Distribution of n-Alkane Indicative of Paleoclimatic Change in Paleolake of Yanqing, Beijing

N-alkanes in lacustrine sediments could be well preserved and have documented the paleoenvironmental variations. By the aid of GC method, n-alkanes were identified in lacustrine sediments from Fugaoying profile within Yanqing basin of Beijing, one of the core regions in the North China plain, to characterize the paleoclimatic variations in this area. The results show that the n-alkanes with carbon numbers ranging from C₁₆ to C₃₃ exhibit different distribution patterns. Most samples show a single peak with high carbons (C₂₉ or C₃₁ in particular) and have an odd carbon number predominance, while a few have double peaks with lower and high carbons. The middle and short n-alkanes have no obvious carbon number characteristics. The results suggest the organic origin from terrestrial, some algae and few aquatic plants. According to ESR sequence, organic carbon isotope, ACL (average chain length), CPI (carbon preference index), and Paq, alternative paleoclimatic conditions have been reconstructed in the study area since 56.8 ka. From 56.8 to 45.6 ka, the pretty hot-humid climate results in a higher lake level. During 45.6 and 31.5 ka, the climate became warm and humid, producing a slightly declined lake level. After that, cold-dry climate and seriously declined lake level were distinct between 31.5 and 20.0 ka. From 20.0 to 13.4 ka, the climate was cold and dry, but with a warming trend. During 13.4 to 9.2 ka, the climate became warm slightly and the resulted lake level was lower. Since 9.2 ka, the climate became dry, thus leading to a shrunken lake. Distribution of n-alkanes indicates that the paleoclimatic changes of Yanqing basin are basically parallel to summer solar radiation, grain size of Lijiayuan profile, and oxygen isotope records in Guliya core and Sulu Sea, potentially suggesting the control of solar radiation.