The Upper Carboniferous-Lower Permian (benxi formation, Taiyuan Formation and Shanxi Formation) is divided into three compound sequences: compound sequences I, II and III. These composite sequences are mainly formed in the coastal sedimentary environment far away from the clastic source area, and are obviously affected by sea level changes, with clear cyclicity, and the characteristics of fourth-order sequences and sequence groups are easy to identify, but the development degree of fourth-order sequences and sequence groups is different in different regions. Sequence ⅰ consists of transgressive sequence groups and high-level sequence groups, sequence ⅱ only develops high-level sequence groups in most areas, and sequence ⅲ mainly consists of transgressive sequence groups and high-level sequence groups except low-level sequence groups in some areas. Coal-bearing cyclic deposits in the epicontinental marine environment developed in the late Carboniferous benxi formation and Taiyuan formations in the study area, including peat swamp facies coal seam, subtidal limestone, lagoon facies aluminum mudstone and tidal flat sandstone.
(1) complex sequence Ⅰ
It mainly includes the lower strata of benxi formation and Taiyuan Formation, and some areas only include benxi formation, which is equivalent to the Late Carboniferous. The total thickness of compound sequence ⅰ is the smallest among the seven sequences, which is generally 50 ~ 120 m and can reach 140 m in some cases. This sequence is greatly influenced by the fluctuation of the antique surface at the bottom, so the thickness changes greatly. Generally speaking, the thickness decreases from northeast to southwest, and the stratum thickness is 60 ~ 140m in Tangshan and Tianjin, 70 ~ 90m in Cangzhou, Dacheng and Fucheng, and only 30 ~ 50m from the south of Fengfeng to Zibo and tengxian (Figure 3.24).
The thickness of limestone in this layer is mostly between 5 ~ 5 ~ 20m, and some areas (such as Well Konggu 4 and Well Tai 10) are about 35m. The thickness of limestone generally decreases from northeast to southwest, and the thickest zone is near Konggu 4 well. Judging from the number of limestone beds, there are 7 beds in Kailuan area of Tangshan, only 4 beds in the south of Shijiazhuang and only 2 beds in Fengfeng area in the southwest, indicating that transgression mainly comes from the northeast (Figure 3.25).
Coal and carbonaceous mudstone are generally formed in swamp environment, and their quantity indicates the development degree of swamp environment. According to the contour map of coal and carbonaceous mudstone, the thickness of coal seam and carbonaceous mudstone in sequence I in the study area is generally between 5 ~ 10m, mainly along the vicinity of Beidagang and Nangong and Julu, and the thickness of coal seam and carbonaceous mudstone is about 10m (Figure 3.26).
Sandstone in this sequence is undeveloped, but judging from the sandstone contour map, there are two sandstone-rich zones in this area, one is the northeast zone from Baodi to Bazhou in the northwest of Tianjin, and the other is the area from Beidagang to Dezhou in the south of Tianjin. The thickness of the two sandstone belts is between 10 ~ 15m, and sandstone is also enriched in the south of Puyang. For example, near Gu Qing 1 well, the thickness of sandstone is about 12m, and there is near 10m deposit in Yuanshi County (Figure 3.27).
The distribution of sand-mud ratio is similar to sandstone. On the contour map, the sand-mud ratio is above 0.6 in Bazhou-Wen 'an-Hejian area in the southwest of Tianjin and Beidagang area in the south of Tianjin. Although the thickness of Dezhou sandstone is relatively large, its sand-mud ratio is relatively low, which is basically less than 0.2 in the low-value area south of Dezhou-Julu-Nangong-Wudi line, and the sand-mud ratio in the north is between 0.2- 1. The highest sand-mud ratio reaches 1.2 in Yuanshi County, and can also be reached near Gu Qing 1 well in the southwest of the study area.
Based on the above single index, combined with the results of sand-mud ratio isoline map and sequence stratigraphy and sedimentary facies correlation map, the plane distribution of composite sequence I sedimentary system can be outlined. The two sand-mud ratios in Bazhou-Wen 'an-Hejian area and Beidagang area in the south of Tianjin represent two barrier bar facies areas, and the sand-mud ratio in Gu Qing 1 well area near Puyang in the southwest is also high, which should be a small barrier bar facies area at that time. The area east of Kailuan-Tianjin-Dezhou-Linqing-Puyang line is thick, which was the main sedimentary area of carbonate rocks at that time, so it is an offshore carbonate shelf facies area. To the west of this line is the lagoon tidal flat facies area. In a word, during the deposition of sequence I, the paleogeographic landscape of the study area was dominated by carbonate shelf and lagoon tidal flat, and tidal sand bars and barrier sand bars developed locally (Figure 3.29). From the perspective of the whole North China Basin, the seawater came from the northeast at that time, but in this area, the seawater came from the east.
