1. Formation stage of giant sequence TS
During the formation of giant sequence TS, Tarim Basin developed from continental rift to passive continental margin. Super-sequence TSA develops large-scale low-water level deposits in Maingard sag, which is a reflection of deep rift sedimentary filling in the early stage of basin formation. At the top of the supersequence TSA, large-scale progradation superprecipitation develops, which is a large-scale transgression feature. Reflected in the curve of datum level change, it shows a rapid and continuous rising process until the formation of supersequence TSC. Although there is a slight decline (corresponding to the jacking sequence on the earthquake) and stagnation, the general trend is upward, reaching the highest water level in the early TSC deposition (equivalent to the early Early Ordovician). What followed was a sharp drop in sea level.
In the development stage of giant sequence TS, there are three obvious second-order cycles in the datum change curve. The first cycle is mainly a continuous and stable rising process, corresponding to the northern part of Tarim, with shallow water, land and offshore carbonate platform and tidal flat facies deposits as the main ones. In the second cycle, Tabei developed into a passive continental margin, and from west to east it was carbonate open platform facies-shelf facies-deep basin facies. Multi-stage progressional sequences are developed in the platform facies area, with large progressional angle between sequences, topping, progradation and accretion appearing alternately. In the continental shelf facies area, with the rise and fall of sea level, the edges and corners of the continental shelf migrate to the sea or land. On the seismic profile, there are multi-stage mound reefs with chaotic internal reflection. In the deep basin facies area, a low-level system tract is developed, and progradation and bottom can be seen at the top of the low-level system tract, which has typical marine sequence structure characteristics. The third cycle is the maximum and highest water level period in the northern part of Tarim Sea, and there are under-compensated deposits in Maingard Depression. The sedimentary strata in the western platform are relatively thick, and the deep basin in the east is rapidly thinning.
2. Formation stage of giant sequence TTP—TKA
The development stage of giant sequence TTP-TKA (O2+3-D) is the transformation stage of basin to active continental margin and back-arc foreland. Due to the southern Tianshan ocean (? ), the northern Xinjiang Ocean subducted to the south, the Ordovician continental volcanic island arc belt appeared in the northern margin of Tarim, and the rhythmic layer of sandy and argillaceous slate mixed with thin layer of biological limestone appeared in the Kuruktag back-arc basin in the east. Underwater fans with a thickness of nearly 3000 meters, turbidite and pelagic dark mudstone in the trough basin are developed in the Peacock River trough area.
In the datum change curve, the seismic overshoot curve is in good agreement with the accommodation space change curve. It can be divided into three secondary cycles. In the first cycle (equivalent to O2+3), the bottom water level is the lowest, corresponding to a large sequence interface. In the earthquake, the middle and upper Ordovician is characterized by the development of a large-scale low water level system. The stratum is thin in the west and thick in the east, and the superstructure is obviously wedge-shaped from east to west. According to the analysis of the south-north regional profile, in the southeast area of Tazhong Uplift, a large incised valley extending from southeast to Maingard Depression was seen on the NS585 seismic line, and a high-angle large-scale progradation from south to north was seen, which indicated that the large basin-bottom fan in Maingard Depression was the result of southeast provenance.
The second cycle and the third cycle correspond to TTPB(S) and TKA(D) respectively. The existing drilling wells are located in the Silurian-Devonian marginal facies belt, revealing that the sedimentary environment is terrigenous clastic deposits with shallow water background. However, according to the seismic sequence analysis, there are low-water level deposits characterized by the above-mentioned top facies and a faintly visible lower top surface indicating the position of the maximum flooding surface in Mangar deep depression, which indicates that the Silurian Mangar depression has developed deep-water deposits and has the conditions to form oil-bearing layers.
3. Development stage of giant sequence TKB—TLA
TKB—TLA giant sequence is equivalent to Carboniferous-Permian. The early Hercynian movement fundamentally changed the paleogeographic pattern of Carboniferous relative to Sinian-Devonian, and began a brand-new sedimentary cycle. Under the influence of this movement, the Kuruktag Aola Trough and the Tarim foreland basin were closed and uplifted into land, while the southwest region was distorted and fractured, forming an internal craton basin, which was connected with the surrounding basins in the southwest region of Tarim Craton. Tabei area inherited the regressive sedimentary pattern since the late Devonian, and the seawater retreated to the southwest on a large scale.
On the seismic overshoot curve, there are two secondary cycles in Carboniferous and one secondary cycle in Permian. On the curve of logging accommodation space, Carboniferous is also two second-order cycles, including four third-order cycles, and the curve of Permian is missing. The first second-order cycle developed in the early Early Carboniferous, and its maximum flooded surface corresponds to the "double-peak limestone" section, and the low water level system in northern Tarim is undeveloped or thin. It is mainly transgressive system tract and high water level system tract. In the process of transgression, a thick transgressive sand layer was formed, which became the main target layer of Carboniferous. In the first cycle, tidal flat facies and evaporite facies also developed in Tabei area. The second cycle corresponds to the late Early Carboniferous and the late Carboniferous, and its highest water level appears in the late Early Carboniferous. Corresponding to this cycle, the river-delta sedimentary system developed in northern Tarim.
In the southwest of the basin, multi-stage and long-distance lead products can be seen along the Hetian River profile (Figure 2-23), which constitutes the main oil-generating area of Carboniferous.
Permian sedimentary cycle is mainly developed in the southwest of the basin and distributed in the west of well Sha 10 in the north of Taba. Earthquakes are characterized by progradation high-frequency sequences, and there are large areas of igneous rocks.
4. The developmental stage of giant sequence TUA
The giant sequence TUA corresponds to Triassic and Jurassic. Only the Lower Jurassic is developed in northern Tarim, so the upper part of TUA giant sequence is incomplete.
After filling and filling in Triassic and Late Permian, Tabei area entered the development stage of Mesozoic-Cenozoic continental basin. Awati-Maingard area is surrounded by Keping-Bachu Gulong, Xinhe-Luntai low hills and Korla-Yuli Gulong, becoming a depressed inland basin with high in the north and low in the south. Awati area, affected by Aqia fault and Shajingzi fault, has the nature of depression and has become the sedimentary center of early Triassic in northern Tarim.
On the curve of datum level change, two secondary cycles developed in this period. The lower part of the first cycle is at a low water level, and the corresponding sedimentary range is limited to Awati fault depression, and the sedimentary strata overlap from west to east. The highest water level was reached in the middle and late Early Triassic, and a continuous strong reflection with stable characteristics appeared on the earthquake. With the formation of Triassic strata, Awati area gradually rose, the lake moved from west to east, and the sedimentary center moved to Maingard area, thus developing a small-scale low-level system tract. By Jurassic, the sedimentary center moved further eastward, and only the sedimentary facies area at the edge of the basin was seen in Tabei area.
5. the developmental stage of giant sequence tz-tte
The Cretaceous and above strata in northern Tarim are stable in distribution and gentle in occurrence, so it is difficult to find the super-point on the strata. The curve of the super-point at this stage is not comparable to the curve of global sea level change. The reason is probably that the reliability of the upper super-point curve is reduced in Cretaceous and above strata. The curve of accommodation space change obtained from logging has a good correspondence with the cyclicity of formation lithology, and although it is quite different from the curve of global sea level change, it is comparable to some extent. The curve is embodied in two secondary cycles, and the overall change is slow. There is a peak water level corresponding to Kapshaliang group.