Since 2019, there have been significant discoveries in deep oil and gas exploration in the southern margin of the Junggar Basin in Xinjiang. In the west section of the Gaoquan anticline, a high-yield oil and gas flow has been obtained from the Cretaceous Qingshuihe Formation at a depth of 5770 m in the Well Gaotan 1, with a daily crude oil output of 1213 m³ and daily natural gas output of 32.17×10⁴ m^{3 [1]}. In the middle section of the Hutubi anti-cline, a major hydrocarbon breakthrough has been made from the Cretaceous Qingshuihe Formation in Well Hutan 1 in the Hutubi anticline, with daily natural gas production of 61×10⁴ m³ and daily crude oil production of 106.3 m³, which indicated that the Jurassic-Cretaceous deep layers in the southern margin of the Junggar Basin have great oil and gas exploration potential. The discovery of large-scale deep oil and gas reserves needs to be confirmed by large-scale reservoirs. The oil and gas exploration level is low in the lower assemblage (the Mesozoic) of the Junggar Basin. Field outcrop studies have shown that the Jurassic-Cretaceous sand bodies are distributed widely, with large thickness and good reservoir performance ^[2]. However, due to the considerable burial depth, limited drilling data and the complexity and versatility of seismic imaging ^[3,4], it is difficult to predict the distribution of sedimentary sand bodies by combining cores and outcrops with seismic facies. This is also one of the key issues restricting large-scale oil and gas exploration in the deep to ultra-deep reservoirs in the southern margin of the Junggar Basin.

In the past, massive researches have been conducted on the types of sedimentary facies and the distribution of favorable reservoirs in the southern margin of Junggar Basin. However, due to limited drilling data, the complexity and versatility of seismic imaging, results of previous studies exhibit three deficiencies: (1) Previous studies mainly focused on the sedimentary facies and sandbody architecture of individual strata by field outcrops in the orogenic belt ^{[5,6,7,8,9,10]}, with low research degree. (2) Although the sedimentary facies and sand body distribution in the whole area including deep layers has been studied ^[11,12,13], the distribution range of sandy conglomerate bodies in the basin was mainly based on speculation, and the reliability was low. (3) The study area is 3×10⁴ km^{2 [6]}. Most sedimentary facies diagrams took the edge of the basin as the lake shoreline, and from west to east, there were extensive braided river delta fronts, fan delta fronts and other types of sand bodies. However, there were very few researches on the lithofacies and paleogeographic characteristics of the prototype basin. Therefore, due to the poor understanding about the lithofacies and paleogeography of the prototype basins, the low reliability of the distribution of sedimentary sand bodies, it is necessary to carry out thermo-chronological research to determine the location of the macro-provenance. Based on the principle of "the present being a key to the past", with the parameters such as the relationship between the average gravel diameter ($\bar{d}$) and the sediment transport distance, and the amount of structural shortening, we restored the provenance area and the evolution position of the lake shoreline, analyzed the sedimentary petrology and sedimentary structure of drilling cores and field outcrops, and compiled a series of maps of lithofacies paleogeography evolution and sandy conglomerate body distribution. This study establishes a new method for the study of lithofacies and paleogeography of the foreland orogenic belt, clarifies the distribution of large-area sandy conglomerate bodies of the Jurassic-Lower Cretaceous, which can provide a geological knowledge base to support oil and gas exploration of the deep lower assemblage in the southern margin of the Junggar Basin.

