山西晋中盆地晚新生代地层划分、沉积环境及其先秦以来气候和湖泊演化

魏荣珠; 庄其天; 闫纪元; 魏云峰; 杜艳伟; 范俊辉

doi:10.12029/gc20220316

山西晋中盆地晚新生代地层划分、沉积环境及其先秦以来气候和湖泊演化

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)

摘要

摘要:
研究目的 晋中盆地位于汾渭断陷盆地带的中部，新生代最大沉积厚度超过3800 m，建立晋中盆地精确地层年代框架和高分辨率沉积层序对于理解汾渭断陷盆地带的演化、华北地区气候变化具有重要意义。
研究方法 本文对晋中盆地东北部晚新生代标准孔ZK01(钻孔深度870.5 m)岩心开展了年代学和沉积学研究。
研究结果 将ZK01孔揭示的松散沉积物分为6个岩性组。首次通过磁性地层学研究，划分出13个正极性时段和12个负极性时段，建立了ZK01孔地层年代框架。晋中盆地新生代沉积物底部最老年龄约8.1 Ma，将晋中盆地活动的起始时间从前人一般认为的上新世初期，确定为中新世晚期，提前了约3 Ma。区内晚新生代地层划分为新近系中新统灞河阶(N₁⁴)和保德阶(N₁⁵)，上新统高庄阶(N₂¹)和麻则沟阶(N₂²2)，第四系下更新统泥河湾阶(Qp¹)，中、上更新统和全新统。
结论构造活动与气候变化是盆地沉积环境的主要控制因素，共同导致了上新世早期和早更新世中晚期的两次湖泊大规模发育。全新世时期，早中期即先秦(约2.5 ka以前)，盆地中仍是河湖共存阶段；晚期(2.5 ka以来)，出现湖消河长的局面，直至明、清时期湖泊全部消失，气候变化和人类活动影响是盆地中湖泊最终消失的主要原因。

Abstract:
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.

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