(Anhui Geological Survey Institute, Hefei 23000 1)

This paper describes the division and correlation of Wutong Group strata from late Devonian to early Carboniferous in Tongling and Huangshan areas. The weathered exposed surface near the top of Wutong Group indicates that there was a sedimentary discontinuity at that time, with the Leigutai Formation below the discontinuity and the Chenjiabian Formation above it. According to the lithology, sedimentary structure and paleontological characteristics of Wutong Group, the division and correlation of Wutong Group are discussed.

Keywords: Wu Tong Group; Stratigraphic division; Variation characteristics; Tongling, Anhui; Mount Huangshan

Whether there is an early Early Carboniferous stratum at the top of Wutong Group in Tongling and Nanling areas of Anhui Province has long been controversial. The1:50,000 Tongling map shows that there is Gaolishan Formation, and the1:50,000 Daijiahui map is rich in plant fossils from the original "Gaolishan Formation", in which the genus Pteris belongs to the lower Yangtze region. According to the sporopollen fossils, Chen Hongming and Zhang Ying thought that the early Carboniferous Chenjiabian Formation (or Cishan Formation) was in contact with the late Devonian Leigutai Formation as a whole. In the regional geological survey of1:250,000' an Green Sheet, the author found weathered outcrops near the top of Wutong Group in Liu Jia section of Huangshan City, Anhui Province. Based on the study of paleontology, lithofacies and sequence stratigraphy on the profile, the late Devonian Guanshan Formation, Leigutai Formation and early Carboniferous Chenjiabian Formation are collectively called Wutong Group. The early Carboniferous Chenjiabian Formation in this area has great vertical and horizontal changes, which are obviously controlled by sea level change, paleogeography, paleoclimate and paleostructure.

Figure 1 Stratigraphic Profile of Late Devonian Leigutai Formation and Early Carboniferous Chenjiabian Formation in Liujiabei, Huangshan City

1 stratum profile

From top to bottom:

Compilation of geological survey results in East China: 1999~2005

Compilation of geological survey results in East China: 1999~2005

Compilation of geological survey results in East China: 1999~2005

2 Stratigraphic division and correlation

2. The strata from late Devonian to early Carboniferous in this area are terrigenous clastic deposits. By measuring stratigraphic section and collecting biological fossils, combined with lithologic and lithofacies characteristics, we should use the name of lithostratigraphic unit in Lithostratigraphy of Jiangsu Province and divide it into Guanshan Formation and Leigutai Formation. Combined with the regional survey data of 1: 50,000 and1:200,000 in Jiangsu and Anhui provinces, the lithostratigraphic units in the map have been re-divided or determined, so the meaning of the lithostratigraphic unit name has changed (table1).

Table 1 Wu Tong Formation Stratigraphic Division Evolution Table

2. 1 Guanshan Formation

Guanshan Formation originally belonged to the lower part of Wu Tong Formation (or Wu Tongqun) and was founded by Li Xingxue (1963) in Guanshan, Longtan, Nanjing, Jiangsu. This formation is widely distributed in northwest Zhangbei, dongzhi county-Mei Jie, Chizhou-Jingxian Langqiao, and is subordinate to Yangtze Stratigraphic Division.

The bottom is light gray, gray-white thick-layer timely conglomerate and fine-grained timely sandstone interbedded, and the rocks at the bottom are in reverse grain order, first in fine-grained timely sandstone, then gradually into gravelly quartz sandstone, and then into conglomerate with grain support and timely sandstone as gravel component; Up, it is grayish yellow and grayish white medium-thick timely sandstone with grayish white and grayish black thin layers of argillaceous siltstone and mudstone. The latter is mostly in the form of interlayer, and the timely sandstone has unidirectional oblique bedding. The argillaceous siltstone is mainly composed of plant fossils, and there are bivalves locally. A Plant Found in Guanshan Formation of Majia Section in Tongling City: Subbark Tree. , butterfly wing? Species tongue-shaped shellfish fossils. The total thickness is 150.5438+07m. ..

According to the fact that mudstone (shale) mainly contains plant fossils, which are mostly fragmented and well preserved, and sometimes marine brachiopod tongue-shaped shellfish and bivalve fossils appear, it shows that the main sedimentary environment in this area is river deposition, and seawater once infiltrated into this area at the maximum transgression surface, so the shale deposits containing marine brachiopod fossils are mainly delta plain-river deposits according to the characteristics of biological fossils and sedimentary structures.

