Sulfur Cycling Through the Neoproterozoic Interglacial Interval: An Integrated Field and Geochemical Study of the Abenab Subgroup in Northern Namibia

新元古代间冰期的硫循环：纳米比亚北部阿贝纳布亚群的综合野外和地球化学研究

• 批准号: 0720045
• 负责人: Matthew Hurtgen
• 金额: $ 19万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-01 至 2011-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0720045&HistoricalAwards=false
• 关键词: Sulfur; Cycling; Through; Neoproterozoic; Interglacial

The late Neoproterozoic witnessed among the most extreme climatic events in Earth history, including perhaps two snowball glaciations (Sturtian and Marinoan). Considerable attention has been focused recently on testing the validity of the snowball Earth hypothesis, radiometrically dating the glacial deposits, and understanding what geological conditions were responsible for the onset of global cooling in the middle Neoproterozoic. However, only limited work has been done on the geochemistry of sediments deposited between the Sturtian and Marinoan ice ages, despite the fact that these preserve the most direct and continuous record of the Neoproterozoic Earth system during this tumultuous climatic epoch. This proposal represents an unparalleled investigation into dynamics of the global sulfur cycle during the ca.55 Myr interglacial interval, using both the sulfur and oxygen isotope composition of carbonateassociated sulfate (CAS) and the sulfur isotope composition of sedimentary pyrite from sediments of the Abenab Subgroup in northern Namibia. The principal objectives of the proposal are to constrain ocean chemistry in the aftermath of the Sturtian glacial event, examine the relationship between ocean redox and the geochemical cycles of carbon and sulfur for the middle Neoproterozoic, and test hypotheses regarding possible trigger mechanisms for the Marionan glaciation. In recent years, significant improvements to the understanding of the Precambrian exogenic sulfur cycle have been made possible by advances involving the sulfur isotope composition of CAS. Typically, these research efforts characterize sulfur isotope evolution for a given time period by assessing the sulfur isotope composition of CAS through a single stratigraphic section at one locality. In this proposal, a different approach is taken. The sulfur isotope evolution of interglacial seawater sulfate will be evaluated using the sulfur isotope composition of CAS and pyrite in multiple sections along a transect perpendicular to the paleo-shoreline. Recent work has shown that large lateral d34Ssulfate gradients developed in the aftermath of the Marinoan glaciation (Hurtgen et al., 2006). These results have important implications for the reconstruction of the Neoproterozoic 34Ssulfate record and the timing of the growth of the marine sulfate reservoir. This project will focus on both the temporal and spatial variability of CAS d34S and d18O data to establish the intrinsic scatter in isotopic compositions preserved in CAS, evaluate the effects diagenesis and of sea level on marine sulfur isotope composition, and determine whether lateral d34S gradients were a feature of interglacial times or if they were typical only of the post-glacial ocean. Tandem d34S-d18O data will be used to compare the oceanographic conditions following the Sturtian and Marinoan glaciations and to constrain the trigger mechanisms for the onset of glaciation. The results of this project will also establish d34 S(sulfate-pyrite) and help to ascertain the complex set of feedbacks that link ocean redox and the geochemical cycles of carbon and sulfur and how these feedbacks may have operated to influence climate in the middle Neoproterozoic.Broader Impacts: (1) This project will provide training to one graduate student in field research techniques and analytical isotope geochemistry and an opportunity for that student to work collaboratively with colleagues from another institution. (2) The data generated from this project will be the nucleus of a new website devoted to the storage of all Neoproterozoic sulfur data generated through publicly funded projects. Other workers in the field will be encouraged to contribute their published data to be archived in an easily accessed and consistent manner. (3) In order to attract under-represented youth to the Earth Sciences, the PI will participate in the Project EXCITE program, which links Northwestern's Center for Talent Development with local schools to identify scientifically-inclined minority students and support the development of their math and science skills through high school. The PI will recruit an EXCITE student to participate in this project.

新元古代晚期见证了地球历史上最极端的气候事件，其中可能包括两次雪球冰川（斯特阶和马里诺阶）。最近相当多的注意力集中在测试雪球地球假说的有效性，放射性测年的冰川沉积物，并了解什么地质条件是负责在新元古代中期全球变冷的开始。然而，只有有限的工作已经做了沉积物的地球化学之间的斯特和马里诺冰期，尽管事实上，这些保存最直接和连续的记录新元古代地球系统在这个动荡的气候时代。这一建议代表了一个无与伦比的调查全球硫循环的动态在约。55万年间冰期，使用的硫和氧同位素组成的carbonatesociated硫酸盐（CAS）和硫同位素组成的沉积黄铁矿沉积物的Abenab子群在北方纳米比亚。该提案的主要目标是限制海洋化学在斯特阶冰川事件的后果，研究海洋氧化还原和碳和硫的地球化学循环之间的关系，为中新元古代，并测试假设可能的触发机制的Marionan冰川。近几年来，由于中科院硫同位素组成研究的进展，对前寒武纪外生硫循环的认识有了很大的提高。通常，这些研究工作通过在一个地点的单个地层剖面评估CAS的硫同位素组成来表征给定时间段的硫同位素演化。本提案采取了不同的做法。利用沿沿着垂直于古海岸线的多个断面的CAS和黄铁矿的硫同位素组成，评价间冰期海水硫酸盐的硫同位素演化。最近的研究表明，在马里诺冰川作用之后，形成了大的横向d34 S硫酸盐梯度（Hurtgen等人，2006年）。这些结果对新元古代34 S硫酸盐记录的重建和海相硫酸盐储层的发育时间具有重要意义。该项目将侧重于CAS d34 S和d18 O数据的时间和空间变化，以确定CAS保存的同位素组成的内在分散性，评估成岩作用和海平面对海洋硫同位素组成的影响，并确定横向d34 S梯度是否是间冰期的特征，或者它们是否仅是冰后期海洋的典型特征。串联d34 S-d18 O数据将被用来比较海洋学条件下的斯特阶和马里诺冰川，并限制触发机制的冰川作用的开始。该项目的结果还将建立d34 S（硫酸盐-黄铁矿），并有助于确定海洋氧化还原与碳和硫的地球化学循环之间的一系列复杂反馈，以及这些反馈如何影响新元古代中期的气候。（一）该项目将为一名研究生提供实地研究技术和分析同位素地球化学方面的培训，学生与来自另一个机构的同事合作。(2)该项目产生的数据将成为一个新网站的核心，该网站专门用于存储通过公共资助项目产生的所有新元古代硫数据。将鼓励该领域的其他工作人员贡献其公布的数据，以便以易于访问和一致的方式存档。(3)为了吸引代表性不足的青年到地球科学，PI将参加项目EXCITE计划，该计划将西北大学人才发展中心与当地学校联系起来，以确定有科学倾向的少数民族学生，并支持他们的数学和科学技能的发展。PI将招募一名EXCITE学生参与该项目。