Lipid distributions in loess-paleosol sequences from northwest China

Molecular stratigraphic analyses using GC/MS have been performed on the top section of the Jiuzhoutai loess-paleosol sequences near Lanzhou in northwest China, with a record extending from the second-last interglacial through the present interglacial. The various molecular fossils identified from the second-order loess and paleosol layers include C14–C35 n-alkanes, C8–C30 n-alkanoic acids, C12–C30 n-alkanols and C23–C33 n-alkan-2-ones. The CPI (carbon preference index) values and the ratio of C29/C31 n-alkan-2-ones display alternations between loess deposits and paleosols. They show a significant correlation with the loess magnetic susceptibility, an indicator of the East Asian summer monsoon. The observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re-working of higher plant inputs in the paleosols.