Study on Devonian sequence stratigraphy in Sichuan, Yunnan, Guizhou and Guangxi
The Devonian in Youjiang Basin is widely exposed, with well-developed lower, middle and upper series, rich sedimentary types and fossils, and has a good foundation for biological, chronological and sedimentological research (Chen Daizhao et al.,1994; Chen Hongde et al.,1990; Zeng Yunfu et al.,1993; Wu Yi et al.,1997; Chen Daizhao et al.,1995; Chen (1995) is an ideal area for outcrop sequence stratigraphy research. Due to the influence of basement tectonic activity, the overall paleogeographic pattern of Devonian is a basin that deepens southward. From the Lower Devonian to the Upper Devonian, it gradually changed from continental clastic deposits to carbonate deposits. Generally speaking, it is a set of sedimentary sequences formed under the background of transgression. Coupled with the control of contemporaneous fault activity, the sedimentary differentiation pattern of carbonate isolated platform and deep-water platform appeared in the late Devonian, which made the Devonian sequence stratigraphy in Youjiang Basin unique.
8.8.2 Characteristics of Key Interface of Sequence
8.8.2.1I interface
The identification of type I interface is mainly based on the field outcrop observation data, that is, the interface exposure marks such as paleoweathering crust, weathered residual iron-aluminum layer, paleokarst and corresponding low-water level deposits below the "slope break zone". In addition, combined with the indoor test and analysis data, and considering the regional tectonic background characteristics. According to the above basis, 10 I-type interfaces have been identified in Devonian of Sichuan, Yunnan, Guizhou and Guangxi, which are sequence S 1, S4, S6, S7, S8, S 10, S1. Their characteristics are detailed as follows.
Fig. 8.3 1 Devonian-Cambrian boundary relationship in Daliantang, Yunnan Province
① Weathering residual system; (2) Filling dissolved pores and joints; ③ granular dolomite; ④ Silty shale; Sb1-I interface
S 1 bottom interface: the obvious sign is the unconformity between Devonian and the eastern Hugli fold belt, resulting in obvious regional angle unconformity, which is manifested by uneven erosion of the underlying strata, the existence of breccia at the bottom of the ancient weathering crust or overlying strata, or the corresponding regional weathering residual facies, that is, the development of aluminum mudstone deposits in the relatively depressed depression areas. 87Sr/86Sr (Wu Yi et al., 1997), trace elements and major elements (Wu Yi et al., 1997) and δ 13C all changed obviously. Biological evolution is as follows: ① the prosperity of fish and the appearance of primitive amphibians; ② Development of terrestrial plants; ③ Major innovation and development of marine invertebrates (Chen Daizhao et al., 1995). Such as conodonts P. Pesavis, A. Delf, O. Eurekemis, I.w.unchmidyi and ammonite belt, and the first bamboo stone N.acuaria belt.
Fig. 8.32 Interface Relationship of S 13/S 12 Sequence in Guilin East Village Profile
① Dolomite at the top of Tangjiawan Formation, containing comb calcite cement; ② Erosion surface; ③ Limestone breccia in the low-lying area at the bottom of Tang Min Formation.
S4 bottom interface: the area from southeastern Yunnan to western Guangxi and Danchi in northern Guangxi is a lithofacies transition surface, or it coincides with the transgressive upper or lower super interface, but it is a parallel unconformity interface on the edge of central Guangxi, northeastern Yunnan, Yangtze continent and Yunkai ancient land, where conglomerate or eluvial facies deposits are developed, and the conodont E-groove belt, ammonite M-rope belt and bamboo stone N. Ocarui belt appear for the first time. In addition, 87Sr/86Sr shows slight fluctuation.
S6, S7, S8, S 10 bottom boundary: uplift, exposure and erosion, overlapping composite interface. S6, S7 and S8 have similar bottom boundary characteristics, but their distribution ranges are different. The three interfaces overlap step by step from south to north and from morning till night, and the scope is expanding. Their main bodies in Yunnan, Guizhou and Guangxi are still characterized by early karst outcrops, such as Wenshan in southeast Yunnan, Xichou section, Debao section in southwest Guangxi, Napo section in south Guangxi, Hengxian section in south Guangxi and Changle section in Xiangzhou. However, they are characterized by land boundaries on the edge of the ancient land, such as Qujing and Xuanwei sections in eastern Yunnan, Dushan section in central and southern Guizhou, Wudang section in Guiyang, and Dafengmen section in the northbound direction on the western edge of Yunkai ancient land. The corresponding biological evolution showed the prosperity of conodont and ammonite belts, and the δ 13C curve increased obviously (Chen, 1995).