The sediments in the basin derived from the denudation and exposure of the mountains. Through restoration of the distribution range of the mountains during the depositional period, the provenance area on a macroscopic scale was determined. Located in the southern part of the Junggar Basin, the Tianshan Mountains are 1700 km long from east to west and 250-350 km wide, with north-south branches in both east and west sections^{[6, 14]}. In the northwest of the basin, there are Zaire Mountain and the Ararat Mountain. In this study, through apatite fission track age, the uplifting time of the Tianshan, Zaire and Ararat mountains have been determined ^{[14,15,16,17]}. According to the uplift time, the uplift sequence and distribution range of the surrounding mountains in the Early Jurassic-Early Cretaceous have been made clear (Fig. 1): (1) In the Early Jurassic (180-200 Ma), the uplift of the mountains in the southern part of the basin was mainly located in the central Tianshan Mountains and southern Kuitun on the Zhaosu-Ili line (the green area in Fig. 1), and the uplift range was relatively small. There was almost no mountain uplift in the northwestern part of the basin. (2) During the Late Jurassic to Early Cretaceous (100-150 Ma), the uplift in the southern part of the basin was located in Qiongbola Forest Park in the central Tianshan Mountains, the upstream of the Manas River in the northern Tianshan Mountains-Bogda Mountain, and the Ouxidaban area of the Duku Highway in the southern Tianshan Mountains, as well as the northern part of Kuruktag Mountain on the northern margin of the Tarim Basin. The range of uplift during this period was relatively large. The Zaire Mountain and Ararat Mountain in the northwestern part of the basin were uplifted (the orange area in Fig. 1). The distribution of macroscopic provenance areas on the periphery of the Junggar Basin has the following evolutionary characteristics: (1) During 180-200 Ma, the main divide of the Tianshan Mountains was located in the southern part of the Tianshan Mountains. The uplift height of the southern edge of the central Tianshan and the southern Tianshan was greater than the northern edge of the central Tianshan and the northern Tianshan. The ancient topography of the southern Tianshan was higher than that of the central Tianshan and the northern Tianshan. The southern part of Tianshan provided sources for the northern piedmont ^[18,19]. The provenance of the west section of the southern margin of Junggar Basin was located in the area in the south of the Jinghe-Kuitun line. The topography of the area was much gentler than the present profile. The ancient Tianshan Mountains may be in the middle-low mountain and hills. The Junggar Basin was a dustpan-shape basin, shallow in the north and deep in the south ^[20], where alluvial fans, fan deltas and other deposits were well developed. In the middle section of the southern margin of Junggar Basin, that is the vast area along the Kuitun- Urumqi line, where rivers, deltas and other remote deposits were well developed. The provenance was from the current central Tianshan area. (2) During the geological period of 100-150 Ma, the main divide of Tianshan Mountains moved gradually from the southern Tianshan Mountains towards the northern Tianshan Mountains ^[18,19]. The provenance area in the western section changed little, and fan delta deposits still dominated the basin. With the large-scale uplift of the northern Tianshan and Bogda Mountains in the southern part of the Kuitun-Urumqi line, the middle part of the basin gradually evolved from distant river and delta deposits to proximal alluvial fans and fan delta deposits. During this period, the Zaire Mountain and Ararat Mountain also uplifted on a large scale, and provided sandy conglomerate deposits for the northwestern margin of Junggar Basin.

There are super-thick conglomerate sections at the edge of the basin. Correspondingly, there are thick layers of sandstone extending into the basin. The gravel composition directly reflects the composition of the parent rock in the provenance area ^[21-22], and the gravel size reflects the distance from the provenance area. Measuring the grain size of gravel and establishing the relationship between sediment size and sediment transport distance can determine accurately the migration characteristics of the provenance area ^[23]. The grain size of the gravel can be obtained by measuring the length of a-axis (long diameter), b-axis (medium diameter) and c-axis (short diameter) of each gravel, followed by calculation and statistical analysis. The average gravel diameter ($\bar{d}$) is equal to the cubic root of the product of the average gravel diameter of the a-axis, the average gravel diameter of the b-axis and the average gravel diameter of the c-axis ^[24,25,26]. The average gravel diameter is the largest close to mountains, and progressively decreases in the middle part of the mountains, being the smallest at the front edge ^[26].

The gravel length of a-axis, b-axis and c-axis was measured which in the channels of the Huangshuigou alluvial fan braided channel, the Malan Hongshan fan delta plain, and Kaidu River in the northern margin of Bosten Lake at the foot of the southern Tianshan Mountains. The relationship between the average gravel diameter and the transport distance of gravels in modern alluvial fans, fan delta plains, rivers and other sedimentary systems has been established ^{[23, 27]} (Fig. 2). The gravel composition and gravel diameter of major conglomerate layers in the Jurassic to Cretaceous of the Haojiagou-Toutunhe, Hutubi River, Manas River and Anjihai River outcrops were analyzed and measured. After obtaining the data, according to the sedimentary facies types of the measured intervals and the established relationship between gravel diameter and transport distance of different sedimentary facies, the sediment transport distance of thick conglomerate in the alluvial fan, fan delta and fluvial sedimentary body in ancient outcropped areas were calculated by comparing ancient and modern. The distance to the provenance area calculated from several outcrops in the same period is connected to a line, which defines the inferred provenance area (Fig. 3).

Due to the tectonic movements, the deep layers in the southern margin of Junggar Basin have been transformed since the Neogene, and the original appearance of the Jurassic-Early Cretaceous sedimentary has changed significantly. Nowadays, three rows of Cenozoic thrust structural belts extend from east to west in the middle section of southern margin of Junggar Basin. These are the first row of the Qigu anticline and the second row of the Tugulu anticline in seismic profile A-A' in Fig. 4, and third row of Hutubi anticline in seismic profile B-B' in Fig. 4. The three rows of anticlines are about 500 km long and 30-50 km wide ^[28]. Guan et al. ^[28] believed that from east to west in southern margin of Junggar Basin, through balance restoration, a structural shortening of 37 km was obtained for the Santunhe outcrop, and 19.5 km for Jingouhe-Anjihai River outcrop. That is the location of the current Toutun River-Haojiagou outcrop, Hutubi River outcrop, Manas River outcrop and Anjihai River outcrop (solid triangle in Fig. 3). Compared with the Jurassic- Cretaceous period, it moved 19.5-37.0 km northward. To restore to the original depositional position before the thrust nappe, these four outcrops need to be pushed back 19.5-37.0 km southward, which is the hollow triangle position in Fig. 3. This is the initial deposition position of the 4 outcrops. For the restoration of the Jurassic-Cretaceous sediment provenance area, this value should be the sum of the calculated gravel transport distance (S) and the structural shortening since the Neogene (Fig. 3).

