Sedimentary Characteristics and Paleogeographic Evolution of the Me-so-Neoproterozoic in the Southwestern Ordos Basin and Their Influence on the Ediacaran

The Meso-Neoproterozoic strata in the Ordos Basin are old in age, deeply buried, scattered in outcrop, and lack well logging data; their primary sedimentary structures have also been severely damaged. These factors increase the difficulty of research on Ediacaran strata. This paper focuses on field outcrop sections around the southwestern part of the basin. Combined with analyses of field outcrops, key well cores and petrographic thin sections, this study discusses the distribution and sedimentary characteristics of the Meso-Neoproterozoic strata in the basin, as well as their paleogeographic influence on the Ediacaran. The results show that among the Meso-Neoproterozoic strata in the southwestern Ordos Basin, the Changcheng System is the most widely distributed and thickest, dominated by muddy, sandy and argillaceous deposits; the Jixian System is dominated by siliceous carbonate deposits; the Sinian System has the smallest distribution area and is dominated by tillitic conglomerates. In the southwestern Ordos Basin during the Mesoproterozoic, the depositional evolution followed a path from terrigenous clastic coasts, through carbonate platforms, to glacial deposits. The Changcheng Period, marked by terrigenous clastic deposition, represented the strongest rifting activity in the basin, forming four major rift systems in the southwestern part, where delta, littoral, shallow marine, and bathyal-abysmal facies developed. Affected by the Zhartai Movement during the Jixian Period, marginal rifting occurred, with deposition dominated by epeiric-sea carbonate platforms featuring abundant stromatolites. The main sedimentary facies include littoral, restricted platform, open platform and platform margin slope facies. In the late Jixian, the basin was further uplifted and eroded. The Sinian strata are characterized by glacial clastic deposits with limited tillite beds, displaying glacial and glaciomarine facies. The Changcheng and Jixian systems of the Mesoproterozoic formed a stable cratonic basement. Their sedimentary characteristics and paleogeographic evolution provided the basement framework and paleogeographic reference for the widespread development of passive continental margins during the Ediacaran.