(1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing10037; 2. Chinese Academy of Geological Sciences, Beijing 100037) 1 sarawusu acid stage name and its origin.

Salawusuan stage was put forward by the Quaternary Working Group of the Second National Stratigraphic Committee during the working meeting of the Ming Tombs Dating Working Group held by the National Stratigraphic Committee in February, 1999 (National Stratigraphic Committee, 200 1), and was officially listed in the China regional chronostratigraphic table in 2002. The order name comes from the lithostratigraphic unit "Salawusu Formation" with the same name. Salawusu Formation is named after Salawusu River (also known as Hongliu River) in Inner Mongolia. In the 1920s, E. Sang Zhihua and P. De Jinri first named a set of rivers and lakes exposed in the basin as the Salawusu River Formation, and its age was defined as the Late Pleistocene (table 1). 1959 The National Stratigraphic Committee was formally established, named as the Salawusu River Formation, and later renamed as the Salawusu Formation in 1964. The Salawusu Formation is famous at home and abroad for its "Ordos people" (or "Hetao people"), traces of human activities and rich mammalian fossils. It is the representative stratum of fluvial facies and lacustrine facies of Upper Pleistocene in northern China. In 1960s and 1980s, vertebrate paleontology Institute of China Academy of Sciences, together with the Institute of Paleoanthropology, the Institute of Geology and the Institute of Desert Research, conducted two large-scale excavations and investigations, and gained a deeper understanding of the Sarawusu Formation, which was divided into the Lower Sarawusu Formation (narrow sense) and the Upper Chengchuan Formation.

Table 1 salawusu formation stratigraphic division and comparative evolution table

2 salawusuan stage stratigraphic section position

Salawusuan stage is a hierarchical profile, located at the left bank of Salawusu River, 2km downstream of Milanggou Bay, Wudinghe Town, Uxin Banner, Inner Mongolia, and at the steep wall on the west side of Jiufangtai (Figure 1). Geographical coordinates: 37 46' N,108 33' E, highest altitude1283m. There are buses to Wudinghe Town from Yulin in northern Shaanxi, Jingbian in Inner Mongolia or Wushenqi.

In addition, predecessors have done a lot of work in the upper reaches of the stratigraphic section under construction, such as Dishaogou Bay, Fanjiagou Bay and Milanggou Bay, and established better stratigraphic sections. These profiles provide important information and data for the study of lithostratigraphy, biostratigraphy, chronostratigraphy and climate stratigraphy of Jiufangtai building hierarchy profile.

Figure 1 Location Map of Layered Section of Sarawusu River Basin

3 salawusuan stage stratigraphic profile description

The hierarchical profile of Jiuwu terrace consists of Quaternary loose sediments on the steep wall of Jiuwu terrace on the left bank of Salawusu River (Figure 2). The stratum continuity is good, with a total thickness of 61.61m. According to the color, lithology, structure and contact relationship with the underlying stratum, the section is divided into 32 layers from bottom to top (Figure 3). On the basis of 32 layers, according to the sedimentary cycle, lithofacies characteristics and dating data, it was merged into the Lishi Formation in the middle Pleistocene. Salawusu Formation in the lower part of Upper Pleistocene (narrow sense), Chengchuan Formation and Holocene Formation in the upper part of Upper Pleistocene.

Salawusu Formation is 32.77 meters thick and divided into 5 sections from bottom to top.

1 section: yellowish brown and grayish brown silty clay interbedded with grayish yellow and variegated clayey silty sand, with several layers of reddish brown thin paleosol and yellowish brown silty sand at the bottom. Contains mollusk fossils. The thickness11.11m is in integral contact with the reddish-brown paleosol layer at the top of the middle Pleistocene Lishi Formation.

Section 2: Loess soil, yellow silt layer, dense and massive, containing more calcareous nodules. 3 meters thick.

Member 3: yellow-brown clayey silty sand layer, mixed with fine sand and calcium flake layer, containing mollusk fossils, with freeze-thaw folds. 7.4 meters thick.

