川西地区成都粘土的光释光年代学

摘要

在野外地质调查的基础上,对川西地区广泛分布的风成堆积物——成都粘土进行了光释光测年,获得了一组74.67±9.59 ～18.60±0.33ka的年龄数据.这一结果表明,成都粘土的时代为晚更新世晚期,为末次冰期的堆积物,与黄土高原马兰黄土相当.末次冰期干冷的气候条件为川西地区风尘堆积提供了丰富的物质来源,从而形成了分布较为广泛的成都粘土.%West of Sichuan basin is the western part of the very large Sichuan basin,in the Southwest China,lies just to the south of the Loess Plateau and to the east of the Tibetan Plateau.Chengdu clay which is silty clay sediment widely distributed in the basin surfaces,intrabasinal river terraces and surrounding mountains at different altitudes,it covered in the Early and Middle Pleistocene vermiculated red soil or Mesozoic strata.It has a general thickness of 2 ～7m with a maximum thickness of greater than 10m.Geological and geochemical evidence (spatial variation of thickness and grain size,distributive features,common and trace elements,REE,surface textures of quartz particles,etc.)have demonstrated that the Chengdu clay in western Sichuan basin is eolian,it record important information for reconstructing the Pleistocene environments.However,Chengdu clay has not been dated by modern dating techniques,this hampers paleoenvironment significance discussion.In this study,six optically stimulated luminescence (OSL)samples of Chengdu clay were taken at different section,fine quartz particles (4 ～ 11 μm) were chosen for OSL dating,following the combined pretreatment methods of Lu et al.(1988)and Aitken(1998).Luminescent signals were excited by blue laser(47±5nm)and measured on a Daybreak 2200 at the State Key Laboratory of Crustal Dynamics,Institute of Crustal Dynamics,China Earthquake Administration,Beijing.The results show that Chengdu clay age is 74.67±9.59ka ～ 18.60±0.33ka,suggesting that it accumulated during the Last Glaciation in Late Pleistocene,correspond to Malan loess on the Chinese Loess Plateau.Dry and cool conditions has provided abundant sources for aeolian deposits in the Last Glaciation in Late Pleistocene,thus accumulated Chengdu clay in west Sichuan basin.