广西东攀二叠系-三叠系界线剖面基于岩石磁参数的米兰科维奇旋回特征和地层对比

二叠纪-三叠纪之交发生了地质历史上最大的生物集群绝灭。通过对广西东攀二叠系-三叠系界线剖面不同的磁学数据进行频谱分析,其结果均具一致的功率谱峰,对比煤山剖面的同位素年龄将厚度频率35.7∶15.6∶7.7cm/cycle换算为时间周期95∶41.6∶20.5kyr/cycle,分别与米兰科维奇旋回偏心率、斜度、岁差相当,从而将地层研究的精度提高到万年级,为生物绝灭和众多地质事件提供时间上的约束。不同的磁学参数分别受控于不同的天文周期,磁性矿物种类主要受偏心率旋回控制,同时也受斜度周期的影响,而岁差周期则是促使岩石携磁能力高频变化的原因。不同二叠系—三叠系剖面(集中在界线附近)的磁化率曲线具有一致特征,可作为界线点确定的辅助依据。

CYCLOSTRATIGRAPHY AND STRATIGRAPHIC CORRELATION BASED ON ROCK-MAGNETIC PARAMETERS ON THE PERMIAN-TRIASSIC BOUNDARY IN THE DONGPAN SECTION IN GUANGXI

The Permian-Triassic boundary is marked by the most severe mass extinction in the geologic record. Frequency analysis of different magnetic parameters on the Permian-Triassic boundary section in Dongpan, Guangxi shows consistent power spectral peaks. Correlation with the dated Meishan section shows that the stratigraphic thickness cycles (35.7:15.6:7.7 cm/cycle) can be translated into temporal periods (95:41.6:20.5 kyr). These cycles are identified as Milankovitch cycles (eccentricity, obliquity, precession), and they significantly enhance the resolution for stratigraphic correlation to 10~4 yrs and provide temporal constraint on faunal extinction and other catastrophic events. Cycles of different magnetic parameters are controlled by different orbit periods: magnetic minerals are mainly controlled by eccentricity and partially by obliquity, whereas precession period is the cause for high-frequency fluctuation of rock magnetic competence. Susceptibility curves at the Permian-Triassic boundary at different sections have a consistent pattern which could assist us recognizing stratigraphic boundaries.