Palynological records of environmental changes in the middle part of Inner Mongolia, China

A 2.4-m-long core was extracted from Diaojiao Lake (41degrees18'N, 112degrees21'E) at the foot of the northern part of Daqingshan Mts. High-resolution pollen analysis results of two sites showed 10 arboreal genera, including Pinus, Betula, Picea, Abies, Carpinus, Quercus, Ulmus and more than 20 non-arboreal genera, mainly of Artemisia, Labiatae, Nitraria, Polygonaceae. Ranunculus, Thalictrum, Umbelliferae, Caryophyllaceae and Cyperaceae dominating the record. Fern spores, aquatic pollen and algae were also observed in some sections of the cores. The sequence was divided stratigraphically into six pollen assemblage zones by a stratigraphically-constrained cluster analysis using an incremental sum of squares method. The vegetation underwent the following stage changes: steppe with sparse trees, steppe, forest, and steppe. During the middle Holocene, a mixed forest of Pinus, Betula and Quercus occurred on the mountainous areas, and Pinus forest dominated the frontal plains. Six climatic stages were inferred from total pollen flux and pollen percentage from the two sites using a transfer function: humid-cool (10000-7800 aBP), arid-cold (9200-7800 aBP), arid-warm (7800-7100 aBP), humid-warm (7100-4400 aBP), arid-warm (4400-3000 aBP), arid-cold (3000-2100 aBP) phases were identified.