Paleoenvironmental Changes In The Zhangwei River Basin Under The Background Of The Neotectonic Movement 2.5MaB.P.

The Zhangwei River Basin is located in the Linqing Fall.The Cixian-Daming fault and the Guantao fault run through it.The Neotectonics movement of these fault has a certain influence on the flow direction of the river and provides the dynamic conditions for the sediment deposition.The study area is located in arid and semi-arid areas,affected by the Pacific monsoon,with four distinct seasons and abundant plant species.The ZKD-3 borehole deposit reveals the climatic changes since the early Pleistocene,and the chronological grid established by combining the geomagnetic and photoluminescence dating results of the grain size characteristics and the sporopollen zone characteristics of the borehole sediments.Studying the paleoenvironmental climate of the study area,studying its changing laws,and exploring the characteristics of sporopollen assemblages in the Weihe River Basin since the early Pleistocene and its sedimentary environment significance.Combining the results of paleomagnetism and photoluminescence dating with the lithological characteristics of the borehole,the stratigraphic age of the ZKD-3 borehole from bottom to top was divided into lower pleistocene series Gu'an Formation(Qp~1)(502-215.5m)of lower pleistocene?The Yangtze Formation(Qp~2)(215.5-25m)of the Middle Pleistocene?the Ouzhuang Formation(Qp~3)(25-12.6m)of the Upper Pleistocene and the Qh(12.6-0.5m)of the Pleistocene.Combining ZKD-3 borehole grain size measurement with paleomagnetic and photoluminescence dating results,reducing the sedimentary environment changes of the study area since the early Pleistocene:Early Pleistocene(2500-780ka B.P.):sidebank deposition-top of sidebank deposition-natural bank deposition-burst fan deposition-flood plain deposition-flood plain lake deposition-flood plain swamp deposition-sidebank deposition-bank deposition-burst fan deposition;Medium Pleistocene(780-123ka B.P.):natural bank deposition-flood plain lake deposition-flood plain swamp deposition-bank deposition-oxbow lake deposition;Late Pleistocene(123-9.8 ka B.P.):abandoned river channels deposition-interfluvial lowlands deposition;Holocene(9.8ka B.P.-present):flood plain deposition.Combining the results of pollen identification in ZKD-3 boreholes with dating data,the paleo-vegetation and paleoclimate changes in the study area since the early Pleistocene were restored:Early Pleistocene:the vegetation was a broad-leaved forest-grassland landscape-coniferous-broad mixed forest-Grassland landscape-pine-dominated broadleaf mixed collar-grassland landscape,climate change is warm and humid-warm and cool dry-mild humid;Middle Pleistocene:vegetation is dark coniferous forest or coniferous forest-grassland landscape-broad-leaved forest The dominant forest and grassland vegetation landscape,the climate is cold and dry-warm and humid-cold and dry;Late Pleistocene:coniferous grassland vegetation landscape dominated by Pinus-Artemisia-Chenopodiaceae,the climate is cold and humid;Holocene:vegetation Forest and steppe,the climate is warm and humid.