The bottom boundary of this formation is in parallel unconformity contact with the underlying Fentou Formation, Maoshan Formation or Tangjiawu Formation in different areas.

2.2 Leigutai Formation

Leigutai Formation originally belonged to the upper part of Wu Tong Formation (or Wu Tongqun) and was discovered by Li Xingxue (1963) in Leigutai, Longtan, Nanjing, Jiangsu. This formation is widely distributed in northwest Zhangbei, dongzhi county-Mei Jie, Chizhou-Jingxian Langqiao, and is subordinate to Yangtze Stratigraphic Division. The lithology is gray-white seasonal sandstone mixed with gray-black thin-layer argillaceous siltstone and silty mudstone, and the top is root rock. The sandstone is one-way oblique bedding, and the argillaceous siltstone contains plants: Pteris Usyapidong, Pteris mirabilis, Pteris taihuensis, Pteris squamosa, and Brachiopoda: Pteris linguata.

1984, Li Hanmin et al. found plant fossils in the gray and gray-black quartzite sandstone and shale of the Dingleigutai Formation in Li Mao, Jin Lang Township, Tongling City: ancient fern in Dongling Mountain, ancient fern in central Fujian, ancient fern in variation, fern in tiger skin, fern in Ustilago, fern in lepidoptera, fern in Longtan and fern in tiger skin.

It can be seen from the above fossils that the plant fossils are mainly the standard fossil molecules of the Late Devonian, among which Archaeopteris, an ancient fern fossil, was first discovered in the lower Yangtze region, which is the standard fossil of the Late Devonian in the world, so the age of this group should be the Late Devonian.

According to the fact that mudstone (shale) mainly contains plant fossils, which are well preserved, and occasionally marine brachiopod tongue-shaped shellfish and bivalve fossils, it shows that the main sedimentary environment in this area is river deposition, and seawater has infiltrated into this area at the maximum transgression surface. Therefore, according to its biological fossils and sedimentary structure characteristics, shale deposits containing marine brachiopod fossils are mainly delta plain-river deposits.

The bottom boundary of this formation is in integral contact with the underlying Guanshan Formation.

2.3 Chenjiabian Formation

Chenjiabian Formation is a lithostratigraphic unit newly established by Yan (1986) in Stratigraphy of the Middle and Lower Reaches of the Yangtze River, which represents the early Early Carboniferous deposits in this area. Established in Chenjiabian, Jiangning, Jiangsu. Lithology is grayish white, yellowish green, khaki, grayish black, purple mudstone, siltstone and rotary rock, with a thickness of 9m, and brachiopods are produced at the top. It produced spore fossils and suspected provenances in the early Early Carboniferous. This formation was previously classified as the Leigutai Formation, and was later identified as the Early Carboniferous according to spore fossils, but it was separated and called the Chenjiabian Formation. Li Hanmin et al. (1987) called this horizon Cishan Formation, and the name of Chenjiabian Formation was established too early, so it was quoted. According to their overall contact with and merger with the underlying strata, some of them are collectively called Wu Tong Formation or Leigutai Formation.

This group is mainly distributed in northwest Zhangbei, dongzhi county-Mei Jie, Chizhou-Jingxian covered bridge. The total thickness of this formation is 6.08 ~13.76m, represented by the Liu Jia section of Huangshan City, and the lithology is black thin-layer carbonaceous shale, argillaceous siltstone, gray thin-medium thick-layer seasonal sandstone mixed with a small amount of siltstone, including suspected provenance: algae. Leiosphaeridia spp., reticulate algae. ，Cymatophora sp .； Mi Long nematodes, perimembranous nematodes, Elaeagnus mollis. ; Fossil spores: Knox spores (? )sp。 ，Leiotriletes labiatus，Punclatisporites debilis，Schopfites(？ ) claviger, leiotriletes-punclatisports spp. , holmium spore ore (? )miautus，Murospora dubitata，Foveosporites sp .，Aneurospora(？ )spinuliber，Cymbosporitesspp。 , Porphyra, Micromykia, Reticularia. Densitosporium. ，Crandispora(？ ) Cornus officinalis, Coccidium tricornutum, Retusotriletes sp., Acrospora Gannan, Macrosporium. , non-holospora. ，Aneurospora？ Species, Spinozonotriletes sp., Cristatisporites sp., non-holospora. ，Dictyotriletes？ Species, echinococcus? Species and plant fragments (? Trachea), plant vascular bundle fragments (ladder tracheid). From the above fossil age to the early Early Carboniferous, due to Schopfites (? ) claviger, Tumulisporatriangulata, etc. The appearance indicates that it should be inclined to the early Early Carboniferous. Suspicious class: Haematococcus glabratus. On the Danicun section of Tongling City, it is found that this formation intersects with the underlying stratum at a slight angle, and the upper layer is gray-white thin-layer timely sandstone interbedded with gray-white and gray-yellow thin-layer argillaceous siltstone, containing plant fossils: Usia Pidenwood and Pseudosassafras. The GUANLING section in Jingxian County is characterized by gray-white thin-layer timely sandstone and bluish-gray thin-layer argillaceous siltstone, with carbonaceous shale locally and sporopollen fossils in the lower part: Leiotriletes-Puntatispolities spp. Microreticular spores, see Microreticular spores.

