Geochemical characterization of the loess-paleosol sequence in northeast China

Authors: WANG, QUI BING - Shenyang Agricultural University; JIANG, YING YING - Shenyang Agricultural University; SUN, ZHONG XIU - Shenyang Agricultural University; Owens, Phillip

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2018
Publication Date: 7/1/2018
Citation: Wang, Q., Jiang, Y., Sun, Z., Owens, P.R. 2018. Geochemical characterization of the loess-paleosol sequence in northeast China. Geoderma. 321:127-140. https://doi.org/10.1016/j.geoderma.2018.02.012.
DOI: https://doi.org/10.1016/j.geoderma.2018.02.012

Interpretive Summary: Soils form over geologic time and this formation affects the current use and management of soils. This research used chemical data coupled with microscopic techniques to identify differences in a very old and deep soil section in China to understand how past climatic conditions affected the soil development. In looking at this very deep section, there were sections where iron and manganese were enriched due to an increase in rainfall. In the same areas with increase iron, there were losses in sodium, potassium and calcium. There were depths in the section there appeared to be periods with much less rainfall where the soil did not appear different from the period of deposition. This research illustrates the importance of climate to changes in soil chemical properties and how historical climate patterns can be reflected in the soil environment.

Technical Abstract: Long-term weathering patterns in northeastern China are not well known due to few well-preserved terrestrial paleo-environmental archives in this area. The Chaoyang section is a typical well-preserved loess-paleosol sequence in northeast China with continuous deposition since 423 ka BP; the deposit thus represents an archive of climate change for this region. The sequence was geochemically characterized by major elemental compositions, elemental ratios, a ternary diagram of Al2O3-(CaO*+Na2O)-K2O, improved quantitative reconstruction and elemental distributions with respect to the average for the upper continental crust (AUCC). Another typical loess paleosol sequence of Lingtai section from the central Chinese Loess Plateau was used for comparison with the loess-paleosol one. The similar AUCC-normalized major elemental distributions and strong correlation of the major elemental compositions between the loess-paleosol sequences indicate that they may have originated predominantly from a similar loess source. Based on the variability in chemical indices corresponding to soil magnetic susceptibility (SUS) and field observations, the loess-paleosol formation period of 423–77 ka BP was separated into eight sub-periods including four periods with greater chemical weathering intensity (paleosols) and four periods characterized by the relative lesser chemical weathering intensity (loess). Relatively intense desilication and fersiallitization primarily occurred in the loess-paleosol sequence from northeast China with greater losses of SiO2 (3.54% in average) and gains of Fe2O3 (0.77%) and Al2O3 (0.33%). Such processes also were reflected in an increase in the amount of K2O (0.41%). Ca and Na leaching was still predominant in the loess-paleosol sequence from the central Chinese Loess Plateau with greater losses of CaO (28.03%) and Na2O (14.03%). The sequence from northeast China records chemical weathering during 423–77 ka BP, which is comparable to the weathering cycles in the sequence from the central Chinese Loess Plateau.