The chemical and structural evolution of sporopollen using vibrational spectroscopy

Yule, Barbara Lynn (1998) The chemical and structural evolution of sporopollen using vibrational spectroscopy. University of Southampton, Doctoral Thesis.

Abstract

Spore colour scales are petrographic techniques used to evaluate potential hydrocarbon source rocks. However, the intrinsic difficulty of assessing and recording palynomorph colour has restricted the application of such scales. A possible way to increase the sophistication of maturity assessments using spore colour would be to develop a kinetic model describing spore maturation. However, before that can be attempted, the complex chemical alterations that control spore colour need to be understood. This research aimed to i) produce a quantitative spore colour scale which has a one-way linear relationship with maturity, ii) understand the complex structural and chemical changes that control the colour of the spore wall, and iii) investigate the microscopic behaviour of spores and pollen to investigate whether a kinetic model could accurately describe spore colour. A synopsis of results is as follows:

1) Two new quantitative and replicable spore colour scales (Colour Image Analysis and Spore Spectral Transmittance) were developed. Both spore colour scales have the potential to be used in maturity determinations, having one-way, quantitative and replicable relationships with maturity that can be directly related to the chemical phases of the spore wall. Both scales have been directly compared to independent organic maturity indicators confirming that the depth related changes seen correspond to the effects of progressive maturation. A relationship between spore colour and vitrinite reflectance can be defined in a single geological basin but it cannot be transferred to another basin with a different geothermal history. The Spore Spectral Transmittance technique has the advantage over the Colour Image Analysis method because it is numerically defined, being derived from innate spectral properties.

2) The chemical modifications controlling spore colour were investigated using micro-spectrometry techniques (Raman and infrared). The results showed that i) no spore colour changes occur before a threshold temperature is reached which is required to break the bonds involved in the thermal decomposition of a sporopollenin ii) in the immature phase, colour changes in slow progressive intervals (through yellows and oranges). FT-IR data shoed a loss of >C=O groups and an increase in the relative proportion of CH₂. CH₃ and C=C (aromatic) during this phase, iii) in the mature phase the colorimetric parameters change rapidly over a small temperature range.

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