Resumen de Sediment Records from Qilu Hu and Xingyun Hu, Yunnan Province, China: Late Pleistocene to Present*

Mark Brenner, Thomas J. Whitmore, Song Xueliang, Long Ruihua, David A. Hodell, Jason H Curtis

• Qilu Hu (area =37 km-, zmax = 7 m) and XingyunHu (area =39 km-, zmax =12 m) lie at 1797m and 1723mabove mean sea level (Whitmore et al. 1997), respectively,on the Yunnan Plateau, southwest China (Figure1). Analyses of water-column nutrients and Secchidisk measurements show that Qilu Hu is currentlyeutrophic and Xingyun Hu is meso-eutrophic (Mooreet al., 1988; Whitmore et al., 1994a, 1997). Upper Tertiarydeposits in Yunnan Province are rich in browncoalbut karsted limestone dominates the surface rock(Li and Walker, 1986). Valleys in the region often possessfluvial and lacustrine deposits of Quaternary age.An 11.0-m sediment core was collected from Qilu Huin 1987and an 8.4-m section was obtained from XingyunHu in 1989. Chronologies for the sediment cores were established by standard 14C dates on bulk organic matter and an AMS 14C date on wood (Figure 2). Sediment profilescontain records of lacustrine deposition from the latePleistocene to present (Brenner et al., 1991;Whitmore etal., 1994a, 1994b).The 14C date on wood at 7.39m in QiluHu is younger than the date on bulk organic matter from5.99-5.81 m, suggesting that hard-water-Iake error makesdates on lacustrine organic matter about 1800 yr olderthan true 14C ages (Brenner et al., 1991).Paleoecological studies in Yunnan Province have employed ostracod remains (Jiang, 1990) or magneticmeasurements in lake sediments to infer paleoenvironmentalconditions (Yu et al., 1990). Fang (1991) presentedreconstructions of past lake levels.Paleoenvironmental inferences for the 1987 Qilu Hucore and the 1989 Xingyun Hu core were based on geochemical,palynological, and diatom analyses (Brenneret al., 1991; Deevey et al., 1988; Long et al., 1991;