Sedimentary Characteristics Of A Typical Loess-paleosol Sequence Xiajiahe Section In South Liaoning Province

The coastal loess in southern Liaoning province is an important geological record of the rise and fall of east Asian winter and summer monsoon and the rise and fall of bohai Sea level since quaternary.Sedimentary age information is a prerequisite for the study of paleoenvironment.Only by understanding the formation process of Binhai loess in southern Liaoning,can the paleoclimate information be extracted from the paleosol sequence of the loess.This paper typical loess,paleosol sequence in southern liaoning area Xia Jiahe section as the research object,described in the specification detailed observation on the basis of morphological features,36 soil genetic horizon collected and 5 cm equal-spaced sample 328,analysis of the profile of the forming time,magnetic susceptibility and grain composition,physical and chemical properties such as rare earth elements,the system analyzes the physical and chemical properties,The sedimentary characteristics of typical loessie-paleosol sequences in southern Liaoning are revealed,which will expand the spatial scope of loess research in southern Liaoning and provide new data for paleoclimate research in the region.,and the following conclusions were obtained:1.According to the characteristics of soil morphology,the section(1735cm,no bottom boundary)can be divided into S0,L1,S1,L2 and S2 five strata;OSL results show that the age of the Xiajiahe section is 208.97 ± 11.58 ka BP,indicating that the section is sediments since the late Pleistocene;according to the magnetic susceptibility age model,the depth-age relationship of the Xiajiahe section is established,and the depositional ages of each strata are as follows:Holocene soil S0(0～48 cm):deposition time is between 0～13.00 ka BP;loess L1(48～708 cm):deposition time is between 13.00～56.19 ka BP;paleosol S1(708～1200 cm): deposition time is between 56.19～136.33 ka BP;loess L2(1200～1562 cm): deposition time was between 136.33 and 159.82 ka BP;paleosol S2(1562-1735 cm): deposition time was between 159.82 and 208.97 ka BP.The Xiajiahe section recorded the process of the Binhai Loess from scratch since the Late Pleistocene.The average sedimentation rate of the section is 7.85 cm/ka.The dust deposition rate fluctuates obviously in different sedimentary periods,which may be related to environmental changes and transport power in the provenance area,and even the occurrence of gravel can be judged as the abrupt change of sedimentary environment during the deposition of Xiajiahe section.2.The morphological characteristics of the section,the fractal dimension of particle size,the composition of particle size,the distribution curve of rare earth elements,and the DF discrimination show that the substances in the formation of the Xiajiahe section have been fully mixed and have aeolian origin;however,the characteristics of particle size composition and the discriminant formula indicate this.There may be periods of interaction between wind and water during the formation of the loess paleosol strate.3.According to the regional stratigraphic correlation,particle size composition,particle size frequency curve,particle size accumulation curve,REE characteristic triangle diagram,and rare earth element characteristic value,it shows that the Xiajiahe section is mainly composed of near-source sedimentation,supplemented by far-source sedimentation,material source is more complex.The changes in climate during the formation of the section have led to changes in the content of near-source and far-source components in the Xiajiahe section in different periods.the comparison of the particle size frequency curves of the loess in different areas of Dalian shows that the near-source components of the Xiajiahe section are Not only supplied by the material supply from the exposed Bohai shelf,but the fluvial sediments around the section may also provide important material inputs.The scatter diagram of ree characteristic values shows that the provenance of Xiajiahe loess is inconsistent with that of typical loess in northern China,and the Otindag sandy land and Horqin Sandy land may provide part of fine dust for the formation of this section.