Chemical characterisation of a 45 million year bark from Geodetic Hills fossil forest, Axel Heiberg Island, Canada

Abstract

A bark from the litter of a Canadian Arctic fossil forest 45 million years old is chemically investigated to assess the extent of degradation of its labile components in particular of its lipophilic extracts. Comparisons are made with the recently analysed fossil woods of Canadian Arctic, a Turkish sequoia fossil bark and a modern sequoia bark. Chemical composition shows changes similar to those exhibited by fossil woods, namely the decrease of polyose and cellulose content and the increase of lignin amount. The GC/MS analysis of dichloromethane extract shows a number of components much larger than that of coeval fossil woods, whereas the classes of components, namely terpenes, higher alcohols and linear alkanes, are slightly fewer. Terpenes are made up of unaffected monoterpenes, which are hardly present in geological woods, and of sesquiterpenes and diterpenes which undergo the same structural changes of residual terpenes of fossil woods and bark. Higher alcohols are preserved as in fossil woods whilst fatty acids show to be completely absent as they were decarboxylated to linear hydrocarbons from C14 to C30. The hydrolysis of both polysaccharides and fatty acid esters and the decarboxylation of fatty acids are the more important reactions ascribable to diagenesis. In spite of these changes the lipophilic extractives of this Canadian bark are preserved much better than those of coeval Arctic fossil woods which show, as a rule, only few individuals in the occurring classes of compounds.