Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction

Abstract

Multiple episodes of extensive oceanic anoxia delayed the marine ecosystem recovery from the latest Permian mass extinction.

Global marine redox changes drove the rise and fall of the Ediacara biota

“…The spike‐sample mixtures were evaporated to dryness and taken up in 3N HNO 3 . Uranium was purified using the UTEVA method for isotopic analysis (Brennecka et al, ; Chen et al, ; Kendall et al, ; Romaniello et al, ; Weyer et al, ; Zhang, Algeo, Cui, et al, ; Zhang, Algeo, Romaniello, et al, ; Zhang, Romaniello, et al, ; Zhang, Xiao, et al, ). All samples were put through UTEVA resin twice in order to completely remove matrix ions.…”

“…However, subsequent work by Chen et al () and Tissot et al (), who revisited the dolomitization question with a larger sample set from several cores through the Bahamian carbonate platform, shows no statistically significant differences between calcite and dolomite. There are now δ 238 U data from seven widely spaced carbonate sections spanning the Permian–Triassic boundary [the Dajiang (Lau et al, ), Guandao (Lau et al, ), Dawen (Brennecka et al, ), and Daxiakou (Elrick et al, ) sections in South China; the Taşkent section in Turkey (Lau et al, ); the Zal section in Iran (Zhang, Romaniello, et al, ); and the Kamura section in Japan (Zhang, Algeo, Romaniello, et al, )]. All of these sections show strikingly similar trends in δ 238 U across the Permian–Triassic boundary, which is remarkable because they span 1,000s of km—even in different ocean basins—and have experienced very different diagenetic histories, including dolomitization.…”

“…Marine carbonate sediments have been demonstrated to record the δ 238 U of seawater, subject to a 0.2‰–0.4‰ offset, which likely reflects incorporation of U(IV) into shallow sediments from anoxic porewaters (Chen et al, ; Romaniello, Herrmann, & Anbar, ; Tissot et al, ). Studies comparing the trends and absolute values of δ 238 U in coeval Permian–Triassic carbonate sediments from around the world have shown excellent agreement, demonstrating that carbonates may provide a robust record of variations in seawater δ 238 U (Brennecka et al, ; Elrick et al, ; Lau et al, ; Zhang, Algeo, Romaniello, et al, ; Zhang, Romaniello, et al, ).…”

“…The U isotope system ( 238 U/ 235 U, denoted as δ 238 U) measured in carbonate sedimentary rocks is a more direct probe of global ocean redox conditions and can be used to place quantitative constraints on the extent of global redox changes (Brennecka, Herrmann, Algeo, & Anbar, ; Clarkson et al, ; Elrick et al, ; Lau et al, ; Tostevin et al, ; Wei et al, ; Zhang, Algeo, Cui, et al, ; Zhang, Algeo, Romaniello, et al, ; Zhang, Romaniello, et al, ; Zhang, Xiao, et al, ). The power of U isotopes as a global proxy derives from the fact that in the modern ocean U has a long residence time, ~500 kyr (Dunk, Mills, & Jenkins, ), and hence, δ 238 U is uniform in the open ocean (e.g., Tissot & Dauphas, ).…”

A dolomitization event at the oceanic chemocline during the Permian-Triassic transition

“…Changes in the seawater carbonate system are reflected in the widespread precipitation of "anachronistic" carbonates, e.g., microbialites, synsedimentary seafloor cements, ooids, and pisoids (e.g., Baud et al, 2005;Kershaw et al, 2012;Woods, 2014) and in controversial evidence for localized chemical erosion of marine carbonates (Payne and Kump, 2007). PTB oceans were also influenced by concurrent changes in seawater temperatures (Sun et al, 2012), pH values (Clarkson et al, 2015), and redox conditions (Wignall and Twitchett, 2002;Elrick et al, 2017;Zhang et al, 2018aZhang et al, , 2018b.…”