Paleoclimatic evidence inferred from soluble salt deposits in the Pleistocene sediments at Jijiazhuang site, Nihewan Basin

The Nihewan Basin, a Late Cenozoic basin in North China filled by fluvio-lacustrine deposits, preserves a large number of Pleistocene archaeological sites, which well recorded the occupation history of early hominins. The Yuxian Basin, as a major part of the Nihewan Basin (senso lato), is a key region for study of such a relationship between early hominin evolution and climatic changes during Middle Peistocene. The Jijiazhuang site is a newly discovered site complex of human occupation, located in the center of the Jijiazhuang-Huangmei fluvio-lacustrine platform in the northeast Yuxian Basin. It was discovered in 2003 and excavated three years later. The Jijiahzuang-B section (JJZ-B), a key section of the Jijiazhuang site complex, is located along a lake shore. The section includes the fluvio-lacustrine fine sand, silt, and clay of brown-grey, brown-yellow, grey-green, dark-grey in color, capped by loess, with a total thickness of more than 20 m. Based on the soluble salts and stable C-O isotopes from carbonate deposits of the section, the studies of hydro-chemical and climatic evolution as well as human activities are carried out by the author. The results suggest that the Paleo-Nihewan lake at the section of JJZ-B site is characterized by HCO₃⁻-SO₄²⁻-Na⁺ions, and the average content of the total soluble salts is around 0.67‰, which indicate a brackish paleo-lake in a carbonate and sulphate phase of lake evolution in a semi-arid area. The variation and distribution patterns of SO₄²⁻, Cl⁻, Na⁺, Ca²⁺and Mg²⁺are well correlated with the total content of soluble salts. Upon the basis and by the changes in total soluble salt and soluble salt indicators as well as the content of carbonate δ¹³C and δ¹⁸O, four paleo-climatic stages corresponding to paleohydro-climatic changes of the lake were recognized: 1) the stage relatively cold and humid with a high lake water level; 2-3) the stages relatively cool and dry with a low lake water level and 4) the warm and humid stage with relatively high lake water level. The period occupied by early hominins corresponds to the early episode of stage 2 after the recession of the lake level evidenced by the sporadic lithic artifacts discovered, and the possible behaviors of animal dismemberment and utilization. In conclusion, the results bear great significance to the research of the adaptive environment and behaviors adopted by early hominins at the Jijiazhuang site and even the Yuxian Basin.