The loess deposits in Northeast China: The linkage of loess accumulation and geomorphic-climatic features at the easternmost edge of the Eurasian loess belt

摘要

The study of the loess deposits is the key for understanding the linkage between dust accumulation, tectonics, landform and climate change. However, little is known about loess accumulation in NE China. Loess deposits at the easternmost edge of the Eurasian loess belt are represented by those in the Xinwopu (XWP), Kulungou (KLG) and Huangshan (HS) sections of NE China. These loess deposits are much coarser than the loess in the southern Chinese Loess Plateau, with a sand ( 63 mu m) content of 6-39% in the loess deposits, and show distinct grain size distribution with a trimodal or bimodal pattern. There are markedly different geochemical compositions between the studied loess deposits: the XWP loess is characterized by the highest content of CaO (9.81%) and MgO (2.06%), and the highest Sr-87/Sr-86 ratios (0.713119); the KLG loess is highlighted by the lowest content of the element Sc (7.68 ppm), V (54.1 ppm), Cr (36.4 ppm), Co (6.32 ppm), Ni (15.6 ppm), Cu (16 ppm), Zn (38.8 ppm), Ga(12.8 ppm) and Sigma REE (113 ppm); the HS loess is of the lowest content of CaO (1.15%), and the highest content of the element Y (84.8 ppm), Zr (242 ppm), Nb (18.1 ppm), Hf (7.2 ppm), Ta (1.45 ppm), Th (12.7 ppm) and Sigma REE (185 ppm); the XWP and KLG loess samples have similar epsilon(Nd)(0) values (-7.9), moderately higher than those (-8.9) of the HS loess. The comparison between various geochemical indicators (e.g., low values of SiO2/Al2O3, Zr/Sc and CIA, and high ICV values) shows that these loess deposits have undergone a different and low degree of chemical weathering with a low maturity and recycling history. Integrated methods including grain size, elemental and isotopic composition, multidimensional scaling as well as physical geographical elements (including the geomorphic and climatic features), clearly revealed the Onqin Daga Sandy Land, the Horqin Sandy Land and the Songnen Sandy Land as main dust provenances of the XWP, KLG and HS loess, respectively.