Collaborative Research: Comparative Geochemistry of the Late Cambrian (SPICE) and Toarcian (Jurassic) Positive Carbon Isotope Excursions: New Perspectives on Paleozoic OAEs

古生代的记录被多个，大的正碳同位素偏移打断，这些偏移即使不是全球性的，也是区域性的。在较新的记录中，通过直接观察，类似的漂移往往与海洋规模的有机碳埋藏增强事件有关-通常是在特征明确的缺氧条件下。在较老的层序中，缺乏保存完好的深海底，大规模的海洋氧化还原的性质只能通过使用地球化学代用品来推测，这些代用品在较年轻的环境中通常是地面真实的。特别是，我们的工作和其他研究人员的工作已经照亮了巨大的潜力，钼同位素代用品量化全球深海氧化还原，当仔细考虑到当地的氧气条件和盆地钼库存。在这项研究中，我们扩大了海洋缺氧事件的概念-第一次定义的情节普遍的深海和陆缘黑色页岩沉积在中生代-以解决海洋规模的氧化还原在古生代的性质。我们专注于晚寒武世SPICE事件（Steptoean正碳同位素漂移），建议我们的初步C和S同位素数据从陆架碳酸盐和我们的地球化学盒模型是一个主要的候选人早古生代OAE。在瑞典的明矾黑色页岩显示出明显的迹象，SPICE漂移的有机碳馏分和证据，至少本地euxinia之前，期间和之后的事件-使其成为一个理想的候选人钼同位素分析。因此，一个中心目标是将OAE概念外推到古生代，古生代有许多不同全球表达的正C同位素偏移，但深海条件的物理证据很少。我们将专门测试SPICE是否是OAE。碳和硫同位素行为，黑色页岩地球化学和生物灭绝的强烈类似模式已被描述从更好地了解Toarcian事件。因此，我们试图比较页岩地球化学和支持碳酸盐代用品的海水成分为这两个间隔问：1）Mo同位素记录从上寒武统明矾页岩在瑞典点全球扩大缺氧从我们的高分辨率三角洲13 C和三角洲34 S碳酸盐数据从美国推断？2)SPICE和Toarcian C同位素偏移是否显示类似的Mo同位素和C-S-Fe痕量金属行为，从而对寒武纪事件的性质有重要的新认识？3)与SPICE相关的有机生物标志物模式是否与Toarcian OAE观察到的模式相匹配，表明euxinia变浅，因为其面积范围增加？4）通过类比，我们是否可以推断出Toarcian的模型来理解早古生代无脊椎动物的灭绝模式，包括有问题的三叶虫灭绝？5)使用我们的综合数据的SPICE作为模板，是古生代间隔明显的正三角洲13 C和陆缘黑色页岩沉积类似的中生代的OAE？所有这些问题都将通过在每个时间间隔与专家合作并通过使用我们联合研究小组的斯台普斯地球化学代理来解决--特别是Fe形态、微量金属化学（强调Mo）以及S的新型同位素方法、Fe和Mo。更广泛的影响。在真诚的努力，以扩大本研究的影响以外的里昂/安巴尔研究小组，我们已经设计了一个双管齐下的方法，在更大的河流，洛杉矶地区的推广。首先，里昂/安巴尔/吉尔将在项目的每一年参加UCR指导夏季研究实习计划，使学生从历史上在科学（特别是地球科学）代表性不足的民族群体将在两个实验室获得实践经验。其次，里昂/安巴尔/吉尔将与加利福尼亚州长滩的太平洋水族馆合作，设计一个以人为沿海缺氧的全球流行病为中心的展览。令人高兴的是，洛杉矶地区近年来沿海水质有所改善。从这一成功和从过去吸取的经验教训-包括非常深刻的过去-我们希望以一种信息丰富，乐观，希望娱乐的方式向公众宣传沿海环境的健康。鉴于每年有130万游客参观水族馆，我们相信我们的信息将广泛传播。

The Paleozoic record is punctuated by multiple, large positive carbon isotope excursions that are expressed regionally if not globally. In younger records, similar excursions are often linked through direct observation to ocean-scale events of enhanced organic carbon burial--typically under well-characterized anoxic conditions. In older sequences, lacking preserved deep seafloor, the nature of oceanic redox on the broad scale can only be surmised through use of geochemical proxies that are typically ground-truthed in younger settings. In particular, our work and that of other researchers has illuminated the great potential of the molybdenum isotope proxy for quantifying global deep-ocean redox, when applied with careful consideration to local oxygen conditions and the basinal Mo inventory. In this study we expand the concept of an Oceanic Anoxic Event--first defined for episodes of pervasive deep-ocean and epicontinental black shale deposition during the Mesozoic--to address the nature of ocean-scale redox in the Paleozoic. We focus on the Late Cambrian SPICE event (Steptoean Positive Carbon Isotope Excursion), suggested by our preliminary C and S isotope data from shelf carbonates and our geochemical box model to be a prime candidate for an early Paleozoic OAE. The Alum black shale in Sweden shows clear signs of the SPICE excursion in the organic C fraction and evidence for at least local euxinia before, during, and after the event--making it an ideal candidate for Mo isotope analysis. A central goal, then, is to extrapolate the OAE concept to the Paleozoic, which has numerous positive C isotope excursions of varying global expression but little physical evidence for conditions in the deep ocean. We will specifically test whether the SPICE is an OAE. Strongly analogous patterns of C and S isotope behavior, black shale geochemistry, and biotic extinction have been described from the better-known Toarcian event. We therefore seek to compare the shale geochemistry and supporting carbonate proxies for seawater composition for these two intervals to ask: 1) Do Mo isotope records from the Upper Cambrian Alum Shale in Sweden point to the globally expanded anoxia inferred from our high-resolution delta13C and delta34S carbonate data from the United States? 2) Do the SPICE and Toarcian C isotope excursions show analogous Mo isotope and C-S-Fe-trace metal behavior, such that significant new light is shed on the nature of the Cambrian event? 3) Do organic biomarker patterns associated with the SPICE match those observed from the Toarcian OAE, suggesting that euxinia shallowed as its areal extent increased? 4)By analogy, can we extrapolate models for the Toarcian to understand invertebrate extinction patterns in the early Paleozoic, including problematic trilobite extinctions? 5)Using our integrated data for the SPICE as a template, are Paleozoic intervals of pronounced positive delta13C and epicontinental black shale deposition analogous to the OAEs of the Mesozoic? All of these questions will be addressed through collaboration with experts on each time interval and through use of the geochemical proxies that are staples in our combined research groups--specifically Fe speciation, trace metal chemistry (emphasizing Mo), and novel isotope approaches for S, Fe, and Mo.Broader Impacts. In a sincere effort to extend the impact of this study beyond the Lyons/Anbar research groups, we have designed a two-pronged approach for outreach in the greater Riverside-LA area. First, Lyons/Anbar/Gill will participate during each of the project years in the UCR Mentoring Summer Research Internship Program, whereby students from ethnic groups historically underrepresented in the sciences (particularly the earth sciences) will receive hands-on experience in the two labs. Second, Lyons/Anbar/Gill will work with the Aquarium of the Pacific in Long Beach, CA, to design an exhibit centered on the global epidemic of anthropogenic coastal hypoxia. Happily, the LA area has seen an improvement in its coastal water quality in recent years. Building from this success and lessons learned from the past--including the very deep past--we expect to reach out to the public about the health of coastal environments in an informative, optimistic, and hopefully entertaining way. Given the 1.3 million annual visitors to the aquarium, we are certain our message will spread widely.