Member 4: yellow-brown medium-fine sand layer with horizontal bedding and cross bedding. It is 4.75 meters thick.

Paragraph 5: grayish brown and grayish green clayey silty sand layer, containing mollusk fossils. The bottom is muddy gravel, and the top is red-brown paleosol layer. 6.5 1 m thick.

Fig. 2 Geological landscape of Jiufangtai section of Salawusu River

In the above five sections, the yellow-brown sand layer at the bottom, the grayish-brown silty clay layer (or silt layer) at the bottom, the freeze-thaw fold layer in the middle and the brown paleosol layer at the top can all be used as marker layers.

Chengchuan Formation is 25.19m thick and divided into three sections from bottom to top.

1 section: grayish yellow silty sand mixed with grayish brown silty sand, with horizontal bedding and cross bedding, mixed with calcium lamellae. Near the bottom, it contains rhinoceros stone. The thickness is12.69m, and it is in erosive contact with the underlying stratum.

Section 2: grayish green and grayish yellow silty sand layer with horizontal bedding, with medium-fine sand layer at the bottom. Freeze-thaw folds are developed at the top and middle, containing mollusk fossils. 7. 19 meter thick.

The third section: the grayish yellow silty sand layer is sandwiched with grayish brown silty sand layer and calcium sheet layer, with horizontal bedding and cross bedding. 5.3 1 m thick.

Among the above three sections, two freeze-thaw fold layers containing mollusk fossils in the middle of the second section can be used as marker layers.

According to the analysis of sedimentary facies, the Salawusu Formation 1 member is dominated by lacustrine facies, and the bottom is yellow-brown sand layer, which represents ancient lacustrine sediments. Lacustrine sediments contain many layers of paleosol and mollusk fossils, indicating that the water body is shallow. The second stage is loess-like soil accumulation and lake disappearance. The third section is yellow-brown clay silt layer, which represents water inflow. The fourth section is a thick yellow medium-fine sand layer, which is deposited by river wind, and the lake is temporarily replaced by river wind deposition. The fifth stage is the deposited mud gravel layer and the gray-green clayey silty sand layer containing mollusk fossils, which means that the lake enters the development period again until the brown paleosol at the top develops and the Sarawusu Lake disappears again.

Aeolian sand and swamp facies deposits are developed in Chengchuan Formation 1 member. Large-scale high-angle plate cross bedding is the symbol of aeolian sand structure; Horizontal layered grayish brown silty clay strips are swamp facies deposits in the depressions between dunes. After the sediments at the top of the depression dry up, calcium flakes often develop. The sediments in the second member of Chengchuan Formation are coarse, reflecting abundant water, and have entered the stage of lake development. There are many molluscs in lakes and swamps, and the water body is not deep. The third member of Chengchuan Formation was replaced by aeolian sand and swamp facies deposits between sand dunes. It can be seen that the Salawusu Formation and the Chengchuan Formation experienced four obvious water body expansions and four obvious aeolian sand attacks.

4 Determination of the bottom boundary of salawusuan stage

The bottom boundary of salawusuan stage is located at the bottom of the third member (narrow sense) of Salawusu Formation in Jiufangtai section, and its symbol is:

4. 1 Lithology and sedimentary facies

The bottom of salawusuan stage is yellowish brown silty sand and clayey silty sand, which has obvious freeze-thaw folds and contains many mollusk fossils, belonging to lake and swamp facies deposits. Among them, freeze-thaw folds are widely distributed in the Salawusu River basin, which is an obvious marker layer.

Comprehensive histogram of Salawusu stratigraphic section in Salawusu River basin, Inner Mongolia.

4.2 isotopic age

According to the data of Li Baosheng et al, the age of the top of the freeze-thaw fold layer at the bottom of salawusuan stage is (148000 12500) a (TL). Therefore, it is estimated that its lower bound age is about 0. 15Ma, which is slightly older than the upper bound age of Pleistocene (128000 a).