The bottom boundaries of S 1 1, S 12 and S 13 are short-term exposure-transgression overlapping genetic interfaces with relatively inconspicuous identification marks. In continental margin background and sedimentary highlands (such as platforms and their margins), exposure features are the main features, which can only be identified by combining lithofacies conversion marks, but in platform basins or slopes or deep-water basins, lithofacies is continuous and difficult. In almost all measured profiles, conodont triangle, nautilus belt and bamboo stone belt appear in large numbers above the interface, and the corresponding geochemical indicators are as follows: ① The values of Ca/Mg (Sr) or CaO/MgO, K2O and Na2O increase sharply (Wu Yi et al. ); ②δ 13C value jumped from the background value (average-1.273 ‰, PDB) to 2. 137‰ (average) (Chen Daizhao et al.,1994); ③ Trace elements and their corresponding ratios have changed in different degrees (Wu Yi et al., 1997).
S 17 bottom interface: it is a typical regressive interface, and the typical signs are ① karst dissolution surface with obvious platform background, and red oxide scale of iron mud can be seen on the interface, such as Wenshan ancient wood section; ② The karst erosion surface of granular dolomite and its karst breccia in the background of platform margin, such as Liu Jing section in Hengxian county; (3) The slope profile of Chehe section in Nandan shows that the gravity flow of calcium chips is deposited on the erosion surface; ④ Profiles on the southern margin of Yangtze ancient land (such as Tien Miao profile and Dushan profile) show that there is a thin layer of residual iron and mud on the erosion discontinuity; ⑤ There are obvious lithofacies transition surfaces in the background of platform basin, such as siliceous mudstone series below the middle interface of Ba Du section of Tianlin and lentiform marl assemblage on it. The corresponding biomarkers are the first appearance of conodont Pa.expansa and ammonite Clymenia, while the δ 13C curve shows the beginning of the descending or regressive cycle (Chen Daizhao et al., 1995).
8.8.2.2 Ⅱ interface
Devonian in Sichuan-Yunnan-Guizhou-Guangxi area * * * identified seven type II sequence interfaces, namely the bottom interfaces of S2, S3, S5, S9, S 14, S 15 and S 16 sequences. Type ⅱ interface in this area is set in the coastal zone of ancient continental margin, carbonate platform or isolated platform, characterized by obvious identification marks, land exposure, short-term erosion or transgression overlap, shelf and gentle slope of craton as the background, and land exposure or coastal unconformity. In the deep-water basin of platform basin, the discontinuous unconformity of underwater denudation and the corresponding phase sequence structure transformation surface are dominant; On the other hand, in the exposed area, ancient karst dissolution surface, or coal seam, clay layer or calcified shell, dolomite cap and characteristic karst fracture zone can be developed. Generally speaking, type II interface is far less easy to identify than type I interface, which needs to be determined by comparing and analyzing the development of land and underwater interfaces.
The largest flood surface or condensation layer in 8.8.2.3.
The Devonian in Sichuan, Yunnan, Guizhou and Guangxi have identified 17 maximum flood surfaces or equivalent interfaces, which are mainly distinguished by the characteristics of condensed layers. The background of different sedimentary basins may be different, which is manifested as follows: under the background of gentle slope platform dominated by carbonate deposition, the maximum flooding period is often composed of thin marl, biological nodule limestone, siliceous banded limestone and biostratigraphic limestone. , which is rich in small shell benthos or plankton. On the continental shelf under the background of continental clastic deposition, the condensed layer is characterized by shale or bioclastic limestone or argillaceous limestone rich in phosphorus, manganese and pyrite nodules; In the platform basin slope environment, the condensed layer is characterized by thin limestone rich in plankton and siliceous limestone deposits or thin biolimestone, such as Chehe section in Nandan. In the background of platform margin, it is characterized by bioclastic limestone or bioclastic limestone with planktonic facies; In the background of shallow platform basin, thin siliceous mudstone and siliceous limestone are developed, and plankton assemblages are developed, such as CS 16 and CS17. In the Luofu section of Nandan; Under the background of deep-water platform basin, it is characterized by tuffaceous siliceous rocks and siliceous rocks interbedded (Tianlin Ba Du section) or thin siliceous rocks (such as Napopinggen section); It is obviously difficult to distinguish in deep-water basins (such as Qinfang Trough), but it can be roughly identified by the most abundant horizons of radiolarian chert and siliceous shale in each sequence. Based on the sedimentary records of all these basins, it can be found that the maximum flooding surface is generally an "ecological transition surface", that is, a large number of shallow benthic communities mutate upward into deep-water assemblages rich in plankton. At the same time, compared with other interfaces or system tracts, it also shows the evidence that organic carbon, total hydrocarbon content, strontium content and carbon-oxygen isotope value have reached the highest value, and the paleooxygen value, porosity and cathodoluminescence characteristics have changed greatly.
