Ultrastructural characterization of wood from Tertiary fossil forests in the Canadian Arctic

Abstract

Micromorphological and ultrastructural characterization of fossil gymnosperm wood from Comwallis Island, Axel Heiberg Island, and Ellesmere Island in the Canadian High Arctic showed the changes that have occurred in cell walls of wood during 20–60 million years of burial. No evidence of permineralization was observed. Wood with rounded cells, thick secondary walls, and intercellular spaces was common in all samples. Secondary walls were eroded and swollen. A transition from an organized secondary wall, with altered but visible microfibrillar structure, to an electron-dense, amorphous material was evident in cell walls. The amorphous material appeared to form primarily in the secondary walls near cell lumina and along cracks that extended into the walls. The middle lamellae were often expanded in size and had convoluted shapes. Hemicellulose degradation appeared to precede cellulose degradation. Samples exhibiting cell walls with increased amorphous material had the greatest lignin and lowest cellulose concentrations. Hemicellulose concentration was extremely low in all Eocene and Paleocene samples. The lignin content of Miocene wood was 47.9%, whereas the Eocene and Paleocene samples ranged from 66 to 84%. Tracheids from extensively degraded samples were distorted and collapsed, and in some cases the cells appeared compressed together. Although the residual amorphous middle lamellae and secondary walls were fused together, the outlines of original cells were visible. Chemical analyses and ultrastructural data indicated that a nonbiological degradation was responsible for the deterioration of the arctic fossil wood samples. Key words: wood deterioration, lignin, hemicelluloses, cellulose, wood ultrastructure, coal formation, fossil wood.