Vegetation variation of loess deposits in the southeastern Inner Mongolia, NE China over the past ∼1.08 million years

Abstract

The stable carbon isotopic composition of organic matter of aeolian silt deposits is regarded as an appropriate proxy index of paleovegetation, especially in the Chinese Loess Plateau in central China. In this study, a loess–paleosol sequence in the southeastern Inner Mongolia Autonomous Region in northeastern (NE) China, which is located outside the Chinese Loess Plateau, is chosen to reconstruct the vegetation history since ∼1.08 Ma. Temperature exhibits a threshold value, which determines the growth of C4 plants in this study area. The organic matter of the samples is derived from two different vegetation types, namely, the mixed C3 and C4 plants and the pure C3 plants. The δ13C of the organic matter shows negative values in loess units and higher values in paleosol units. This finding reflects the influence of temperature and summer monsoon intensity on the vegetation dynamics over glacial–interglacial cycles. On a longer time scale, the δ13C values are higher between ∼1.1 and ∼0.9 Ma and after ∼0.35 Ma, and lower between ∼0.9 and ∼0.35 Ma, which may be attributed to a long-term temperature variation. Our analysis shows that regional temperature is the most important limiting factor that forces vegetation changes at the glacial–interglacial time scale in NE China.