Initial submerged surface of 8.8.2.4
The initial flooding surface is the physical interface between the transgressive system tract and the underlying low water level or shelf margin system tract. The initial flood surface in Devonian sequence stratigraphy in Sichuan, Yunnan, Guizhou and Guangxi has two manifestations: ① It includes S 1, S4, S6, S7, S8, S 10, S 1, S1. (2) The initial flood surfaces of the other seven sequences coincide with the type II interface (Taiwan Province area), or lie between the transgressive system tract and the shelf marginal system tract, which is equivalent to transgressive hyperplane. The identification marks of initial flooded surface of type I sequence in different basins and different sedimentary types are inconsistent. In the onshore coal-forming environment, sandstone with biological crust is directly covered on carbonaceous shale and coal seam, and siltstone and fine sandstone with rich bioclastic deposits are covered on continental strata of continental shelf. The environmental system of carbonate platform is reflected by granular limestone overlying argillaceous limestone and granular marl, as well as shale and thin siliceous rocks or tuffaceous turbidites in deep-water basins. In addition, in the platform or continental background, the interface often has scouring and erosion surfaces, and gravel and fine gravel limestone are relatively developed on the interface, forming a typical parallel unconformity erosion surface. The identification characteristics of the initial flooded surface coincident with the bottom interface of type II sequence can be found in the description of the bottom interface of type II sequence.
8.8.3 Sequence division and characteristics
According to key interfaces, regional tracking and correlation, characteristics of phase sequence change and quasi-sequence superposition model, typical profile sequence characteristics of different facies belts (coast, platform, platform margin, slope, platform basin and deep-water basin) of various basin types, combined with the data of corresponding bio-fossil belts (conodont belt is the main one, followed by ammonite belt, graptolite belt and slubby stone belt), the Devonian system in Sichuan, Yunnan, Guizhou and Guangxi is divided into 65433. Among them, there are 3 in Rockoff stage (S1~ S3), 2 in Prague stage (S4 ~ S5), 2 in Ames stage (S6 ~ S7), 2 in Eiffel stage (S8 ~ S9) and 2 in Givi stage (S10 ~ S12). The average delay is about 2 187Ma, and 10 type I sequences (S 1, S4, S6, S7, S8, S 10, S1,S/. Of course, not every type of sedimentary basin has 17 complete sequences. For example, the facies section near the ancient continental margin usually lacks the 1 ~ 3 sequence of Lokov period and early Prague period, namely s 1, S2 and S3.
8.8.4 Sequence regional correlation
The correlation basis includes interface properties, cohesive layer, internal structure of sequence, biological assemblage and sequence number. In addition, the sequence development characteristics and evolution trend of different sedimentary backgrounds are also considered.
