Effects of experimental coalification on texture, composition and compaction in Indonesian peat and wood

Artificial coalification can fill a gap in our understanding of the processes of natural maturation of coal in a time frame reasonable for scientific investigation. This study focused on two main aspects of the coalification process. These aspects were, first, the effects on carbonised components in peat and, second, the amount and location of compaction during coalification. It was found that the proportion of the carbonised components increased during artificial coalification while the proportion of amorphous matrix decreased. These relative changes in proportion of constituents may be the result of the differing reactivities of these components. Compaction during artificial coalification resulted in a 72% volume loss (Or a 5.7:1 compaction ratio). Most of the volume loss was from a decrease in pore space (45%) between the particles of organic material, although compression of plant parts accounts for 17% of the volume loss. The remaining 10% of the compaction was from organic mass loss, in out-gassing and fluid expulsion. Finally, although it was observed that compaction of wood was of the order of 2.5:1, it does not occur uniformly across all anatomical structures. Xylem tracheids appear to have compacted little and the majority of wood compaction appeared in the ray parenchyma. However, the compaction ratio in the rays was relatively low (1.5:1), considering that ray parenchyma should compress easily as they lack secondary cell walls and the cells thus have less inherent strength to withstand compression than xylem tracheids. However, it appears that the ray parenchyma are filled with solid organic residues at or before the time of burial, which prevents the compression of cell lumens. This suggests that the tissue would have originated from the heartwood of trees where tannins and other waste products are stored in ray parenchyma cells. Although the above observations are based on a limited sample set, the results do pose interesting subject matter for further study. In particular it is essential that different peat types be examined in order to understand the changes in proportion of organic components during coalification. It has also been demonstrated that compaction occurs mainly as a loss of pore space between organic particles; however, the degree of material loss still needs to be documented in different peats of varying decomposition states. Copyright (C) 1996 Elsevier Science Ltd