POLLEN AND PHYTOLITH RECORDS FROM A HOLOCENE PALEOSOL PROFILE AT THE SOUTHERN MARGIN OF HUNSHANDEKE SANDY LAND, INNER MONGOLIA, NORTHERN CHINA

The loess and desert-marginal regions of northern China, situated at the northwestern edge of East Asian summer monsoon, has long been considered as sensitive to Quaternary climatic change. Holocene paleosol layers are widely distributed in this area (42¨¬- 44¨¬N, 114¨¬-124¨¬E). Current vegetation and climate reconstruction during the Holocene in the studied area are mainly based on the pollen records. However, pollen records often represent the vegetation of a large area, it is difficult to reconstruct local vegetation because of over-representation of Artemisia and Chenopodiaceae pollen in the semi-arid and arid area. Phytolith analysis provides a more detailed vegetation and climate history in grassland ecosystem. Taipusi profile (41¨¬58°Ç30°ÈN, 115¨¬10°Ç32°ÈE, 1340m asl), located at the southern margin of Huishandake sandy land in Inner Mongolia, is about 1.4m thick mainly consisting of sandy soil. Three 14C age are measured at the depth of 30-40cm, 70-80cm and 130-140cm, dated to 2300°¾95, 4830°¾130 and 9495°¾50 calBP respectively. 28 pollen and phytolith samples are collected from the profile, with an internal of 5cm. Pollen and phytolith records from the Taipusi profile demonstrate the grassland component variations during the Holocene. From 10000 to 7330 cal BP, grassland was dominated by Aneurolepidium chinese - Pennisetum centrasiaticum (Setaria viridis) - Koeleria cristata, with a mesic condition. Between 7330 and 5320 cal BP, pollen and phytolith assemblages suggest Aneurolepidium chinese - Cleistogenes squarrosa - Koeleria cristata grassland, weeds (such as Compositae, Leguminosae, etc.) flourished, some tree (Pinus, Betula, Juglans et al.) was present at or near the site, corresponding to Holocene thermal maximum. From 5320 cal BP, Aneurolepidium chinese-dominated grassland was replaced by Stipa-dominated grassland, mesic weeds reduced because of xeric condition. Between 2500- 0 cal BP, pollen and phytolith records support Stipa grandis,Stipa krylovii, Koeleria cristata-dominated grassland with Artemisia, Caragana shrub, salty plants (such as Chenopodiaceae, Tamarix, Niatraria) developed gradually in the grassland, indicating the degradation process of grassland ecosystem.