Sedimentary filling sequence and tectonic cycle of late Jurassic-Cretaceous basin

(1) Tectonic-stratigraphic sequence correlation and tectonic cycle division

Table 4- 1 shows the tectonic-stratigraphic sequence correlation of some major late Jurassic-Cretaceous basins in northeast China and the division of basin tectonic cycles.

In stratigraphic division and correlation, the idea of tectonic-stratigraphic sequence is adopted, that is, according to the structural evolution, tectonic movement and sedimentary filling characteristics of the basin, the extensional rifting activity, compressional inversion activity and corresponding stratigraphic contact relationship reflecting the basin's tectonic cycle (including volcanic eruption) are considered, and the tectonic-stratigraphic sequence and tectonic cycle of the basin are divided into four sequences or cycles: pre-rifting period dominated by volcanism, rifting period dominated by rifting, and weak extensional period dominated by hot and cold. During the Yanshan movement, there were many obvious tectonic movements, namely, one at the end of late Jurassic, two at Yingcheng and Dengloukumu in late Early Cretaceous, and two at Nenjiang or Mingshui in late Cretaceous.

(1) Pre-rift period. It is mainly equivalent to the late Late Jurassic, and some areas can be extended to the early Early Cretaceous. It is mainly characterized by large-scale volcanic activities, such as Xing 'anling Group, Huoshiling Group, Didao Group, Yunshan Group and Yixian Group. Volcanic rocks erupt in a wide range and have a large thickness, and their distribution is not limited to the rift valley.

(2) Rift period (or rift period). It is mainly equivalent to the Early Cretaceous and the sedimentary period from Shahezi Formation to Denglouku Formation in Songliao Basin. During the development of rift valley, the eruption degree of volcanic rocks weakened, and volcanic rocks of different degrees were sandwiched in different areas. During the relatively quiet period of intermittent volcanic eruption, the climate becomes moist, the forest vegetation recovers, and all kinds of creatures multiply rapidly, which becomes an environment and conditions conducive to the generation of coal and oil. This area is dominated by kerosene-bearing deposits, which can be traced back to Su Chang and Suifenhe basins on the south coast of Russia. Laosuchang Formation and Beisuchang Formation are two main coal-bearing measures, which can be compared with Chengzihe Formation, Muling Formation, Shahezi Formation, Yingcheng Formation and Shahai Formation in Northeast China. It should be pointed out that although the volcanic rocks in the late rift are not as widely distributed as those in the late Jurassic, they are also more widely distributed than those in other periods, such as the Ou Ken Formation in the northern part of the North Xing 'an Mountains block, the Haosonggou in Zhaoduba Township of Chaoyang County, the Jinshengbeigou in the Heichengzi area of the northern standard, and the volcanic rocks in the Daxingzhuang area of Jinzhou (Li Zhitong called Daxingzhuang Cycle (1994)). Volcano-sedimentary deposits corresponding to this cycle are located in northeast China, and Aotou Formation, Jinjiatun Formation, Sanshu Formation, Quanshuicun Formation and Dongshan Formation are widely distributed from west to east and from north to south. The average age of volcanic rocks is t =102.9 ma6.11ma, and the isochron age is t =1kloc-0/.2ma1.22ma. However, the geochemical characteristics of volcanic rocks in this cycle are different from those in the pre-rift period and. The latter generally does not develop volcanic rocks. Although there are volcanic rocks in Qingshankou Formation in Songliao Basin, their geochemical characteristics are quite different and belong to basic alkaline series. This feature can be used to distinguish rift strata from strata developed in post-rift depression.

Table 4- 1 Comparison Table of Late Jurassic-Cretaceous Basin Structure-Stratigraphic Sequence Division in Northeast China

(3) Depression. It is equivalent to the late Early Cretaceous to the early and middle Late Cretaceous, and the sedimentary period from Quantou Formation to Nenjiang Formation in Songliao Basin. During the depression period, the subsidence and deposition were mainly in the Songliao Basin in the middle, forming a depression basin with large area and huge stratum thickness, presumably due to thermal cooling and weak extension. The thermal cooling sag shows that the ancient heat flow decreases with time and the settlement rate decreases with time. Weak extension is characterized by weak syngenetic extension normal faults and a small amount of volcanic lava. Depression and depression sequence are not developed in the west and east, but only in a few large basins, such as Hulun Formation in Hailaer Basin in the west, Hailang Formation in Sanjiang-Jixi Basin in the east and Longjing Formation in Yanji Basin.