The relationship between the characteristics of the modern sediments on the northern margin of Bosten Lake and the distance between the lake shoreline was analyzed. It has been found that when the sedimentary slope of the Kaidu River delta decreased from 0.39° to 0.02°, the channel transited from gravel to sand in the upper reaches of the meandering river, about 65 km from the shoreline of Bosten Lake. The gravels were mainly deposited in the channel, with an average diameter of 1.02-3.33 cm ^[23]. In the Malan Hongshan fan delta plain, the distance from the mountain pass to the shoreline of Bosten Lake is about 30 km, and the sedimentary slope was reduced from 2.5° to 0.05°. The section of the braided channel was gravel dominated changed to sandy, about 15 km from the shoreline. The gravel was mainly deposited in the channel, with an average gravel diameter of 3.83 cm ^[23]. The source supply of fan delta was sufficient, and the distance from gravel to sand was close to the lake shoreline. The supply of sediments in the river deltas was relatively small, and the distance from gravel to sand was far from the lake shoreline. The greater the sedimentary slope, the closer the transition from gravel to sand is to the lake shoreline. The smaller the sedimentary slope, the greater the distance of the transition from gravel to sand is to the lake shoreline.

Based on the sedimentary slope of the multiple types of sedimentary system, the relationship between the occurrence of gravel and the distance to the lake shoreline, the average gravel diameter, and the distance between the water system outlet and the lake shoreline, we calculated the distance between the current position of the Jurassic-Cretaceous and the evolution of the lake shoreline in the Haojiagou-Toutun River outcrop, Hutubi River outcrop, Manas River outcrop, Anjihai River and other outcrops. At the same time, the structural shortenings of the Santunhe outcrop and the Jingouhe-Anjihai River outcrop are 37 km and 19.5 km ^[28]. The current Toutun River outcrop, Hutubi River outcrop, Manas River outcrop and Anjihai River outcrop have moved 19.5-37.0 km northward compared with the Jurassic-Cretaceous period. Therefore, the four outcrops and the calculated lake shoreline are pushed back 19.5 to 37.0 km southward to restore the Jurassic-Cretaceous lake shoreline variation range (Fig. 3). Judging from the distribution characteristics of the provenance area marginal line and lake shoreline restored in Fig. 3, the marginal line lies about 100 km south of the current basin marginal line (the solid line in the lower left corner of Fig. 3). The lake shoreline is distributed within a range of tens of kilometers to the north of the current basin edge (the dotted line in Fig. 3). During the depositional period of the Middle Jurassic Xishanyao Formation and Toutunhe Formation, the marginal line of the restored provenance was distributed in the southernmost part of the current basin margin (the solid blue line in Fig. 3). During the depositional period, the Upper Jurassic Kalazha Formation and the Lower Cretaceous Qingshuihe Formation were close to the current basin margin. The restored lake shoreline was evolved with the migration of the marginal line of the provenance area and changed accordingly. The evolution characteristics of this provenance area and the lake shoreline are in good agreement with the research results of Zhou et al. ^[29] and Fang Y et al. ^[30], and a quantitative determination has been made.

