Advanced

Mechanism for Burgess Shale-type preservation

Gaines, Robert R.; Hammarlund, Emma U LU ; Hou, Xianguang; Qi, Changshi; Gabbott, Sarah E; Zhao, Yuanlong; Peng, Jin and Canfield, Donald E (2012) In Proceedings of the National Academy of Sciences of the United States of America 109(14). p.4-5180
Abstract

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... (More)

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."

(Less)
Please use this url to cite or link to this publication:
author
publishing date
type
Contribution to journal
publication status
published
keywords
Journal Article
in
Proceedings of the National Academy of Sciences of the United States of America
volume
109
issue
14
pages
5 pages
publisher
National Acad Sciences
external identifiers
  • scopus:84859467083
ISSN
1091-6490
DOI
10.1073/pnas.1111784109
language
English
LU publication?
no
id
4e754521-bdd7-44ec-ad1a-c5b9233943ee
date added to LUP
2017-05-17 11:21:03
date last changed
2017-10-01 05:34:29
@article{4e754521-bdd7-44ec-ad1a-c5b9233943ee,
  abstract     = {<p>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."</p>},
  author       = {Gaines, Robert R. and Hammarlund, Emma U and Hou, Xianguang and Qi, Changshi and Gabbott, Sarah E and Zhao, Yuanlong and Peng, Jin and Canfield, Donald E},
  issn         = {1091-6490},
  keyword      = {Journal Article},
  language     = {eng},
  month        = {04},
  number       = {14},
  pages        = {4--5180},
  publisher    = {National Acad Sciences},
  series       = {Proceedings of the National Academy of Sciences of the United States of America},
  title        = {Mechanism for Burgess Shale-type preservation},
  url          = {http://dx.doi.org/10.1073/pnas.1111784109},
  volume       = {109},
  year         = {2012},
}