Junggar Basin

[3] The basement of the basin was largely formed during the development of the Pangea supercontinent during complex tectonic events from Precambrian to late Paleozoic time.

The layers continuously deposited fluvial and lacustrine facies until the present day, mostly containing conglomerate, sandstone, siltstone, and mudstone.

[1] The westerlies contained the lesser moisture that has come from the northwest since the marine areas gradually minimized to the recent Caspian Sea.

[16] Xinjiang paleocraton was pulled apart for a continental rifting episode to form extensional basins in Late Cambrian.

[17] The continuous divergence of the continental crust during late Cambrian to Ordovician shaped the West Junggar Ocean.

[17][12][4] Three plates (Tarim, Kazakhstan, and Siberian) converged together to form a trapped ocean that surrounded volcanic arc and orogens in Mid-Carboniferous.

The following cooling crustal episode led to part of the mountain belt sink by thermal subsidence, which ended up forming the Junggar Basin.

[22][11] This was forming heterogenic silica-rich igneous rocks due to the partial melting of numerous oceanic crusts contaminated with mantle wedge.

[23][3] Then, the area gradually became a mountain-trapped peripheral foreland basin due to high-temperature and relaxing subsidence from the regional extension.

[1][3][23] Some also suggested this landform caused by the combined effect of shearing and extension or thrusting from crustal shortening.

[1] There presented extensional shearing and continuous deposition of non-marine foreland basin-fill till Triassic.

[1] Afterward, the southward lake depression leading the basin centre shift to the south in the Upper Cretaceous period.

[1] At the same time, there was rapid uplift of Tian Shan since Himalayan orogeny formed by the collision between Indo-plate and Eurasian Plate.

[1] This developed an alluvial-rich delta system around shallow lakes with the clastic sediments influx from uplifted Tian Shan and the northern part of the basin.

[3][26] For Carboniferous oil and gas deposits in this area, they were moved upward and accumulated in the Permian period and Mesozoic era sandstones.

[25] Besides, Tian Shan Foredeep in the southern Junggar Basin (including Urumqi) is also available for the petroleum resources.

[26] The petroleum there were formed due to rapid subsidence, regional ductile with mobile intrusion, and cross-cutting on anticlines by orogenic activity (probably in Neogene) from the Tian Shan.

[3] Ore deposits in the Junggar Basin were mainly formed in the Paleozoic era which was related to tectonic development.

The location of Junggar Basin (in red)
Simplified Geological map shows the main geological setting of Junggar Basin. Modified from Cao et al. (2017) [ 7 ]
Cross-section of Junggar Basin. This shows the thickness of each sedimentary layers and structures across the basin area. Modified from Bian et al. (2010) [ 1 ]
The simplified geological evolutionary diagrams of basement evolution in the Junggar Basin region. 1. Rifting formed West Junggar Ocean (WJO) basin (in deep blue). 2. the termination of intra-plate oceanic magmatism, and subduction events formed the present Tangbale and Hongguleleng ophiolites (they represent the integration for the crust of West Junggar Ocean). 3. Maylia ocean basin (in pale blue) formed by rifting. 4. Continental plates converged and folded up the ocean to form West Junggar residue sea. 5. Rifting occurred again to form Junggar Ocean (JO) (in pink) and Kelamaili Ocean (KO) (in brown), which showed separation from Bogda arc (BA), Kalameili arc (KA) and Altai Arc (AA). 6. JO subducted over KA while KO subducted over AA. 7. Junggar ocean crust subducted over the combined Kelamaili-Altai arc and showed slab rollback . 8. With the influence of Tian Shan collision and anorogenic magmatism from local extensional events, Junggar area subsides to form Junggar basin. Modified from Zhao et al. (2003), Carroll et al. (1990), Buckman et al. (2004), Han et al. (2018). [ 4 ] [ 12 ] [ 17 ] [ 18 ]
The animated schematic geological evolutionary map shows the change of facies and the corresponding locations, from Triassic to Paleogene. This showed the basin evolution through three stages: (1) foreland basin from Permian to Triassic. (2) Intracontinental depression from Jurassic to Palaeogene. (3) Reactivated foreland basin from Neogene to the present. Modified from Bian et al. (2010). [ 1 ]
The schematic map shows the distribution of oil and gas fields in the Junggar Basin. Mostly accumulated in West Uplift area. Modified from Zhang et al. (2015). [ 25 ]