After obtaining the high-yield oil and gas flow from Well Gaotan 1 in the western section of the southern margin of Junggar Basin, a lot of cores of the Jurassic- Lower Cretaceous Qingshuihe Formation were described, including wells Gao 101, Gao 102 and Gao Quan 5 in the study area, Well Ka 8 and Well Ka 10 in the north of the study area. The core from Well Gao 101, located 1.65 km southwest of Well Gao Tan 1, is relatively complete, and the core at the Lower Jurassic Badaowan Formation is 6901-6909 m in burial depth. There is a positive rhythm deposition of small gray conglomerate to coarse-medium sandstone, dominated by dark volcanic gravel, which is subangular to subrounded, supported by grains, and filled with medium-coarse sand between the gravels. The gravel diameter is less than 1 cm, and the composition contains black volcanic rock and quartzite, with gypsum cemented between the gravels. It is fluvial deposits on the whole. The core at the Lower Jurassic Sangonghe Formation is 6465-6473 m in burial depth, and is dominated by gray conglomerate. The gravel becomes thicker and larger, with a diameter of 1.0 to 2.5 cm and up to 7 cm locally, and in a subangular to subrounded shape. The gravel composition includes dark volcanic rock, gray-green sedimentary rock, and flesh-red tuff, supported by grains, with anhydrite cementation between the gravels. The gravel roundness is improved when the contact distance decreases. The conglomerate was mixed with gray, gray-green medium-fine sandstone and was of massive structure. As a whole, it is a braided channel deposit in the fan delta plain. The core at the Middle Jurassic Toutunhe Formation is 6191-6200 m in burial depth (Fig. 5a), with gray conglomerate and coarse sandstone in the lower part. The gravel diameter is 1 to 3 cm, and the maximum is 5 cm. The gravel composition includes flesh-red tuff and gray-green sedimentary rock. The color of the conglomerate is more grayish-green than that of the Badaowan and Sangonghe Formations. The middle part is gray medium-fine sandstone with massive structure and undeveloped bedding. The upper part is a brown, brown-gray silt-bearing mudstone with gray thin siltstone bands. The whole is fluvial or fan delta plain braided channel sedimentation. The core of the Qingshuihe Formation of the Lower Cretaceous is 6017-6025 m in burial depth (Fig. 5b), with brown conglomerates in the lower part, and brown sand and argillaceous fillings between the gravels. The diameter of the gravels is 0.5-1.0 cm. The gravel in the middle and upper part becomes larger, up to 4 cm in diameter, supported by grains, with a subangular to subrounded shape, and mainly composed of sedimentary rock and volcanic rock. There are gray-green and gray conglomerates in the upper part, supported by grains and local calcite cementation between the gravels, and the remaining space is filled with gray-green sand and argillaceous fillings. The physical properties are inferior to the brown conglomerate section, and the upper gravel diameter is smaller. As a whole, it is a braided channel deposit in the fan delta plain. Based on these samples, through correlation analysis of the combined wells, the sedimentary characteristics of the Toutunhe Formation and the Qingshuihe Formation were compared (Fig. 6). It is believed that from the Sikeshu River outcrop in the western section to the Kayindike well area in the north, the Toutunhe Formation is dominated by the braided river delta plain-front deposits from the near-source, and the sandy conglomerate deposits are thick and widely distributed. During the depositional period of the Qingshuihe Formation, near-source fan delta front deposits were dominated. The sandy conglomerate body was thinner. Later, with the gradually rising of the lake level, a large area of thick layered mudstone was deposited on the sandy conglomerate body (Fig. 6).

In the middle-east section of the southern margin of Junggar Basin, the Jurassic-Lower Cretaceous deposits are rarely penetrated. After investigating the Toutun River-Haojiagou outcrop, Hutubi River outcrop, Manas River outcrop and Anjihai River outcrop, it is believed that alluvial fan facies are well developed in all formations of Jurassic-Lower Cretaceous. Alluvial fans were well developed in the Mid-Late Jurassic arid to semi-arid climate, with obvious seasonality and suddenness. In lithology, it is mainly variegated thick sandy conglomerate quickly accumulated, with coarse grain size, poorly sorted and rounded, poorly developed bedding, and common scour at the bottom. The sediments are primarily reddish, with no animal and plant fossils. The Upper Jurassic Kalazha Formation in the Manas River outcrop belongs to large- scale alluvial fan deposits. In lithology, it is reddish- brown massive conglomerate and sandy conglomerate, poor in sorting and roundness. It has a large scouring structure with inconspicuous graded bedding. Due to different weathering, a steep cliff was formed with the underlying stratum (Fig. 5cVIII). Braided river deposits are well developed in all Jurassic-Lower Cretaceous formations, whereas for braided channel, deposits are dominated by braided bar micro-facies. Braided bars are mostly coarse-grained sediments, such as conglomerate, sandy conglomerate, coarse sandstone, etc., and large-scale trough-like and plate-like cross-bedding can be seen. The floodplain is dominated by alluvial plains, with red and purplish muddy deposits mainly. The floodplain is an interbed with sandstone and thin mudstone. Braided river deposits can be seen in the Badaowan Formation of the Toutun River-Haojiagou outcrop (Fig. 5cII). The point bar deposits are medium-coarse sandstones, with oversized trough-like cross-bedding, parallel bedding, and prominent positive rhythms. The bottom of the floodplain eroded as a result of common channel erosion, forming a clear surface. The alluvial plain is dominated by redish-brown mudstone, located at the top of the channel, often eroded by the late channel. Meandering river deposits are developed in all formations of the Jurassic, with a binary structure and a positive cycle from coarse to fine (Fig. 5cV, VII). The lower part of the cycle is channel sediments, including riverbed sediments and point bar micro-facies. The channel sandstone is generally lenticular, and the thickness is obviously reduced on both sides, resulting in plate-shaped, trough-shaped (Fig. 5cVI, VII), wavy, wedge-shaped cross-bedding, parallel bedding, corrugated bedding, etc. Natural levee and crevasse fans are poorly developed, with dominated floodplains. The reddish-brown and purple mudstones of the floodplains constitute the main body of meandering river deposits, and the channel sandstones are intercalated with mudstones. Braided river delta is the most common type of sedimentary facies, developed in multiple outcrops. In lithology, the braided channels in the braided delta plain is mainly sandy conglomerate, conglomeratic sandstone and sandstone (Fig. 5cI), and the argillaceous content between braided cannels is relatively high. In lithology, the underwater distributary channel in the braided river delta front (Fig. 5cIII) is conglomeratic sandstone and sandstone. The distributary channels are dominated by argillaceous sediments, and the mudstone is gray-green, gray and other reduction colors. The estuary bar is composed of medium-fine sandstone, which is well sorted and has a reverse rhythm. The fan delta is mainly developed at the bottom of the Qingshuihe Formation in the Lower Cretaceous (Fig. 5cIX, X). There are fan delta front deposits in the Hutubi River outcrop. In lithology, the fan delta front deposits are mainly gray, gray-green conglomerate, sandy conglomerate, interbedded with grayish-black, grayish-green mudstone. Based on the above analysis of core and field outcrops, some parameters were counted, including the formation thickness, sandstone thickness, sandstone formation ratio, main sedimentary facies types, and physical characteristics of the reservoirs of the Toutunhe Formation-Qingshuihe Formation (Table 1), which provided an important foundation for the restoration of lithofacies and paleogeography and the distribution of favorable sandy conglomerate bodies in the southern margin of Junggar Basin.

