1) Burial characteristics of paleontology
The paleontological fossils in Nihewan Basin have the following characteristics:
(1) No complete animal skeleton has been found. Even complete skulls and limb bones are rare. In most cases, the broken bones of animals of different species are buried together. The living environments of these animals are quite different.
(2) Mammalian fossils are mostly buried in lakeside gravel layers or riverside bed sand layers.
(3) Except for fish and plant fossils, few mammal fossils are found in the thin-bedded clay in the center of the lake.
(4) Mollusc fossils are mostly buried in black mud of swamp phase or floodplain phase.
The above taphonomic characteristics indicate that the mammal fossils in the Nihewan Basin are both buried in situ and buried in other places. The opposite example is the Salawusu River fauna. The fossils have many complete skeletons. Sometimes five or six woolly rhino fossil skeletons of different ages can be found in one excavation pit. The carnivorous fossils also have complete skeletons. This shows that when these animals go to the lake to drink water, they get stuck in the mud and cannot extricate themselves, and adults and juveniles can be seen buried together. The carnivores found the trapped animals and went to prey on them. As a result, they also became trapped in the mud and were destroyed. In the Nihewan Basin, the location where skeletons of the same individual animal are more concentrated is found in Maquangou, but not the complete skeleton. Elephant fossils were found here, buried in the lakeside clay layer. Many elephant footprints were found in the excavation pit, and the stratum was disturbed by elephant legs on the profile. Along with elephant fossils, there are various other mammals, and their fossils are mostly broken limb bones. Paleolithic tools can be found near the fossils. These burial phenomena indicate that although this is a lakeside clay deposit, elephants can walk on it and leave footprints. Therefore, no complete elephant fossil skeleton has been found trapped in the mud. Human activities here have not resulted in the tragedy of getting stuck in the mud. Therefore, it can be speculated that this is a drinking spot for animals and a good place for humans to hunt. Captured animals are dismembered on the spot and even eaten. Perhaps occasionally, ancient humans were able to capture weak or young large animals. Therefore, it is speculated that this is the site of ancient human activities, and the paleontological fossils can be classified as buried in situ.
Other mammal fossil sites are also completely composed of scattered skeletons of various animals, which are the remains of animals brought into the lake by rivers or sloping water. After they were rotten and fragmented, they were further transported and scattered irregularly over a large area, making it difficult to find intact individuals. The animal fossils found in ancient human sites are even more broken and scattered, and traces of manual chopping can also be found, indicating that these fossils are the remains of animals that were transported and eaten by humans. Therefore, it can be said that such mammal fossil sites are ex-situ burials.
Most of the mollusk fossils are complete clam shells, which have not been washed away. The sedimentary phases of the buried strata are consistent with the living conditions of the corresponding molluscs. They are buried in situ.
(2) Burial characteristics of ancient human sites
Many Paleolithic sites have been discovered in the Nihewan Basin, and they have the following characteristics:
(1) Paleolithic Early ruins were discovered in the lakeside area, and some were buried by lake gray-green sub-clay, reflecting the progress of the lake water.
(2) Late Paleolithic sites were discovered in terrace sedimentary facies. At that time, the lake had disappeared and ancient humans lived by the river. The hydrological environment was generally consistent with that of today.
(3) The stone flakes and cores of some Paleolithic sites can be put together, indicating that they were buried in situ.
(4) Paleolithic sites are accompanied by mammal fossils, which are broken and have signs of knocking or cutting.
(5) There are bedrock outcrops or river gravel near the site, which provided ancient humans with raw materials for making Paleolithic tools.
The above taphonomic characteristics indicate that most Paleolithic sites were buried in situ, which can reflect the living environment of ancient humans at that time.