This formation is obviously different from the underlying Leigutai Formation in lithology and lithofacies, while the upper Jinling Formation is bounded by carbonate deposits, so it is appropriate to call the clastic rock above the weathered surface of Leigutai Formation as Chenjiabian Formation (see table 1).

Generally speaking, the stratum thickness gradually becomes thinner from southeast to northwest. For example, the thickness of Guanling section in Jingxian County is 13.76m, that of Liu Jia section in Huangshan City is 7.48m, and that of Danicun section in Tongling City is 6.08m.

The basic sequence of Chenjiabian Formation in this area is mainly composed of fine-grained timely sandstone (or siltstone) and carbonaceous mudstone. The bottom and lower part of sandstone are abrupt and gradually change upwards, which represents estuary deposition.

Chenjiabian Formation in this area is equivalent to Laokan Formation along the coast of northern Jiangsu and Cishan Formation in Nanjing. The Laokan Formation in the coastal area is a lithostratigraphic unit newly established by Zhang et al. (1988) in the Sinian-Triassic biostratigraphy of the lower Yangtze Platform in Jiangsu Province. It was found in the drilling in the coastal area, Dafeng and Baoying, etc., and its lithology is gray-black, dark gray mudstone and siltstone. Guan's conodont, polycystic conodont, common conodont, etc. Wangyou Formation, produced in Shuhua, Changshun, Guizhou, is the main molecule of the Early Carboniferous. When the Regional Geological Survey Team of Anhui Bureau of Geology and Mineral Resources (1988) carried out the project of "Study on Carboniferous Lithofacies Paleogeography and Mineralization in Anhui Province", there were obvious spore fossils in the Dibolisposities-Aurora Spora Maera-Schonfites Claviger combination zone in the upper part of the former Wu Tong Formation in Jinjiashan, Chaohu and Longwangshan, Huaining. As far as lithology, lithofacies and horizon are concerned, the sediments on the weathered exposed surface and micro-angle unconformity surface in this area should be the same as those in the Dibolisposities distinotus-Aurorasporamaera-Schonfites claviger composite zone (containing spore fossils) in the upper part of the Leigutai section of the former Wu Tong Formation. , should be equivalent to the above Chenjiabian Formation, Laokan Formation and Cishan Formation. Chen Hongming and others discovered the LN band and VI-PC band of western European spores in Lijia, Tongling, which were equivalent to the late Late Devonian and early and middle Early Carboniferous respectively, which proved the existence of Chenjiabian Formation in this area. According to the above fossil data, the age of this group indicates that it should be Yan Guan in the early Early Carboniferous.

According to the contact relationship between the formation and the underlying strata, a weathered outcrop was found at the top of the original Wu Tong formation in Liu Jia section of Huangshan City, and root soil rocks were seen, so it was considered as parallel unconformity contact.

2.4 Early Carboniferous Wanghucun Formation and Early Carboniferous Jinling Formation

The early Carboniferous Wang Hu Village Formation is represented by Wang Hu Village in Xuancheng, and its lithology is gray and grayish yellow thin layers of timely fine sandstone, siltstone and shale, with a thickness of 6.89 meters. , Tolmatchoffia sp., shuck's bacteria. , Tomiproductus sp., Sabina Jinlin, Sabina Xuancheng, Sabina Deutschland. Wait. The Xujiatan section of Guichi is gray and grayish yellow thin-layer calcareous cemented timely siltstone with ash, and dark gray medium-thin silty micrite limestone with a thickness of 5.42 meters, including brachiopod Linoproductus sp. Schizoster. ,? Straight hook algae. ，Schuchertellasp。 In1:200,000 regional geological survey, et al. classified this formation in Guichi area as Hezhou Formation. According to brachiopod fossils, the 324 geological team finally determined that it was equivalent to the early Carboniferous Jinling Formation, which was called Jinling Formation. Now it is mainly clastic rock, so it should be called Wanghucun Formation. There is a scouring surface between this formation and the underlying Chenjiabian Formation.