4.3 Paleovertebrate fossils and cultural relics

The representative vertebrate fossils found above the lower boundary of salawusuan stage include Homo sapiens (Ordos), Sinomegac-eros ordosianus (Hetao China Bighorn Deer), Bubalus wansjocki (King Buffalo), paleoloxodonnaumanni(Noctus Elephant) and so on. According to the data, from 1922 to 1923, the "Hetao people" and "Hetao culture" layers were first discovered in the sand layer 10 meter away from the river surface in Shaojiagou Bay. 1978 ~ 1979, Dong Guangrong and others discovered Hetao human jaws and molars in the primary stratum, which are located in the lower part of the Sarawusu Formation, more than 0/0 meters away from the riverbed/kloc-0. In addition, a large number of small paleolithic tools were found in the silty clay and silty sand layer of Salawusu Formation in Fanjiagouwan section.

It can be seen that these ancient human fossils and cultural relics, as well as vertebrate fossils such as China Bighorn Deer and King Buffalo in Hetao, can be used as paleontological indicators of the lower bound of salawusuan stage.

4.4 Sporopollen characteristics

Sporopollen analysis shows that the third member of Salawusu Formation in Jiufangtai section, that is, the bottom of salawusuan stage, is poor in sporopollen. There are a few Pinus, Artemisia and Chenopodiaceae)； at the bottom; There are a few Betula and Quercus)； in the middle. There are more spores in the upper part. Reflect the change of climate from cool and dry to warm and humid.

4.5 Characteristics of Ostracoda Fossils

Ostracoda fossil analysis shows that the third member of Salawusu Formation in Jiufangtai section contains a small amount of white blood cells. Belonging to lake and swamp sedimentary environment.

In a word, the bottom boundary of salawusuan stage is lacustrine facies, containing mammal fossils such as Homo sapiens, China Bighorn Deer, Norfolk Elephant, King Buffalo, etc., with poor sporopollen and a small number of plump white-flowered ostracods as the bottom boundary symbol.

Five-level biostratigraphic sequence in unit stratotype and its characteristics description

5. 1 mammalian fossils

Up to now, in Shaojiagou Bay, Yangshugou Bay, Dishaogou Bay, Fanjiagou Bay and Jiufangtai in this area, in addition to human fossils, 34 species of salawusuan stage mammal fossils have been found, including birds 1 1 species (Table 2).

Among them, there are 8 extinct species, including Gu Long, ultimate crocodile, camel bird, spotted back dragon, spiro plug, Chinese monitor lizard, buffalo, primitive cow and so on. Palae-oloxodon naumanni, Spirocerus kiakhtensis, Sinomegaceros ordosianus and Bos primigenius are only found in the Salawusu formation in the lower part of salawusuan stage.

5.2 Sporopollen assemblage characteristics

The bottom-up sporopollen assemblage has the following characteristics:

(1) salawusu formation 1 profile

Below: The pollen content is low, but there are many spores, and the climate is warm and humid.

Central China: Sporopollen is poor, with only a few Pinus, Artemisia and Chenopodiaceae, and the climate is cool and dry.

Upper part: abundant sporopollen, with woody pollen accounting for 38.3% ~ 62. 1% and herbaceous pollen accounting for 37.9% ~ 6 1.7%. The pollen of woody plants is mainly Pinus, accounting for 37.3% ~ 57.6%, and there are a few Ulmus and Betula. Artemisia is the main herb pollen, accounting for 19.7% ~ 35.3%, followed by Chenopodiaceae. , reflecting the grassland vegetation landscape of coniferous forest and coniferous and broad-leaved mixed forest, with warm and humid climate.

Table 2 Sarawusu Fauna

(2) The second member of Salawusu Formation

Sporopollen is dominated by Pinus (37.3%) and Artemisia (53.3%), and the climate is cool and dry.

(3) The third member of Salawusu Formation (i.e. the lower part of salawusuan stage).

Lower part: Sporopollen is poor, with only a few plants of Pinus, Artemisia and Chenopodiaceae, and the climate is cool and dry.

