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Isson TT, Love GD, Dupont CL, Reinhard CT, Zumberge AJ, Asael D, Gueguen B, McCrow J, Gill BC, Owens J, Rainbird RH, Rooney AD, Zhao MY, Stueeken EE, Konhauser KO, John SG, Lyons TW, Planavsky NJ. Tracking the rise of eukaryotes to ecological dominance with zinc isotopes. Geobiology 2018; 16:341-352. [PMID: 29869832 DOI: 10.1111/gbi.12289] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2017] [Accepted: 03/31/2018] [Indexed: 05/19/2023]
Abstract
The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time. Given the higher affinity of eukaryotes for Zn relative to prokaryotes, we suggest that a shift toward a more eukaryote-rich ecosystem could have provided a means of more efficiently sequestering organic-derived Zn. Despite the much earlier appearance of eukaryotes in the microfossil record (~1700 to 1600 million years ago), our data suggest a delayed rise to ecological prominence during the Neoproterozoic, consistent with the currently accepted organic biomarker records.
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Affiliation(s)
- Terry T Isson
- Geology and Geophysics, Yale University, New Haven, Connecticut
| | - Gordon D Love
- Earth Science, University of California, Riverside, Riverside, California
| | - Christopher L Dupont
- Microbial and Environmental Genomics, J. Craig Venter Institute, San Diego, California
| | | | - Alex J Zumberge
- Earth Science, University of California, Riverside, Riverside, California
| | - Dan Asael
- Geology and Geophysics, Yale University, New Haven, Connecticut
| | - Bleuenn Gueguen
- Earth Science, Université de Bretagne Occidentale, Brest, France
| | - John McCrow
- J. Craig Venter Institute, Rockville, Maryland
| | - Ben C Gill
- Geosciences, Virginia Tech, Blacksburg, Virginia
| | | | | | - Alan D Rooney
- Geology and Geophysics, Yale University, New Haven, Connecticut
| | - Ming-Yu Zhao
- Geology and Geophysics, Yale University, New Haven, Connecticut
| | - Eva E Stueeken
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, Scotland, UK
| | - Kurt O Konhauser
- Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada
| | - Seth G John
- Earth Science, University of Southern Carolina, Los Angeles, California
| | - Timothy W Lyons
- Earth Science, University of California, Riverside, Riverside, California
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Bykova N, Gill BC, Grazhdankin D, Rogov V, Xiao S. A geochemical study of the Ediacaran discoidal fossil Aspidella preserved in limestones: Implications for its taphonomy and paleoecology. Geobiology 2017; 15:572-587. [PMID: 28397387 DOI: 10.1111/gbi.12240] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 03/22/2017] [Indexed: 06/07/2023]
Abstract
The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three-dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13 Ccarb , δ18 Ocarb , δ13 Corg , δ34 Spyr , and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13 Corg values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide-oxidizing bacteria. δ13 Ccarb , δ18 Ocarb , and δ34 Spyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non-euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion.
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Affiliation(s)
- N Bykova
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
| | - B C Gill
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
| | - D Grazhdankin
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
- Novosibirsk State University, Novosibirsk, Russia
| | - V Rogov
- Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia
| | - S Xiao
- Department of Geosciences, Virginia Tech, Blacksburg, VA, USA
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