(4) Reversal period (or atrophy period). It is equivalent to the late Late Cretaceous and the end of Nenjiang to the end of Mingshui in Songliao Basin. At the end of the depression development (such as the end of Nenjiang River in Songliao Basin), there was a tectonic movement. During the depression, the strata reversed, but the degree of inversion was low and the distribution was limited. After that, it entered the basin inversion period or contraction period (such as Sifangtai period and Mingshui period of Songliao basin), when the basin was obviously under the compression background. This set of strata in inversion period or contraction period is also mainly distributed in Songliao basin and Sunwu-Jiayin basin in the middle. At the same time, Qingyuangang Formation developed in Hailaer Basin in the western region, Erlian Dabusu Formation developed in Erlian Basin, and basically not developed in the eastern region. At the end of Late Cretaceous (equivalent to the end of Mingshui in Songliao Basin), the basin structure was reversed by intense compression, which led to a series of structural deformations such as inversion structure, fold thrust and so on.

Songhua River biota developed in depression period, Mingshui biota developed in inversion period or atrophy period; In addition, the coal measures strata developed in the rift period and were absent in the depression period and contraction period; Moreover, the arid climate is dominant in Quantou period, Sifangtai period and Mingshui period, which can be used as an auxiliary sign of stratigraphic division and correlation.

(2) Sedimentary filling characteristics of the basin.

The Upper Jurassic, represented by Xing 'anling Group, consists of a set of volcanic eruption rock series. This unconformity covers the pre-Late Jurassic strata, and its thickness is larger in the west of Yilan-Yitong fault, reaching 6500m in the middle of Daxing 'anling, which fully shows the strength of the rift. In the eastern part of Northeast China, the pyroclastic rock series corresponding to Xing 'anling Group belongs to Didao Formation. Although volcanic eruption rocks are not developed, deep intrusive rocks have increased. The Cretaceous system is widely distributed in the whole Northeast China, with a large sedimentary thickness, generally about 3000 m ~ 6000 m, in which the Lower Cretaceous system is located on the structural layer of volcanic eruption rock series of Xing 'anling Group, mainly a set of continental coal-bearing clastic rock series, which is widely developed in various basins. For example, Bayanhua Group in Erlian Basin, Zhalainuoer Group in Hailaer Basin, Rehe Biota in Songliao Basin, Jixi Group and Longzhaogou Group in the eastern part of Northeast China. The sedimentary thickness is relatively large, generally above 1000m, and the maximum thickness can reach above 6000 m. In the early Cretaceous, lacustrine sandstone and mudstone deposits, source rocks and reservoir rocks were widely developed in Northeast China, which is the main exploration target layer in Northeast China at present. Only in the early Early Cretaceous, marine and continental deposits developed in Longzhaogou area, Suibin, Shuangyashan and Jixi. The Upper Cretaceous (Songhua River Formation) is mainly distributed in Songliao Basin and its eastern region, and the sedimentary thickness can reach 1 150m~2700m. The western part of Songliao basin is only scattered, and only the upper strata of Upper Cretaceous are developed in most areas. Lacustrine sandstone and mudstone deposits are developed in Songliao basin and its eastern region. At present, the main oil-producing series in Songliao basin is Upper Cretaceous.

1. Pre-rift period (late Late Jurassic)

(1) West Zone. ① Northern area: Hailaer basin is a large area volcanic rock distribution area, and its facies belts are volcanic eruption facies and volcanic eruption facies, mainly volcanic lava and pyroclastic rocks. During the intermission of volcanic eruption, alluvial facies and terrigenous clastic freshwater lake facies developed in some intermountain basins. The climate is mild and humid. (2) Southern area: Erlian basin group presents large-scale volcanic eruption and gully landform, with only local depression water accumulation, alluvial fan facies and shore-shallow lake facies; Volcanic rocks are widely distributed in Unit and Tengger Sags, but volcanic eruption rocks, red mudstone and glutenite deposits are only occasionally seen in Su Nite Uplift and Northern Sag. It shows that volcanic activity was strong in the southeast and weak in the northwest, and the basin was in a dry and hot climate.

