The biomarkers of paleosol S4 and adjacent loess layers in the Luochuan loess section, NW China and their paleoecological and paleoclimatic significance

摘要

This study provides a reconstruction of paleovegetation and paleoclimate of paleosol S4 on the central Chinese loess plateau. We identified n-alkanes and n-alkane-2-ones of biomarkers from the loess-paleosol samples collected from the S4 and adjacent L5, L4 of the Luochuan loess section by using gas chromatography-mass spectrometry (GC-MS) technique. Based on these biomarkers and high-resolution magnetic susceptibility and grain size data, the paleoenvironment and paleovegetation history during S4 was reconstructed. The correlation between n-alkanes and magnetic susceptibility and grain size data demonstrates that the biomarkers in paleosol and loess layers is derived from organism under relative environment and can reconstruct the paleovegetation during the loess-paleosol formation. The ACL (average chain length) index is correlated well with paleomagnetic susceptibility and grain size variations, displaying their good synchrony with warm and humid climate. However, it relatively lagged behind the paleomagnetic susceptibility and the grain size variations when the climate began to deteriorate. During the formation period of paleosol, the n-alkanes was dominated by C31 homologue, indicating that the primary organic input was originated from herbs, which revealed that there was no typical forest vegetation developed in the studied period on the central Chinese loess area.