Paleozoic Stratigraphic Regionalization and Paleogeographic Evolution in Western Junggar, Northwestern China

Both general and special stratigraphic regionalizations have been worked out in this study according to (1) geotectonic environments and sedimentary association types; (2) stratigraphic sequences and contact relationships; (3) paleogeographic framework and paleoenvironmental conditions; (4) paleontological taxa and paleobiogeography; (5) deformational and metamorphic specialty of strata, as well as (6) boundary types of stratigraphic regionalization and their criterion. Both general and special stratigraphic regionalizations can be subdivided into four hierarchies of the stratomegaregion, stratoregion, stratosubregion, and stratomicroregion. The Paleozoic strata of western Junggar can be divided into four stratomicroregions from north to south, i. e. the Saur Mountains, Shaerbuerti Mountains, Mayili Mountains and Karamay stratomicroregions based on the mentioned-above six aspects, and new data and progresses gained in recent studies. Paleozoic western Junggar is featured by its archipelagic ocean and soft-collisional orogenics in tectonopaleogeography. The Late Silurian till Early Carboniferous represents the prime of such tectonic pattern and regimes, forming the Paleozoic stratigraphic regionalization. Western Junggar emerged from ocean and stepped into an intracontinental orogenic period from the Late Carboniferous to Permian, announcing a gradual disappearance of stratigraphic regionalization. In paleobiogeography, the Early Paleozoic of western Junggar is distinguished by its mixed fauna between the Pacific and Atlantic biomegaprovinces, and also different from the bioprovince represented by the Tuvaella fauna in the southern part of the Siberian plate. The fossil assemblages of western Junggar during the Silurian to Devonian periods show a prominent relevance to the tropical-subtropical palaeo-tethys biomegaprovince.However, an Angara flora typical of the north temperate zone dominates the Late Carboniferous to Permian continental strata in western Junggar. In sedimentary paleogeography, the processing facies of Paleozoic western Junggar include both normal and event sedimentary facies, with the latter particularly developed such as volcanic eruption, volcanic overflow and seismite facies, which reflects its active tectonic background. The environmental facies comprise palaeo-continental, fluvial, littoral-shallow-marine and bathyal-abyssal facies.