Tracing dispersed coaly-derived particles in modern sediments: an environmental application of organic petrography

A crucial aspect in environmental sciences is related to the transportation, accumulation and
fate of solid organic particles not native to the sediments. In this study we present the
petrographical features of seven sediment samples obtained from aquatic environments in
Sweden, Finland and The Netherlands. Most of the samples represent the uppermost layers,
which accumulated during the recent past. Their total organic carbon content ranges between
1.5 and 20%. Density separations using heavy liquids were applied, in order to concentrate
the organic matter and thus to facilitate the petrographical determinations. The microscopic
approach revealed significant variations in the origin and hence, the type of the contained
organic matter. Apart from modern plant debris and the algae indicating water-logged
conditions, several particles of naturally and artificially derived solid-organic material were
identified. The latter constitute organic contaminants, and include unburnt residues of highrank
coals and chars. The petrographic data show a significant comparability with the ‘black
carbon’ data determined by chemo-thermal oxidation at 375°C, demonstrating the applicability
of the microscopic analysis in environmental studies.