The ∼1100Ma Sturgeon Falls paleosol revisited: Implications for Mesoproterozoic weathering environments and atmospheric CO2 levels

Mitchell, Ria L.; Sheldon, Nathan D.

doi:10.1016/j.precamres.2010.09.003

Cited by 59 publications

(38 citation statements)

References 37 publications

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“…Major and trace element concentrations and ratios (e.g., Fe and Cr) show a change in elemental mobility starting ca. 0.6 Ga. From 3.0 to 1.1 Ga, most paleosols show overall Fe and Mn loss relative to parent or least weathered material (Table ), as has also been previously reported (Driese et al, ; Mitchell & Sheldon, , , ; Sutton & Maynard, , ), which is consistent with a broadly reducing surface environment (<1% PAL, c.f. Pinto and Holland ()).…”

Section: Resultssupporting

confidence: 86%

“…Traditional estimates for Proterozoic atmospheric oxygen levels following the GOE range between 1% and 40% PAL, based on assumed retention of iron in paleosols, and the assumed presence of an anoxic deep ocean (Kump, ). However, this interpretation was based heavily on the 1.1 Ga Sturgeon Falls paleosol (Zbinden, Holland, Feakes, & Dobos, ), which has subsequently been found to exhibit iron and manganese loss instead of retention (Mitchell & Sheldon, , , ), an observation now repeated for at least two other penecontemporaneous paleosols (Planavsky et al, ).…”

Section: Introductionmentioning

confidence: 99%

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A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic

et al. 2019

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Atmospheric oxygen levels control the oxidative side of key biogeochemical cycles and place limits on the development of high‐energy metabolisms. Understanding Earth's oxygenation is thus critical to developing a clearer picture of Earth's long‐term evolution. However, there is currently vigorous debate about even basic aspects of the timing and pattern of the rise of oxygen. Chemical weathering in the terrestrial environment occurs in contact with the atmosphere, making paleosols potentially ideal archives to track the history of atmospheric O2 levels. Here we present stable chromium isotope data from multiple paleosols that offer snapshots of Earth surface conditions over the last three billion years. The results indicate a secular shift in the oxidative capacity of Earth's surface in the Neoproterozoic and suggest low atmospheric oxygen levels (<1% PAL pO2) through the majority of Earth's history. The paleosol record also shows that localized Cr oxidation may have begun as early as the Archean, but efficient, modern‐like transport of hexavalent Cr under an O2‐rich atmosphere did not become common until the Neoproterozoic.

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Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic

et al. 2019

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“…They found that if terrestrial cyanobacterial mats covered 8%-10% of the Earth's surface, clement conditions would have been maintained even at the relatively low pCO 2 values indicated by palaeosols (Sheldon, 2013) and, as reported herein, microbialites. Calculated pCO 2 estimates (<20 PAL and most likely <5 PAL) agree with (A) cyanobacterial calcification (Kah and Riding, 2007), (B) minimum isotopic , (C) palaeosol mass balance (Sheldon, 2006(Sheldon, , 2013Mitchell and Sheldon, 2010) and (D) carbon reservoir modelling (Bartley and Kah, 2004) estimates. Roberson et al, 2011).…”