Middle part: there are a small amount of birch, oak and so on. And there are more fungal spores in the upper part, reflecting the temperature and humidity in the middle and upper parts.

(4) The fourth paragraph of Salawusu Formation

Lower part: The sporopollen is dominated by Pinus (89.8%) and Artemisia (6.8%), and the climate is relatively warm and humid.

Upper part: poor sporopollen, cool and dry climate.

(5) The fifth paragraph of Salawusu Formation

Lower part: Sporopollen is poor, with only a few plants of Pinus, Artemisia and Chenopodiaceae, and the climate is cool and dry.

Upper part: The pollen is mainly Pinus (72.2%) and Abies (16.5%), and the climate is relatively warm and humid.

(6) Chengchuan Formation 1 section (starting from the upper part of salawusuan stage)

Sporopollen is poor, and only a few plants of Pinus, Artemisia and Chenopodiaceae are cold and dry.

(7) Second member of Chengchuan Formation

Sporopollen is abundant, and the woody pollen is mainly Pinus, accounting for 47% ~ 8 1%, followed by Picea (12% ~ 14%) and Abies (10% ~ 12%). There are also Quercus (7%) and Ulmus (3. 1%). Chenopodiaceae (accounting for 1 1% ~ 13%), Artemisia (accounting for 8%) is the main pollen, in addition to the aquatic herb pollen typhae and spores.

It reflects the vegetation landscape of coniferous and broad-leaved mixed forest grassland, and the climate is mainly warm and humid.

(8) Member 3 of Chengchuan Formation

Lower part: abundant sporopollen, with Pinus as the main woody pollen (accounting for 15% ~ 52%) and Artemisia as the main herbaceous pollen (accounting for 22% ~ 28%). In addition, there are aquatic herbs Typha (accounting for 10%) and so on. Reflect the vegetation landscape, climate temperature and humidity of coniferous forest grassland.

Upper part: poor sporopollen.

It can be seen from the above sporopollen combination that the grassland vegetation landscape in salawusuan stage is dominated by coniferous forests.

5.3 Characteristics of Ostracoda Combination

The characteristics of the bottom-up ostracod combination are:

(1) salawusu formation 1 profile

Below: As a lacustrine sedimentary environment, there are many leukocytosis and a small amount of Illicium.

No OSTRACODA fossils were found in the middle and upper parts.

(2) No ostracods were found in the second member of Salawusu Formation.

(3) In the third member of Salawusu Formation (i.e. entering the lower part of salawusuan stage), only a small amount of leucocyte-rare earth surplus was found in the freeze-thaw folded layer in the middle and lower part, which belongs to lake sedimentary environment.

(4) No ostracods were found in the fourth member of Salawusu Formation.

(5) Ostracoda fossils were not found in the middle and lower part of the fifth member of the Salawusu Formation, but there were many in the upper gray-green and gray-brown clayey silty sand layers.

Ostracoda rocks, such as Cyclocypris serena, Ilyocypris biplicata, Ilyocypris dunschanensis, Candoniella suzini, Candoniella albicius, etc. It belongs to the sedimentary environment of streams and lakes.

(6) No ostracods have been found in Chengchuan Formation 1 member (i.e. entering the upper part of salawusuan stage).

(7) There are many Candida albicans, litsea cubeba, northern Jiangsu carp, etc. In the freeze-thaw fold layer of the second member of Chengchuan Formation, limnetic algae were found in the yellow-brown sand layer above it. Reflect the sedimentary environment of lake and swamp facies.

(8) Cyprinidae. The swollen Eucheuma and leukocytosis were found in the lower part of the third member of Chengchuan Formation, which reflected the sedimentary environment of lakes and marshes.

In short, from the analysis of OSTRACODA species, most of them reflect the sedimentary environment of lakes, swamps or streams and ponds.

Isotopic chronostratigraphy and magnetostratigraphy

6. 1 end age of sarawusu acid stage

(1) Qi (1975), Zhou Kunshu (1982), Yuan Sixun (1983), etc. According to the age of Paleolithic cultural sites and the combination of vertebrate fossils and sporopollen, it is considered that the age of Salawusu Formation is not earlier than the middle of Late Pleistocene.