In the past, it was thought that the southern Anhui area was dominated by clastic rocks, so it was called Wanghucun Formation. We have seen carbonate-dominated sediments in many places in southern Anhui, so it should be renamed Jinling Formation. This formation, represented by the Liu Jia section of Huangshan Mountain, is 7.52 meters thick, with gray-black thick microcrystalline limestone, sandy biological debris, gray-black thin calcareous seasonal sandstone and brachiopods. Li Chu. , Spirulina. Pustular disease. ，Fusellasp。 ; Cyclic algae ，Producyus kinlingensis Chu，Marginifera？ Species; Bivalves aviculopecten cf. plicatus (Sowerby); Michelini coral. ; The stems of sea lilies form an sp. ; Trilobites and other fossils. There is a scouring surface between this group and the underlying Chenjiabian Group, and the bottom is uneven, which is a parallel unconformity contact.

The horizons of Wanghucun Formation and Jinling Formation in the Early Carboniferous should be equivalent. The former is mainly distributed in Xuancheng and Guichi, representing a relatively shallow part of the basin, dominated by clastic rocks. The latter is mainly distributed in Huangshan and Jingxian, representing the relatively deep carbonate deposits in the basin. Brachiopod: Eocene strata appeared in the Wanghucun Formation and Jinling Formation in the Early Carboniferous, which proved that their age was quite early. It is found that Jinling Formation and Chenjiacun Formation are in transgressive parallel unconformity contact in Liu Jia, Huangshan.

3 Stratigraphic age

The Wutong Group in this area is mainly composed of clastic rocks, and plants were only found in biological fossils in the past. Through the investigation of Liu Jia section in Huangshan City, plants and bivalve fossils were found in Guanshan Formation in Liu Jia, Huangshan City. Plants found in Leigutai Formation: Hamatophytonvericilatum, H.cf.vericilatum, H.SP, Stigmaria rugulosa, CF. Sublepidoderon Wusihhense; Species containing suspicious substances: phosphorus bacteria. , Leiosphaeridia spp., reticulate algae. , cyclophosphamide Michaelis, cyclophosphamide around membrane, pterocarpus. ; Fossil spores: Retusotriletes sp. ，Raneurospora？ Species, Spinozonotriletes sp., Cristatisporitessp. , Anchorage. , echinochloa? Species; The Leigutai Formation contains plant fossils: Sublepidodendron wusihense, S.mirabile, S. sp., Pteris Taihu, S.? Species, LEPIDOPTERA worms; Brachiopod: Tongue-shaped animal.

According to the data of 1:50000 daijiahui map (1984), the leigutai formation in the top section of Li Mao, Tongling city contains a large number of plant fossils, such as sapwood, sapwood, protofern, Dryopteris squarrosa, Pteris squarrosa and so on. According to the data of Chen Huacheng et al. (1989), It is pointed out that Li Hanmin et al. found plant fossils in the gray and gray-black quartzite sandstone and shale of the Dingleigutai Formation in Li Mao, Jin Lang Township, Tongling City on 1984: ancient ferns, such as tonnglingiana, A.zhongmingiana, A.mutatoformis, A.CF. Sphenophilifolia, Sublepidodendron mirabilile、Eolepidodendron wusihense、lepidodendron

It can be seen from the above fossils that the Leigutai Formation is dominated by the standard fossil molecules of the Late Devonian, among which Archaeopteris, an ancient fern fossil, was first discovered in the lower Yangtze region, which is the standard fossil of the Late Devonian in the world. Widely distributed in Ireland, Scotland, Belgium, Germany, Norway, North America and Shpits, Gaspas, Esme Islands, and Zhongshan, Aihui, Heilongjiang, Chongyi, Du Yu, Longnan and other places in Guangdong.

4 several points of understanding

(1) Wutong Group in Tongling and Huangshan can be divided into three lithostratigraphic units, Guanshan Formation, Leigutai Formation and Chenjiabian Formation, according to their rock assemblage, contact relationship and paleontological fossils.

