Paleoenvironment Of Longhu Wetland In Huaiyang Since Late Pleistocene

Huaiyang lies in the compound area of north Qinling fold belt and north China depression,Among them,the nearly east-west tectonic belt runs through the whole area,playing a controlling role,It provides conditions for the late sediment accumulation.Huaiyang area belongs to huaihe river basin,It is a transitional zone between subtropical and warm temperate zones,The climate fluctuates dramatically,the area difference is big,the plant species is complex.The sediment from the HY4 bore well records the climate change since the late pleistocene,By studying climate change in the region,It can provide scientific guidance for land use planning of agricultural production in this area.Palynology analysis is an important method to study ancient environment,Pollen and spores in sediment are direct evidence of past vegetation conditions.At the same time,vegetation is very sensitive to climate change,Therefore,the climate change law of huaiyang longhu wetland can be revealed through the palynology combination.In addition,the evolution of sedimentary facies in the study area was elucidated with the analysis of the grain size characteristics of HY4 borehole.AMS-¹⁴C dating results are used as framework in this paper,The lithologic palynology particle size indicators was used,Based on the previous data,this paper reveals the climate change and sedimentary environment of longhu wetland since late pleistocene.The following conclusions are obtained:?1?According to the dating results,Combining previous data,The HY4 drill hole from bottom to top is divided into the lower section of the upper pleistocene xincai group?Qp³XC-1??30.4-20.75m?,The upper pleistocene XinCai group upside?Qp³XC-2??20.75-14.05m?,Holocene XiangCheng group?QhXC??14.05-0m?.?2?The grain size parameters,debris content,frequency accumulation curve and probability curve of sediment in the HY4 borehole were analyzed.In the late pleistocene?21.067-10.467ka BP?,the dynamic condition change of the HY4 borehole in the wetland of huaiyang longhu was medium high energy-high energy,The sedimentary environment underwent two stages:fluvial facies sedimentation to fluvial facies sedimentation;After entering the holocene?10.467-0ka BP?,the change trend of dynamic condition is low energy-high energy-low energy,The sedimentary environment experienced alluvium-alluvium-lake deposition.?3?Climatic information revealed according to the pattern of spore-powder combination of HY4 borehole,Combined with lithologic petrofacies grain-size characteristics,Huaiyang longhu wetland since late-pleistocene?21.067-10.467ka BP?,The climate experienced a Ch-ange process of warm and wet-warm and cool and slightly dry-cold and dry.Since the Holocene?10.467-0ka BP?,the climate experienced the evolution process of warm and dry-warm and wet-warm and wet.?4?The sedimentary environment revealed by the grain size characteristics of the sediments in the HY4 borehole can be roughly compared with the climate information revealed by the combination rule of palynology.The late regeneration of the longhu wetland experienced river facies sedimentation-river facies sedimentation accumulation,In line with this phase of climate change from wet to wet characteristics,After entering the holocene,the sedimentary environment experienced alluvium-alluvium-lake deposition,It's a per-ferect flection of the climate going back to wetness.