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Mechanism for Burgess Shale-type preservation

Proceedings of the National Academy of Sciences - PNAS, 2012-04, Vol.109 (14), p.5180-5184 [Peer Reviewed Journal]

copyright © 1993-2008 National Academy of Sciences of the United States of America ;Copyright National Academy of Sciences Apr 3, 2012 ;ISSN: 0027-8424 ;ISSN: 1091-6490 ;EISSN: 1091-6490 ;DOI: 10.1073/pnas.1111784109 ;PMID: 22392974

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  • Title:
    Mechanism for Burgess Shale-type preservation
  • Author: Gaines, Robert R ; Hammarlund, Emma U ; Hou, Xianguang ; Qi, Changshi ; Gabbott, Sarah E ; Zhao, Yuanlong ; Peng, Jin ; Canfield, Donald E
  • Subjects: alkalinity ; Carbonates ; Cements ; exceptional preservation ; Fossils ; Geochemistry ; geokemi ; Geological time ; Geology ; Isotopes ; Marine ; microbial activity ; ocean chemistry ; Oceans ; permeability ; Physical Sciences ; Pyrites ; Sea water ; seawater ; Sedimentation & deposition ; sedimentology ; Sediments ; shale ; Shales ; Sulfates ; sulfur
  • Is Part Of: Proceedings of the National Academy of Sciences - PNAS, 2012-04, Vol.109 (14), p.5180-5184
  • Description: Exceptionally preserved fossil biotas of the Burgess Shale and a handful of other similar Cambrian deposits provide rare but critical insights into the early diversification of animals. The extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft-bodied fossil assemblages has remained enigmatic since Walcott’s initial discovery in 1909. Here, we demonstrate the mechanism of Burgess Shale-type preservation using sedimentologic and geochemical data from the Chengjiang, Burgess Shale, and five other principal Burgess Shale-type deposits. Sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation. Low sulfate concentrations in the global ocean and low-oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability. Subsequently, rapid entombment of fossils in fine-grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments. A permeability barrier, provided by bed-capping cements that were emplaced at the seafloor, is a feature that is shared among Burgess Shale-type deposits, and resulted from the unusually high alkalinity of Cambrian oceans. Thus, Burgess Shale-type preservation of soft-bodied fossil assemblages worldwide was promoted by unique aspects of early Paleozoic seawater chemistry that strongly impacted sediment diagenesis, providing a fundamentally unique record of the immediate aftermath of the "Cambrian explosion."
  • Publisher: United States: National Academy of Sciences
  • Language: English
  • Identifier: ISSN: 0027-8424
    ISSN: 1091-6490
    EISSN: 1091-6490
    DOI: 10.1073/pnas.1111784109
    PMID: 22392974
  • Source: GFMER Free Medical Journals
    PubMed Central
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