VEGETATION COVERAGE AND MONSOON VARIATION RECORDED BY STABLE CARBON ISOTOPE OF LOES SINCE 2.5MA: VEGETATION COVERAGE AND MONSOON VARIATION RECORDED BY STABLE CARBON ISOTOPE OF LOES SINCE 2.5MA

The organic carbon isotopes of the Luochuan section show that the δ13C values vary from-18.7‰ to-23.5‰,and the downcore distribution of organic carbon isotope could be divided into three stages with similar trends with the magnetic susceptibility in the glacial-interglacial scales.The results demonstrate that 1) the vegetation coverage in the Luochuan area was mainly a mixture of C3 and C4 grassland,2) the δ13C value of loess sequence better recorded the summer monsoon change in the glacial-interglacial scales just as magnetic susceptibility trend.Comparing with the organic carbon isotope of the Duanjiapo and Weinan sections,two times of evident transition on tectonic time scales are recognized since 2.5 Ma.