Section: Comparison Of Temperature Pco 2 and Mesoproterozoic Aogcmssupporting

confidence: 55%

Terrestrial microbialites provide constraints on the mesoproterozoic atmosphere

Hren

Sheldon

2019

The Depositional Record

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Palaeoclimate data indicate that Earth surface temperatures have remained largely temperate for the past 3.5 Byr despite significantly lower solar luminosity over this time relative to the present day. There is evidence for episodic early and late Proterozoic glaciation, but little evidence of glaciation in the intervening billion years. A prolonged equable Mesoproterozoic Earth requires elevated greenhouse gas concentrations. Two endmember scenarios have been proposed for maintaining global warmth. These include extremely high pCO 2 or more modest pCO 2 with higher methane concentrations. This paper reports on the δ 13 C of organic matter in 1.1 Ga stromatolites from the Copper Harbor Conglomerate (CHC) of the Mesoproterozoic Midcontinent Rift (North America) and δ 18 O and Δ 47 temperatures of inorganic stromatolite carbonate to constrain formation and burial conditions and the magnitude of ancient carbon isotope discrimination. CHC sediments have never been heated above ~125-155°C, providing a novel geochemical archive of the ancient environment. Stromatolite Δ 47 data record moderate alteration, and therefore, the occluded organic matter was unlikely to have experienced significant thermal alteration after deposition. The δ 13 C values of ancient mat organic matter and inorganic carbonate show isotope discrimination (ε p ) values ~15.5-18.5‰, similar to modern microbial mats formed in equilibrium with low concentrations of dissolved inorganic carbon.In combination, these data are consistent with a temperate climate Mesoproterozoic biosphere supported by relatively modest pCO 2 . This result agrees with Atmosphere-Ocean Global Circulation Model reconstructions for Mesoproterozoic climate using 5-10 times present atmospheric levels pCO 2 and pCH 4 of >28 ppmv. However, given marine modelling constraints of CH 4 production that suggest pCH 4 was below 10 ppm, this creates a methane paradox. Either an additional source of CH 4 (e.g. from terrestrial ecosystems) or another greenhouse gas, such as N 2 O, would have been necessary to maintain equable conditions in the Mesoproterozoic. K E Y W O R D Sclumped Isotopes, Mesoproterozoic, mid-continent rift system, pCO 2 , stromatolites

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“…Thus, Zbinden et al (1988) modeled the retention and oxidation of iron during the weathering of the 1100 Ma Sturgeon Hills paleosol, developed on hydrothermally altered Keweenawan basalt, obtaining a minimum atmospheric oxygen concentration of 0.1 % PAL. Other studies of the same paleosol profile, however, have not reproduced the same chemistry (Mitchell and Sheldon, 2010), indicating that further work on this paleosol is likely required.…”

Section: Introductionmentioning

confidence: 85%

The oxic degradation of sedimentary organic matter 1400 Ma constrains atmospheric oxygen levels

et al. 2017

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Abstract. We studied sediments from the ca. 1400 millionyear-old Xiamaling Formation from the North China block. The upper unit of this formation (unit 1) deposited mostly below storm wave base and contains alternating black and green-gray shales with very distinct geochemical characteristics. The black shales are enriched in redox-sensitive trace metals, have high concentrations of total organic carbon (TOC), high hydrogen index (HI) and iron speciation indicating deposition under anoxic conditions. In contrast, the green-gray shales show no trace metal enrichments, have low TOC, low HI and iron speciation consistent with an oxygenated depositional setting. Altogether, unit 1 displays alternations between oxic and anoxic depositional environments, driving differences in carbon preservation consistent with observations from the modern ocean. We combined our TOC and HI results to calculate the differences in carbon mineralization and carbon preservation by comparing the oxygenated and anoxic depositional environments. Through comparisons of these results with modern sedimentary environments, and by use of a simple diagenetic model, we conclude that the enhanced carbon mineralization under oxygenated conditions in unit 1 of the Xiamaling Formation required a minimum of 4 to 8 % of present-day atmospheric levels (PAL) of oxygen. These oxygen levels are higher than estimates based on chromium isotopes and reinforce the idea that the environment contained enough oxygen for animals long before their evolution.

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The ∼1100Ma Sturgeon Falls paleosol revisited: Implications for Mesoproterozoic weathering environments and atmospheric CO2 levels

Cited by 59 publications

References 37 publications

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic

A paleosol record of the evolution of Cr redox cycling and evidence for an increase in atmospheric oxygen during the Neoproterozoic

Terrestrial microbialites provide constraints on the mesoproterozoic atmosphere

The oxic degradation of sedimentary organic matter 1400 Ma constrains atmospheric oxygen levels

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