运城盆地ZK301钻孔中新世保德组孢粉组合及地质意义

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

中新世保德组沉积时期是青藏高原向北东方向隆升扩展影响到鄂尔多斯周缘新生代盆地的关键时期。文章对运城盆地峨嵋台地ZK301钻孔中新世晚期保德组岩芯进行了孢粉学研究,系统鉴定了沉积孢粉和再沉积孢粉的特征,探讨了保德组沉积时期的古气候与古构造背景。运城盆地中新世保德组沉积孢粉自下而上可以划分为麻黄科-藜科-禾本科和蒿属-藜科-葎草属2个孢粉组合带,说明运城盆地中新世晚期是从以麻黄科-藜科-禾本科为主的荒漠草原发展为以蒿属-藜科为主的荒漠草原,气候由相对寒冷干燥过渡为偏冷偏干,这种变化过程与中新世晚期青藏高原隆升扩展远程效应对气候的影响有关。再沉积孢粉组合主要集中在保德组下部,以麻黄科含量最高,其次是松属、云杉属、柏科、藜科、胡桃科和蕨类植物孢子,还有少量的克拉梭粉属和胡颓子科等,反映了温暖湿润的气候环境。再沉积孢粉主要来自于中条山北缘山前的古近纪地层,说明在保德组沉积初期,中条山存在一期快速的隆升剥蚀,保德组经历了古近纪地层的剥蚀-搬运-再沉积过程。

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.