地球化学记录揭示的柴达木盆地北缘地区中—晚侏罗世古环境与古气候*

沉积岩的地球化学特征是古环境变化良好的示踪剂,柴达木盆地北缘地区侏罗系记录了中国西北地区古环境、古气候演化的重要信息。本研究通过对柴达木盆地北缘地区大煤沟侏罗系标准剖面沉积岩的元素地球化学分析,尝试恢复了研究区中—晚侏罗世的古环境特征。结果显示:(1)研究区中—晚侏罗世以富氧的浅水环境为主,仅在短期内出现较深湖相沉积;整体上侏罗纪湖盆水体盐度较低,而部分层段沉积物盐度增大系降雨量相对减小导致。(2)基于多元地球化学参数建立的古气候演化曲线表明,中—晚侏罗世柴达木盆地北缘地区古气温、古湿度均在一定幅度内频繁变化;自中侏罗世晚期开始,研究区古气候开始由温暖潮湿向炎热干旱转变,至晚侏罗世进入了干热环境主导的阶段。多元地球化学参数剖面的建立为中国西北地区中—晚侏罗世“干热化事件”和区域古气候的研究对比提供了新的证据和材料。

Palaeoenvironment and palaeoclimate of the Middle to Late Jurassic revealed by geochemical records in northern margin of Qaidam Basin

Geochemical characteristics of sedimentary rocks can indicate palaeoenvironment evolution process. The Jurassic sediments in northern margin of Qaidam Basin recorded significant palaeoenvironmental and palaeoclimatic information of northwest China. Based on the geochemical analysis of sedimentary rocks from the Dameigou standard geological profile in northern margin of Qaidam Basin,palaeoclimate and palaeoenvironment of the Middle to Late Jurassic were reconstructed. The results revealed that: (1)From the Middle to Upper Jurassic,it showed a shallow-water environment with oxic condition,deep lacustrine facies with anoxic condition only appeared in a short time occasionally. In general,the lacustrine water-body in the Jurassic displayed moderate palaeosalinity,but the decrease in precipitation may lead to salinity increase in some intervals. (2)Comprehensive utilization of multiple geochemical parameters,palaeoclimate evolution sequence of the Middle to Late Jurassic in northern margin of Qaidam Basin was established. According to the long-term records,the palaeotemperature and palaeohumidity fluctuation varied within a certain range. From the late Middle Jurassic,the palaeoclimate changed from warm and humid into hot and arid,which triggered the hot and arid palaeoenvironment of the Late Jurassic. The diversified geochemical profile of this study will provide new evidence and materials for the research on the Middle to Late Jurassic hot-arid climate event and palaeoclimate correlation in northwest China.