Ghent University Academic Bibliography

Advanced

Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco

Robert R Gaines, Derek EG Briggs, Patrick J Orr and Peter Van Roy UGent (2012) PALAIOS. 27(5). p.317-325
abstract
The recently discovered Fezouata Biota, from the early Ordovician (late Tremadocian to late Floian) of Morocco preserves a diverse soft-bodied fauna. While preservation is mostly of Burgess Shale-type, giant anomalocaridids also occur in siliceous concretions. A petrographic and geochemical analysis of these concretions reveals their growth history and the circumstances that led to the fossilization of non biomineralized anatomy within them. The large (>1m) concretions are homogeneous in composition and geochemical characteristics, indicating rapid pervasive growth of mineral frameworks during decay of the large animals at or near the sediment-water interface. Concretions are comprised of ultra-fine grained (2-20μ) authigenic quartz, Fe-chlorite, and calcite, a composition unlike other known marine concretions. Abundant pyrite, now represented by oxide pseudomorphs, grew adjacent to the anomalocaridid carcasses, but rarely within the matrix of the concretions. This distribution indicates that sulfate reduction around the carcasses was vigorous within otherwise organic-poor sediments resulting in the establishment of prominent chemical gradients around the giant anomalocaridids that led to early precipitation of mineral overgrowths around non-biomineralized tissues. Rapid precipitation of intergrown silica and Fe-chlorite required an abundant source of silica, iron, and aluminum. These ions were most probably derived from dissolution of volcanic ash in the sediments. Limited intergrown calcite (δ13C avg. -12.2‰, n=23) precipitated from bicarbonate generated largely by sulfate reduction of organic tissues of the carcasses. Whereas Burgess Shale-type preservation of fossils in the Fezouata biota required suppression of degradation, exceptional preservation of anomalocaridids within the siliceous concretions resulted from extensive microbial decomposition of a large volume of organic tissues. Rapid mineralization was facilitated by localization of microbial activity around the large carcasses and must have required an unusually reactive sediment composition.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
EXCEPTIONAL FOSSIL PRESERVATION, BURGESS-SHALE-TYPE, SOFT-BODIED FOSSILS, CARBONATE CONCRETIONS, ORGANIC-MATTER, HUNSRUCK SLATE, TRILOBITE BED, MINERALIZATION, PYRITIZATION, SEDIMENTS
journal title
PALAIOS
Palaios
volume
27
issue
5
pages
317 - 325
Web of Science type
Article
Web of Science id
000306304900006
JCR category
PALEONTOLOGY
JCR impact factor
1.785 (2012)
JCR rank
10/50 (2012)
JCR quartile
1 (2012)
ISSN
0883-1351
DOI
10.2110/palo.2011.p11-093r
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
2125933
handle
http://hdl.handle.net/1854/LU-2125933
date created
2012-05-31 19:48:26
date last changed
2012-10-19 15:42:14
@article{2125933,
  abstract     = {The recently discovered Fezouata Biota, from the early Ordovician (late Tremadocian to late Floian) of Morocco preserves a diverse soft-bodied fauna. While preservation is mostly of Burgess Shale-type, giant anomalocaridids also occur in siliceous concretions. A petrographic and geochemical analysis of these concretions reveals their growth history and the circumstances that led to the fossilization of non biomineralized anatomy within them. The large ({\textrangle}1m) concretions are homogeneous in composition and geochemical characteristics, indicating rapid pervasive growth of mineral frameworks during decay of the large animals at or near the sediment-water interface. Concretions are comprised of ultra-fine grained (2-20\ensuremath{\mu}) authigenic quartz, Fe-chlorite, and calcite, a composition unlike other known marine concretions. Abundant pyrite, now represented by oxide pseudomorphs, grew adjacent to the anomalocaridid carcasses, but rarely within the matrix of the concretions. This distribution indicates that sulfate reduction around the carcasses was vigorous within otherwise organic-poor sediments resulting in the establishment of prominent chemical gradients around the giant anomalocaridids that led to early precipitation of mineral overgrowths around non-biomineralized tissues. Rapid precipitation of intergrown silica and Fe-chlorite required an abundant source of silica, iron, and aluminum. These ions were most probably derived from dissolution of volcanic ash in the sediments. Limited intergrown calcite (\ensuremath{\delta}13C avg. -12.2{\textperthousand}, n=23) precipitated from bicarbonate generated largely by sulfate reduction of organic tissues of the carcasses. Whereas Burgess Shale-type preservation of fossils in the Fezouata biota required suppression of degradation, exceptional preservation of anomalocaridids within the siliceous concretions resulted from extensive microbial decomposition of a large volume of organic tissues. Rapid mineralization was facilitated by localization of microbial activity around the large carcasses and must have required an unusually reactive sediment composition.},
  author       = {Gaines, Robert R and Briggs, Derek EG and Orr, Patrick J and Van Roy, Peter},
  issn         = {0883-1351},
  journal      = {PALAIOS},
  keyword      = {EXCEPTIONAL FOSSIL PRESERVATION,BURGESS-SHALE-TYPE,SOFT-BODIED FOSSILS,CARBONATE CONCRETIONS,ORGANIC-MATTER,HUNSRUCK SLATE,TRILOBITE BED,MINERALIZATION,PYRITIZATION,SEDIMENTS},
  language     = {eng},
  number       = {5},
  pages        = {317--325},
  title        = {Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco},
  url          = {http://dx.doi.org/10.2110/palo.2011.p11-093r},
  volume       = {27},
  year         = {2012},
}

Chicago
Gaines, Robert R, Derek EG Briggs, Patrick J Orr, and Peter Van Roy. 2012. “Preservation of Giant Anomalocaridids in Silica-chlorite Concretions from the Early Ordovician of Morocco.” Palaios 27 (5): 317–325.
APA
Gaines, R. R., Briggs, D. E., Orr, P. J., & Van Roy, P. (2012). Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco. PALAIOS, 27(5), 317–325.
Vancouver
1.
Gaines RR, Briggs DE, Orr PJ, Van Roy P. Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco. PALAIOS. 2012;27(5):317–25.
MLA
Gaines, Robert R, Derek EG Briggs, Patrick J Orr, et al. “Preservation of Giant Anomalocaridids in Silica-chlorite Concretions from the Early Ordovician of Morocco.” PALAIOS 27.5 (2012): 317–325. Print.