Compound-specific Carbon Isotopic Characteristics of n-alkanes in Xianghai Lake Sediments of Northeast China and Their Paleoenvironmental Implications.

The section of 1 420 cm lake sediment from Xianghai in the western of Songnen Plain was investigated. According to the AMS 14C dating, the chronology of lake sediment since Last Deglaciation was established; combined with the types of sediment and the abundance of organic matter, molecular organic geochemical characteristics including carbon isotopic compositions of n-alkanes and long-chain n-alkanes in the samples were analyzed; compared with the climatic indicators of sediment core, the changes of paleovegetation and paleoclimate since Last Deglaciation were evaluated. The results show that the organic matters in lake sediment are mainly derived from algae and higher plant according to the distribution of n-alkanes from lake sediment in Xianghai; the n-alkanes exhibit strong odd-carbon number predominance, and the main peak of high carbon number of n-alkanes is nC31, so that the organic matters are mainly derived from terrestrial higher plants, especially herbaceous higher plants; the carbon isotopic compositions of long-chain n-alkanes (nC27, nC29 and nC31) are positive in whole, and the main higher vegetation type in the lake is C3 plant dominantly by the means of binary pattern, and the relative biomass of C4 plant increases from Last Deglaciation to the megathermal of Holocene; the change of climate fluctuates since Last Deglaciation, and the climatic and environmental changes in the study area can be divided into five stages including cold and dry in Last Deglaciation, cold and wet in Early Holocene, warm and dry in the early megathermal of Holocene, warm and wet in the late megathermal of Holocene, and warm-cool and drying in Late Holocene. [ABSTRACT FROM AUTHOR]