(2) Central area. ① North-central area: including Songliao Basin and Sunwu-Jiayin Basin, Huoshiling Formation is developed, which is mainly a large area of volcanic rocks, mainly volcanic eruption facies. Volcanic lava and pyroclastic rocks are dominant in the northern part of this area; In the southern Songliao basin, pyroclastic rocks are the main rocks, and there are a lot of normal continental deposits. At this time, there is a small rift sedimentary basin with strong division, mainly alluvial, and the climate is warm and humid. Sedimentary facies include alluvial fan facies, fluvial facies and fan delta facies. Shallow lake facies exists in some areas, and the distribution of deep lake area is very limited. The above characteristics reflect that the volcanic activity in Songliao basin is weaker than that in the western belt and the northern basin adjacent to it, and a normal continental sedimentary environment has emerged. ② Southern region: It is the sedimentary period of Yixian Formation. Volcanic rocks and pyroclastic facies are very developed, thick and widely distributed, and distributed in all basins in the whole region. In the early stage, it was dominated by eruption facies, forming various pyroclastic rocks, and in the late stage, it was dominated by eruption facies, forming various volcanic lava systems.

(3) Eastern District. ① Northern region: including Sanjiang, Boli and Jixi basins. The basins in the west and southeast of this area are mainly pyroclastic rocks with a large number of normal continental deposits. In the east, there is a volcanic eruption facies in the transition from continental facies to marine facies, which reflects that this area is a marine sedimentary environment and is affected by volcanic activities at the same time. Palaeoclimate belongs to temperate humid climate zone. ② Southern region: volcanic rocks and pyroclastic rocks are dominant, with normal sedimentary clastic rocks. Volcanic rocks mostly develop eastward, while clastic rocks and coal seams mostly develop westward. For example, Yanji area is a volcanic basin, Hunjiang area and Liaoyuan and Shuangyang basins are volcanic rocks, with lacustrine deposits and some coal seams. It reflects that the region is dominated by temperate humid climate.

2. Early Rift Period (Early Cretaceous)

(1) West Zone. ① Northern area: Hailaer Basin is the sedimentary period of Tongbomiao Formation and Nantun Formation, and there are 13 fault basins extending northeast in Hailaer Basin. It has the characteristics that alluvial fan facies, river facies, fan delta facies and lakes coexist at the same time (Figure 4-9), in which alluvial facies is absolutely dominant, lake facies is dominated by shore-shallow lake subfacies, and the distribution of deep lake subfacies is very limited. On the whole, it presents the paleoenvironmental characteristics of alternating basins and ridges, and is in a temperate humid climate zone. ② South area: Erlian basin group was in the sedimentary period of Aershan Formation, and 24 rifts divided 32 small lakes. Land sediments are widely distributed, with small lake area and shallow water body, including alluvial fan facies, river facies, delta facies and underwater fan facies. The northern depression zone is the main distribution area of deep lake facies, with large lake basin area and deep water body; The southern depression zones are all coastal shallow lakes, with small lake basin, shallow water body, dispersion and poor connectivity, which indicates that the basin has the characteristics of sedimentary environment in north-south zoning.

Figure 4-9 Sedimentary System Development Model of Early Cretaceous Fault Basin in Northeast China

(2) Central area. (1) North-central region: Volcanic facies is developed in small basins in the north. In the middle of Songliao basin, it is the sedimentary period of Shahezi Formation. In the warm and humid climate, it is dominated by continental deposits with volcanic rocks. The small fault basins that began to develop in the late Jurassic were further expanded, and a number of new fault basins were developed, and the number of fault basins increased to 10. There are alluvial fan facies, river facies, river delta facies, fan delta facies and lake facies. The area of lacustrine facies increased obviously in the late Jurassic. (2) Southern region: Jiufotang Formation is in the sedimentary period, with a warm and humid subtropical-tropical climate. Shore-shallow lake facies is widely distributed, and the ancient water depth changes from shallow to deep from bottom to top. There are alluvial fan facies, braided delta facies and fan delta facies. Semi-deep lake-deep lake facies is not developed or distributed in other areas except Lujiapu fault depression.