(2) compound sequence II
Including the upper and middle Taiyuan Formation, equivalent to the early Early Permian. From the floor of 8 # coal seam under Daqing limestone to the bottom boundary of Shanxi Formation. It is equivalent to Zhaogezhuang Formation in Tangshan area in the north and the upper part of Xiayangjiatun coal measures in Xishan area in Beijing. The lithology of composite sequence II is mainly composed of coal seam, limestone, aluminum mudstone, siltstone and sandy mudstone. The sedimentary facies cycle structure is that peat swamp facies evolved upward into offshore carbonate shelf facies, barrier bar facies and lagoon swamp facies, which constituted several complete secondary transgression-regression sedimentary sequences.
The total thickness of complex sequence II strata is between 50-220m, and the areas with the thickness greater than 1 00m are mainly in Jingxi-Tianjin-Beidagang-Cangzhou area (230m in Konggu 4 well), Xingtai-Jize-Puyang area (1well reaching130m) and the area near the north of the Yellow River in the west of Jinan. Compared with the underlying compound sequence I, the thickness center of limestone in compound sequence II shifts from northeast to south. Although the subsidence center is still in the northeast, the sedimentation center has moved to the south, which may be caused by the seesaw movement of the structure at that time and the direction of transgression changed from northeast to southeast.
According to the limestone distribution map, the maximum thickness of limestone in composite sequence II is distributed in Jining-Puyang area in the south, with a thickness of 15 ~ 40m, Fengfeng mining area and Xingtai mining area with a thickness of 5 ~ 15~40m, and only in Kailuan-Tianjin Baodi area in the north with a thickness of10. It can be clearly seen that the transgression mainly came from the southwest at this time.
In the north, due to less chance of seawater flooding, post-barrier swamps and lagoon swamps are widely developed, forming thick coal seams and carbonaceous mudstone. In the study area, the thickness distribution characteristics of coal seams and carbonaceous mudstone in composite sequence II are as follows: Puyang-Jize-Nangong area, with the total thickness of coal seams ranging from 10 ~ 18m; the thickness of coal seams and carbonaceous mudstone in the south of Beidagang, Baxian and Wen 'an is relatively large, ranging from 10 ~ 30m; coal seams and carbonaceous mudstone in other areas. According to the number distribution of coal seams and carbonaceous mudstone layers, there are more layers in areas with large thickness of coal seams and carbonaceous mudstone in the north, and this feature also exists in Puyang area in the south, but Fengfeng mining area and Xingtai mining area have more layers although the total thickness is not large (Figure 3.33). This may have been deposited in the process of regression after many transgressions. Due to frequent transgression, the swamp did not develop for a long time, which led to the thinning of coal seam (Table 3.3).
Sandstones of compound sequence II are mainly concentrated in the north-central part, but not developed in the south when the thickness is large, and the lithology is mainly medium-fine sandstone. The thickness of Konggu 4- Guqi 1 well area in the south of Beidagang is 30 ~ 60m, which is the thickest area, followed by the east of Renqiu and the north of the Yellow River in the west of Jinan, reaching more than 45m, and the mining area in the north of Xingtai is between 15 ~ 30m. Therefore, on the ore body, there are three sandstone enrichment zones with a thickness greater than 30m, namely Renqiu-Dacheng-Beidagang area, Xingbei mining area and Huanghebei mining area west of Jinan (Figure 3.34).
From the calculation results of sand-mud ratio, the high-value area of sand-mud ratio does not coincide with the high-value area of sandstone, and only in Beidagang and the south of Xingbei mining area is the area with large sandstone thickness and high sand-mud ratio, while in Jingxi and Baodi, although the sandstone thickness is not large, the sand-mud ratio is relatively high, both above 5, and it increases from the west of Baodi Xiang Jing. The sand-mud ratio in the mining area on the north side of the Yellow River west of Jinan is only 0.4, and the thickness of sandstone in Nangong area is also small, but the sand-mud ratio is above 5 (Figure 3.35).
