Ediacaran Marine Redox Heterogeneity and Early Animal Ecosystems

Abstract

Oxygenation has widely been viewed as a major factor driving the emergence and diversification of animals. However, links between early animal evolution and shifts in surface oxygen levels have largely been limited to extrapolation of paleoredox conditions reconstructed from unfossiliferous strata to settings in which contemporaneous fossils were preserved. Herein, we present a multi-proxy paleoredox study of late Ediacaran (ca. 560-551 Ma) shales hosting the Miaohe Konservat-Lagerstätte of South China and, for comparison, equivalent non-fossil-bearing shales at adjacent sections. For the fossiliferous strata at Miaohe there is geochemical evidence for anoxic conditions, but paleontological evidence for at least episodically oxic conditions. An oxygen-stressed environment is consistent with the low diversity and simple morphology of Miaohe Biota macrofossils. However, there is no evidence for euxinic (anoxic and sulphidic) conditions for the fossiliferous strata at Miaohe, in contrast to adjacent unfossiliferous sections. Our results indicate that Ediacaran marine redox chemistry was highly heterogeneous, even at the kilometre-scale. Therefore, our study provides direct—rather than inferred—evidence that anoxia played a role in shaping a landmark Ediacaran ecosystem. If the anoxic conditions characteristic of the studied sections were widespread in the late Neoproterozoic, environmental stress would have hindered the development of complex ecosystems.

Constraining oceanic oxygenation during the Shuram excursion in South China using thallium isotopes

“…For example, Scholz et al () have reported low Fe HR /Fe T and Fe T /Al ratios in the modern Peru margin oxygen minimum zone resulting from the loss of Fe (II) through Fe shuttling. Therefore, given the context of other similar data, the Fe speciation data from these three samples still likely record reducing conditions or close proximity to a ferruginous water column (Li et al, ).…”

Earth: Atmospheric Evolution of a Habitable Planet

“…In the Ediacaran (645-541 Ma), episodes of microfossil diversification may also correlate with pulses of oxygenation (Li et al 2015;McFadden et al 2008). Morphological and behavioral complexity, both requiring relatively high levels of O2, finally emerge in the late Ediacaran (e.g., Droser and Gehling 2015), perhaps as long as 100 million years or more after the earliest molecular traces of simple animals with comparatively low O2 requirements ( Although the data are not definitive regarding an O2 threshold for the emergence of animals on Earth, the existing data do suggest that, at minimum, O2 availability was an important constraint on the tempo and mode of their subsequent diversification.…”

Global and regional controls on marine redox changes across the Ordovician-Silurian boundary in South China

“…A detailed description of these routine methods can be found in Li et al (2015aLi et al ( , 2015b, with a brief summary given below.…”

“…The amounts of Fe carb , Fe ox and Fe mag were measured using the sequential extraction procedure described in Poulton and Canfield (2005), with quantification by Atomic Absorption Spectroscopy (AAS). Due to the present lack of internationally certificated standards for sequential extraction of Fe species, we used two shale standards (CUG-2, CUG-3) that have been repeatedly tested in the Lyons biogeochemistry laboratory at the University of California-Riverside (UCR) as a control during sequential Fe extractions (Li et al, 2015b).…”