(3) Eastern District. ① North area: Dongrong Formation is in sedimentary period. The western part is dominated by volcanic continental deposits and belongs to temperate humid climate. The eastern part is the coastal zone, which is a temperate humid climate zone controlled by maritime climate. Land and sea are dominant, and volcanic rocks are very underdeveloped. In a word, during this period, the marine invasion in this area was large, mainly in coastal and shallow sea environment. The eastern part of the sea is deep and the marine strata are many and thick; The sea water becomes shallower to the west, and the ocean layer is few and thin. From east to west, it is a shallow sea-coast-lagoon landscape with alluvial fan facies, river facies, fan delta facies, triangle facies, lagoon facies and coastal-shallow sea facies. ② Southern region: The paleoclimate is still dominated by temperate humid climate, with less volcanic rocks. All basins are clastic sediments with coal seams, and various animal and plant fossils are found in the strata. Lacustrine facies is developed, and the area of semi-deep lake-deep lake facies is large. The margin of the basin is mainly filled with fan delta facies, river facies and delta facies, and some are alluvial fans.

3. Middle Rift Period (Middle Early Cretaceous)

(1) West Zone. ① Northern area: Hailaer basin group is in the sedimentary period of Damoguaihe Formation. Compared with the previous period, the area of each faulted basin is enlarged, and the proportion of deep lakes and semi-deep lakes is obviously increased. The paleogeographic characteristics are alternating basin ridges, alluvial fan facies, fan delta facies, lake facies and local swamp facies. The sedimentary environment of a single basin is monotonous, with only alluvial facies. This area has a humid subtropical to warm temperate climate. ② South area: Erlian basin group was in the sedimentary period of Tengger Singh Formation, and the lake basin was sinking continuously, and the lake water received a large area of lacustrine dark mudstone deposition under the background of continuous expansion, forming a sedimentary situation with wide water area, deep water body and good connectivity. The sedimentary environment is dominated by shore-shallow lake facies, followed by fan delta and river facies. The formation of well-developed deep lake facies, deep-water turbidite, nearshore subaqueous fan and shore-shallow lake beach shows the environmental evolution characteristics of the lake basin in the high tide period.

(2) Central area. ① North-central area: except for a few northern faulted basins where volcanic facies are still developed, most other areas lack sedimentary strata. The proportion of Yingcheng Formation sedimentary area in the middle of Songliao Basin has obviously increased, from the original small fault basin to an adjacent larger continental basin. At the same time, some new small sedimentary basins have been formed. Inherently developed fault basins are dominated by river facies, fan delta facies and lake facies, while newly developed fault basins are dominated by alluvial fan facies and river facies. The paleoclimate is still hot and humid subtropical to warm temperate climate. (2) Southern region: It is the sedimentary period of Shahai Formation, with a warm and humid subtropical-tropical climate. The shallow lake-semi-deep lake-deep lake environment is dominant, and the water depth is deeper than that of the early Jiufotang Formation. Shore-shallow lake facies is very developed, and semi-deep lake-deep lake facies is also very developed and widely distributed. From bottom to top, the ancient water depth changed from shallow to deep. There are alluvial fan facies, fan delta facies, lake facies and swamp facies locally.

(3) Eastern District. ① Northern area: Chengzihe Formation is in the sedimentary period and belongs to humid subtropical to warm temperate climate. During this period, the regression is large and the time is long. From the edge of the sedimentary area to the inside, the sequence is foothill-nearshore alluvial plain, land-sea transitional environment, coastal and shallow sea environment. These environments seem to be distributed in a ring to the west with the ocean as the center, and gradually transition to each other. River facies, delta facies, lagoon facies and coastal facies are developed. ② Southern area: Yanji Basin is the sedimentary period of Cai Chang Formation, and the basin scope is enlarged, and the supply of terrigenous detritus is increased, forming fluvial facies, delta facies and shore-shallow lake facies. Semi-deep lake-the range of deep lake is reduced. It belongs to temperate humid climate zone.