Looking at the profile and sequence correlation profile in Sichuan, Yunnan, Guizhou and Guangxi (Figure 8.34), we can see that the most complete Devonian sequence is the Qinfang Trough and its marginal Hengxian Liu Jing profile, as well as the Napoping 'en profile with platform basin background, followed by the Daliantang profile in southeast Yunnan, with a general sequence of S 1 ~ S 17. However, the lower 1 ~ 4 sequence (S 1 ~ S4) is usually absent in shallow waters near the inherited ancient land margin or sedimentary highlands. From the Qinfang Trough in the south to the Youjiang area in the middle to the southern margin of the Yangtze ancient land in the north, the number of missing sequences at the bottom increases, such as the bottom sequence S 1 in southeastern Guangxi, southern Guangxi and southeastern Yunnan. For example, Fusui, Longzhou, Napo and Wenshan Gumu sections usually lack S 1 sequence, while central Guangxi and north central Yunnan usually lack 1 ~ 2 sequence, such as Qujing section in southeast Yunnan, Tianlin Ba Du section in west Guangxi, Luofu, Donghe, Li Yong section in Danchi area in north Guangxi and Tangjiawan section in northeast Guangxi all lack 65438+. Further north to Dushan, Duyun, Kaili and Guiyang, 2 ~ 3 or even 4 sequences (S 1 ~ S4) are generally missing. For example, the lower sequence S 1 ~ S3 is missing in Tien Miao and Tianba sections of Guiyang. This is due to the pre-Devonian tectonic palaeogeography and Caledonian movement, and the sea level gradually invaded and overlapped from south to north in the early Devonian.
For Lokov sequence S 1 ~ S3, the bottom is Caledonian tectonic movement interface, and the top is also I-type interface, which has obvious identification characteristics and is easy to identify. The sequence S 1 ~ S3 bounded by two interfaces is obviously an isochronous stratigraphic unit, which can be compared. In addition, the fossil belts corresponding to sequence S 1, S2 and S3 are manfidocera monome as, M. Praebercyniais and M.thomasi respectively. Combined with the internal structure of the sequence and its changes, it is obvious that the sequence S 1, S2 and S3. In addition, coarse-grained sedimentary assemblage is also an important correlation sign.
Table 8.7 Devonian sequence division and characteristics in Youjiang basin
sequential
Fig. 8.33 Sequence regional comparison of typical sections with different sedimentary backgrounds in Devonian.
For Prague sequence (S4 ~ S5), the top and bottom are also I-type interfaces, indicating that they are comparable isochronous stratigraphic units. S4 ~ S5 sequences can be identified in Guangxi and eastern Yunnan. In general, TST is deposited with silty mudstone and mudstone on the continental shelf, with slight retrogradation, and CS is calcareous mudstone and marl on the continental shelf, rich in brachiopods, bivalves, ostracods and thick-shelled bamboos. HST is usually a progradational parasequence group composed of gray dolomite and silty mudstone, such as Liu Jing section in Hengxian County and Daming Mountain area in the west (Figure 8.34). The line from Longzhou and Debao to the west (Qinjia section) corresponds to the Nagaoling Formation, and then the line from Jingxi to Longlin gradually becomes a land island. The deposits in Kunming and Wenshan in eastern Yunnan correspond to the Posongchong Formation, which is equivalent to the Nagaoling Formation in Wuding, Xiangzhou and Nandan areas in eastern Guangxi. The biological basis of comparison is conodont Po. Piranat, E. Kindley and E. Sur.
Ames sequence S6 ~ S7, with I-shaped interface from top to bottom, has also been manifested in the following biological events in Sichuan, Yunnan, Guizhou, Guangxi and even the whole South China: First, the first flourishing period of conodont Po. Second, the first appearance of the ammonite belt. Obviously, the boundary and time frame of sequence correlation in different regions are obviously different. Sequences S6 and S7 are both typical transgressive sequences, with increasing limestone assemblages. The TST of sequence S6 is usually shelf siltstone and mudstone deposits, the CS is usually mudstone and thin-layer biological limestone and nodules, and the HST is usually medium-thick argillaceous limestone and biological mound, such as Longzhou, Debao Qinjia, Liu Jing, Beiliu Fengmen and Xiangzhou Dale areas in Hengxian County, which transited to Cangwu Shiqiao section and became continental margin clastic coastal shallow sea deposits. The bottom interface of sequence S7 is an exposed I-type interface, which can be recognized in most carbonate platform backgrounds (such as Liu Jing, Debao, Longzhou, Gui Zhong and Wenshan). ), but in the areas where LST develops, such as Napoping 'en, Tianlin Ba Du, Luofu in Nandan and Daliantang in Guangnan, it is difficult to identify. In the above-mentioned carbonate platform background, TST is characterized by retrogradation sequence composed of thin-layer biological limestone and plaster. HST is characterized by medium-thick limestone and dolomite, such as Sanchahe section in southern Nanning, Liu Jing section in Hengxian County, Dafeng Gate section in Beiliu, Dale section in Xiangzhou and Gumu section in Wenshan. However, the Guanyang section in the northeast of Guilin and the south of Guizhou are all clastic deposits.