(2) There is a weathered exposed surface at the top of the former Wu Tong Formation in Liu Jia section of Huangshan City, and there are root rocks under the weathered denudation surface; On the Danicun section of Tongling City, it is found that the early Carboniferous Chenjiacun Formation intersects with the Leigutai Formation underlying the purple thick clastic conglomerate at a micro angle. It is proved that there should be parallel unconformity between the late Devonian Leigutai Formation and Chenjiabian Formation in Huangshan City and Tongling City.

(3) Affected by the early and late tectonic movements and weathering and erosion in Wu De, the strata between Tongling, Huangshan Wutong Group and Gaolishan Group are often exposed incompletely. In this work, a set of purplish red thick layered massive clastic conglomerate (equivalent to Devonian deposition) was found above the early Carboniferous Chenjiacun Formation or Leigutai Formation in Danicun, Jingxian Langqiao, Jingde Zhexi, Jingxian Guanling, Nanling Daihui and other places in Tongling City, reflecting that the early Carboniferous was in an environment of frequent uplift movement, and some early Carboniferous strata were completely eroded.

refer to

National stratigraphic committee. Description of Chronostratigraphy (Geological Age) Table of China Region. Beijing: Geological Publishing House, 2002.

Anhui bureau of geology and mineral resources. Regional geology of anhui province. Beijing: Geological Publishing House, 1989.

Jiangsu bureau of geology and mineral resources. Regional geology of Jiangsu and Shanghai. Beijing: Geological Publishing House, 1984.

Jiangxi bureau of geology and mineral resources. Regional geology of jiangxi province. Beijing: Geological Publishing House, 1984.

Jiangxi bureau of geology and mineral resources. Regional geology of jiangxi province. Beijing: Geological Publishing House, 1984.

Liu baojun Sedimentary petrology. Beijing: Geological Publishing House, 1980.

Liu Baojun, Xu, et al. Evolution of sedimentary crust and mineralization of ancient land in southern China. Beijing: Science Press, 1993.

Liu Baojun, Xu, et al. Lithofacies palaeogeographic atlas of southern China. Beijing: Science Press, 1994.

Liu Baojun, Zeng Yunfu. Lithofacies palaeogeography foundation and working method. Beijing: Geological Publishing House, 1985.

[10] Chen Huacheng, Wu Qiqie et al. Strata in the middle and lower reaches of the Yangtze River (Cambrian-Quaternary). Hefei: Anhui Science and Technology Press, 1989.

[1 1], Li, Tang Zairu. Carboniferous sedimentary geology and related minerals in the lower Yangtze basin. Nanjing Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences Supplement No.4, 1987.

[12], Wu Xianghe, Li, et al. Carboniferous lithofacies palaeogeography and mineralization in southern China. Beijing: Geological Publishing House, 1994.

[13] Meng Xianghua et al. Sedimentary basins and tectonic sequences. Beijing: Geological Publishing House, 1993.

[14] Wang Zengji, Hou, et al. China Strata (8) Carboniferous in China. Beijing: Geological Publishing House, 1990.

[15] Li Hanmin et al. Clastic rocks and their plant fossil ages under the dolomite section of Huanglong Formation of Middle Carboniferous in Tongling area, Anhui Province. Journal of Nanjing Institute of Geology and Mineral Resources,1984,5 (1).

Zhang Ying, Ying Zhonghua, Zhang Xiaodong, Liu Weihong. Early Strata of Yan Guan in Nanjing-Cishan Formation. Stratigraphy, 1987, 1 1(2).

Stratigraphic division and comparative study of Indus Group in Tongling-Huangshan area, Anhui Province

Wei Xu, Du Jianguo, Du Senguan, Sun Chengyun, Wang Yousheng

(Anhui Geological Survey Institute, Hefei 23000 1)

Abstract: The stratigraphic division, correlation and distribution of Wutong Group formed from late Devonian to early Carboniferous in Tongling-Huangshan area, Anhui Province are studied. This is a new discovery of weathering and outcropping at the top of the Indus Group, indicating that there is sedimentary discontinuity. According to lithology, sedimentary structure and paleontology, Wutong Group is divided into Guanshan Formation, Leigutai Formation and Chenjiabian Formation.

Keywords: Wu Tong Group; Stratigraphic division; Change personality; Tongling-Huangshan area in Anhui Province