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Title: A comparative biogeochemical study of extant, and fossil gymnosperm wood from Axel Heiberg Island, Canada
Author: Baki, Alexander
ISNI:       0000 0001 3440 8264
Awarding Body: University of Newcastle upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2007
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An analysis of the main lignin, polysaccharide and hemicellulose components of modern and fossil Metasequoia and Larix woods was conducted through the application of Py-GC/MS, tetramethylammonium .hydroxide (TMAH) thermochemolysis, 13C NMR, Py-MS and TG-DSC in order to discern the main similarities and differences between modern and fossil woods, an~ to discover the main reasons for their preservation, the main processes involved in the initial stages of fossilisation, and the palaeoenvironment associated with their depositional sites in Axel Heiberg Island, Canada. Four modern Larix species woods were compared to each other, and then to the only extant Metasequoia species wood to discover the exact similarities and .any differences between them. This was done because the exact species of fossil Larix and Metasequoia are unknown. No differences were found and it is assumed that as no differences exist between modern species, no differences exist between fossil species. The Py-GC/MS total ion chromatogram of the modern woods showed carbohydrate and guaiacyl lignin-derived compounds indicative of gymnosperm wood. A decrease in carbohydrates relative to the modern woods was discovered in the fossil woods and a relative increase in methoxyphenols and tannins. Similarities to the effects of degradation through fungal invasion were noted in the analysis of the fossil woods with a relatively decreased polysaccharide compared to their modern counterpart, with the possibility of fungal degradation during early diagenesis. The TMAH thermochemolysis total ion chromatograms showed an increase of threo/erythro 1-(3,4-dimethoxyphenyl)-1,2,3-trimethoxypropane (G14/G15 - long chain) over 3,4-dimethoxybenzaldehyde/3,4-dimethoxybenzoic acid methyl ester (G4/G6 - short chain) guaiacyl structures from modern to fossil. Similarities to the effects of degradation through fungal invasion were again noted in the analysis of the fossil woods where long chain guaiacyl structures dominate over the short chain guaiacyl structures, reinforcing the possibility of fungal input during early diagenesis. 13C NMR analysis highlighted an increase in side chain degradation from the guaiacyl units thus forming condensed guaiacyl structures, and a decrease in carbohydrate content from the fossil woods relative to the modern woods. Possible tannin input was detected contributing to wood preservation. TG-DSC and Py-MS analysis showed carbohydrate content decreased from modern relative to fossil sample and condensed lignin structures increased. Polysaccharides were shown to be more in abundance within the Metasequoia than Larix sample indicating less degradation had occurred. The fossil woods although degraded, had maintained their basic carbohydrate/lignin structure and were comparable to modern woods degraded through fungal invasion. In addition the nature of the degradation was found to resemble that caused by white rot fungi. The general state of degradation was less severe in the Metasequoia than the Larix. The Metasequoia wood had probably been deposited after that of the Larix and in different environmental conditions, being slightly anoxic, with less fungal input. The presence of tannins together with the subsequent extreme cold of Axel Heiberg Island probably contributed to the woods preservation over time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available