How to make a Burgess Shale fossil: an experimental approach
The Burgess Shale fauna represents a taphonomic conundrum. A number of theories have been proposed to explain its preservation, ranging from a simple lack of bioturbation or increased anoxia to the heightened preservation potential by burial within sediments of particular physical or chemical properties, notably clay minerals. While several taphonomic experiments have been conducted with an aim to understand ‘soft-part’ decay and preservation, none have investigated the effect that different sediment properties have on taphonomy.
A series of experiments have thus been carried out looking at the preservation potential of four end-member sediment types. The results are certainly intriguing, and it appears that the non-smectite clay kaolinite has a preservation potential that far exceeds those of the other sediments, including montmorillonite. This reaffirms the idea that the presence of clay minerals may markedly enhance soft-part preservation, but suggests that the more reactive smectite clay minerals may not be responsible. This is supported by the suggestion that the premetamorphic sediment of the Burgess Shale was likely to have been an illite-smectite-kaolinite clay assemblage, with an absence of highly reactive species such as nontronite or Na-montmorillonite (Powell, 2003).