甘肃张掖白垩纪早Aptian期黑色页岩揭示的气候岁差驱动及其意义*

白垩纪中期是温室气候的典型代表,在该时期地球经历了深刻的环境变化。有研究表明白垩纪中期欧洲低纬(约20°~30°N)地区海相地层的黑色页岩呈现斜率信号,同一时期同样纬度的中国地区以陆相沉积为主,但陆相低纬黑色页岩的轨道尺度周期研究较少。因此本研究选择甘肃张掖南台子白垩纪早Aptian期下沟组黑色页岩(古纬度约23°N)作为研究对象,以CaCO₃含量作为高分辨率古气候替代性指标,利用平均频谱拟合差和年代标尺优化法分析了南台子早Aptian期下沟组黑色页岩段的轨道周期变化,并利用频谱分析方法对调谐后的时间域序列进行分析。结果显示南台子下沟组黑色页岩段以岁差周期为主导,与欧洲低纬地区相关研究显著不同。这一气候变化的探索不仅提供了中国西北地区白垩纪轨道尺度气候变化的新证据,而且也有助于更全面认识白垩纪中期低纬地区气候变化的驱动机制。

Detection of climatic precession variability of black shale in the early Aptian of Cretaceous in Zhangye of Gansu Province and its significance

The earth experienced profound environmental changes at the mid-Cretaceous when a typical representative of the greenhouse climate occurred. In the mid-Cretaceous,studies have shown that black shale in low-latitude(ca.20°~30°N)marine strata in Europe records presents obliquity signals,continental deposits are prevalent in inland China at the same latitude and during the same period,but there are few studies on the orbital-scale periodicity of continental low-latitude black shales. In this study,CaCO₃ content is used as an alternative high-resolution indicator of paleoclimate,and average spectral misfit(ASM)and time scale optimization(TimeOpt)analyses are used to explore the orbital periodicity of the black shale in the Xiagou Formation of the early Aptian of Cretaceous in Nantaizi (palaeoatitude of ca 23°N),Zhangye of Gansu Province, China. The result shows that the climate is dominated by precession and eccentricity cycles,which is significantly different from the result in Europe. The exploration of this climate change not only provides new evidence for the cretaceous orbital-scale climate change in the Northwest China,but also contributes to a more comprehensive understanding of the driving mechanism of climate change in the mid-Cretaceous.