TY - JOUR

T1 - Constraining marine anoxia under the extremely oxygenated Permian atmosphere using uranium isotopes in calcitic brachiopods and marine carbonates

AU - Wang, Wen-qian

AU - Zhang, Feifei

AU - Shen, Shu-zhong

AU - Bizzarro, Martin

AU - Garbelli, Claudio

AU - Zheng, Quan-feng

AU - Zhang, Yi-chun

AU - Yuan, Dong-xun

AU - Shi, Yu-kun

AU - Cao, Mengchun

AU - Dahl, Tais W.

N1 - Publisher Copyright: © 2022 Elsevier B.V.

PY - 2022

Y1 - 2022

N2 - The redox chemistry change in ancient oceans has profoundly shaped the evolutionary trajectories of animals. Uranium isotopes (δ238U) in marine carbonate sediments have widely been used to place quantitative constraints on the oxygenation state of the oceans through geological history. However, syndepositional and post-depositional diagenesis impose a positive and variable δ238U offset in the carbonate sediments relative to contemporaneous seawater, leaving uncertainties on quantification of anoxic seafloor areas in the past. Studies from modern settings suggest that Low-Magnesium Calcite (LMC) in articulate brachiopod shells are diagenetic resistant materials that may faithfully record the δ238U value of ancient seawater. However, this notation has not yet been validated in geological records. Here, we test this hypothesis by analyzing paired brachiopod shells and the host carbonate rocks from several Permian stratigraphic successions in South China. Forty-nine articulate brachiopod fossil shells and twenty-six host carbonate rocks from the Early Permian to the Late Permian were investigated. We performed a rigorous screening to monitor the diagenetic process that might have influenced the δ238U of the shells using a scanning electronic microscope, cathodoluminescent microscopy, and major and trace elements. We estimate that 53% of the shells preserve the primary seawater δ238U signals. Using the screened δ238U values of shells and bulk carbonates, we suggest there were four episodes of expanding marine anoxia during the Permian that are temporally coincident with periods of volcanism. The first two oceanic anoxic events occurred at a time when atmospheric pO2 levels were predicted to be higher than today. The last two events are temporally coincident or immediately preceding the end-Guadalupian and the end-Permian mass extinctions, respectively, confirming previous suggestions that marine anoxia was a critical factor in driving marine animal extinctions.

AB - The redox chemistry change in ancient oceans has profoundly shaped the evolutionary trajectories of animals. Uranium isotopes (δ238U) in marine carbonate sediments have widely been used to place quantitative constraints on the oxygenation state of the oceans through geological history. However, syndepositional and post-depositional diagenesis impose a positive and variable δ238U offset in the carbonate sediments relative to contemporaneous seawater, leaving uncertainties on quantification of anoxic seafloor areas in the past. Studies from modern settings suggest that Low-Magnesium Calcite (LMC) in articulate brachiopod shells are diagenetic resistant materials that may faithfully record the δ238U value of ancient seawater. However, this notation has not yet been validated in geological records. Here, we test this hypothesis by analyzing paired brachiopod shells and the host carbonate rocks from several Permian stratigraphic successions in South China. Forty-nine articulate brachiopod fossil shells and twenty-six host carbonate rocks from the Early Permian to the Late Permian were investigated. We performed a rigorous screening to monitor the diagenetic process that might have influenced the δ238U of the shells using a scanning electronic microscope, cathodoluminescent microscopy, and major and trace elements. We estimate that 53% of the shells preserve the primary seawater δ238U signals. Using the screened δ238U values of shells and bulk carbonates, we suggest there were four episodes of expanding marine anoxia during the Permian that are temporally coincident with periods of volcanism. The first two oceanic anoxic events occurred at a time when atmospheric pO2 levels were predicted to be higher than today. The last two events are temporally coincident or immediately preceding the end-Guadalupian and the end-Permian mass extinctions, respectively, confirming previous suggestions that marine anoxia was a critical factor in driving marine animal extinctions.

KW - brachiopod shells

KW - mass extinctions

KW - oceanic anoxia

KW - paleoredox proxy

KW - Permian

KW - uranium isotopes

U2 - 10.1016/j.epsl.2022.117714

DO - 10.1016/j.epsl.2022.117714

M3 - Journal article

AN - SCOPUS:85134694744

VL - 594

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

M1 - 117714

ER -