Based on the age of the apatite fission track, the macro- provenance has been determined, and the lake shoreline position has been restored according to the parameters such as the relationship between the gravel diameter and the sediment transport distance and the amount of structural shortening. The sedimentary characteristics of the cores from more than 20 wells and more than 10 field outcrops (Table 1) have been analyzed. Combined with the previous understanding ^{[29, 31-34]}, the lithofacies paleogeographic characteristics of the Early Jurassic to Early Cretaceous in southern margin of Junggar Basin have been restored (Fig. 7). It is believed that the provenance area expanded gradually from south to north, with a process of expanding-shrinking-expanding for the lake basin, and the overall evolution characteristics of the paleoclimate are wet-dry-wet. (1) Ancient provenance.

During the Early-Middle Jurassic, large continental depression basin was developed in the Junggar Basin. During this period, the southern Junggar Basin was dominated by provenances from the ancient Tianshan Mountains, with the western section continuously developing proximal deposits (Fig. 1), and the middle-eastern section evolving from far-source to near-source. The boundary line between the western and middle provenance areas is inferred to be the Hongche fault zone. The reason is that the Hongche fault zone is nearly north-south trending, 80 km long and 20 km wide, which is a fault zone formed during the Triassic-Jurassic period. Affected by the Hercynian-Yanshan movement in the early and mid-term, the western mountains pushed eastward, forming multiple north-south inverse faults ^[35]. The Hongche fault zone was the largest transverse faulted structural zone in the west-middle sections of the southern margin, which divided the basin-mountain transition zone from Junggar to North Tianshan into the western section and the middle section. The basement properties and deformation characteristics of each section are significantly different^[36]. From the Late Jurassic to the Early Cretaceous, the southern Junggar Basin gradually evolved into the ancient Tianshan Mountains in the south, and the Chepaizi-Mosuowan uplift in the north-west and north, with multi-directional provenances. The Chepaizi salient in the northwestern Junggar Basin was uplifted in the Late Jurassic ^[37]. He et al. ^[38] believed that the end of the Jurassic was the peak period of the development of the Chepaizi-Mosuowan paleo-uplift, and the mid-Yanshan period was the stage of the development and finalization of the paleo-uplift, which was consistent with the uplift time of the northwestern Junggar Basin, as shown in Fig. 1. (2) The ancient lake shoreline. The lake shoreline when the restored Jurassic-Early Cretaceous sandy conglomerate body extended toward the basin with the maximum extent, presents an angle that opens to the north-west with the current basin edge line. In the early period of Early Jurassic, the lake shoreline was far from the provenance area, and distributed along the northern part of Well Ka 6-northern Kuitun-northern Shawan-Shihezi- southern Hutubi-Changji-northern Fukang. The influence range of lake level was relatively small. From the late period of the Early Jurassic to the Middle Jurassic, the lake level rose sharply, and the lake shoreline migrated to the south across a large area. It was distributed along the eastern part of Well Ka 6-Well Xihu 1-southern Shawan-Well Qigu 1-southern Urumqi-southern Fukang, with a large lake basin area. During the Late Jurassic, with the uplifting of the Bogda Mountain Chepaizi-Mosuowan paleouplift, the lake level dropped, and the lake shoreline moved northward. It was distributed along the eastern Kuitun-southern Shawan-southern Shihezi-the northern part of Qigu 1 well-southern Changji-northern Urumqi-Fukang. In the Early Cretaceous, the Chepaizi- Mosuowan paleouplift sank as a whole, and the lake shoreline moved southward to the current basin edge line. It was distributed along the west of Well Gaotan 1-the southern part of Dushan 1-the southern part of Qigu 1-southern Urumqi-southeastern Fukang, and the Cretaceous deposits were deposited in the lake basin. (3) Paleoclimate. The climate in the Junggar Basin was warm and humid during the mid-period of Early-Middle Jurassic. From the late period of the Middle Jurassic, the paleoclimate changed into a semi-humid to semi-arid climate, and the plant decreased significantly. From the Early Cretaceous, the paleoclimate changed into a warm and humid climate environment ^[20], and vegetation were well developed.

