A Study On The Genetic Features And Geochemical Characteristics Of Dunhua Loess Profiles In Jilin Province, China

The loess in northeast China, the main type of Quaternary sediments, is different from inland loess. Dunhua is distributed in the eastern end of China’s loess deposition. The studied loess profile is located in Dunhua of Jilin province(the Dunhua loess profile). It has argillic and bleaching features in the upper part of the loess profile, and a volcanic ash horizon was found in the lower part. Because the volcanic ash horizon can be an age discriminant indicator, the Dunhua loess profile has the potential to ascertain the time of loess deposition and development. Furthermore, a solid foundation is built to explore the formation time and mechanism for the argillic horizon and the bleaching horizon. In addition, research on the Dunhua loess profile recording abundant paleo-environment information will provide evidence for interpreting changes in paleo-environments. In this paper, sedimentary characteristics, genetic characteristics, geochemical characteristics, and weathering characteristics of the Dunhua loess profile were studied. Conclusions were listed below.1. Dunhua loess profile thickness is 352 cm, consists of two geological strata of loess and volcanic ash. Dunhua loess profile (9-310 cm) has been deposited continuously since 144 ka BP. At its bottom (310-352 cm) volcanic ash from Changbai Mountain volcanic eruption was found.2. According to the morphological features of the Dunhua loess profile, the upper part loess strata is divided into 7 horizon, which are A, E1, E2, BtS1, BtS2, BtS3, Bs. The main properties and characteristics of each horizon showed that it has argillic and bleaching features in the upper part of the loess profile; the exchangeable cations were mainly Ca2+ and Mg2+in acidic soil of the profile; organic carbon content decreased gradually with the depth of the profile; iron oxide gathered in the illuvial horizon; because of the long time of weathering and the deposition pressure from the upper layer, the volcanic ash layer in the bottom has not been possessed of the characteristics of volcanic ash.3. The macro-element and micro-element in the upper loess strata of the Dunhua loess profile are more Fe, Cr, Pb less Na, K, Ba, Ni compared with the UCC. And element content trend is consistent with the Luochuan loess profile; the eigenvalues of the rare earth element reveals a deficit of light rare earth and enrichment of heavy one, the Eu and Ce showed negative anomaly; the rare earth elements of ash layers was no significant change compared with loess upper part loess strata, while the contents of some macro-element and micro-element are affected by the addition of volcanic ash.4. Through the study on the weathering degree of the loess section in Dunhua shows that the variation law of soil development degree was "weak-strong-weak"; the development of soil is still in the primary or intermediate stage; the fluctuant soil development intensity in the Dunhua loess profile shows the typical continental weathering trend.The results can provide scientific basis to further study the soil genesis in Dunhua loess area, explore the formation time and mechanism of the argillic horizon and bleached horizon in soils of loess parent material.