Sporopollen Assemblage And Evolution Of Palaeoclimate In Inxiang Area Since Quaternary

According to special subject of Controlling Borehole Detection and the Establishment ofstandard Quaternary Section subordinate to Xinxiang Active Fault Detection and Seismic Riskassessment Project, standard borehole drilling was carried out in Xinxiang, Based on controllingstrata, dating results sporopollen complex and OSL sample granularity analysis, combined with thecharacteristics of temperature changes in Quaternary, the writer comes up with a comprehensivemethod of Xinxiang Quaternary strata division. Compared with deep sea oxygen isotope,sporopollen complex in Xinxiang is highly affected by ice age and interglacial stage. Conclusionsare drawn as follows:(1)Stratigraphic classifications: the bottom line of Holocene (Qh) is about15.3m underground;according to the depositional cycle and sporopollen information, the bottom of upperPleistocene(Qp3) is constrained at81.05m underground; the bottom of middle Pleistocene (Qp2) isabout166.55m underground; the lower Pleistocene (Qp1) drill reached195.65m, but still not get tothe bottom of Qp1.(2) The controlling standard Quaternary sporopollen profiles in Xinxiang can be classified in tofive sporopollen assemblage zone from bottom to top. According to the sporopollen complex anddating results, we can conclude that the pollen assemblage zone in the middle Pleistocene includesthe first two zones, the third and the forth belong to the upper Pleistocene, and the fifth zone belongsto the Holocene.(3) Poropollen complex, to some extent, reflects vegetation categories. Sporopollen assemblagezone I (104.46to89.08m, Qp2), assemblage zone II (89.08to76.08m, Qp2), assemblage zone III(76.08to28.22m, Qp3), assemblage zone IV (28.22to15.3m, Qp3), assemblage zone V (15.3to1.55m, Qh). Sporopollen analysis implies Xinxiang area has experienced cold-dry, cold-damp,mild-wet, cold-dry, and warm-dry periods since late Pleistocene. And the vegetation also underwentthe two grassland vegetation periods successively, sparse forest-grassland vegetation, grasslandvegetation, forest steppe vegetation. However, the sporopollen complex is dominated by quinoa, andthe climate tended to be cold and dry.(4) Compared with the deep sea oxygen isotope, the ice age and interglacial stage has profoundimpact on climate changes and vegetation succession in xinxiang. At MIS1phase, the Holocene (15.3-1.55m) sporopollen assemblage zone V indicates dry and warm climate and a warmperiod, when a transgression happened (Huanghua transgressive8ka. B.P.-3ka. B.P.). At MIS2stage, the upper Pleistocene (28.22to15.3m), sporopollen assemblage zone IV implies a cold anddry climate, in the heyday of late Dali ice age, and reflect a cold climate.