Collaborative Research: Did the Formation of the Great Unconformity Trigger Oxygenation and the Cambrian Explosion?

合作研究：大不整合面的形成是否引发了氧化作用和寒武纪大爆发？

• 批准号: 1916698
• 负责人: Francis Macdonald
• 金额: $ 9.12万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1916698&HistoricalAwards=false
• 关键词: Collaborative; Research; Did; Formation; Great

The Great Unconformity (GU) represents one of the largest gaps of time in the rock record. Since it is followed by the Cambrian Radiation, one of life's most significant increases in biodiversity and complexity, it has long been thought that these phenomena are linked. Geoscientists have proposed that the GU was caused by large-scale erosion of Earth's crust. As rocks weathered and dissolved, an element critical to life, phosphorous, was released and carried to the ocean by rivers. The increase in phosphorous is proposed to have spurred photosynthesis among cyanobacteria, which then increased the oxygen content of the ocean and atmosphere. This oxygenation was perhaps the fuse that led to the Cambrian Radiation since complex life requires oxygen. Despite the GU's potential role in one of life's most important transformations, very little is known about when and where it occurred. Determining when the GU developed and the size of the last erosion event that lead to its formation are critical for identifying viable mechanisms for life and environmental change during this pivotal interval of Earth history. This research project is making use of advances in zircon and titanite (U-Th)/He methods to decipher GU development. Results are directly testing hypotheses that relate continental erosion to oxygenation and the explosion of life. The project is also advancing scientific and technological understanding through the training of undergraduate and graduate students and K-12 teachers. It has been proposed that the erosion below the Great Unconformity occurred as the result of supercontinental breakup, Snowball Earth glaciation, or global eustasy, and may have delivered bio-limiting nutrients to the ocean that fueled the Cambrian Radiation. However, the timing, proposed global synchroneity, and magnitude of the Great Unconformity have not been previously tested or constrained. Recent advances in (U-Th)/He thermochronology allow access to the thermal histories required to unravel the history of this iconic feature. This project will acquire zircon and titanite (U-Th)/He data for samples along two transects across two different cratonic margins. Study sites will be targeted to fully exploit Neoproterozoic and Cambrian geologic constraints, which will be vital for narrowing the range of viable thermal histories to enable discrimination between GU formation models. The results will dramatically improve constraints on the Neoproterozoic cooling history of each margin, which will be used to test competing models for GU development and significance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

巨大的不整合（GU）代表了摇滚记录中最大的时间差距之一。由于其随后是寒武纪辐射，这是生命中生物多样性和复杂性最显着的增长之一，因此长期以来一直认为这些现象是联系在一起的。地球科学家提出，GU是由地壳大规模侵蚀引起的。随着岩石的风化和溶解，对生命至关重要的磷，磷，并被河流释放到海洋。提出磷的增加是在蓝细菌中刺激了光合作用，然后增加了海洋和大气的氧含量。这种氧合可能是导致寒武纪辐射的融合，因为复杂的寿命需要氧气。尽管GU在人生最重要的转变之一中的潜在作用，但何时和何时何地知之甚少。确定GU何时发展以及最后一次侵蚀事件的大小导致其形成对于确定地球历史的关键间隔期间的生命和环境变化的可行机制至关重要。该研究项目正在利用锆石和钛铁矿（U-th）/HE方法的进步来破译GU开发。结果是直接检验将大陆侵蚀与氧合和生命爆炸相关的假设。该项目还通过培训本科生和研究生以及K-12老师来提高科学和技术理解。有人提出，由于超大分子的分裂，雪地地球冰川或全球-耐热而发生的巨大不整合性侵蚀发生了，并且可能已将生物限制的养分传递到了助长寒武纪辐射的海洋中。然而，以前尚未对其进行计时，提出的全局同步性和巨大不整合性的幅度。 （u-th）/HE热量学的最新进展允许访问揭示此标志性特征历史所需的热历史。该项目将沿两个不同的cratonic边缘沿两个样品沿两个样品获取锆石和钛铁矿（U-th）/HE数据。研究地点将针对完全利用新元古代和寒武纪地质约束，这对于缩小可行的热历史的范围至关重要，以使GU组模型之间的区分。结果将显着改善对每个边距的新元古代冷却历史记录的约束，该历史将用于测试GU发展和重要性的竞争模型。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的审查标准来通过评估来获得支持的。