L'état de conservation de certains échantillons de bois fossile de l'Ère Tertiaire, provenant de carottagesde kimberlite dans la zone du Lac de Gras (région subarctique canadienne) et autrefois identifiés commeSequioxylon canadense Blokhina, a été évalué chimiquement. Les causes possibles de leur dégradation ontaussi été discutées. La composition chimique des fossiles (mesurée avec les teneurs en holocellulose, enlignine et en minéraux) a été évaluée avec des méthodologies d'analyse gravimétrique et avec des analyseschromatographiques sur l'extrait au dichlorométhane. Des mesures de capacité d'échange cationique(CEC) ont été en outre conduites sur des fossiles. Les analyses ont montré la complète disparition de lateneur en holocellulose (sauf pour 2 échantillons sur 9), tandis que la lignine est devenue le composéle plus abondant, ainsi que la cendre (dont le montant atteint 47,5 % dans un cas). Les données de laCEC ont aussi mis en évidence que le carboxyles acides ont été transformés en carboxyles salifiés, quireprésentent la forme restante de carboxyles la plus importante dans les fossiles (encore plus abondantsque dans le bois de référence). Toutes ces circonstances indiquent que les fossiles sont très dégradés.Cette dégradation est une conséquence de l'écoulement pendant l'enfouissement, qui a causé l'hydrolysedes groupes estérifiés et la dépolymérisation de la lignine.
Some fossil wooden samples of the Tertiary period, extracted from the crater of the kimberlite BHP-Panda pipe from the Lac de Gras region (in the Canadian sub-Arctic area), and previously identified as Sequioxylon canadense Blokhina, were chemically examined to both assess their state of preservation and discuss about the possible causes of their decay. The chemical composition of fossils (in terms of holocellulose, lignin and ash amounts) was evaluated by means of wet analyses, together with the chromatographic analysis of dichloromethane extracts, and additionally measurements of the cation exchange capacity (CEC) of fossils were also carried out. The analyses revealed the complete loss of holocellulose (except for 2 out of 9 samples), whereas lignin became the predominant component, together with ash (whose amount in one case was as high as 47.5%). Moreover, CEC data showed that all acid carboxyls were transformed into carboxylates. They represented the most important form of residual carboxyl groups in the fossils, and were even more abundant than in the reference (fresh) wood. All these occurrences evidenced a generally high level of decay for the fossils, as a consequence of water leaching during burial, which determined both the hydrolysis of esters groups and the partial depolymerisation of lignin. © 2013 Elsevier Masson SAS.
Decay of fossil wood from kimberlite pipes of Lac de Gras in the Canadian sub-Arctic area
Santoni I;Pizzo B
2014
Abstract
Some fossil wooden samples of the Tertiary period, extracted from the crater of the kimberlite BHP-Panda pipe from the Lac de Gras region (in the Canadian sub-Arctic area), and previously identified as Sequioxylon canadense Blokhina, were chemically examined to both assess their state of preservation and discuss about the possible causes of their decay. The chemical composition of fossils (in terms of holocellulose, lignin and ash amounts) was evaluated by means of wet analyses, together with the chromatographic analysis of dichloromethane extracts, and additionally measurements of the cation exchange capacity (CEC) of fossils were also carried out. The analyses revealed the complete loss of holocellulose (except for 2 out of 9 samples), whereas lignin became the predominant component, together with ash (whose amount in one case was as high as 47.5%). Moreover, CEC data showed that all acid carboxyls were transformed into carboxylates. They represented the most important form of residual carboxyl groups in the fossils, and were even more abundant than in the reference (fresh) wood. All these occurrences evidenced a generally high level of decay for the fossils, as a consequence of water leaching during burial, which determined both the hydrolysis of esters groups and the partial depolymerisation of lignin. © 2013 Elsevier Masson SAS.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
