Collaborative Research: Biogeochemistry of Neoproterozoic Snowball Earth and Its Aftermath in South China

新元古代的地质记录包含了极端气候变化的证据，这些气候变化可能深刻地影响了生物进化的进程，特别是在所谓的雪球地球时期，即斯图亚特、马里诺和盖斯基冰川时期。在新元古代，尽管目前在斯图亚特冰期和马里诺冰期之间的某个时期，基底动物的辐射还没有得到很好的限制，但已经报道了被解释为来自多细胞动物的身体化石和分子生物标志物。本文通过分子生物标志物分析、有机和无机稳定同位素（13C、2H和34S）记录以及古氧化还原无机地球化学指标，对华南南华盆地4个剖面新元古代海洋生物地球化学进行了详细的时间记录。这将使我们能够研究低纬度新元古代冰川作用对浅海陆架-深海盆古环境样带初级生产、碳循环和氧化还原结构的影响。考虑到科学对华南陡山沱组动物化石和其他化石的兴趣，目前华南新元古代没有详细的分子生物标志物记录似乎令人惊讶。这无疑是由于某些剖面的高热成熟度，以及在石油衍生污染物的重要背景下识别低浓度的真正新元古代生物标志物信号的固有问题。研究表明，华南盆地四个剖面的地层热成熟度对保存可探测的生物标志烃信号没有问题。本文提出的生物标志物脂质工作的独创性和主要优势在于获得干酪根结合的生物标志物记录，这使我们能够获得华南盆地保存的大部分生物标志物记录，基本上不受污染影响。PI的研究证明了连续流催化加氢热解（HyPy）技术的有效性，该技术可以分解油根并释放共价结合的生物标志物成分，从而获得所有生物标志物脂质数据。我们将解决有关中国南方新元古代生物地球化学历史的一些基本问题：-我们是否可以使用我们的无机和生物标记代用物检测到斯图亚特和马林农冰期后海洋氧化还原结构的重大变化，如果是这样，是否有强有力的证据表明来源生物输入的波动？在氧化还原剖面和生物群方面，我们能否辨别出浅水环境和深水环境对冰期后果的显著不同反应？-我们是否可以在南华盆地检测到基础动物（海绵）的特定类固醇标记，如果可以，这些标记相对于斯图特和马里诺冰期是什么时候首次出现的？更广泛的影响。该研究将通过改变低纬度海洋环境中的营养循环、溶解氧可用性和创造环境生态位，显著提高我们对斯图尔特和马里诺冰期强烈气候冲击对海洋微生物群落的影响程度的理解。在提供教育机会方面，Love和Lyons将在每个项目年参与UCR指导暑期研究实习计划，来自历史上在科学（特别是地球科学）中代表性不足的少数民族的本科生将在两个实验室获得实践经验。最后，我们的项目将受益于中国科学院地质与地球物理研究所褚学雷教授及其课课组的合作，他们在中国南方新元古代冰川地层的研究方面有着丰富的经验。在项目进行过程中，Chu和他的同事将访问加州理工学院和加州大学洛杉矶分校的南加州生物地球化学社区，讨论研究结果并促进长期合作关系。

The Neoproterozoic geological record contains evidence for extreme climatic change which may have profoundly influenced the course of biological evolution, particularly around the so-called Snowball Earth episodes of the Sturtian, Marinoan and Gaskiers glaciations. During the Neoproterozoic, body fossils and molecular biomarkers interpreted as being derived from multicellular animals have been reported although the radiation of basal animals is presently poorly constrained at sometime between the Sturtian and Marinoan glaciations. In this study, we aim to produce detailed temporal records of Neoproterozoic marine biogeochemistry from molecular biomarker analyses, organic and inorganic stable isotope records (including 13C, 2H and 34S) and from inorganic geochemical proxies of paleoredox for four sections in the Nanhua Basin in South China. This will allow us to investigate the effects of low-latitude Neoproterozoic glaciation on primary production, carbon cycling and redox structure applied to a shallow shelf-to-deep basinal paleoenvironmental transect. Given the scientific interest in fossilized animal fauna and other fossils from the Doushantuo Formation in South China, it may seem surprising that no detailed molecular biomarker records currently exist for the Neoproterozic in South China. This is undoubtedly due to the high thermal maturity of some sections and due to the inherent problems of discerning low concentrations of genuine Neoproterozic biomarker signals above a significant background of petroleum-derived contaminants. A scoping study has revealed that the thermal maturity of strata in our four sections in Nanhua Basin is not problematic for preserving detectable biomarker hydrocarbon signals. The originality and principal strength of the biomarker lipid work proposed here lies in obtaining kerogen-bound biomarker records which allow us to access a high proportion of the preserved biomarker record in Nanhua Basin essentially free from contamination effects. The PI's research has demonstrated the efficacy of a continuous flow catalytic hydropyrolysis (HyPy) technique for fragmenting kerogen and releasing covalently-bound biomarker constituents to essentially ground-truth all the biomarker lipid data obtained. We will address some fundamental questions regarding the biogeochemical history of the Neoproterozoic in South China: -Can we detect significant changes in marine redox structure in the immediate aftermath of the Sturtian and Marinon glaciations using our inorganic and biomarker proxies and, if so, is there strong evidence for concomitant fluctuations in source organism input? -Can we discern significantly different responses of shallow- versus deep-water settings to the aftermath of the glaciations in terms of their redox profiles and biota? -Can we detect specific steroid markers for basal animals (sponges) in the Nanhua Basin and, if so, when do these first appear relative to the Sturtian and Marinoan glaciations? Broader Impacts. The research will significantly improve our understanding of the extent to which the intense climatic shock of the Sturtian and Marinoan glaciations impacted on marine microbial communities by modifying nutrient cycling, dissolved oxygen availability and creating environmental niches in low latitude marine environments. In terms of providing educational opportunities, Love and Lyons will participate during each of the project years in the UCR Mentoring Summer Research Internship Program, whereby undergraduate students from ethnic groups historically underrepresented in the sciences (particularly the earth sciences) will receive hands-on experience in the two labs. Finally, our project will benefit greatly from collaboration with Professor Xuelei Chu (Institute of Geology and Geophysics, Chinese Academy of Sciences) and his research group, who have considerable experience of studying Neoproterozoic glacial strata in South China. Chu and colleagues will visit the Southern California biogeochemical community at Caltech and UCR during the course of the project to discuss findings and to promote long-term collaborative links.