Paleolithic sites are all located on lakeside or river terraces. Because they are close to water sources, not only is it convenient for ancient people to obtain water, but it is also a place where various animals drink or eat, making it convenient for ancient humans to hunt. The Donggutuo site, the Cenjiawan site, and the Xujiayao site were all obviously buried by later lacustrine sediments. Some of the Paleolithic tools in the sites can be pieced together, and some were found with many stone balls concentrated in them, indicating that they were basically not buried. Moved. Therefore, it is speculated that when ancient humans lived here, there was still a certain distance from the lake. It was relatively dry here. Later, the lake level rose and ancient humans had to move away. The Paleolithic tools and animal bones left behind were buried in the lake sediments. However, due to the shallow water of the lake and the limited carrying capacity of the lakeside waves, the Paleolithic artifacts basically stayed in place, with only a few showing signs of wear.
Micromark analysis of the Paleolithic tools discovered at the Xiaochangliang site shows that ancient humans used them mainly for meat processing, indicating that ancient humans may have adopted a "corpse-eating" lifestyle at that time. In addition, some paleolithic tools were found to have parallel scratches on their surfaces, and some had cracked surfaces. This shows that after the lake water rose, it was affected by waves for a short period of time, and some scratches or cracks appeared. But it was quickly buried by lacustrine sediments, so it should be of the type buried in situ.
A strip of ash can be observed in the excavation section of the Xujiayao site, and the bone fossils have no obvious directional arrangement. The mixed accumulation of stone balls, stone flakes and fossils shows that when the lake water rose, they were quickly buried without any disturbance, so there was no directional arrangement and sorting phenomenon, and they also have the characteristics of in-situ burial.
A large number of Paleolithic tools were found at the Cenjiawan site. Stone flakes and stone cores can be pieced together, indicating that this is a place where ancient humans lived and made stone tools. These Paleolithic tools were not transported when the lake flooded the site, which is also the original reason. Burial characteristics.
Based on the above analysis, the distribution patterns of paleontological fossil sites and Paleolithic sites in the Nihewan Basin can be summarized as follows:
(1) Distributed in lakeside or river terrace sediments.
(2) Areas close to bedrock outcrops or river gravel layers.
(3) Paleontological fossil sites and Paleolithic sites are mostly found in profiles where gullies have been eroded or steep cliffs have been formed on the edge of lake platform or residual hills.
When further searching for paleontological fossils or ancient human sites, full attention should be paid to the above distribution characteristics.
2. Analysis of ancient human living environment
As a special geomorphological unit formed by plate tectonic movements, the Nihewan Rift Basin has been in an open basin surrounded by mountains on both sides for a long time since the Neogene. in the landscape pattern. The ecological environment of the basin is controlled by two factors: tectonic movement and global climate change. From the Pliocene to the Middle Pleistocene, tectonic movements were active, and lakes existed in the basin for a long time. During this period, the environment of the Nihewan Rift Basin responded to the global climate and environmental change process with its unique landform conditions. The process of global climate change since the Pliocene has been studied in depth. The following takes the research results of the North Sea ice raft sedimentary facies and the Loess Plateau of my country as examples to summarize the history of global climate change since the Pliocene.
Research on global climate and environmental changes shows that the earth’s climate has cooled step by step since the early Eocene 50 MaB.P. in the Cenozoic. The main reasons are the changes in ocean current channels caused by plate movement, the uplift of the Tibetan Plateau and the reduction of atmospheric CO2. As the earth cools, ice caps develop at the poles, so changes in the content of ice raft debris in ocean cores should be an indicator of the earth's climate. The gamma ray logging curve of the ODP883 hole in the near-Arctic Pacific Ocean area of ??the Ocean Drilling Program (ODP) shows that ice raft debris suddenly increased starting from 2.75 Ma ago (de Monocal P, 1993), indicating that the global climate has undergone a sudden cooling process. (Figure 5-5).
