Late Cenozoic stratigraphic division and sedimentary environment of Jinzhong Basin in Shanxi Province, with the climate and lake evolution since the pre-Qin period (2500 years ago)

This paper is the result of environmental geological survey engineering.

Objective Jinzhong Basin is located in the middle of the Fen-Wei Fault Depression Basins, in which the maximum thickness of the Cenozoic sedimentary layer exceeds 3800m. The establishment of the precise stratigraphic framework and the high-resolution sedimentary sequence of Jinzhong Basin is vital to understanding the evolution of the Fen-Wei Fault Depression Basins and the climate changes in North China.

Methods In this paper, the chronology and sedimentology methods were used on the drill cores of the late Cenozoic standard borehole ZK01 (870.5m in depth) in the northeast of the Jinzhong Basin.

Results The loose sediments in the borehole ZK01 were divided into 6 lithological formations. By means of magnetostratigraphy, the stratigraphic time frame was built with 13 normal polarity periods and 12 reverse polarity periods for the first time. The oldest Cenozoic sediments at the bottom of Jinzhong Basin is approximately 8Ma, moving the starting time of Jinzhong Basin activity forward about 3 Ma, from early Pliocene as previously believed to late Miocene. The late Cenozoic strata in this region are divided into Neogene Miocene Baodean Stage (N₁⁴) and Bahean stage (N₁⁵), Pliocene Gaozhuangian Stage (N₂¹) and Mazegouan Stage (N₂²), Quaternary lower Pleistocene Nihewanian Stage(Qp¹), middle Pleistocene, upper Pleistocene, and Holocene.

Conclusions Tectonic activity and climate change are the main controlling factors of the sedimentary environment in the basin, which results in two periods of large- scale lake development in the early Pliocene and middle- late early Pleistocene. In the early- middle Holocene, i.e., pre- Qin period (circa 2.5ka ago), rivers and lakes were in the coexistence stage in the basin; In the late Holocene (circa 2.5ka after), lakes atrophied, and rivers dilated; Then the lakes vanished in Ming and Qing period. Climate change and the impact of human activities are the main reasons for the eventual disappearance of the lakes in the basin.