A Pulsed Oxygenation in Terminal Paleoproterozoic Ocean: Evidence From the Transition Between the Chuanlinggou and Tuanshanzi Formations, North China

Abstract

The mid-Proterozoic (ca. 1.8-0.8 Ga) witnessed a period of stable carbon cycling and long stasis in eukaryotic evolution, which was commonly ascribed to the persistently low oxygen levels in the atmosphere-ocean system. Recently, several pulsed marine oxygenations were identified from different continents, and presumed to have facilitated the short-term diversification of eukaryotes in the early Mesoproterozoic Era. To test this hypothesis, an integrated study of iodine species [I/ (Ca + Mg)], paired carbon isotopes (δ 13 C carb and δ 13 C org ), and elemental abundances was conducted on the fossilbearing Tuanshanzi Formation (∼1.64-1.63 Ga), North China. The near-zero I/(Ca + Mg) ratios (0.00 ± 0.01 μmol/mol) coupled with low δ 13 C org (−30.2 ± 1.4‰) in the strata below the fossil-bearing interval suggests anoxic conditions in shallow seawater. An increase of I/ (Ca + Mg) up to ∼1.54 μmol/ mol coupled with a ∼2‰ negative shift in δ 13 C carb and a ∼11‰ positive excursion in δ 13 C org in the fossil-bearing interval point to an increased oxygen concentration. Above the fossil-bearing interval, I/ (Ca + Mg) decrease to <0.5 μmol/mol, suggesting deoxygenation and a return to anoxic to suboxic conditions. Combined with relevant data from other mid-Proterozoic sections of North China and Australia, these data likely indicate dynamic redox conditions in the shallow seawaters of this period, with multiple pulses in oxygenation in otherwise anoxic conditions. These pulsed oxygenations may have facilitated short-term proliferation and diversification of early eukaryotes in shallow seawaters, but the overall low oxygen levels have impeded their continuous development and the rise to ecological dominance until late Neoproterozoic.

Early Prosperity of Iron Bacteria at the End of the Paleoproterozoic Era

“…The Yunmengshan IF samples have markedly positive δ 53 Cr auth values (δ 53 Cr auth = 1.11–2.53‰), higher than records of the BSE (−0.12‰) and the shale and other ironstones before 1.6 Ga (δ 53 Cr auth < 0‰; Figure S4 in Supporting Information ), while compatible with the highly positively fractionated δ 53 Cr auth record of sediments shales between 1.45 and 1.33 Ga, but lower than the shales formed in a more oxidized atmosphere between 0.8 and 0.63 Ga with the atmospheric oxygen concentration >10% (Figure S4 in Supporting Information ; Canfield et al., 2018; Cole et al., 2016; Gilleaudeau et al., 2016; N. J. Planavsky et al., 2014; W. Wei et al., 2021). These results imply the aqueous environments and atmosphere were similarly oxidized as the time interval from 1.45 to 1.33 Ga with the atmospheric oxygen content below 9% PAL (Liu et al., 2020; Lyons et al., 2021; Zhang et al., 2021).…”

Mesoproterozoic Molar Tooth Structure Related to Increased Marine Oxygenation

“…In our case, most samples (50/55) from Stage I and Stage III have I/(Ca + Mg) values lower than the Proterozoic baseline (0.5 μmol/mol; W. Lu et al., 2017; Shang et al., 2019) but higher than zero, suggesting that during Stages I and III carbonate rocks were deposited under weakly oxygenated (suboxic–anoxic) conditions, with oxygen concentrations higher than 1–3 μM but less than 10 μM (cf. A. Liu et al., 2020; Reinhard et al., 2016; Wei et al., 2021). According to studies of modern anoxic basins (Hardisty et al., 2017; Z. Lu et al., 2016), I/(Ca + Mg) > 2.6 μmol/mol may be used as an indicator of water column oxygen concentration >20–70 μM (Hardisty et al., 2017; Shang et al., 2019).…”

“…A. Liu et al, 2020;Reinhard et al, 2016;Wei et al, 2021). According to studies of modern anoxic basins (Hardisty et al, 2017;Z.…”

Macroscopic fossils from the Chuanlinggou Formation of North China: evidence for an earlier origin of multicellular algae in the late Palaeoproterozoic

“…2019; Wei et al . 2021). Though during most time of this period the low‐oxygen conditions would have suppressed the development of macroscopic eukaryotes, in the oxygenated pulses, however, locally elevated oxygen in shallow seawater would have allowed macroscopic eukaryotes to evolve.…”