气候变化领域集成服务门户(CCPortal): Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid-Proterozoic habitability

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DOI	10.1111/gbi.12329
	Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid-Proterozoic habitability
	Nguyen K.; Love G.D.; Zumberge J.A.; Kelly A.E.; Owens J.D.; Rohrssen M.K.; Bates S.M.; Cai C.; Lyons T.W.
发表日期	2019
ISSN	14724677
起始页码	247
结束页码	260
卷号	17 期号:3
英文摘要	By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate–carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and an absence of organic biomarker fingerprints for those organisms, suggesting low diversity and relatively small populations compared to the Neoproterozoic era. Nevertheless, the search for diagnostic biomarkers has not been performed with guidance from paleoenvironmental redox constrains from inorganic geochemistry that should reveal the facies that were most likely hospitable to these organisms. Siltstones and shales obtained from drill core of the ca. 1.3–1.4 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid-Proterozoic redox landscape. The group is well dated and minimally metamorphosed (of oil window maturity), and previous geochemical data suggest a relatively strong connection to the open ocean compared to other mid-Proterozoic records. Here, we present one of the first integrated investigations of Mesoproterozoic biomarker records performed in parallel with established inorganic redox proxy indicators. Results reveal a temporally variable paleoredox structure through the Velkerri Formation as gauged from iron mineral speciation and trace-metal geochemistry, vacillating between oxic and anoxic. Our combined lipid biomarker and inorganic geochemical records indicate at least episodic euxinic conditions sustained predominantly below the photic zone during the deposition of organic-rich shales found in the middle Velkerri Formation. The most striking result is an absence of eukaryotic steranes (4-desmethylsteranes) and only traces of gammacerane in some samples—despite our search across oxic, as well as anoxic, facies that should favor eukaryotic habitability and in low maturity rocks that allow the preservation of biomarker alkanes. The dearth of Mesoproterozoic eukaryotic sterane biomarkers, even within the more oxic facies, is somewhat surprising but suggests that controls such as the long-term nutrient balance and other environmental factors may have throttled the abundances and diversity of early eukaryotic life relative to bacteria within marine microbial communities. Given that molecular clocks predict that sterol synthesis evolved early in eukaryotic history, and (bacterial) fossil steroids have been found previously in 1.64 Ga rocks, then a very low environmental abundance of eukaryotes relative to bacteria is our preferred explanation for the lack of regular steranes and only traces of gammacerane in a few samples. It is also possible that early eukaryotes adapted to Mesoproterozoic marine environments did not make abundant steroid lipids or tetrahymanol in their cell membranes. © 2019 John Wiley & Sons Ltd
关键词	biomarker carbon isotope carbonate environmental gradient environmental indicator eukaryote fossil record geochemistry historical record marine environment metamorphism open ocean paleoenvironment Proterozoic redox conditions speciation (chemistry)Australia McArthur Basin Bacteria (microorganisms)Eukaryota biological marker sea water chemistry eukaryote fossil metabolism Northern Territory oxidation reduction reaction sediment Biomarkers Eukaryota Fossils Geologic Sediments Northern Territory Oxidation-Reduction Seawater
语种	英语
来源机构	Geobiology
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/133234
推荐引用方式 GB/T 7714	Nguyen K.,Love G.D.,Zumberge J.A.,et al. Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid-Proterozoic habitability[J]. Geobiology,2019,17(3).
APA	Nguyen K..,Love G.D..,Zumberge J.A..,Kelly A.E..,Owens J.D..,...&Lyons T.W..(2019).Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid-Proterozoic habitability.,17(3).
MLA	Nguyen K.,et al."Absence of biomarker evidence for early eukaryotic life from the Mesoproterozoic Roper Group: Searching across a marine redox gradient in mid-Proterozoic habitability".17.3(2019).