From the distribution of the above single parameter on the plane and the comparison results of sequence stratigraphy and sedimentary facies (Figure 3. 18 ~ Figure 3.2 1 and Figure 3.30 ~ Figure 3.35), we can basically get the distribution of main sedimentary systems during the deposition of composite sequence II. Baodi-Tianjin-Beidagang area is a delta sedimentary facies area (lower delta plain), Nangong-Julu area and Xingbei mining area (Baozicun area) are barrier sand bar facies areas, offshore carbonate shelf facies develops in the east and south of Shi-Heng-Cangzhou line, and lagoon facies develops in the north. In a word, the paleogeographic landscape in this area was dominated by offshore carbonate shelf and lagoon environment during the sedimentary period of sequence II, with barrier dams and delta environment locally developed (Figure 3.36). On a large scale, seawater had invaded the area from the southeast.
Fig. 3.24 Isothickness line of composite sequence I in western Bohai Bay.
Fig. 3.25 Isothickness lines of limestone in composite sequence I in western Bohai Bay.
Fig. 3.26 Isothickness lines of coal and carbonaceous mudstone in Carboniferous-Permian composite sequence I in western Bohai Bay.
Figure 3.27 Isogram of Carboniferous-Permian Composite Sequence I Sandstone Thickness in Western Bohai Bay Figure 3.27 Isogram of Composite Sequence I Sandstone Thickness in Western Bohai Bay
Figure 3.28 Isogram of Sand-Mudstone Ratio of Carboniferous-Permian Composite Sequence I in Western Bohai Bay Figure 3.28 Isogram of Sand-Mudstone Thickness Ratio of Composite Sequence I in Western Bohai Bay.
Fig. 3.29 Distribution Map of Sedimentary System of Compound Sequence Ⅰ (bottom of benxi formation and Taiyuan Formation).
Fig. 3.30 thickness contour map of Carboniferous-Permian composite sequence II in western Bohai Bay; Tu Tu 3.30 contour map of composite sequence II strata in western Bohai Bay.
Fig. 3.3 1 thickness contour map of carboniferous-Permian composite sequence II limestone in western Bohai bay; Tu Tu 3.3 1 contour map of composite sequence II limestone in western Bohai bay.
Table 3.3 Statistical Table of Limestone Thickness and Underlying Coal Seam Thickness in Sequence II (thickness unit: m) Table 3.3 Statistical Table of Limestone and Underlying Coal Seam Thickness in Compound Sequence II
Fig. 3.32 Contour map of Carboniferous-Permian composite sequence II coal seam+carbonaceous mudstone thickness in western Bohai Bay Fig. 3.32 Contour map of composite sequence II coal+carbonaceous mudstone thickness in western Bohai Bay.
Fig. 3.33 Isogram of Coal Seam+Carboniferous Mudstone in Compound Sequence Ⅱ in the western Bohai Bay.
Fig. 3.34 isopleth map of sandstone thickness of Carboniferous-Permian composite sequence II in western Bohai Bay.
Fig. 3.35 Isogram of Sand-Mudstone Ratio of Carboniferous-Permian Composite Sequence II in Western Bohai Bay 3.35 Isogram of Sand-Mudstone Thickness Ratio of Composite Sequence II in Western Bohai Bay.
Figure 3.36 Distribution Map of Sedimentary System of Compound Sequence Ⅱ (Main Body of Taiyuan Formation) Figure 3.36 Distribution Map of Sedimentary System of Compound Sequence Ⅱ
(3) compound sequence III
Including the strata corresponding to Shanxi Formation, equivalent to the late Early Permian. From the bottom boundary of Beichagou sandstone to the bottom boundary of camel neck sandstone of Xiashihezi Formation, it is equivalent to Damiaozhuang Formation in Tangshan area and Huangshenshan Formation in Xinglong area.
The lithology of compound sequence ⅲ is mainly medium-fine grained sandstone, siltstone, mudstone and coal seam, and conglomerate is developed in Jingxi area in the north. The stratum thickness varies from 40 ~ 180m, and the areas greater than 100m are mainly Jingxi, Baodi, Beidagang in the north and Huanghe River in the west of Jinan. The 50 ~ 100 m area is mainly in Dacheng, Cangzhou, Fucheng, Nangong, Julu and Jize. The thickness of Xingtai, Fengfeng and Lincheng is between 40 ~ 70 m, generally, the northern part becomes thinner from north to south, and the southern part becomes thicker from west to southeast (Figure 3.37).
