Collaborative Research: Calibrating Rates and Duration for Isotopic Variability During the Early Cambrian Radiation of Animals, Anti-Atlas Mountains, Morocco

合作研究：校准早寒武世动物辐射期间同位素变异的速率和持续时间，摩洛哥反阿特拉斯山脉

• 批准号: 0638634
• 负责人: Samuel Bowring
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 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: 2007-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0638634&HistoricalAwards=false
• 关键词: Collaborative; Research; Calibrating; Rates; Duration

At 542 Ma, a global carbon isotope excursion to -6 permil marked the abrupt last-appearance of most, if not all, Ediacara as well as the prominent calcified animals Cloudina and Namacalathus. Large amplitude, high frequency oscillations in seawater delta13C(CaCO3) followed the end-Ediacaran extinction, culminating in a pair of 9 permil positive delta13C(CaCO3) excursions that likely took 1-3 myr. With the first appearance of abundant calcified animals at the end of the Nemakit-Daldyn (ND), volatility in the delta13C(CaCO3) signal is greatly damped. This pattern is remarkably similar to the record of delta13C(CaCO3) variability and biotic recovery in the aftermath of the Permian-Triassic boundary extinction. In the ca. 5 myr period immediately following the most severe extinction in the Phanerozoic, three delta13C(CaCO3) cycles of 4-10 permil amplitude coincide with an extreme reduction in the size of carbonate secreting animals (Payne, et al. 2004). The return to flatline delta13C(CaCO3) corresponds neatly to the first appearance of large calcified gastropods. In the absence of radiometric age constraints on the rate and duration of delta13C(CaCO3) change, delta13C(CaCO3) records tell us little about the relative sizes of carbon fluxes and reservoirs important to the global carbon cycle. For this reason alone, further work in Morocco is of critical importance, as the Anti-Atlas margin preserves the only expanded (2.5 km of sediment) record of Early Cambrian carbonates in the world that is punctuated by more than forty volcanic ash horizons that may be dated directly using single zircon U/Pb methods. Two U/Pb ages have already allowed us to calibrate the absolute age of the Nemakit-Daldyn"Tommotian (ND-T) boundary, and to show that the 10 permil ND-T negative delta13C(CaCO3)shift took only 430+/-260. PIs will also explore the importance of coupling between carbon and sulfur cycles and the influence of continental weathering by measuring delta13C(CaCO3), delta13C(org), delta 34S(CAS), delta 34S(pyrite) and 87-Sr/86-Sr measurements on the same samples.Minimally, this work will result in a particularly detailed, time-calibrated stratigraphic and isotopic record from the Early Cambrian. Optimistically, this research will shed light on the cause and effect relationship between the evolution of animal hard parts and geochemical cycling during the Early Cambrian.

在542 Ma，全球碳同位素漂移至-6permil标志着大多数(如果不是全部)埃迪卡拉以及突出的钙化动物Cloudina和Namacalatus突然最后出现。埃迪卡拉纪末期，海水三角洲13C(CaCO3)的大幅度、高频振荡，最终以一对9周正的Delta13C(CaCO3)漂移达到顶峰，可能需要1-3 MYR。随着Nemakit-Daldyn(ND)末期首次出现大量钙化动物，Delta13C(CaCO3)信号的波动性大大减弱。这种模式与二叠系-三叠系界线消亡后Delta13C(CaCO3)变异性和生物恢复的记录非常相似。在显生界最严重的灭绝之后紧接着的大约5 MYR期间，3个4-10个珍珠岩幅度的delta13C(CaCO3)旋回与碳酸盐分泌动物的大小极端减少相吻合(Payne等人。2004年)。回到平坦的Delta13C(CaCO3)恰好对应于大型钙化腹足类的第一次出现。在没有对Delta13C(CaCO3)变化的速率和持续时间进行放射性年龄限制的情况下，Delta13C(CaCO3)记录几乎不能告诉我们对全球碳循环重要的碳通量和碳库的相对大小。仅出于这个原因，摩洛哥的进一步工作就至关重要，因为反阿特拉斯边缘保存了世界上唯一扩大的早寒武世碳酸盐岩记录(沉积厚度为2.5公里)，其间点缀着40多个火山灰层，可以使用单一的锆石U/Pb方法直接测定其年龄。两个U/Pb年龄已经使我们能够标定Nemakit-Daldyn“Tommotian”(ND-T)界线的绝对年龄，并表明10 Permil的ND-T负增量13C(CaCO3)只有430+/-260。PIS还将通过测量相同样品的三角洲13C(CaCO3)、三角洲13C(Org)、三角洲34S(CAS)、三角洲34S(黄铁矿)和87-锶/86-锶，来探索碳和硫循环之间耦合的重要性以及大陆风化的影响。至少，这项工作将产生特别详细的、经过时间校准的早寒武世地层和同位素记录。乐观地说，这项研究将有助于阐明早寒武世动物硬质部分的演化与地球化学旋回之间的因果关系。