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FOSSIL DIAGENESIS IN THE BURGESS SHALE
Author(s) -
BUTTERFIELD NICHOLAS J.,
BALTHASAR UWE,
WILSON LUCY A.
Publication year - 2007
Publication title -
palaeontology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.69
H-Index - 63
eISSN - 1475-4983
pISSN - 0031-0239
DOI - 10.1111/j.1475-4983.2007.00656.x
Subject(s) - diagenesis , geology , oil shale , paleontology , geochemistry , facies , aluminosilicate , mineralogy , chemistry , biochemistry , structural basin , catalysis
Abstract: Current models for the exceptional preservation of Burgess Shale fossils have focused on either the HF‐extractable carbonaceous compressions or the mineral films identified by elemental mapping. BSEM, EDX and microprobe analysis of two‐dimensionally preserved Marpolia , Wiwaxia and Burgessia identifies the presence of both carbonaceous and aluminosilicate films for most features, irrespective of original lability. In the light of the deep burial and greenschist facies metamorphism documented for the Burgess Shale, the aluminosilicate films are identified as products of late‐stage volatilization and coincident mineralization of pre‐existing compression fossils, whereas the three‐dimensionally preserved gut‐caecal system of Burgessia is interpreted as an aluminosilicate replacement of a pre‐existing carbonate phase. The case for late diagenetic emplacement of aluminosilicate minerals is supported by the extensive aluminosilicification of trilobite shell and (originally) calcareous veinlets in the Burgess Shale, as well as documentation of other secondarily aluminosilicified compression fossils. By distinguishing late diagenetic alteration from the early diagenetic processes responsible for exceptional preservation, it is possible to reconcile the range of preservational modes currently expressed in the Burgess Shale.