Coal seams and carbonaceous mudstone are mainly distributed in Baodi, Kailuan, south of Beidagang, Wen 'an, Fucheng and other places, with a thickness of more than 30m, followed by Nangong and Jize areas in the south, with a thickness of 10 ~ 20m. There are 5 ~ 10~20m coal seams and carbonaceous mudstone in the southeast of Puyang, and only 5 ~ 0m in Xingbei mining area. Generally speaking, the distribution of coal seams and carbonaceous mudstone is relatively concentrated, with a trend of being thicker in the north and thinner in the south (Figure 3.38). From the perspective of floors, the number of floors in Wen 'an and Renqiu areas is more than 12, but in the south of Beidagang, where the thickness is the largest, the number of floors is less, with only 5-8 floors, showing an obvious merging trend, and the number of floors in the south is less than 5 (Figure 3.39).
Sandstones of compound sequence III are widely distributed, ranging from 15 to 55m. They are mainly distributed in Jingxi, Baodi, Dagang-Cangzhou-Fucheng, north of the Yellow River, Puyang and Jize, among which 1 well near Beidagang, 1 well near Zibo, Dezhou, Wen30 well in Wen 'an and Jize's residence/kloc. The sandstone thickness of the wells north of the Yellow River, Jushen 1 and Gu Qing 1 is between15 and 30m. In southern Cangzhou, Lincheng-Longyao area and Fengfeng mining area, the thickness of sandstone is less than 50m (Figure 3.40).
Judging from the sand-mud ratio, on the isoline map, the areas with sand-mud ratio greater than 1 in sequence III are distributed in two zones, one is the triangle zone of Jingxi-Tianjin Baodi-Beidagang, and the other is the east-west zone of Xingbei mining area-Fengfeng mining area-Jize-Jinan West Yellow River. The sand-mud ratio of the former is 1 ~ 7, and that of the latter is 65438. Other areas are less than 1, and the lowest area is in Cangzhou-Fucheng-Longyao area. It is consistent with the distribution characteristics of sandstone thickness and reflects several sandstone enrichment zones at that time (Figure 3.4438+0).
According to the above distribution characteristics of sandstone, coal seam and low sand-mud ratio, combined with the comparison results of sequence stratigraphy and sedimentary facies profile, the paleogeographic units of composite sequence III can be divided into upper delta plain, lower delta plain, intertidal bay and tidal flat. The upper delta plain is mainly distributed in Jingxi-Tianjin Baodi-Baxian area in the north, Jize-Fengfeng mining area-Xingbei mining area in the south, and Renqiu-Baoding-Wuji area. At that time, the delta was mainly distributed in Jingxi-Baxian area in the north and Handan-Fengfeng area in the south, probably located in the southeast of this area (Figure 3.42).
Paleogeographic characteristics of Middle Permian in 3.7.2.2 (Ⅳ, Ⅴ, ⅵ sequences)
At this stage (including the lower part of the Lower Shihezi Formation and the Upper Shihezi Formation), sequences ⅳ, ⅴ and ⅵ are developed, which are mainly river-type fourth-order sequences. Each fourth-order sequence begins with coarse gravel sandstone riverbed deposition with coarse grain size at the bottom, with river scouring surface at the bottom, and evolves upward into fine grain deposition in natural breakwater, crevasse fan, river flood and other sedimentary environments. Due to the great change of continental sedimentary environment, the lateral distribution of sedimentary sand bodies is unstable, and the lateral comparability of the fourth-order sequence is poor. According to the characteristics of vertical rock sequences, each fourth-order sequence can be roughly divided into low-order system tracts, transgressive system tracts and high-order system tracts. The sequence stratigraphic unit that can be compared horizontally is mainly the sequence group formed by the superposition of these four-level sequences.