Based on the analysis of the ancient provenance, the ancient lake shorelines and the paleoclimate, six major ancient water systems have been restored in the south from west to east, including the ancient Sikeshu River, the ancient Anjihai River, the ancient Manas River-ancient Hutubi River, the ancient Toutun River and the ancient Sangong River. In the north, the lithofacies paleogeographic characteristics were developed under the influence of Mosuowan paleo-river system.

Lower Jurassic Badaowan Formation (Fig. 7a): (1) In the western section, there are proximal fan delta plain- front deposits, and the fan delta deposits under the influence of the ancient Sikeshu River and other paleo-water systems are distributed along the line from Well Ai 4 to Well Dushan 1. From west to east in middle-east section, there are distal braided river-braided river delta deposits under the influence of ancient river systems such as Ancient Anjihai River, ancient Manas River-ancient Hutubi River, ancient Toutunhe River, and ancient Sangong River. In the north, the distal river delta is developed under the influence of the Mosuowan ancient river system. (2) The current Toutun River-Haojiagou outcrop is about 28 km from the restored lake shoreline, and the outcrop is 50-60 km south to the lake shoreline during the depositional time. The Anjihai River outcrop is about 45 km from the restored lake shoreline, and 65-70 km away from the lake shoreline in the south during deposition. The lake shoreline is distributed along the northern part of Well Ka 6-northern Kuitun-northern Shawan-Shihezi- southern Hutubi-Changji-northern Fukang. The Badaowan Formation is composed of braided rivers, braided river deltas, and shallow lake deposits. The climate was humid, and coal-bearing coarse clastic deposits were deposited. The lakes became deeper in the middle and late stages, and semi-deep to deep lake facies were developed in the center of the depression.

During the deposition of the Lower Jurassic Sangonghe Formation, the Junggar Basin experienced two large-scale lake transgressions, which was the largest lake transgression, and was dominated by lake and braided river delta deposits ^{[2, 11-12]}. With the rapid lake transgression, the lake level rose rapidly with no coal seams developed, most of the basin was covered by lakes. The source supply was reduced, and floodplains were developed in some areas.

During the deposition of the Middle Jurassic Xishanyao Formation, due to the lake level decline and the uplifting of Chepaizi-Mosuowan low uplift, a relatively high land was formed. At this time, the climate was warm and humid, and the plants were most prosperous, forming a large area of flooded swamps, lakeside swamps, and river swamp environments, becoming the peak period of coal seam development ^{[2, 11-13]}.

The Middle Jurassic Toutunhe Formation (shown in Fig. 7b): (1) The western section was along the line from Well Ka 6-Well Ka 10-Well Gaotan 1-Well Xihu 1, and the proximal fan/braided river delta plain-front sedimentary system was developed under the influence of the ancient Sikeshu River system. In the middle section, the distal braided river-river delta deposits were deposited under the influence of ancient river systems, such as the ancient Anjihai River, the ancient Manas River-ancient Hutubi River, and the ancient Toutun River. With the uplifting of the Bogda Mountain, braided river delta deposits were deposited under the influence of the ancient Sangong River system in the eastern part of the southern margin of Junggar Basin. Distal river delta deposits were deposited under the influence of the Mosuowan River system in the north. (2) The provenance area of the southern ancient Tianshan Mountain receded southward compared with the deposition period of the Badaowan Formation. (3) The current Toutunhe-Haojiagou outcrop is about 13 km from the restored lake shoreline, and this outcrop was about 50 km south of the lake shoreline during the depositional period. The Anjihaihe outcrop is about 30 km from the restored lake shoreline, and it was about 50-65 km away from the lake shoreline during deposition. The lake shoreline is distributed along the east of Well Ka 6-Well Xihu 1-Southern Shawan-Well Qigu 1-Southern Urumqi- Southern Fukang. The color of the Toutunhe Formation is gray-green, gray, alternated with purple-red and maroon- red, reflecting a depositional background of alternated warm-humid and dry-hot climates. The red bands increased upward indicating that the depositional environment became arid gradually.

