张掖盆地晚更新世至中全新世气候变化:孢粉学和重矿物学证据

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

为确定张掖盆地晚第四纪沉积地层时代和探讨其蕴含的古气候信息,笔者利用孢粉分析、重矿物分析、光释光测年等方法对研究区晚更新世以来气候变化特征进行了重建,并确认了当地全新世和晚更新世地层界限。结果表明:地层自下而上划分为4个孢粉组合带和植被类型及气候特征:①深度为56.8~26.4 m,年龄为112.7~63.3 ka,属末次间冰期,粉组合为松–板栗–藜–菊–蒿,针阔叶混交林草原植被,为晚更新世温暖较湿润气候。②深度为26.4~2.6 m,年龄为63.3~11.8 ka,与末次冰期相当,孢粉组合为松–麻黄–藜–蒿,植被类型为针阔叶混交林草原植被,为晚更新世干燥寒冷气候。③深度为2.6~0.8 m,年龄为11.8~8.9 ka,全新世早期,孢粉组合为松–藜–蒿,稀树针阔叶混交林草原植被,较凉较干气候。④深度为0.8~0.15 m,年龄为8.9~7.8 ka,全新世早期向中期过渡期,孢粉组合为松–藜–菊–蒿,稀树针阔叶混交林草原植被,为温暖较干气候。孢粉组合所揭示的晚更新世—中全新世气候变化特征,对于揭示张掖盆地甚至西北干旱区的古气候变化具有重要意义。

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:①the 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 spore-pollen 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.②the 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 assem-blage 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.③the 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-Chenopo-diaceae-Artemisia,mixed broadleaf-conifer forest steppe vegetation,early Holocene cool and dry climate.④the depth ranges from 0.8 m to 0.15 m(the age is 8.9~7.8 ka),which is the postglacial,the sporepollen as-semblage 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.