(1) complex sequence ⅳ
The composite sequence Ⅰ V includes the Lower Shihezi Formation and its corresponding horizons, and its age is equivalent to the early Middle Permian. Sequence I-V interface is the bottom of sandstone at the bottom of Xiashihezi Formation (equivalent to camel neck sandstone in Xishan, Taiyuan). The lithology of compound sequence I V is mainly grayish yellow, yellowish green and yellowish brown medium-fine grained sandstone, siltstone, shale and sandy shale, with medium-coarse grained sandstone at the bottom, sandwiched with several layers of carbonaceous shale, coal line or thin coal seam, and no minable coal seam is found. This set of superimposed sandstone at the bottom is equivalent to the low-level sequence, and the large section of fine clastic rocks above it is deposited by transgressive sequence, while the upper sandstone-mudstone interbedded section is deposited by high-level sequence. The thickness of this sequence varies greatly, generally 80 ~ 260 m, the thickness of the first line of Kailuan-Dagang-Fucheng-Julu-Xingtai mining area is 180~260m, and the east of Puyang, Dacheng and Jize is about180 ~ 260 m. The formation thickness in other areas is less than100m (Figure 3.43).
Fig. 3.37 thickness contour map of Carboniferous-Permian composite sequence III in western Bohai Bay Tu Tu 3.37 thickness contour map of composite sequence III strata in western Bohai Bay.
Fig. 3.38 Contour map of Carboniferous-Permian composite sequence III coal seam+carbonaceous mudstone thickness in western Bohai Bay Fig. 3.38 Contour map of composite sequence III coal+carbonaceous mudstone thickness in western Bohai Bay periphery.
Fig. 3.39 Isogram of Coal Seam+Carboniferous Mudstone in Compound Sequence Ⅲ in the west of Bohai Bay.
Fig. 3.40 Isogram of Sandstone Thickness of Carboniferous-Permian Complex Sequence Ⅲ in the west of Bohai Bay.
Figure 3.4 1 Isogram of Sand-Mudstone Ratio of Carboniferous-Permian Composite Sequence III in Western Bohai Bay Tu Tu 3.4 1 Isogram of Sand-Mudstone Thickness Ratio of Composite Sequence III in Western Bohai Bay.
Fig. 3.42 Distribution Map of Sedimentary System of Compound Sequence III (Main Body of Shanxi Formation) 3.42 Distribution Map of Sedimentary System of Compound Sequence III
Fig. 3.43 Isothickness line of stratum section IV of composite sequence in western Bohai Bay.
Coal seams and carbonaceous mudstone are not developed in this sequence, which is mainly due to the large-scale retreat of seawater and the drying of climate, which is not conducive to the accumulation of coal and carbonaceous mudstone. However, carbonaceous mudstone was still distributed in some areas of this area at that time. For example, the thickness of carbonaceous mudstone in Ju 1 Well and Bo Gu 1 Well is 12m and 4.35m respectively, while the thickness of carbonaceous mudstone in other areas is less than 3m or undeveloped.
Sandstone and conglomerate are the main lithology of composite sequence, in which the thickness of sandstone is between 20 ~ 120 m, mainly distributed along the Kailuan-Dagang-Fucheng-Dezhou line and near Jingxi, in which the thickness of Kailuan and Baodi is greater than 1 10 m, the thickness of Jingxi is greater than 60 m, and that of Xingbei is west of Jinan. However, conglomerate and gravelly sandstone are regularly distributed, and only in Jingxi-Baxian area and Dagang-Fucheng-Dezhou-Nangong area, the former has a small thickness of 10 ~ 20m, while the latter has a large thickness of 10 ~ 90m, with a thickness of 70 ~ 90m between Fucheng South and Nangong (Figure 3. The thickness distribution of sandstone and gravel sandstone and conglomerate is basically consistent with the stratigraphic contour, indicating that these sandstone and conglomerate are mainly controlled by sedimentary depressions at that time, and rivers are mainly distributed along structural depressions.
According to the statistical results of sand-mud ratio, the sand-mud ratio of this sequence is not high, ranging from 0.2 to 5, in which the sand-mud ratios of Jingxi, Kailuan and Beidagang are all greater than 1, the sand-mud ratios of Xingbei mining area, Handan and Jinan are all greater than 1, and those of other areas are all less than 1. It is worth noting that the sand-mud ratio in Fuchengnan-Dezhou-Nangong area with thick gravel is not high, because gravel is not in the statistical range of sand-mud ratio. If gravel sandstone is included, the ratio is between 1 and 1.5 (Figure 3.46). So from this point of view, it should be obvious that the terrain in this area was low at that time.
