Spore transmittance (% St): a quantitative method for spore colour analysis

The progressive darkening of spores during burial is widely used as a maturation parameter in petroleum basins. The use of this parameter is limited by the subjective assessment of colour and the poor precision of the data. Using a spectral scanning microphotometer the spore colour can be recorded as the amount of light transmitted at different wavelengths in the visible spectrum. The spore transmittance value (% St) is derived from: % St=100×T550/(T450×T650), where T is the transmission at wavelengths of 450, 550 and 650 nm. The % St has been determined from spore colour (SCI) standards, artificially matured spores and pollen, and samples from two wells. The results show that the spore transmittance is determined by palynormorph type, and while this increases the range of % St values obtained in a single sample, the range of % St values obtained from different spore species within a sample overlap. The % St values increase with SCI values of spores used as SCI standards and with the temperature used in the laboratory maturation experiments. In the case of the geological samples the % St value increases with depth. The increase in spore transmittance (% St) with increasing maturity shows that the method has potential for use as a maturation parameter in hydrocarbon exploration.