Global marine redox evolution from the late Neoproterozoic to the early Paleozoic constrained by the integration of Mo and U isotope records

Microbialite development through the Ediacaran–Cambrian transition in China: Distribution, characteristics, and paleoceanographic implications

“…518 to 512 Ma), which is roughly consistent with the higher rates of net atmospheric O2 production and primary production in the global oceans at that time (Fig. 12) (Wei et al, 2021). Thrombolites and stromatolites appeared in considerable quantities in settings from shallow-water shelf to onshore environments in China (this study) and other continents (Riding and Voronova, 1984;Bechstädt et al, 1988;Rowland and Gangloff, 1988;James and Gravestock, 1990;Wood et al, 1993;Zhuravlev, 1996;Feldmann and McKenzie, 1998;Rowland and Shapiro, 2002;Javier Alvaro et al, 2006;Creveling et al, 2013;Cordie et al, 2019), and they could produce adequate O 2 and facilitate the oxygenation of the surface oceans during the Ediacaran-Cambrian transition.…”

“…(C) Net atmospheric O2 production, and net marine primary productivity. Date from Wei et al (2021). The development of microbialites and diversity of calcified microbes are roughly consistent with the higher rates of atmospheric O2 production and marine primary productivity during the Ediacaran-Cambrian transition.…”

Continental configuration controls ocean oxygenation during the Phanerozoic

“…Furthermore, the step changes in early Paleozoic seafloor oxygenation are indicative of bistability between deep-ocean circulation states; that is, for certain continental configurations multiple advection and convection patterns will co-exist (what is observed depends on the initial conditions of the simulation). Switches between such states could provide an explanation to the swings 5 in early Paleozoic global anoxia extent documented on grounds of δ 238 U 37-39 and δ 98 Mo 38,40 . Finally, our results have implications for the evolution of marine animal ecosystems through the Phanerozoic.…”

Calcium Isotopic Constraints on the Transition From Aragonite Seas to Calcite Seas in the Cambrian

“…As Mg and ferrous Fe readily substitute for each other in many authigenic clays (e.g., chlorite, glauconite, saponite) (Michalopoulos & Aller, 1995), changes in ocean redox may have been closely linked to extents of removal of seawater Mg via reverse weathering and oceanic crust alteration (Andrews, 1980; Hood & Wallace, 2018; Krissansen‐Totton & Catling, 2020; Wallmann et al., 2008). Recent studies have indicated that the Cambrian ocean was likely characterized by highly dynamic redox states and relatively low background dissolved oxygen and sulfate concentrations (e.g., Sperling et al., 2015; Krause et al., 2018; Wood et al., 2019; Wei et al., 2018; Wei, Planavsky, et al., 2021). The persistence of ferruginous anoxic ocean waters through the Neoproterozoic and early Paleozoic (e.g., Song et al., 2017; Sperling et al., 2015) may therefore have inhibited the reverse weathering or oceanic crust alteration pathways of Mg removal, resulting in a substantially lower Mg marine scavenging flux relative to in a fully oxidized ocean (e.g., Hood & Wallace, 2018).…”

“…(c) Petrographic compilations denote the distribution of different minerals (dolomite, aragonite, high‐Mg calcite, low‐Mg calcite) in non‐skeletal carbonate phases (i.e., cements and ooids) from the upper Ediacaran to the Cambrian (see Table S1 in Supporting information S1). (d) Estimations of global anoxic seafloor area (red curve, based on U isotope data) (Wei, Planavsky, et al., 2021), atmospheric oxygen level (black curve, based on GEOCARBSULFOR model; Krause et al., 2018), and atmospheric/oceanic oxygenation level (gray area, based on Fe speciation data; Sperling et al., 2015).…”