In the Upper Jurassic Qigu Formation, fluvial-coastal shallow lake deposits were deposited ^{[2, 7, 9]}. In the middle section, meandering river deposits were dominated. In the Toutunhe profile outcrop and the Manas River outcrop, an obvious “binary structure” of thin sand and thick mud is developed. The color of the sediment is purple-red and dark red, reflecting the dry and hot climate.

The Upper Jurassic Kalazha Formation (shown in Fig. 7c): (1) The Chepaizi-Mosuowan salient continued to move, and provided provenance for the western section together with the northern Tianshan Mountains. Due to the two-way provenances of the ancient Tianshan Mountains in the south and the Chepaizi salient in the north, the paleo-water system was converted into a system which is dominated by north-west axis and north-south two-way provenances with near source as subordination. Onshore sedimentary systems were developed, such as alluvial fans-rivers. (2) The provenance area in the middle-east section moved northward and northwestward, and was controlled by ancient rivers such as the ancient Anjihai River, the ancient Manas River-ancient Hutubi River, the ancient Toutun River, and the ancient Sangong River from west to east. The proximal alluvial fan-fan delta and braided river delta were developed. The distal river delta was deposited under the influence of the Mosuowan water system in the northern part. (3) The current Toutun River-Haojiagou outcrop is about 23 km from the restored lake shoreline, and the Anjihai River outcrop is about 40 km from the restored lake shoreline. The lake shoreline is distributed along the line of eastern Kuitun-southern Shawan-southern Shihezi-north part of Well Qigu 1-southern Changji-northern Urumqi-Fukang. It is characterized by rapid denudation and rapid deposition on the whole, with purple-red, dark red, and red sediments as the main components, reflecting a dry and hot climate environment.

The Lower Cretaceous Qingshuihe Formation (shown in Fig. 7d): (1) In the west section, sedimentation occurred under the Chepaizi-Mosuowan paleo-uplift, and fan delta deposits were deposited in the Sikeshu sag under the influence of the ancient Sikeshu River system of the southern part of northern Tianshan Mountains. In addition, the distal river delta deposits were deposited, sourced mainly from the northern Chepaizi low uplift area. In the middle-east section, the provenance range is similar to that of the Kalazha Formation, or moved slightly to the north. Alluvial fan-fan delta and braided river delta deposits were deposited from the west to the east under the influence of the ancient Anjihai River, the ancient Manas River-ancient Hutubi River, the ancient Toutun River and the ancient Sangong River systems. In addition, distal river delta deposits were deposited under the influence of the Mosuowan water system in the north. (2) The current Toutun River-Haojiagou outcrop is about 3 km from the restored lake shoreline, and the Anjihai River outcrop is about 8 km from the restored lake shoreline. The lake shoreline is distributed along the line of west of Well Gaotan 1-south of Well Dushan 1-south of Well Qigu 1-southern Urumqi-southern Fukang. The subsidence range increased in the lake basin, and the climate changed from hot and dry to humid. The lake basin continued to expand, and the lake water advanced northward and eastward. Most of the basin was occupied by shallow lakes in Early Cretaceous ^{[1, 5-6]}.

In the southern margin of Junggar Basin, influenced by strong tectonic movement in the later period, obvious denudation occurred in the Jurassic-Lower Cretaceous formations ^[38]. The distribution range of the sandy conglomerate bodies in the basin is limited by the current stratum denudation line and basin edge line. Within this range, the restored lake shoreline controls the heterogeneity characteristics of the sandy conglomerate bodies in the delta plain facies and front facies on both sides. The following are the distribution characteristics of the deep sandy conglomerate reservoirs: (1) Under the influence of six ancient water systems in southern Tianshan Mountains, in the Toutunhe Formation, fan delta sandy conglomerate bodies were developed in the western section, and braided river-fluvial delta sand bodies were developed in the middle and eastern section. The denudation line of the Toutunhe Formation runs from west to east along the northern part of Well Sican 1-Well Ka 11-northern part of Well Xihu 1 and Kuitun-Shawan- northern Shihezi-northern Mosuowan. Alluvial plain and delta plain sandy conglomerate bodies are distributed along the lake shoreline that is the area in west and south of the Hutubi River outcrop-Kuitun, and the basin edge- Well Ai 4 area, within the range of the stratum denudation line and the edge of the basin. The thickness decreases from about 300 m to about 100 m, and the mud between the distributary channel and the channel is characterized by strong heterogeneity. To the east and north of the lake shoreline, the delta front sandy conglomerate bodies were developed from the basin margin to the north of Shihezi, and the thickness decreases from about 300 m to less than 100 m. The underwater distributary channel and sand bar are developed, and the sandstone reservoir is well sorted, with good physical properties (Table 1). Thick delta front sand bodies are distributed in the southern area of Mosuowan (Fig. 8a). (2) Under the joint control of the paleo-water system from the southern Tianshan Mountain and the Chepaizi uplift in the northwest of the Kalazha Formation, sandy conglomerate bodies of the alluvial fan-river deposition are developed in the western section, and sandy conglomerate bodies of alluvial fan-fan delta and braided river delta are developed in the middle-east section. The denudation line of the Kalazha Formation runs from west to east along the southern part of Well An 5-southern Shawan-Shihezi- Manas-areas between Hutubi and Well Fangcao 1-northern Fukang, wtih extensively denuded area. Sandy conglomerate bodies of the fan dalta-braided river delta plain are distributed in the basin and its margin area along the Urumqi-Shawan line to the west and south of the lake shoreline, within the range of the stratum denudation line and the edge of the basin. The reservoir thickness reduces from about 300 m to about 200 m with serious reservoir heterogeneity. In the southern area of the Well Fangcao 1 from the basin margin to inner basin, the sandy conglomerate bodies of the braided river delta front are developed, with a thickness of about 300 m to less than 100 m. Thick delta front sand bodies are distributed in the southern area of Mosuowan (Fig. 8b). (3) The lake shoreline restored by the Qingshuihe Formation is close to the position of the current basin edge line, with unobvious stratum denudation. In the western section, the delta front sand bodies are developed with the provenance from the northern Chepaizi uplift, and the thickness decreases from about 100 m to about 25 m in the southeast. The fan delta front sandy conglomerate bodies decreases from 80 m to about 10 m in thickness from the basin margin to the south of Kuitun, and the provenance is from the southern Tianshan Mountain. In the middle-east section, fan delta and delta front sandy conglomerate bodies are dominated, and the provenance is from southern Tianshan Mountain. The thickness of the sandy conglomerate body decreases from 50 m to 10 m from the basin margin to the Shihezi and Hutubi line. A large number of delta front sand bodies are distributed in the Mosuowan and its southern area, with good reservoir physical properties (Table 1, Fig. 8c).