For Eifelian sequence (S8 ~ S9), the bottom is I-type interface, and the corresponding conodont belts are Polygnathus C. Costatus and Polygnathus C. Partitus. In Liu Jing section of Hengxian County, the correlation marks of sequence S8-S9 are thin-layer nodular dolomite of sequence S8, thin-layer nodular dolomite of S9 and red thin-layer iron-calcium mudstone at the top of HST thick-layer dolomite. The Dafengmen section of Beiliu in Northeast China is platform margin-platform facies deposition-Yarang Formation, and reaches the Dale section in Xiangzhou, east of Liuzhou in the north, which is equivalent to the shelf facies deposition of Tang Ying Formation. From Xiangzhou to the northeast to Hexian County, it gradually changed into intertidal zone-subtidal zone-Xindu Formation, S9 turned into gray-green mudstone, and the top of HST turned into pea-shaped hematite. In the corresponding horizon in eastern Guangxi, the transition is tidal flat facies deposition; The Eiffel Stage in Dushan section of Guizhou Province consists of Dahekou Formation and Tunshang Formation (S9), and its top is parallel and unconformity with the overlying Jizhao Formation. Influenced by the Variscan Movement, the S8 ~ S9 sequences in Qiandongnan, Huanjiang, Kunming and Xuanwei are mostly coastal facies and delta facies, while Duyun and Dushan in Guiyang, Guizhou are mainly delta facies. The bottom of the Giveyian sequence (S 10 ~ S 12) is an I-type interface, but the coral tree-striped coral trigemme can appear as the bottom boundary for the first time, and the top is an I-type interface, and the corresponding conodont zones are P. Cockelianus, P. Varcus, P. X. Ensensia, N.C.
Fig. 8.34 sequence stratigraphic framework of D 1 ~ D 12 in Youjiang basin
As can be seen from Figure 8.33, three sequences can be identified along Huaning, Wuding to Wudang, Dushan, Buzhai and Huanjiang Shang Chao in southeastern Yunnan and northwest Guangxi. S 10 is a type I sequence, and S 1 1 ~ S 12 is a type II sequence, but in Wuding and other places, S12 is a type II sequence. At the same time, after passing through Napo, Debao and Hengxian in southwest Guangxi, it turned to Xiangzhou, Guilin, Hexian and Guanyang in north east longitude. The bottom boundary of sequence S 10 is located on the palaeokarst outcrop, which seems to be an I-shaped interface on the profile and the corresponding platform, but it can be traced back to the Xindu profile in Hexian County in the sea direction (Wu Yi et al., 109).
The Frazier period is the Devonian maximum sea level rising period, and * * has deposited three sequences, namely S 13, S 14 and S 15. The top boundary is type II interface, and the bottom boundary is type I interface, and the corresponding conodont belts are Palmatolepis Punctata, P. Hassi and P. At the same time, the horizon of Liu Jing section in Hengxian County is Guguan Formation, and the important correlation marks in the three sequences are nodular limestone with thin flint band and argillaceous limestone with thin manganese striation in CS 14 and CS 15. Dushan section in southern Guizhou is equivalent to Wangchengpo Formation. The lower part of S 13 ~ S 14 is the Hejiazhai section, and the upper part of S 15 is the Lujia Village section, which is mainly composed of carbonate gentle slopes and carbonate platform deposits. Under the background of inter-platform trough represented by Di Yang section in Yangshuo, S 13 ~ S 14 sequence corresponds to Liujiang Formation, and S 15 corresponds to Guguan Formation, in which TST is usually a retrogressive sequence composed of black thin-bedded microcrystalline limestone, marl and calcareous mudstone, and CS 15 is black manganese-bearing mortar rock and manganese-bearing mudstone.
From the above comparative data, it can be seen that the development and evolution of sequence stratigraphy in Frazier period, although different sedimentary backgrounds and sequence combinations have their own characteristics, can identify three sequences, indicating that the sea level changes in this period tend to be consistent, which proves that the characteristics of global sea level rise in Frazier period are synchronized with the sea level changes in Yunnan, Guizhou and Guangxi.