(2) Dong Guangrong and others (1983, 1986) think that the Salawusu Formation is equivalent to the Yumu-Reese interglacial period from 65,438 to 70,000 years ago, and the Chengchuan Formation is equivalent to the Yumu Ice Age from 70,000 to 65,438+020 years ago. 1998, Dong Guangrong and others further confirmed that the Salawusu Formation was formed in 140 ~70 ka and the Chengchuan Formation was formed in 70 ~ 10 ka, respectively, compared with the last interglacial period and the last glacial period.

(3) Li Baosheng et al. (200 1, 2004), according to the thermoluminescence dating of the Milanggouwan section, think that the age of the Salawusu Formation is 150 ~ 70ka, and that of the Chengchuan Formation is 70 ~ 150~70ka.

In 2004, the former was further determined to be 150000 ~ 75000 a, which can be compared with S 1 in the Loess Plateau and 5 stages of deep-sea oxygen isotopes. The latter is 75000 ~ 10000 a, which can be compared with L 1 on the Loess Plateau and 2 ~ 4 periods of deep-sea oxygen isotopes.

(4) Zheng (1989) determined the age of the lower section of Dishaogouwan section as (177 14) Ka (TL), and considered the age of Sarawusu fauna as 160 ~ 180 Ka.

(5) Sun (1996), age 136000a(TL), measured the stratum near the bottom of Dishaogouwan section.

(6) Fan et al. (2002) studied the rock magnetism of the Dishaogouwan section, and considered that the age of the Salawusu Formation was roughly 180 ~ 10ka.

(7) Jin et al. (2007) compared the section on the right bank of Shaogou Bay with other sections, and considered that the age of Salawusu Formation was 80 ~ 140 Ka, and that of Chengchuan Formation was 1 1.5 ~ 80 Ka.

(8) Min et al. (2007) measured the bottom boundary of Salawusu Formation in Jiufangtai section, and determined it as ≥ 130ka (measured by State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration).

The above massive age data show that there are two opinions on the age of the bottom boundary of the Salawusu Formation, namely 140 ~ 150 Ka and 180ka, due to different views on regional stratigraphic correlation, determination of bottom boundary markers and different dating methods. According to the dating data above 130ka, the sedimentation rate and the characteristics of multi-layered paleosol layers developed in the Salawusu Formation, and compared with the Milanggou Bay profile, the author prefers the age data of the latter. The bottom boundary of salawusuan stage should be at the bottom of the third member of Salawusu Formation in Jiufangtai section, and its age value is about 150ka.

6.2 Boundary between upper and lower parts of salawusuan stage.

According to the data of Li Baosheng (2004), the age of Chengchuan Formation is (75080 7400) a (TL). Min Longrui (2007) obtained the age ≥80ka(OSL) of the gray-green clayey silty sand layer below the surface. Therefore, it is inferred that the age of the upper and lower boundaries of salawusuan stage is about 75ka.

6.3 The top age of Sarawusuan stage.

According to Li Baosheng (2004), the age of the top of Chengchuan Formation (about 1.7m from the top boundary) is (1445867) a (TL). The age of the overlying Holocene bottom is (9880 900) a (TL). Therefore, the salawusuan stage zenith age is about 10 ~ 1 1ka.

7 Paleoclimatic characteristics

With the development of global change research and the deepening of regional climate change research, many scholars have discussed the climate evolution of the Salawusu Formation. Represented by Dong Guangrong and Li Baosheng, the Salawusu Formation is considered to be equivalent to the last interglacial period. Compared with the last glacial period, Chengchuan Formation can be divided into interglacial climatic periods. In recent years, Li Baosheng has done a lot of research on the percentage of chemical elements in Milanggouwan profile, and further compared Salawusu Formation with MlS5, Chengchuan Formation with MLS2-4. Zheng compared the lower part of Salawusu Formation with MlS6, representing a cold period, which can be compared with MlS5, representing a warm period. In a word, scholars have done a lot of research on the paleoclimate characteristics of Salawusu Formation and Chengchuan Formation, and achieved remarkable results. However, as mentioned in the discussion on the chronology framework of salawusuan stage above, the bottom age of salawusuan stage is still under study. Therefore, this paper only roughly discusses its evolution characteristics based on stratigraphic lithology, lithofacies and paleontological characteristics (Figure 2).