Figure 5-5 The gamma ray logging curve of ODP883 hole in the near-Arctic Pacific Ocean indicates that ice raft debris deposition increased significantly 2.6 million years ago (according to de Menocal, 1993)
The Ocean Drilling Program (ODP) has conducted in-depth research on the δ18O records of deep-sea drilling cores. The research results of δ18O of ODP677 by Shackleton et al. are the most representative (Shackleton et al., 1990). The δ18O record of ODP677 is divided into 106 deep-sea oxygen isotope stages. The aeolian sedimentary profile (loess-paleosol series) of my country's Loess Plateau preserves complete Quaternary environmental information. Ding Zhongli et al. established the "Chinese Loess Grain Size Time Cycle" (Chiloparts) based on the particle size analysis results of five loess-palaeosoil sequence profiles on the Loess Plateau, and compared it with the deep-sea δ18O record (Figure 5-6). There are four high peaks of particles in Chiloparts. They are L2, which is equivalent to MIS6, with an age of 0.128-0.19Ma; L9 is equivalent to MIS22-24, with an age of 0.865-0.943Ma; L15 is compared with MIS38, with an age of 1.24-1.263Ma; L33 is MIS101-103 comparison, 2.547~2.59Ma. However, this special climate phase is not clearly reflected in the deep-sea oxygen isotope curves, and they may be caused by regional extreme climate events (Ding et al., 2002).
Figure 5-6 Comparison between the MIS stage and the Chiloparts climate curve (according to Gradstein et al., 2004; Ding et al., 2002)
In the context of global climate change , North China will definitely respond. The bottom of the Xifeng loess profile in the Loess Plateau is dominated by the loess layer, which ranges from 2. 5 Ma B. P. to 1. 909 Ma B. P.. The accumulation time of the loess layer is 0. 34 Ma, and the formation time of the paleosol layer is 0. 17 Ma. The former is The latter takes twice as long. In other words, roughly during the period from 2. 5 Ma B. P. to 2. 0 Ma B. P., the dry and cold climate was dominant, which should be a reflection of the expansion of the Arctic ice sheet in the Loess Plateau region. During the period from 2. 0 Ma B. P. to 0. 8 Ma B. P., the loess-palaeosol sequence experienced a period of time showing that the loess accumulation period was 0. 48 Ma, and the paleosol formation period was 0. 742 Ma, with the latter being 1 of the former. . 5 times. This shows that during this period, the dry and cold period was much less than the warm period, and the overall climate environment was much warmer and more suitable than that of 2. 5 ~ 2. 0 Ma B.P. (Ding et al., 1994).
According to the results of the Ocean Drilling Program and Chinese loess research, 2. 6 Ma B.P. was an important period of climate change. On May 21, 2009, the International Commission on Stratigraphy voted that the "Quaternary Period" is an era in the "New Table of Geological Time and Stratigraphy", with its lower limit being 2. 6 Ma B.P.. This voting result appropriately reflects the above research results ( Yang Xiaoping, 2009). The Nihewan Rift Basin exposes continuous sedimentary sections from 2. 6 Ma B.P. to the present. Based on the results of mammalian fossil and magnetostratigraphic studies of these sections, combined with the records of MIS and Chiloparts, it can be divided into five stages: Early Early Pleistocene (2. 6 ~ 2. 0 Ma B. P. ), middle and late Early Pleistocene (2. 0 ~ 0. 8 Ma B. P. ), middle Pleistocene (0. 8 ~ 0. 128 Ma B. P. ), late Pleistocene (0. 128 ~ 0. 011 Ma B. P.), Holocene (0. 011 Ma B. P. to the present).
The following is a discussion of the living environment of ancient humans at that time based on the ecological characteristics reflected in lithology, lithofacies, vertebrate and invertebrate fossils.
(1) Early Early Pleistocene (2. 6 ~ 2. 0 Ma B. P.)
Currently, magnetostratigraphic studies believe that the Hongyanangou section is the only one at the bottom of the strata in the study area A section that reaches the M/G boundary (Zhu Rixiang et al., 2007). In 1983, Zhou Kunshu et al. collected samples at the bottom of this section at an altitude of 835 to 865 m. The results of pollen analysis found that coniferous forest belts from fir, spruce, pine, etc. were recorded here. It evolved into a grassland belt of Artemisia and Chenopodium, and then evolved into a coniferous forest belt of pine, spruce and fir (Zhou Kunshu et al., 1983). It represents a period of relatively dry and cold climate, and its occurrence period is roughly between 2. 6 and 2. 0 Ma B.P. (see Figure 3-10). The climate characteristics shown by the expansion of the Arctic ice sheet and the loess-paleosol sequence in the Loess Plateau in the early Early Pleistocene are quite consistent with this (de MonocalP, 1993; Ding et al., 1994). At present, no mammal group with clear dating results has been found in the Nihewan Basin during this period, which may reflect that the climate at that time was not suitable for the survival of most animals in the Nihewan fauna. Hipparion sp. and Chilotherium sp. found in the Hongyanangou section should be remnants of the Pliocene Epoch, representing a few remnants of the climate transition period that lasted until that time.
