Origin of the second terraces in the Huangshui drainage area, Qinghai, China, studied based on sporopollen records.

Abstract: The study of the origin of river terraces at the edges of the Qinghai-Tibet Plateau has long been a hot topic. Analysis of the sporopollen on the second terrace of the Huangshui River drainage area indicates that during the period of formation of the second terraces, a distinct vertical vegetation zone with simple structure occurred in the area, with forest dominated by Picea growing in higher places of mountainous areas and herbaceous plants dominated by Artemisia and Chenopodiaceae growing in valleys. According to these features, combined with the sporopollen data in the neighboring areas during that period and a comparison with the characteristics of modern vegetations, the vegetations in the second terraces of the Huangshui drainage area show the features of the vegetations in the glacial period, the alluvial deposits on the terraces were also piled up in the glacial period and the river probably incised the strata in the interglacial period. The climatic change might play an innegligible role in the formation process of the river terraces.