According to the above analysis and well correlation results, the sedimentary units of composite sequence I-V can be divided into braided river, meandering river and delta plain, in which braided river is mainly distributed in areas with sand-mud ratio greater than 2, namely Jingxi-Kailuan-Tianjin area and Xingbei mining area-Fengfeng mining area, and the delta plain to the east of Puyang-Guanshen-Linqing-Dezhou-Wudi line and meandering river to the west, mainly distributed in Dagang-Wudi.
(2) compound sequence ⅴ
The composite sequence ⅴ includes the lower strata of the first and second members of the Upper Shihezi Formation, which is equivalent to the late Middle Permian. Lithology is mainly gray, grayish white medium-fine grained sandstone, gravelly sandstone, purplish red argillaceous siltstone and mudstone, with conglomerate locally developed. The thickness of this sequence is between 120 ~ 280 m, in which the strata in Tangshan-Tianjin-Zibo area are relatively thick, with the thickness between 200 ~ 280 m, the thickness in Fucheng South-Dezhou-Nangong-Xingbei mining area is 160 ~ 240 m, and the thickness in southern Puyang and Jining areas is less than1.
Sandstone of composite sequence is mainly distributed in two areas: one is the area north of Fucheng; Second, the area south of Yuanshi County-Nangong-Linqing-Jinan-Zibo and the area north of Puyang-Jining. Among them, the thickness of sandstone in the north is reduced from 1 10m in the north to 20m in the south, from over 70m in the west to below 60m in the south, and there are more than 90m deposits in Zibo area (Figure 3.49). The distribution characteristics of conglomerate, gravelly sandstone and composite sequence Ⅰ V are similar, mainly distributed in Kailuan-Tianjin-Cangzhou-Dezhou-Nangong-Jize-Xingtai mining area, with a thickness of 0 ~ 0 ~ 35m. The main thickness points are Kailuan, Zhuanggu 1, Xinge 4, Donggu 1 and Ju 1 well. In addition to these areas, there are 25m-thick glutenite in Well Mao 4 in the east of Puyang, and 15m-thick sediments in Zibo area (Figure 3.50). There are no coal and carbonaceous mudstone deposits in the compound sequence ⅴ.
The distribution of sand-mud ratio of compound sequence V is similar to that of sandstone thickness, and its high value area is mainly distributed in two areas: one is the area north of Fucheng; Second, the area south of Yuanshi County-Nangong-Linqing-Jinan-Zibo and the area north of Puyang-Jining. Sand-mud ratio 1 ~ 40 in the north and 0.6 ~ 1 in the south. The sand-mud ratio on the west side of Nangong-Fucheng line may be higher than 1, and lower than 0.2 on the east side. In addition, it is less than 0.2 in Puyang area (Figure 3.5 1).
According to the information reflected by the above parameters and the comparison results of sedimentary facies profiles, it can be considered that the sedimentary environment of compound sequence V is mainly meandering river and braided river. Judging from the marl developed in the Zhuanggu 1 well complex sequence in the south of Beidagang, lake facies may have developed in the eastern part of Zhuanggu 1 well during the complex sequence V. Therefore, it can be determined that the delta plain may develop in Cangzhou-Dezhou-Jinan-Jining of Peking University (Figure 3.52).
Paleogeographic characteristics of the Late Permian (sequence ⅵ and ⅶ) in 3.7.2.3.
Judging from the exposed strata in the study area, the compound sequences ⅵ and ⅶ mainly developed in the Late Permian, in which the compound sequence ⅵ mainly consists of the fourth-order sequence of fluvial facies, and the compound sequence ⅶ includes the fourth-order sequence of fluvial facies and the fourth-order sequence of lacustrine facies.
Fig. 3.44 isopleth map of sandstone thickness of Carboniferous-Permian composite sequence ⅳ in western Bohai Bay.
Fig. 3.45 Contour map of thickness of conglomerate+gravelly sandstone in Carboniferous-Permian composite sequence IV in western Bohai Bay Tu Tu 3.45 Contour map of thickness of Congo+gravelly sandstone in composite sequence IV in western Bohai Bay.
Fig. 3.46 Isogram of Sand-Mudstone Ratio of Carboniferous-Permian Composite Sequence IV in western Bohai Bay 3.46 Isogram of Sand-Mudstone Thickness Ratio of Composite Sequence IV in western Bohai Bay.
