Testing models for the origin of the deepest carbon-isotope anomaly in Earth history? The Wonoka Formation of South Australia

地球历史上最深的碳同位素异常起源的测试模型--南澳大利亚的Wonoka组普林斯顿大学的Adam C.Maloof和Amp；Blair Schoene EAR-1121034在过去的二十年里，碳同位素化学地层学已经成为前寒武纪最重要的对比工具。化学地层学家普遍认为，碳酸盐岩中的三角洲13C(Delta13Ccarb)反映了同期海水中溶解无机碳(DIC)的三角洲13C。如果这一假设是正确的，那么为什么我们会观察到持续数百万年的负Delta13Ccarb漂移，远远低于输入到海洋-大气系统的地幔碳的标准值(-6？)？这些漂移实际上代表了与DIC得出的值背离的成岩改造作用吗？即使是成岩作用，这些漂移在本质上是全球性的，使它们在对比中仍然有用吗？为了探索这些问题，我们提出了地球历史上最深的三角洲13Ccarb漂移--“舒拉姆”异常--在动物早期演化期间，在至少七个古大陆的埃迪卡拉纪碳酸盐沉积物中记录的工作。我们将结合详细的野外填图和层序地层学，以及火山灰层的同位素化学地层学和U-Pb年代学，以限制舒拉姆异常的时间和持续时间。特别是，同位素砾岩测试将限制三角洲13Ccarb的获取、峡谷切割、空中暴露、大气成岩作用和埋藏成岩作用的相对时间。我们对埃迪卡拉纪史无前例的同位素变异性的研究将测试delta13Ccarb是否记录了不断演变的全球碳循环，是否可以用作对比工具--这对全球变化的每一个前寒武纪故事(气候、演化、地球化学、构造)都至关重要。

Testing models for the origin of the deepest carbon-isotope anomaly in Earth history -- The Wonoka Formation of South AustraliaAdam C. Maloof & Blair Schoene, Princeton UniversityEAR-1121034ABSTRACTOver the past two decades, carbon isotope chemostratigraphy has emerged as the most important correlation tool for the Precambrian. The dominant paradigm amongst chemostratigraphers is that delta13C in carbonate rocks (delta13Ccarb) reflects the delta13C of dissolved inorganic carbon (DIC) in contemporaneous sea water. If this assumption is true, then why do we observe negative delta13Ccarb excursions lasting millions of years that dip well below the canonical value for mantle carbon input to the ocean-atmosphere system (-6?)? Do these excursions in fact represent diagenetic alteration away from DIC-derived values? Even if diagenetic, are the excursions global in nature, making them still useful for correlation? To explore these questions, we propose work on the deepest delta13Ccarb excursion in Earth history -- the `Shuram' anomaly, recorded in Ediacaran carbonate sediments on at least seven paleo-continents during the early evolution of animals. We will combine detailed field mapping and sequence stratigraphy with isotope chemostratigraphy and U-Pb geochronology of ash beds to constrain the timing and duration of the Shuram anomaly. In particular, isotope conglomerate tests will constrain the relative timing of delta13Ccarb acquisition, canyon cutting, subaerial exposure, meteoric diagenesis, and burial diagenesis. Our investigation of the unprecedented isotopic variability during the Ediacaran will test whether delta13Ccarb is a record of the evolving global carbon cycle and may be used as a correlation tool -- vitally important for every Precambrian story (climatic, evolutionary, geochemical, tectonic) of global change.