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

在542 Ma，全球碳同位素漂移到-6permil，标志着大多数（如果不是全部）Ediacara以及着名的钙化动物Cloudina和Namacalathus的突然最后出现。 埃迪卡拉纪末期灭绝之后，海水中的δ 1 - 3 C（CaCO 3）出现了大幅度的高频振荡，最终出现了一对9 permil的正δ 1-3 C（CaCO 3）偏移，可能需要1-3百万年。 随着在Nemakit-Daldyn（ND）结束时首次出现大量钙化动物，delta 13 C（CaCO 3）信号的波动性大大减弱。 这种模式是非常相似的三角洲13 C（CaCO 3）的变化和生物恢复的记录后，二叠纪-三叠纪边界灭绝。 在CA。紧接着中生代最严重的灭绝之后的500万年期间，3个4-10 permil幅度的δ 13 C（CaCO 3）循环与碳酸盐分泌动物体型的极度缩小相吻合（Payne等人，2004年）。 恢复到平线δ 13 C（CaCO 3）正好对应于大型钙化腹足动物的首次出现。在缺乏对δ 13 C（CaCO 3）变化速率和持续时间的放射性年龄限制的情况下，δ 13 C（CaCO 3）记录告诉我们的碳通量和对全球碳循环重要的储层的相对大小很少。 仅出于这个原因，在摩洛哥进一步开展工作就至关重要，因为反阿特拉斯边缘保存了世界上唯一一个扩大的（2.5公里的沉积物）早寒武世碳酸盐记录，其中有40多个火山灰层，可以直接使用单锆石U/Pb方法测定其年代。 两个U/Pb年龄已经使我们能够校准Nemakit-Daldyn“Tommotian（ND-T）界线的绝对年龄，并表明10 permil ND-T负δ 13 C（CaCO 3）位移仅为430+/-260。 PI还将通过测量相同样品的δ 13 C（CaCO 3）、δ 13 C（org）、δ 34 S（CAS）、δ 34 S（黄铁矿）和87-Sr/86-Sr测量值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。最低限度，这项工作将产生一个特别详细的、经过时间校准的早寒武世地层和同位素记录。 该研究对揭示早寒武世动物硬体演化与地球化学循环之间的因果关系具有重要意义。

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.