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

点击翻译按钮获取中文摘要

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.