Huang Zhenguo et al. drew a distribution map of natural zones in the early Early Pleistocene based on the research results of red weathering crust in China. The Nihewan Basin is located at the junction of temperate and cold temperate zones, while in the Pliocene it was a warm temperate and northern zone. Subtropical zone (Huang Zhenguo et al., 1996). The climate cooling at the beginning of the Early Pleistocene has obtained relatively consistent results in the study of red weathering crust in China and the pollen analysis of the Nihe Bay layer.
(2) Middle and late Early Pleistocene (2. 0 ~ 0. 8 Ma B. P.)
Recent magnetostratigraphic research results show that except for the Nihewan layer, only the Hongya section reaches In addition to Gaussian positive polarity time, it was also found that the bottoms of the Huabaogou, Maquangou and Xiaochangliang sections were only exposed to the Olduvai event. Therefore, the strata below the B/M boundary in most sections of the Nihewan Formation belong to the deposition of this period. Huabaogou Fauna, Dongyaozitou Fauna, Nihewan Fauna (narrow sense), Danangou Fauna, Maquangou Fauna, Xiaochangliang Fauna, Donggutuo Fauna, etc. all live here. The paleontology and ancient human sites of this period were also mainly discovered in this period.
The middle and late Early Pleistocene was a period of relatively intense tectonic activity in the Nihewan Rift Basin. Volcanoes at the edge of the basin erupted along the faults, and the basin subsided rapidly. This was the stage with the largest lake area. During this period, aeolian loess was widely accumulated on the Loess Plateau (Figure 5-7). The Nihewan Basin is located on the eastern edge of the Loess Plateau and also receives a certain amount of wind-induced loess accumulation. Volcanic ash and loess settled in the lakeside area, bringing rich mineral nutrients to the soil. The lakeside and lake surrounding areas were lush with vegetation and various animals were active here. Therefore, this was the period of highest biodiversity in the Nihewan Basin. According to the analysis of the fossil composition of the vertebrate fauna of this period, rodents, lagomorphs, perissodactyls and artiodactyls were the main species, reflecting temperate arid grassland and forest steppe environments.
Figure 5-7 Paleoenvironmental restoration map of the Nihewan Basin in the middle and late Early Pleistocene
A more detailed pollen analysis has been conducted on the Daupao section of the Nihewan Basin (Yuan Baoyin et al., 1996) (Figure 3-13), based on comparison with current magnetostratigraphic research results, it may be that when the bottom only reaches Olduvai subpolar, then the I and II zones drawn by the pollen analysis of this section should be roughly equivalent to 2.0 ~0.8 Ma B.P. Zone Ⅰ is dominated by broad-leaved plants, including some typical subtropical plants, such as Liquidambar, Sapindaceae, Hymenoptera, and Hylophylla. Tree pollen mainly includes pine, oak, chestnut, castanopsis, beech, etc. Gramineae pollen is very abundant, which mainly reflects the subtropical climate environment. The vegetation is dominated by evergreen broad-leaved forest.
The number and species of pollen in zone II are relatively abundant, but the pollen representing the subtropical zone has disappeared. Temperate broad-leaved trees such as elm, birch, and oak are very common, and the pollen of pine, fir, and spruce has increased. Artemisia, ephedra, etc. account for a considerable proportion, and grasses have decreased, showing mild temperate climate conditions. The above results of palynological analysis are consistent with the climate characteristics of the loess-palaeosol sequence from 2. 0 to 0. 8 Ma B.P. During this period, both the MIS curve and the Chilop-arts curve were relatively stable, reflecting that the climate change was relatively small. However, when the climate transitioned to a hot and humid direction, the area could still be in a subtropical environment, so shrews and Rhinoceros meloides were found in some animal groups. and other southern species. Most of the members of the fauna during this period lived in temperate areas, but the Nama elephants and the Mei's rhinos were animals that lived in the tropics and subtropics. Their appearance in the Nihewan area shows that in some periods, the climate conditions in the Nihewan Basin were better. Close to subtropical climate environment, or they can swim back here in summer.
