{"title":"Low oxygen levels and fluctuated redox states of continental shelf seawater after the Cambrian explosion","authors":"","doi":"10.1016/j.gloplacha.2024.104596","DOIUrl":null,"url":null,"abstract":"<div><div>The Cambrian Miaolingian and Furongian (509–485 Ma) represent a critical transitional interval in evolutionary history of animals, bridging the Cambrian explosion to Great Ordovician Biodiversification Event (GOBE). Despite its significance, scant attention has been directed toward understanding the shifts in marine redox conditions and biogeochemical cycles during this epoch, hampering the broader understanding of linkages between marine environment and early animal radiation. Here we present new paired sulfur isotope records from carbonate-associated sulfate (δ<sup>34</sup>S<sub>CAS</sub>) and pyrite (δ<sup>34</sup>S<sub>py</sub>), along with nitrogen isotopes (δ<sup>15</sup>N<sub>decarb</sub>) from a continuous carbonate succession in South China, aiming to better constrain marine redox states and biogeochemical cycles during the middle-late Cambrian (ca. 509–495 Ma). Overall low sulfur isotope offsets Δ<sup>34</sup>S<sub>CAS-py</sub> (Δ<sup>34</sup>S<sub>CAS-py</sub> = δ<sup>34</sup>S<sub>CAS</sub>-δ<sup>34</sup>S<sub>py</sub>, 1.1–46.6‰,median = 21.0‰) indicate continuously low seawater sulfate concentrations during middle-late Cambrian. The consistently low δ<sup>15</sup>N<sub>decarb</sub> values (−1.4–2.3‰,median = 0.4‰) suggest that this period was featured by active nitrogen fixation and a small nitrate reservoir in the shallow ocean. Taken together, the sulfur and nitrogen isotopic data can be best explained by persistently low global oxygenation levels of the middle-late Cambrian oceans. Meanwhile, high variabilities of Δ<sup>34</sup>S<sub>CAS-py</sub> and δ<sup>15</sup>N<sub>decarb</sub> recorded by the studied section also suggest fluctuated marine redox conditions on continental margins during this period. In combination with paleontological records, we propose that persistently low marine oxygenation levels and frequent expansion of anoxic seawater on continental margins may have induced a trough period in animal biodiversification after the Cambrian explosion.</div></div>","PeriodicalId":55089,"journal":{"name":"Global and Planetary Change","volume":null,"pages":null},"PeriodicalIF":4.0000,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Global and Planetary Change","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0921818124002431","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOGRAPHY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
The Cambrian Miaolingian and Furongian (509–485 Ma) represent a critical transitional interval in evolutionary history of animals, bridging the Cambrian explosion to Great Ordovician Biodiversification Event (GOBE). Despite its significance, scant attention has been directed toward understanding the shifts in marine redox conditions and biogeochemical cycles during this epoch, hampering the broader understanding of linkages between marine environment and early animal radiation. Here we present new paired sulfur isotope records from carbonate-associated sulfate (δ34SCAS) and pyrite (δ34Spy), along with nitrogen isotopes (δ15Ndecarb) from a continuous carbonate succession in South China, aiming to better constrain marine redox states and biogeochemical cycles during the middle-late Cambrian (ca. 509–495 Ma). Overall low sulfur isotope offsets Δ34SCAS-py (Δ34SCAS-py = δ34SCAS-δ34Spy, 1.1–46.6‰,median = 21.0‰) indicate continuously low seawater sulfate concentrations during middle-late Cambrian. The consistently low δ15Ndecarb values (−1.4–2.3‰,median = 0.4‰) suggest that this period was featured by active nitrogen fixation and a small nitrate reservoir in the shallow ocean. Taken together, the sulfur and nitrogen isotopic data can be best explained by persistently low global oxygenation levels of the middle-late Cambrian oceans. Meanwhile, high variabilities of Δ34SCAS-py and δ15Ndecarb recorded by the studied section also suggest fluctuated marine redox conditions on continental margins during this period. In combination with paleontological records, we propose that persistently low marine oxygenation levels and frequent expansion of anoxic seawater on continental margins may have induced a trough period in animal biodiversification after the Cambrian explosion.
期刊介绍:
The objective of the journal Global and Planetary Change is to provide a multi-disciplinary overview of the processes taking place in the Earth System and involved in planetary change over time. The journal focuses on records of the past and current state of the earth system, and future scenarios , and their link to global environmental change. Regional or process-oriented studies are welcome if they discuss global implications. Topics include, but are not limited to, changes in the dynamics and composition of the atmosphere, oceans and cryosphere, as well as climate change, sea level variation, observations/modelling of Earth processes from deep to (near-)surface and their coupling, global ecology, biogeography and the resilience/thresholds in ecosystems.
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