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.

大不整合面（GU）代表了岩石记录中最大的时间间隙之一。由于紧随其后的是寒武纪辐射，这是生物多样性和复杂性最显着增加的现象之一，因此长期以来人们一直认为这些现象是相互关联的。地球科学家提出，GU是由地壳大规模侵蚀造成的。随着岩石风化和溶解，对生命至关重要的元素磷被释放并被河流带到海洋。磷的增加被认为刺激了蓝藻的光合作用，从而增加了海洋和大气中的氧气含量。这种氧化作用可能是导致寒武纪辐射的导火索，因为复杂的生命需要氧气。尽管 GU 在生命中最重要的转变之一中发挥着潜在作用，但人们对它发生的时间和地点知之甚少。确定 GU 形成的时间以及导致其形成的最后一次侵蚀事件的规模对于确定地球历史这一关键时期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矿 (U-Th)/He 方法的进步来破译 GU 的发展。结果直接检验了将大陆侵蚀与氧化和生命爆发联系起来的假设。该项目还通过培训本科生、研究生以及 K-12 教师来增进对科学和技术的理解。有人提出，大不整合面下方的侵蚀是超大陆分裂、雪球地球冰川作用或全球海平面稳定的结果，并且可能向海洋输送了生物限制性营养物质，从而促进了寒武纪辐射。然而，大不整合面的发生时间、拟议的全球同步性和规模此前尚未经过测试或限制。 (U-Th)/He 热年代学的最新进展允许了解解开这一标志性特征的历史所需的热历史。该项目将获取沿两个不同克拉通边缘的两条横断面样本的锆石和钛矿 (U-Th)/He 数据。研究地点的目标是充分利用新元古代和寒武纪的地质限制，这对于缩小可行的热历史范围以区分 GU 形成模型至关重要。结果将极大地改善对每个边缘的新元古代冷却历史的限制，这将用于测试 GU 发展和意义的竞争模型。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和重要性进行评估，被认为值得支持。更广泛的影响审查标准。