The distribution map of natural zones in the middle and late Early Pleistocene, drawn based on the results of Chinese weathering crust research, shows that the northern limit of the subtropical zone can reach about 41°N in North China (Huang Zhenguo et al., 1996). However, the vertebrate fossils in the Nihewan Basin reflect the temperate grassland environment, and there are obvious differences in the conclusions between the two research fields. The formation of red weathering crust requires a warm and humid environment. When global climate change shifts to a humid and hot direction, North China can be in a subtropical environment and develop red weathering crust. When the climate changes to a dry and cold direction, North China is in an arid grassland environment, and the red weathering crust stops developing. However, the development of weathering crust is irreversible. When the climate becomes warm and humid again, it will continue to develop on the basis of the original red weathering crust. The remaining red weathering crust may be the product of the superposition of multiple climate cycles, thus indicating a subtropical natural zone. feature. Vertebrate animals can migrate repeatedly during climate changes, and their fossil records reflect the climate environment when these animals lived here. Therefore, the research conclusions in the two fields are not contradictory, and can complement and confirm each other.
It should be mentioned in particular that steppe mammoth (Mammuthus trogontherii) fossils have been found in the Nihewan Fauna (narrow sense) and the Maquangou Fauna, and are the earliest places where this species appeared. Therefore, it is speculated that the evolution from southern elephants (Mam-muthus meridianalis) to steppe mammoths was completed in the Nihewan Basin, and then they radiated around and completed the evolution to true mammoths in Siberia (Wei Guangbiao, 2008) . The reason why the steppe mammoth was able to complete its species evolution here is because the Nihewan Basin maintained a stable and suitable environment over a long geological period, allowing the species enough time to complete the peripatric speciation process. By analogy, the early ancient humans living in the Nihewan Basin during this period should also have suitable conditions and enough time to complete the evolution to Homo sapiens. This is an area that should be studied in depth in the Nihewan Basin.
(3) Middle Pleistocene (0. 8 ~ 0. 128 Ma B. P.)
The study of δ18O records in the core of ODP806 station discovered the "Mid Pleistocene Revolution" event (MRP) . Before 0.9 MaB.P., the change range of the measured curve of δ18O record was smaller than the theoretical calculation value. After that, the change range of the two was basically the same. Since the Quaternary δ18O curve mainly reflects the size of the global ice sheet, it is judged that the MRP caused an increase in global ice volume of approximately 15% (Berger et al., 1993). This important event of global change is clearly reflected in my country's Loess Plateau. From 1. 60 to 0. 8 Ma B. P., the climate change cycle was mainly 41 ka; from 0. 8 Ma B. P. to the present, the climate change cycle is mainly 100 ka. During this period, the loess accumulation period was 0. 45 Ma, and the paleosol formation period was 0. 34 Ma (Ding et al., 1994), indicating that the climate became significantly cooler.
The above-mentioned changes in the loess-palaeosol sequence of the Loess Plateau before and after 0. 8 Ma B.P. should be a reflection of the "Mid-Pleistocene Revolution" in the Loess Plateau. In the upper section of the Nihewan Formation in the Nihewan Basin, the color is mainly yellow-green, so it is called the "Yellow Nihewan Formation". Xia Zhengkai discovered underwater loess in the Nihe Bay layer of this section. These lithological changes reflect that the climate is drier and colder than before.
