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从晚渐新世到早中新世转换时期,大气二氧化碳浓度降低,极地冰盖扩张,全球海平面大幅下降等现象表征的全球性极端气候变冷事件,其发生的原因和机制至今仍存在争议.本文选取赤道大西洋ODP154航次的926站为研究对象,该钻孔的地层记录主要以浅灰色含有孔虫的超微化石白垩软泥与绿灰色的黏土质的超微化石白垩软泥互层沉积为主,从岩芯上可见明显的浅灰色(碳酸钙含量高达80%)-灰绿色(碳酸钙含量60%左右)的米级旋回,据此本文选用能反映碳酸钙含量变化的颜色反射率亮度为古气候替代性指标,对沉积记录进行旋回分析.通过对识别出来的405kyr长偏心率旋回与~40kyr斜率旋回分别进行天文调谐,以渐新世与中新世转换界线处为绝对年龄控制点建立该钻孔的绝对天文年代标尺.通过对时间域序列的亮度指标的频谱变化分析,观察到从晚渐新世到早中新世沉积记录中偏心率周期信号减弱,而斜率周期信号增强;并且在界线处405kyr偏心率周期与~1.2Myr斜率长周期极小值重合,这可能与这一时期的极端气候变冷事件有关.此外,沉积物堆积速率、底栖有孔虫氧同位素及西班牙中部啮齿类动物演替速率都具有~2Myr的变化周期,这或许说明了百万年尺度的地球轨道周期对于地球系统及生态演化有着重要的影响.
The causes and mechanisms of the global extreme climatic events, characterized by the phenomena from the Late Oligocene to the Early Miocene transition, the reduction of the atmospheric carbon dioxide concentration, the expansion of the polar ice sheet and the drastic drop of the global sea level, remain controversial In this paper, 926 stations of the equatorial Atlantic ODP154 are selected as the study objects, and the stratigraphic records of the boreholes are mainly composed of light gray foraminifer calcareous slime and green-gray clayey superficial fossil chalk slime as The main, visible from the core light gray (calcium carbonate content of up to 80%) - gray-green (calcium carbonate content of about 60%) of the rice-level cycle, thus the choice of this paper can reflect changes in calcium carbonate color reflectance brightness For the paleoclimate alternative indicator, the sedimentary records were analyzed by the cycle.According to the identified 405kyr long-eccentricity cycle and ~ 40kyr slope cycle, respectively, astronomical tuning, the transition line from Oligocene to the Miocene as the absolute age control point The absolute astronomical date scale of the borehole was established.Through the spectral analysis of the brightness index of the time domain sequence, it was observed that from the Late Oligocene to the Early Miocene sedimentary record The signal of the heart rate cycle weakened and the signal of the slope cycle increased, and the 405kyr eccentricity cycle coincided with the minimum of ~ 1.2Myr slope at the boundary, which may be related to the extreme climatic cooling events in this period.In addition, The rate, the benthic foraminiferal oxygen isotope and the rodent succession rate in central Spain all have a ~ 2Myr variation cycle, which may indicate that the Earth’s orbital period at the million-year scale has an important impact on the Earth system and ecological evolution.