Fig. 3.47 Distribution Map of Sedimentary System of Compound Sequence IV (Main Body of Lower Shihezi Formation) Fig. 3.47 Distribution Map of Sedimentary System of Compound Sequence IV
Figure 3.48 Isogram of Carboniferous-Permian Composite Sequence ⅴ Stratum Thickness in Western Bohai Bay Figure 3.48 Isogram of Composite Sequence ⅴ Stratum Section in Western Bohai Bay
Fig. 3.49 isopleth map of thickness of sandstone in Carboniferous-Permian composite sequence in western Bohai Bay.
Fig. 3.50 Contour map of thickness of conglomerate+gravelly sandstone in Carboniferous-Permian composite sequence V in western Bohai Bay Tu Tu 3.50 Contour map of thickness of Congo+gravelly sandstone in composite sequence V in western Bohai Bay.
Fig. 3.5 1 contour map of sand-mudstone ratio of Carboniferous-Permian composite sequence V in western Bohai Bay Tu Tu 3.5 1 contour map of sand-mudstone thickness ratio of composite sequence V in western Bohai Bay.
Fig. 3.52 Distribution Map of Sedimentary System of Compound Sequence V (Lower Member of Upper Shihezi Formation)
(1) complex sequence Ⅵ
It corresponds to the upper part of the second member and the third and fourth members of the Shangshihe Formation, and roughly corresponds to the early Late Permian in time. Due to serious erosion, the composite sequence is not developed in most areas, mainly distributed in southern Hebei, Puyang, Henan and Shandong. In addition, well Zhuanggu 1 in the south of Beidagang and well Xinge 4 near Baxian are also well developed. However, other areas in the north only develop low-level sequence groups or low-level sequence groups and the lower part of transgressive sequence groups.
From the correlation diagram of Shabagou-Gu Qing 1 well in Lincheng (Attached Figure 3. 18), the composite sequence consists of low-level sequence group, transgressive sequence group and high-level sequence group. Among them, the lower sequence group is composed of braided river channel sandstone in Xingtai mining area-Jize area, especially in Xingtai mining area, which is mainly composed of multiple sets of thick composite braided river channels, and the eastern part is composed of thin meandering river channel sandstone, which evolved into floodplain and crevasse fan deposits to form a transgressive sequence group, and then the upper channel sandstone increased to form a high sequence group. This sequence is characterized by several upward tapering river sedimentary cycles in the whole area. In the lower sequence group, each cycle consists of channel sandstone with cross bedding and scouring surface at the bottom and purple mudstone and siltstone at the upper part. The transgressive sequence group is mainly composed of purplish red mudstone, argillaceous siltstone, gray siltstone and fine sandstone. The content of sandstone in the high-level sequence group is obviously increased, and medium sandstone and fine sandstone can be seen, mixed with purple mudstone or argillaceous siltstone.
(2) Compound sequence VII
The composite sequence ⅶ includes Shiqianfeng Formation in the area, and the lithology is mainly maroon medium-fine calcareous sandstone, deep purple argillaceous siltstone, blood-red mudstone and several thin layers of fresh water limestone. The bottom is characterized by superimposed thick gravel sand bodies, which represent the sediments in the low water level period, and the thick interbedded sediments of sand and mudstone in the diluvial basin on it represent the sediments in the base level rising period, belonging to the lacustrine transgression system tract sediments. There are several relatively stable layers of fresh water limestone or marl in the upper part, which is the deposit at the highest stage when the lake surface rises, and its bottom surface represents the largest flooding surface in the sequence, and the deposit from fresh water limestone to the upper part is a high system tract. The stratigraphic thickness of this sequence is generally between 1 00 and 300m, and individual wells (such as Guangu1well) reach 479m. ..
The thickness of sandstone and conglomerate in this layer varies from 1 0m to10m, and it is the thickest in Zibo to Guangu1well. When sequence VII was deposited, the study area was already in an inland lake environment, and the climate became hot and dry, so no coal and carbonaceous mudstone were formed at that time.
Referring to the regional geology and the previous research results on the paleogeographic map of Shiqianfeng Formation, the sedimentary environment of Shiqianfeng Formation is analyzed through field measurement of stratigraphic profile. The sedimentary environment of Shiqianfeng Formation includes shallow lakes, lakesides, lakeside deltas and rivers, among which the river facies area is distributed in Shijiazhuang-Yuanshi County-Xingtai-Handan-Puyang-Juye-Jining, and the northeast and southwest of it are large lakes.