In the Nihe Bay layer during the period of 0. 8 to 0. 128 Ma, the mammal species were not as rich and diverse as in the previous stage, mainly including Sanggan River big-horned deer, woolly rhino, and horse. , reflecting an environment dominated by arid grasslands. In the sporopollen analysis of the Dapopo section by Yuan Baoyin et al., this section of the stratum was classified as sporopollen zone III, with Ulmus, Betula and Pinus being less common than in sporopollen zone II; Ephedra, Artemisia and other plants representing arid and colder climates The pollen increased dramatically, the Gramineae pollen decreased significantly, and the Typha and Cyperaceae pollen obviously disappeared, indicating that the climate was obviously developing in the direction of drought, and the pollen assemblage represented a semi-arid temperate climate environment (Yuan Baoyin et al., 1996). Huang Zhenguo et al.’s research results on red weathering crust also show that this area has a temperate climate, which is consistent with the above research results (Huang Zhenguo et al., 1996).
The period when early ancient humans were active in the Nihewan Basin is basically consistent with the era of the Nihewan fauna. Most of the animals in the Nihewan fauna may be their source of food. Ancient human sites Mammal fossils also prove this. Therefore, it can be said that when ancient humans thrived here, the climate environment was temperate. In some periods, subtropical animals could swim back here in summer. Early ancient human sites are all located in the lakeside area. It is speculated that ancient humans lived on the lakeside at that time, so this was also a place where animal activities were concentrated. However, no traces of the use of fire have been found so far, and it cannot be proven whether ancient humans knew how to use fire at that time. However, sporadic fish bone fossils have been found at some sites, and it is possible that they were able to fish.
Another important question is whether the Nihewan ancient lake had an outlet at that time. Was it a freshwater lake or a saltwater lake? Judging from the current results of ostracod research, during the period when early ancient humans lived here, the lake phase The ostracods in the sediment are all freshwater ostracods. Explain that the lake is fresh water. Foraminifera are occasionally found, but the species are single and the shells are strongly deformed, indicating that they were brought here by accident and are just surviving in their unsuitable freshwater environment. This cannot be used as evidence that the lake water is salt water.
Lakes in arid and semi-arid areas must have an outlet to maintain a freshwater environment for a long time. Therefore, it can be inferred that the Nihewan ancient lake had an outlet at that time. Xia Zhengkai and others studied the terraces of Shixia Canyon and found that the highest lake-formed terrace is the same height as Heshangping, and even higher lake-eroded terraces. The terraces at the same height as Heshangping continue to have their remains in Shixia Canyon. Therefore, it can be inferred that Gunihewan Lake has an outlet. At the bottom of the Nihe Bay layer, local gypsum layers of less than 1 cm can be found in individual places. They may be gypsum layers formed in small lakes separated by lower lake levels during drought periods in the lakeside area. No noticeable gypsum layer has been found in the sediments at the center of the lake. These features should be consistent with the lake having an outlet.
Zone III of the sporopollen analysis of the Daodaopo section is roughly 0. 8 to 0. 1 Ma B. P., and the sporopollen pattern shows a decrease in woody plants and an increase in herbaceous plants, with elm, birch, and pine pollen. decreased, while Ephedra and Artemisia increased, and Typha and Sedge pollen almost disappeared. The palynomorph assemblage characteristics indicate that the climate is developing in the direction of aridity, and generally represents the temperate climate of a semi-arid area. Except for the Xujiayao site, few ancient human sites from this stage have been found. The reason is probably that the environmental conditions are not suitable for ancient human life, or it may be that insufficient investigations have not found Paleolithic sites from this period.
(4) Late Pleistocene (0. 128 ~ 0. 01 Ma B. P.)
At the end of the middle Pleistocene and the beginning of the late Pleistocene, the eastern outlet of the Nihewan ancient lake Due to the influence of tectonic movement, the river became unblocked and the river cut down, causing the Nihewan ancient lake to disappear. The lacustrine sediments were eroded and flood deposits accumulated on them. Aeolian loess (Malan loess) accumulated on the lake platform. Although the Nihewan ancient lake was replaced by the Sanggan River, the Sanggan River still provided the necessary water source conditions for ancient humans.
