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

在542 Ma，全球碳同位素偏移到-6 peril，这标志着大多数埃迪卡拉动物（如果不是全部的话）以及著名的钙化动物Cloudina和Namacalathus突然最后出现。在埃迪卡拉末灭绝之后，海水δ 13c （CaCO3）出现了大振幅、高频振荡，最终导致一对9 peril的δ 13c （CaCO3）正偏移，可能需要1-3 myr。随着Nemakit-Daldyn （ND）末期大量钙化动物的首次出现，delta13C（CaCO3）信号的挥发性大大减弱。这一模式与二叠纪-三叠纪边界灭绝后delta13C（CaCO3）变化和生物恢复的记录非常相似。在显生宙最严重灭绝之后的大约5千万年期间，三个幅度为4-10 peril的三角洲13c （CaCO3）旋回与碳酸盐分泌动物的尺寸急剧减少相吻合（Payne, et al. 2004）。回到平坦线的δ 13c （CaCO3）正好对应于大型钙化腹足类动物的首次出现。由于缺乏对δ ta13c （CaCO3）变化速率和持续时间的辐射年龄限制，δ ta13c （CaCO3）记录对全球碳循环重要的碳通量和储集层的相对大小告诉我们的很少。仅仅因为这个原因，在摩洛哥的进一步工作至关重要，因为反阿特拉斯边缘保存了世界上唯一一个扩展的（2.5公里的沉积物）早寒武纪碳酸盐记录，其中有40多个火山灰层，可以直接使用单个锆石U/Pb方法进行年代测定。两次U/Pb年龄已经使我们能够校准Nemakit-Daldyn“Tommotian （ND-T）边界的绝对年龄，并表明10 peril ND-T负δ 13c （CaCO3）位移只需要430+/-260。pi还将通过测量相同样品的δ 13c （CaCO3）、δ 13c （org）、δ 34S（CAS）、δ 34S（黄铁矿）和87-Sr/86-Sr测量来探讨碳硫循环耦合和大陆风化作用的重要性。至少，这项工作将产生一个特别详细的，时间校准的早寒武纪地层和同位素记录。本研究将为揭示早寒武纪动物硬体演化与地球化学循环的因果关系提供线索。

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.