峡东伊迪卡拉纪陡山沱组顶部重晶石特征与地质意义研究

Barite from the Top Ediacaran Doushantuo Formation in the East Yangtze Gorges Area and Its Geological Implications

陡山沱组顶部潮间带泻湖相泥页岩中发现重晶石,其宏观、微观特征以及测试分析结果表明为早期成岩成因。结合产出层位沉积和地球化学特征认为,陡山沱组沉积中期和末期发生显著海平面下降,导致沉积速率降低至无沉积或沉积间断,使已埋藏有机质暴露、氧化和陆源物质输入增加,从而导致早期成岩重晶石和大型钙质结核发育和δ^(13)C高负异常等。深水环境的变迁可能是导致陡山沱组下部发育的大型具刺疑源类生物灭绝的原因。野外沉积学特征考察显示,陡山沱组底部、内部以及与灯影组接触部位可能存在沉积间断、饥饿沉积或平行不整合。上述研究对深入理解陡山沱组顶部年龄、早期生物演化、辐射以及Ediacaran地质历史演化具有新的启示作用。

Barite was found for the first time in the top part of the Ediacaran Doushantuo Formation in the Eastern Yangtze Gorges area. Macroscopic and microscopic sedimentary, mineralogical and geochemical features of the barite show an early diagenetic origin. Studies suggest that there occurred sea-level fall during the middle and the terminal Doushantuo depositional period, which caused slow depositional rates or pauses （or the major breaks） in the sedimentation and oxidation of buried organic materials and the input of mass terrigenous sediments. A turn- over of the deepwater environment related to the sea-level fall resulted in biotic extinction and radiation in early Ediacaran. Field observations in the study area revealed the sedimentary evidence of starvation sedimentation, depositional pause/break （or unconformity） within the bottom, interior and the top of the Doushantuo Formation, which challenges previous geochronology and biotic evolution in the Ediacaran Doushantuo Formation and is useful to decoding the Neoproterozoic Ediacaran geological history.