Summary

The increase in temperature during burial of a source rock results in a series of progressive diagenetic changes in the organic matter, one of them being the generation of oil and/or gas in the maturity zone. These diagenetic changes (maturity level) can be measured by vitrinite reflectance. Microscopical investigation together with extensive vitrinite reflectance measurements on coals and coaly shales indicate that various types of vitrinite can occur. Two main groups of vitrinite can be distinguished:

Vitrinite-1 is a relatively hydrogen-poor vitrinite formed in the peat swamp environment. In the vitrinite-1 group common submacerals such as telinite, telocollinite and corpocollinite are found.

Vitrinite-2 is relatively hydrogen-rich. Vitrinite-2 can be distinguished from vitrinite-1 by its (weak) fluorescence during ultraviolet irradiation and by a lower reflectance. Detrital vitrinite particles are often vitrinite-2.

In conventional coal petrology, vitrinite reflectance is measured exclusively on telocollinite. As the maturity is measured by the same vitrinite reflectance scale, it is of great importance to select the higher reflecting vitrinite-1 for measurements instead of the lower reflecting vitrinite-2. In this paper selection criteria are described for the use of vitrinite reflectance. In a number of examples the variation of reflectance between these two types of vitrinite and its implication for exploration are reported.