Early formation and taphonomic significance of kaolinite associated with Burgess Shale fossils

The role of minerals in Burgess Shale-type fossilization is controversial, particularly that of the clay mineral kaolinite. Kaolinite may have formed on carcasses or attached to them as they decayed, stabilizing organic matter. Alternatively, kaolinite may have formed during metamorphism, playing no...

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Bibliographic Details
Published in:Geology (Boulder) 2021-04, Vol.49 (4), p.355-359
Main Authors: Anderson, Ross P, Tosca, Nicholas J, Saupe, Erin E, Wade, Jon, Briggs, Derek E. G
Format: Article
Language:English
Subjects:
Annelida
Arthropoda
Bacteria
Biomolecules
British Columbia
Burgess Shale
Cambrian
Canada
Canadia
Carcasses
Chlorite
Chordata
Clay
Clay minerals
Diagenesis
Dolomite
Dolostone
EDS spectra
electron microscopy data
fossilization
Fossils
Geology
Heterotrophic bacteria
Kaolinite
Marrella
Metamorphism
Middle Cambrian
Mineralogy
Minerals
Opabinia
Organic matter
Ottoia
Paleontology
Paleozoic
Pikaia
Polychaeta
Polymerization
Preservation
Priapulida
Pyrite
Sedimentary rocks
SEM data
Shale
Shales
sheet silicates
silicates
Soft tissues
spectra
Stabilizing
Survival
Taphonomy
Tissue
Tissues
Western Canada
X-ray diffraction
X-ray diffraction data
X-ray spectra
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Summary:The role of minerals in Burgess Shale-type fossilization is controversial, particularly that of the clay mineral kaolinite. Kaolinite may have formed on carcasses or attached to them as they decayed, stabilizing organic matter. Alternatively, kaolinite may have formed during metamorphism, playing no role in the preservation of soft tissues. Evaluating the formation and taphonomic role of kaolinite is difficult, because the mineralogy of Burgess Shale-type fossils is incompletely known. We used in situ selected-area X-ray diffraction to constrain the mineralogy of fossils from the classic Burgess Shale Formation in British Columbia, Canada. Fossils can be distinguished from the matrix that surrounds them by the presence of dolomite, kaolinite, and pyrite. Chlorite may be more abundant in the matrix. The preferential survival of kaolinite in association with fossils provides evidence of early diagenetic clay-organic interactions that protected the clay from metamorphic transformation. Kaolinite likely played a crucial role in fossilization, inhibiting the growth of heterotrophic bacteria and aiding polymerization of soft tissue biomolecules. This may result in biases in soft-tissue preservation to areas and times where kaolinite was prevalent.
ISSN:0091-7613
1943-2682
DOI:10.1130/G48067.1