4. Late Rift Period (Late Early Cretaceous)

(1) West Zone. ① Northern area: The faulted basins in Hailaer area developed one after another, and the Yimin Formation was deposited. The most obvious sedimentary environment is characterized by a very developed swamp. The sedimentary range of this period is slightly larger than that of the previous period, mainly alluvial facies, swamp facies and lake facies. The region belongs to a warm and humid tropical-temperate climate. ② South area: Erlian basin group is in the sedimentary period of Saihantala Formation, with lake basin shrinking and swamping, characterized by large-scale distribution of alluvial facies and fluvial facies. At that time, the climate was tropical and subtropical, and the temperature was high.

(2) Central area. ① North-central region: A few basins such as Jiayin in the north have been transformed from early volcanic basins to normal continental clastic sedimentary basins, which are alluvial fan facies and fluvial facies sedimentary environments. The Songliao basin in the middle is the sedimentary period of Denglouku Formation. Except for the large basin developed in the early stage of the central fault depression, all other small basins have died out, and the large basin in the central fault depression has inheritance. During this period, fluvial facies, fluvial delta facies and lacustrine facies were dominant, alluvial fan facies and fan delta facies were relatively undeveloped, and the paleoclimate was humid subtropical-warm temperate climate. ⑧ Southern area: The sedimentary period of Fuxin Formation is characterized by alluvial fan facies, fluvial facies, fan delta facies, littoral shallow lake facies and swamp facies. During this period, it was a small freshwater shallow lake environment, and the distribution range of shore-shallow lake facies was obviously smaller than that of Jiufotang Formation and Shahai Formation, and it was shallow. Characterized by well-developed alluvial fan facies, river facies and swamp facies. The paleoclimate is warm and humid subtropical-tropical climate. But it is warmer and wetter than the previous period, and the coal seam is also quite rich.

(3) Eastern District. ① Northern area: The Muling Formation is in the sedimentary period, and the sedimentary environment has changed fundamentally compared with the previous periods, from pre-land-sea mutual deposition to continental deposition. Its sedimentary facies are mainly alluvial fans, fluvial facies and short-term lakes, but the water body is shallow and belongs to shallow lakes. The general trend is that the western edge is slightly higher, and it is a foothill area, which gradually decreases to the southeast, forming a lake or limnetic environment, with a gentle slope between the foothills and limnetic areas. The normal continental deposits in this area contain a lot of volcanic materials. The paleoclimate is still a warm and humid tropical-warm temperate zone. (2) Southern region: Due to the change of climate to dry conditions, coarse clastic deposits dominated by river facies (red beds) have been formed in all basins, and there are certain coastal and shallow lake deposits in the basin, and volcanic rocks and pyroclastic rocks have also appeared in Yanji area. Yanji basin consists of purple conglomerate and mudstone. Compared with before, the paleoclimate in this period has changed to some extent, with the characteristics of changing from wet zone climate to subtropical dry climate.

