Transient marine euxinia at the end of the terminal Cryogenian glaciation

Abstract

Termination of the terminal Cryogenian Marinoan snowball Earth glaciation (~650–635 Ma) is associated with the worldwide deposition of a cap carbonate. Modeling studies suggest that, during and immediately following deglaciation, the ocean may have experienced a rapid rise in pH and physical stratification followed by oceanic overturn. Testing these predictions requires the establishment of a high-resolution sequence of events within sedimentary records. Here we report the conspicuous occurrence of pyrite concretions in the topmost Nantuo Formation (South China) that was deposited in the Marinoan glacial deposits. Sedimentary facies and sulfur isotope data indicate pyrite precipitation in the sediments with H2S diffusing from the overlying sulfidic/euxinic seawater and Fe (II) from diamictite sediments. These observations suggest a transient but widespread presence of marine euxinia in an ocean characterized by redox stratification, high bioproductivity, and high-fluxes of sulfate from chemical weathering before the deposition of the cap carbonate.

Termination of Cryogenian ironstone deposition by deep ocean euxinia

“…Xinyu CIF was deposited in a deep marine setting based on sedimentary facies analysis (Tang et al, 1987) and palaeogeographic reconstruction (Wang and Li, 2003), therefore the spread of ocean euxinia is recorded by the deep Xinyu CIF, but not in other shallow CIFs as Fe(II) delivery was cut in deeper seawater. A recent study reported widespread euxinia at the end of Marinoan glaciation, whereby the abundance of pyrite nodules was significantly greater in deep settings than in shallow settings (Lang et al, 2018). We therefore argue that the spread of euxinia into deep oceans and titration of hydrothermal Fe 2þ by sulfides is a viable mechanism to explain the disappearance of IFs after the Cryogenian Period.…”

Geochemistry of upper Permian siliceous rocks from the Lower Yangtze region, southeastern China: implications for the origin of chert and Permian ocean chemistry

“…3c) and framboidal ( Fig. 4l), suggesting an authigenic origin related to BSR (Lang et al 2018). Secondly, δ 34 S py values range from − 41.20 to − 19.70‰ (unpublished data), all of which are obviously lower than the δ 34 S value (approximately + 10‰) of seawater sulfate in the late Permian (Strauss 1997); thus, fractionation of − 51.20‰ to + 29.70‰ occurred.…”

Desequilibrio del ciclo del azufre y cambio ambiental durante el Período Ediacárico

“…However, unlike the Cenozoic, the low atmospheric oxygen and anoxic deep ocean of the Neoproterozoic allowed evaporite-derived oxidizing power to be effectively transmitted into a negative δ 13 C signal. Such imbalance, potentially driven by weathering events and related positive feedbacks, may be particularly relevant to the ending and immediate aftermath of 'Snowball Earth' glaciations, which are marked by euxinia and anomalously high levels of pyrite deposition (Sahoo et al, 2012;Lang et al, 2018).…”