There are many Late Paleolithic sites in the Nihewan Basin. By this time, the main body of the lake had disappeared, and most of the sites were found in terrace sediments. The mammal fossils found in the site are mainly woolly rhinos, wild horses, etc. There are no fossils of forest and steppe animals, reflecting the arid steppe and desert steppe environments. Pollen analysis shows that the number of pollen has been greatly reduced. Among the woody plants, coniferous trees are dominant, Artemisia and Ephedra are more common, representing a drier and colder temperate climate than the previous stage. However, ancient human activities increased during this period, which shows that the production level of the ancient humans who migrated here at that time has been greatly improved, and their ability to withstand harsh natural conditions has been greatly enhanced. The natural conditions during the life of ancient humans were generally similar to those today, except that humans' ability and scope to utilize and transform nature was very small. The Sanggan River became an important water source and hunting area for ancient humans.
(5) Holocene (11. 5 ka B. P. to the present)
The climate became warmer in the early Holocene, but the cold and arid environment of the last glacial period has not yet completely escaped. Most of the vertebrate fossils at the Hutouliang site are rodents, lagomorphs, odd-dactyls, artiodactyls, etc. However, the fossils of Palae-oloxodon namadicus can be seen, indicating that animals from subtropical areas can migrate back here.
In the middle of the Holocene, the climate in the Nihewan Basin was suitable. Warm-loving animals such as Indian elephants and primitive cattle lived here. There were also birds suitable for living by the water. Most of the mollusk fossils were Species living south of the Yangtze River. This shows that the ecological environment during this period was similar to that of South China today. In the late Holocene, the climate turned dry and cold, reaching the present arid grassland and shrub steppe environment.
To sum up, the climate environment of the Quaternary period in the Nihewan Rift Basin was controlled by two important factors. First, tectonic movements made this area part of the Fenwei Rift System. Second, During the Quaternary Period, neotectonic movements were active and lakes existed for a long time. The other is the process of global climate change. Under the geomorphological and hydrological conditions of the rift basin in this region, every stage of global change and every climate event responds. Together with tectonic movements, they control the first phase of this region. environment of the fourth century. Among them, the middle and late Early Pleistocene (2. 0 ~ 0. 8 Ma B. P.) is the most critical. During this period, the global climate was relatively stable and no major climate events occurred. This area is dominated by arid grassland and forest steppe environments, and a subtropical climate can occur during the warm and humid climate phase. The lakeside area of ??Nihewan Ancient Lake has strong ecological diversity and is suitable for various herbivores and rodents. Early ancient humans could obtain enough food in the Nihewan Basin and were able to thrive here. In particular, such ecological conditions have existed for a long time, allowing ancient humans to maintain long-term evolution here and continue to develop into Homo sapiens who are more adaptable to the environment. Therefore, the Nihewan Rift Basin can be called the base or evolutionary laboratory for ancient human evolution in East Asia. Later ancient humans in East Asia may be related to the early ancient humans in the Nihewan Rift Basin. This is an important topic worthy of in-depth study in the future.
In short, the Nihewan Basin experienced 5 environmental stages during the Quaternary period:
(1) 2. 5 ~ 2. 0 Ma B. P., "Nangou Cold Period" , no traces of ancient human activities have been found.
(2) 2. 0 ~ 0. 8 Ma B. P., mainly in a mild temperate environment, sometimes in a subtropical environment for a short period of time, with lush vegetation and diverse animals, which was the main period of ancient human activities here . Their activities are concentrated in lakeside areas, which are freshwater.
(3)0. 8 ~ 0. 128 Ma B. P., an arid temperate environment, drier and cooler than the previous stage, but Maliang, Queergou, Wujialiang, and Xujiayao are still found Sites such as these illustrate the continuity of the survival and evolution of early ancient humans here.
(4)0. 128 ~ 0. 01 Ma B. P., the Nihewan ancient lake disappeared, the Sanggan River appeared, and the climate environment was drier and colder than the previous stage. However, the productivity level of ancient humans increased and they were widely active on both sides of the Sanggan River.
(5)0. 1 Ma B. P. Up to now, after experiencing the warm and humid stage in the middle of the Holocene, prehistoric civilization has further developed. After 3,000 years ago, the climate conditions were similar to today, but the productivity of ancient humans increased and they were able to withstand harsher environments, opening a new chapter in the development history of ancient humans in my country.