During the Early Jurassic-Early Cretaceous deposition period of Qingshuihe Formation in the southern margin of Jungar Basin, the provenance area expanded from south to north, accompanied by a process of expanding- shrinking-expanding of lake basin. The paleoclimate evolving from wet to dry to wet. In the Early-Middle Jurassic, it was dominated by provenance from the ancient southern Tianshan Mountains, and six major sedimentary systems were developed, including the ancient Sikeshu River, the ancient Anjihai River, the ancient Manas River-ancient Hutubi river, the ancient Toutun River, and ancient Sangong River (flowing from west to east). It developed a proximal fan delta-braided river delta sedimentary system in the west section. The provenance area of the middle-eastern section evolved from far to near, with sedimentary systems such as alluvial fans, rivers, river-deltas, and braided river deltas; the Hongche fault zone is proposed as the provenance boundary line of the middle and west sections. During the Late Jurassic to the Early Cretaceous, the western section evolved from a single provenance in the south to a two-way provenance in the north and south, due to the development of the Chepaizi-Mosuowan paleo-uplift. The river delta deposit changed into a proximal fan delta deposit. In the middle and eastern sections, a proximal braided river delta-fan delta deposits were deposited.

The restored ancient lake shoreline has an angle with the current basin edge, which opens to the northwest, and migrates within a range of tens of kilometers north of the current basin edge. The restored lake shoreline controls the heterogeneity of the delta plains and frontal reservoirs on both sides of the lake shoreline. The lake shoreline, the current stratum denudation line and the basin edge line limit the type and range of sandy conglomerate reservoirs. The fluvial plains and delta plain sandy conglomerate bodies of Toutunhe Formation are located in the western and southern area of the Hutubi River outcrop-Kuitun line with a strong heterogeneity. In the eastern and northern areas, the underwater distributary channel and sand bar bodies of the delta front are well developed, with good physical properties, and well sorted. In the western and southern area of the Urumqi-Shawan line, fan delta-braided river delta plain sandy conglomerate bodies are well developed in the Kalazha Formation. In the eastern and northern of the Urumqi-Shawan line, the braided river delta front sandy conglomerate bodies are well developed, with good physical properties. The fan delta front sand bodies from the Tianshan provenance area in the southern Qingshuihe Formation are mainly distributed in the Sikeshu sag and the Manas- Hutubi anticline. The sand bodies from the northern Chepaizi provenance in the delta front are also good in physical properties.

The above understanding can provide a geological basis for the oil and gas exploration of the deep lower assemblage in the southern margin of Junggar Basin. Meanwhile, a large area of sandy conglomerate body has been restored in the current foreland thrust belt, which can provide a possibility for deep oil and gas exploration in the footwall of the foreland thrust belt.

We are grateful to Zhai Yicheng, Fan Xiaorong, Zhu Lijiang and Fu Qiang for their participation and guidance in the fieldwork. Many thanks to Li Xueyi, Zhang Jian and Wei Lingyun from Xinjiang Oilfield Company of the PetroChina for their help and guidance in the research.