The spore-pollen assemblages of the Miocene Baode Formation from Borehole ZK301 in the Yuncheng Basin and its geological significance

Abstract

The deposition period of the Baode Formation in the Miocene was crucial when the uplift and expansion of the Tibetan Plateau in the NE direction affected the Cenozoic basins around the Ordos Plateau. Previous research has mainly focused on tectonic and sedimentary aspects, with relatively few results on climate and environmental responses. We conducted a systematic sporopollen study on the Borehole ZK301 from the late Miocene Baode Formation in the E’mei tableland, Yuncheng Basin, characterized the deposited and redeposited spore-pollen and discussed the paleoclimate and paleotectonic background of the Baode Formation during its deposition. From bottom to top, the Miocene Baode Formation in the Yuncheng Basin can be divided into two spore-pollen assemblages, which are Ephedraceae–Chenopodiaceae–Gramineae zone and Artemisia–Chenopodiaceae–Humulus zone, indicating that the desert steppe dominated by Chenopodiaceae, Gramineae, and Ephedraceae developed into the desert steppe dominated by Artemisia and Chenopodiaceae in the late Miocene. Accordingly, the climate transitioned from relatively cold and dry to cold and dry, which was related to the influence of the remote effect of the uplift and expansion of the Tibetan Plateau on the climate in the late Miocene. The redeposited spore-pollen assemblages are mainly concentrated in the lower part of the Baode Formation, with the highest content of Ephedraceae, followed by Pinus, Picea, Cupressaceae, Chenopodiaceae, Juglandaceae and Pteridophyte, and a small amount of Classopollis and Elaeagnaceae, reflecting a warm and humid climate. The redeposited spore-pollens were mainly from the Paleogene strata on the northern margin of the Zhongtiaoshan Mountains, which indicates that there was a rapid uplift and denudation of the Zhongtiaoshan Mountains in the early stage of the Baode Formation deposition. The Baode Formation underwent the Paleogene strata’s denudation, transportation, and redeposited process. The research results can provide evidence for the late Miocene paleoclimate in the Yuncheng Basin and new evidence for the uplift of the Zhongtiaoshan Mountains in this period.

Keywords

• baode formation
• palynological records
• paleoclimate
• tectonic implications
• yuncheng basin
• cenozoic