Mechanism for Burgess Shale-type preservation

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Mechanism for Burgess Shale-type preservation. / Gaines, Robert R.; Hammarlund, Emma U; Hou, Xianguang; Qi, Changshi; Gabbott, Sarah E; Zhao, Yuanlong; Peng, Jin; Canfield, Donald E.

I: Proceedings of the National Academy of Sciences of the United States of America, Vol. 109, Nr. 14, 03.04.2012, s. 5180-4.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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Gaines, Robert R. ; Hammarlund, Emma U ; Hou, Xianguang ; Qi, Changshi ; Gabbott, Sarah E ; Zhao, Yuanlong ; Peng, Jin ; Canfield, Donald E. / Mechanism for Burgess Shale-type preservation. I: Proceedings of the National Academy of Sciences of the United States of America. 2012 ; Vol. 109, Nr. 14. s. 5180-4.

RIS

TY - JOUR

T1 - Mechanism for Burgess Shale-type preservation

AU - Gaines, Robert R.

AU - Hammarlund, Emma U

AU - Hou, Xianguang

AU - Qi, Changshi

AU - Gabbott, Sarah E

AU - Zhao, Yuanlong

AU - Peng, Jin

AU - Canfield, Donald E

PY - 2012/4/3

Y1 - 2012/4/3

N2 - 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."

AB - 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."

KW - Journal Article

U2 - 10.1073/pnas.1111784109

DO - 10.1073/pnas.1111784109

M3 - Article

VL - 109

SP - 5180

EP - 5184

JO - Proceedings of the National Academy of Sciences

T2 - Proceedings of the National Academy of Sciences

JF - Proceedings of the National Academy of Sciences

SN - 1091-6490

IS - 14

ER -