Molecular organic geochemical evidence for paleoenvironmental changes at 11.87—12.28 m in GS-1 sedimentary core,Gucheng Lake,East China

Organic lipids with different occurrence modes in a sedimentary core in a subtropicalfreshwater lake, Gucheng Lake, were sequentially extracted, separated and analyzed. Thedown-core variations of OEP index of alkanes, C/Cratios of fatty acids, ratios of boundfatty acids to free fatty acids, thermo-maturity indices of hopanoid hydrocarbons and relativeconcentrations of sedimentary minerals revealed an evident increasing in allochthonous inputfrom rock detritus below 12.28 m in the sedimentary profile. The distribution pattern of tightly-bound β-hydroxy fatty acids indicated a difference in bacterial communities above and below theboundary, as well as the gammacerane index may assign a significant change in lake watersalinity. The evidence, in general, suggested that a significant paleoenvironmental change hadtaken place in ca. 9.6 kaBP on the regional basis.