湖北宜昌茅坪泗溪剖面埃迪卡拉系岩石地层和碳同位素地层研究

华南埃迪卡拉系陡山沱组上部的δ13C巨大负异常事件(DOUNCE)是当前埃迪卡拉系研究最受关注的焦点之一。在对湖北宜昌茅坪泗溪剖面埃迪卡拉系开展高精度的岩石地层和碳氧同位素研究的基础上,通过与黄陵背斜周缘其他剖面的对比,表明峡区陡山沱晚期DOUNCE事件的δ13C值变化由下降—负漂移—短期正漂移—回升4个阶段构成,但DOUNCE事件在不同剖面上的表现存在明显差异。详细的沉积岩相分析和地层对比表明,各剖面δ13C演化差异是由岩相变化导致的岩石地层发育差异引起的。泗溪剖面DOUNCE事件主体部分缺失与该剖面位于台内盆地斜坡环境,发育多层滑塌构造造成的地层缺失有关。研究结果表明在缺乏生物地层控制的埃迪卡拉系,δ13C同位素地层是揭示沉积相变化造成的岩石地层差异和地层对比的重要手段。

LITHO-AND CARBON ISOTOPE STRATIGRAPHY OF THE EDIACARAN SYSTEM IN THE SIXI SECTION (YANGTZE GORGES),YICHANG,HUBEI

The unusual negative δ~(13)C excursion in the uppermost Doushantuo Formation( DOUNCE event) is one of the key events recorded in the Ediacaran, but its causality and age is under debate. High-resolution litho- and carbon isotope stratigraphy of the Ediacaran at the Sixi section and its correlation with other sections in the Yangtze Gorges region, Yichang, indicate that the DOUNCE event shows subtle differences at different sections in the Yangtze Gorges region. Lithofacies analysis and stratigraphic correlation indicate that such differences due to the varied lithostratigraphic sequences at different sections resulting from facies changes. The absence of a major part of the DOUNCE at the Sixi section is due to submarine sliding of the corresponding strata into deeper basin environments in the shelf. Present result indicates that δ~(13)C chemostratigraphy is a powerful tool for the stratigraphic correlation of Ediacaran successions, and the absence of DOUNCE in some different sections could not be a reason against its stratigraphic implication.