Climate Changes of Late Pleistocene to Middle Holocene in Zhangye Basin, NW China: Evidence from Pollen and Heavy Mineral

In order to explore the paleoclimatic evolution characteristics and stratigraphic age of Zhangye basin, we reconstructed the climate change characteristics of the study area since the late Pleistocene by means of sporopollen analysis, heavy mineral analysis and optical luminescence dating, and confirmed the stratigraphic boundary between Holocene and late Pleistocene. The results show that the strata are divided into four spore–pollen assemblage zones, the vegetation types and climatic characteristics from bottom to top: ① the depth ranges from 56.8 m to 26.4 m (the age is 112.7～63.3 ka), which is the last interglacial period, the sporepollen assemblage is Pinus–Castanea–Chenopodiaceae–Compositae–Artemisia, coniferous and broad–leaved mixed forest steppe vegetation, which is the warm and humid climate in the late Pleistocene. ② the depth ramges from 26.4 m to 2.6 m (the age is 63.3～11.8 ka), which is the last glacial period, the sporepollen assemblage is Pinus–Ephedra–Chenopodiaceae–Artemisia, and the vegetation type is coniferous and broad–leaved mixed forest steppe vegetation, which is the dry and cold climate of late Pleistocene. ③ the depth ranges from 2.6 m to 0.8 m (the age is 11.8～8.9 ka), which is the postglacial,the sporepollen assemblage is Pinus–Chenopodiaceae–Artemisia, mixed broadleaf–conifer forest steppe vegetation, early Holocene cool and dry climate. ④ the depth ranges from 0.8 m to 0.15 m (the age is 8.9～7.8 ka), which is the postglacial, the sporepollen assemblage is Pinus–Chenopodiaceae–Compositae–Artemisia, broadleaf–conifer mixed forest steppe vegetation, which is the warmer and drier climate of Holocene. The late Pleistocene to mid–Holocene climate evolution characteristics revealed by the spore–pollen assemblages are of great significance for revealing the paleoclimate changes in the Zhangye basin and even the arid area of Northwest China.