Famen sequence (S 16 ~ S 17) has type II interface at the bottom and type I interface at the top, and type I interface between S 16 ~ S 17. From bottom to top, the dentate spines are Palmatolepis triangularis, Pa.crepida and Pa. Wrinkled spiral ribbon, fully cracked spiral ribbon, expanded spiral ribbon and tubular spiral ribbon. In this period, the sequence material combination is coastal dolomite in Guizhou and Guangxi, and the sequence S 17 strata are usually missing to varying degrees, such as Wudang and Tien Miao sections in Guiyang. The coastal background of Xiang-Gui sea area is sedimentary shelf deposition, especially in S 17 sequence, such as Tangjiawan section, Yangshuo section and Di Yang section in Guilin. The strike sea area is mainly carbonate rocks, such as carbonate platform background in central Guangxi, southeastern Yunnan and western Guangxi (such as Wenshan ancient wood, Xichou Mingbaibai, Hengxian Liu Jing section, etc.). ); In the deepwater platform basin environment, it is mainly composed of argillaceous banded limestone and nodular limestone, such as Ziyun Spark Profile, Yunnan Daliantang Profile, Guangxi Luofu Profile, Wuwei Profile and Tianlin Ba Du Profile. According to the sequence and the plane distribution of conodont data, the middle-upper layer of S 17 is usually missing in Yunnan, Guizhou and Guangxi, which is equivalent to praesulcata belt.
8.8.5 Sequence frame model
Sequence genetic dynamics in Xichang basin and its application in oil and gas exploration
According to the above-mentioned sequence division, characteristics and comparative study, the Devonian sequence stratigraphic framework of Yunnan, Guizhou and Guangxi was initially established (Figure 8.34 and Figure 8.35). As can be seen from Figures 8.34 and 8.35, in Devonian, the main body of the study area showed the development stage of passive continental margin rift basin, with platform-basin alternation and platform-basin deposition pattern, followed by northeastern Yunnan intracontinental depression basin and southern Guizhou intracontinental depression-craton basin, and Qin Fang deepwater trough basin in the east. The whole has experienced two quasi-second-order periodic evolution processes. The Devonian Love-Prague period (S 1 ~ S5) is dominated by shelf-shore facies, and its morphology is strictly controlled by pre-tectonic palaeogeography. The bottom boundary is uneven and gradually flattens. As the basement of continental margin rift basin, the development of sedimentary filling in this period was mainly controlled by basin tectonic activity and related provenance, which represented the original depression-rift product of continental margin. The Ames period (S6 ~ S7) entered a new evolutionary stage (equivalent to the second-order TST) and was in a period of tectonic activity change. The NW-trending syngenetic faults and NE-trending extensional strike-slip strictly controlled the sedimentary palaeogeographic pattern and the differentiation of lithology, lithofacies and biological assemblage, which caused the changes of lithology, lithofacies, biological assemblage and palaeogeographic features. In the basin, there is an obvious pattern of platform around the basin or platform-basin alternation, and the carbonate facies belt obviously extends around the basin and covers isolated platforms. The early Middle Devonian (S8 ~ S9) is equivalent to the HST of the second-order sequence of D 1 ~ D2. The tectonic activity is relatively weak, the sea level is relatively stable, and clastic rocks obviously advance into the basin, resulting in clastic rocks and migmatite facies near the southern margin of Yangtze ancient land and the western margin of Cathaysian ancient land, and carbonate islands and platforms are still alternately distributed far away from the ancient land, thus ending.
0 ~ D3 is the second secondary sequence development period, which basically laid the outline and sea area distribution of Youjiang rift basin, deepened upward as a whole, overlapped in a stepped way from north to east, and the basin area increased rapidly. It is composed of deep-water platform basin facies silicalite series and isolated platform carbonate series. Siliceous rocks are widely distributed, but the thickness is thin, and carbonate rocks are thick, but the spatial distribution is small. The sedimentary sequences of the two are opposite, and ~ (S 10 ~ S 15) belongs to the second-order sequence TST, which indicates that the sequence development is mainly controlled by syngenetic faults and basement structures, and represents the sedimentary products of intense extension stage. The Famen period of the Late Devonian (S 16 ~ S 17) is equivalent to the second-order HST sedimentary period, which basically inherited the early lithofacies paleogeographic pattern, consisting of siliceous rocks-mudstone-lenticular limestone (platform) and carbonate formation (isolated platform), and the isolated platform components gradually increased. The sequence development in this period was mainly controlled by basin tectonic subsidence and sea level change.