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

测试地球历史上最深碳同位素异常起源的模型？

• 批准号: 1121034
• 负责人: Adam Maloof
• 金额: $ 17.93万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1121034&HistoricalAwards=false
• 关键词: Testing; models; origin; deepest; carbon

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.

摘要在过去的二十年里，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。化学地层学的主流范式是碳酸盐岩中的δ - 13c （δ - 13ccarb）反映了同时期海水中溶解无机碳（DIC）的δ - 13c。如果这一假设是正确的，那么为什么我们观察到持续数百万年的负δ 13c漂移，远低于地幔碳输入到海洋-大气系统的标准值（-6?）？这些偏移实际上是否代表了成岩作用的改变，偏离了dic衍生值？即使是成岩作用，这些漂移在本质上是全球性的，使它们仍然对相关性有用吗？为了探索这些问题，我们建议研究地球历史上最深的三角洲碳水化合物偏移——“舒拉姆”异常，在动物早期进化期间至少七个古大陆的埃迪卡拉纪碳酸盐沉积物中记录。我们将结合详细的野外填图和层序地层学、同位素化学地层学和火山灰层的U-Pb年代学来限制Shuram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采集、峡谷切割、地面暴露、大气成岩作用和埋藏成岩作用的相对时间。我们对埃迪卡拉纪前所未有的同位素变化的研究将测试delta13Ccarb是否是全球碳循环演变的记录，并可能被用作一个相关工具——对于全球变化的每一个前寒武纪故事（气候、进化、地球化学、构造）都至关重要。