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

The progressive darkening of spores during burial is widely used as a matur ation parameter in petroleum basins. The use of this parameter is limited b y the subjective assessment of colour and the poor precision of the data. U sing a spectral scanning microphotometer the spore colour can be recorded a s the amount of light transmitted at different wavelengths in the visible s pectrum. The spore transmittance value (% Sr) is derived from: %St = 100 x T-550/(T-450 x T-650), where T is the transmission at wavelengths of 450, 5 50 and 650 nm. The % St has been determined from spore colour (SCI) standar ds, artificially matured spores and pollen, and samples from two wells. The results show that the spore transmittance is determined by palynormorph ty pe, and while this increases the range of % St values obtained in a single sample, the range of % St values obtained from different spore species with in a sample overlap. The % St values increase with SCI values of spores use d as SCI standards and with the temperature used in the laboratory maturati on experiments. In the case of the geological samples the % St value increa ses with depth. The increase in spore transmittance (% St) with increasing maturity shows that the method has potential for use as a maturation parame ter in hydrocarbon exploration. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.