The climate of Salawusu Formation 1 section changed from cool to warm and humid, especially in the upper limnetic layer with several layers of reddish-brown paleosol, which contained mollusk fossils and a small amount of broad-leaved plant pollen, reflecting the warm and humid climate environment. The second stage is loess-like soil accumulation with cool and dry climate. However, paragraphs 1 and 2 have no time limit for entering the Sarawusan phase. The third member of Salawusu Formation began to enter the lower part of salawusuan stage, which is lake sedimentary facies, containing mollusks, a small number of broadleaf plants and a large number of vertebrate fossils, representing a warm and humid climate. However, the lake facies in the middle part experienced a cold climate event after deposition, which made it develop freeze-thaw folds. There are many calcium-containing plates in the upper part and the climate is dry. The fourth yellow medium-fine sand layer has a high content of woody plant Pinus in sporopollen and a humid climate. The fifth lacustrine deposit contains a large number of mollusk fossils, with a thick brown paleosol layer at the top, which is a sign of climate temperature and humidity.

In the upper part of salawusuan stage, Chengchuan Formation 1 section is a swamp facies deposit between aeolian sand and sand dunes, which reflects the cold and dry climate. In the second stage of lacustrine deposition, sediment particles can reach the medium-fine sand layer, including mollusk fossils that like temperature and humidity. The pollen of broadleaf plants and aquatic herbs in sporopollen reflects the warm and humid climate. In the second stage, there are two layers of freeze-thaw folds at the top and middle, indicating that the two layers of lacustrine deposits have experienced two periglacial cold climate events respectively. The paleoclimatic characteristics of the third member are basically similar to those of the 1 member, but the early sporopollen was moist.

In a word, according to the combined analysis results of lithology, lithofacies, paleontology and sporopollen in salawusuan stage, salawusuan stage has a warm and humid climate and a cool and dry climate alternately, and there have been two periglacial cold climate events.

8 contrast relationship

8. Comparison between1and deep-sea oxygen isotope curve

According to the study of chemical elements in Milanggou Bay profile in this area by Li Baosheng, the fifth member of Salawusu Formation (narrow sense) is compared with the fifth stage A, B, C, D and E of deep-sea oxygen isotope respectively. According to paleontological data, the third member of Chengchuan Formation is compared with the second to fourth stages of deep-sea oxygen isotopes.

8.2 Correlation with Late Pleistocene strata in North China

Salawusuan stage is a set of fluvial-lacustrine aeolian strata in North China, which is widely distributed and well contrasted. In the valleys of the Loess Plateau, it is often seen that the Salawusu Formation (in a narrow sense) is sandwiched between Malan loess and Lishi loess, such as Ganxian section; Salawusu Formation and Chengchuan Formation, such as Wanshuiquan and Houshuigou, are also found on the platform or terrace near Baotou at the southern foot of Daqing Mountain in Inner Mongolia. There are also sections that can be compared with Wayao in Dalat Banner, Zhaojun Tomb, Salawusu River Basin in Wangaizhao area, Tuoketuo Zhongtan area in the northeast of Hetao Basin, and Xilamulun River in Guangxingyuan, Inner Mongolia. In addition, the fossils of Dingcun people in Dingcun Formation of Fenhe River Basin in Shanxi Province are contemporaneous with or slightly earlier than those of Ordos people.

Thanks to Professor Li Baosheng from South China Normal University and Teacher Fan Jinshan from Wushenqi Cultural Relics Bureau in Inner Mongolia for providing us with a lot of materials and information in the process of studying the construction of salawusuan stage. I would like to express my heartfelt thanks here.

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