5. Depression period (end of early Cretaceous-early and middle period of late Cretaceous)

At the end of the late Cretaceous, most of the early Cretaceous fault basins in Northeast China shrank and disappeared, resulting in large-scale uplift and erosion, and a large number of upper Cretaceous strata were missing in Erlian, Hailaer and Liaoxi basins. Songliao basin continued to subside and developed into a large-scale depressed lake basin rich in oil and gas. Songliao basin basically formed two sets of sequences during the depression period. The lower sequence consists of Quantou Formation and Qingshankou Formation, which was formed when Songliao Basin was first unified into Dahu Basin. The first and second members of Quantou Formation are low water level system tracts, and the sediments are mainly river alluvial plain facies and lakeside facies, and the south and north water systems provide the main material sources, forming two major sedimentary systems. Since the climate warming in the third section of Quan Quan, the lake invasion began, and the area of the lake basin continued to expand. During the sedimentary period of the third member of Quan Quan, the basin became a depression, and five sedimentary systems developed around it. The fourth lake basin in Quan Quan has been further expanded, and a shallow lake of 400km2~900km2 has been formed in the middle of the basin, and six surrounding water systems converge to the center of the basin. Lake invasion reached its climax in the first member of Qing Dynasty, with a lake area of 87000km2, in which deep lake facies accounted for the vast majority, so deep lake facies black shale and oil shale were widely distributed in the basin. This is the first maximum flooding period of the basin, which has become the formation period of the main oil layers in the basin. In the late period of the first member of Qing Dynasty, it began to retreat to the lake, and in the second and third members of Qing Dynasty, it turned to retreat to the lake system tract. The area of the lake basin is gradually shrinking, from 6.8km2 in the early stage to about 3.5km2 in the later stage, which is the heyday of the development of large-scale delta, and the basin is still controlled by five surrounding sedimentary systems. The upper sequence consists of Yao Jia Formation and Nenjiang Formation, which is the repeated development period of the Great Lakes Basin. The first member of Yao Jia Formation is a low water level system tract. Due to the great contraction of the lake surface and the rapid progradation of the river, the subfacies of the delta plain are widely distributed, mainly grayish green, brownish red and purplish red mudstone interbedded with greenish gray and grayish white sandstone, showing a positive cycle. Dark mudstone is undeveloped, and the oil-generating conditions are poor. However, due to the widespread existence of the delta, the reservoir performance of sand bodies is good, and at the same time, due to moderate burial, it is located just above the source rock of Qingshankou Formation, so Yao 1 member has become the main oil layer in Songliao Basin. During the deposition period of Yao 2 and Yao 3 members, the lake gradually expanded. Due to the differential uplift of the tectonic movement between the north and south of the basin, the lakes in the north of the basin invaded obviously, and the delta complex formed by the interaction of large rivers and lakes developed, and the delta distributary plain subfacies developed very well. The widely and intermittently distributed distributary channel sand bodies provide good lithologic trap conditions. Lake invasion of the first and second members of Nenjiang Formation reached its peak, and no marginal facies deposits were found in Songliao Basin, covering an area of 200,000 km2. Mainly dark mudstone and oil shale, with stable distribution. From Nen 3 member, the lake surface began to shrink obviously, mainly shallow lake, semi-deep-deep lake facies shrank obviously, and delta facies became the main sedimentary type again. The fourth and fifth members of Nenjiang Formation are dominated by fluvial facies, and many rivers flow into the lake around the lake basin, forming numerous small deltas at the edge of the lake basin.

6. Shrinkage (Late Late Cretaceous)

The sediments in the shrinking period are mainly developed in Songliao Basin in the central region, Qingyuangang Formation in Hailaer Basin in the western region, and Erlian Dabusu Formation in Erlian Basin, but not in the eastern region. The Nenjiang Formation mine field in Songliao Basin was affected by intense compression in the late stage, and the basin further shrank, and the eastern uplift suffered extensive erosion. Since then, Sifangtai Formation and Mingshui Formation are only distributed in the middle and west of the basin (Figure 4- 10), forming the uppermost sequence of the basin. Sifangtai Formation and Nenjiang Formation are slightly unconformity superimposed, and a large positive cycle is composed of light brownish red sandstone, brownish red mudstone and grayish green mudstone. The lake water in the first member of Mingshui Formation swells slightly, and consists of grayish black mudstone, grayish green mudstone, brownish red mudstone, sandstone and conglomerate, which constitutes a transgressive system tract. The second member of Ming Dynasty is characterized by extensive alluvial plain deposits and alluvial fan deposits, and a set of brownish red mudstone and variegated sandstone are deposited. Generally speaking, the top of the stratum has been strongly denuded, and it is in unconformity contact with the overlying tertiary.

Figure 4- 10 Sedimentary Thickness Map of Sifangtai Formation-Mingshui Formation in Songliao Basin in Late Cretaceous