Maturity estimation of phytoclasts in strew mounts by micro-Raman spectroscopy

In order to evaluate the potential for petroleum generation of a sedimentary rock, it is important to establish the thermal maturity of its organic matter. In rocks with low total organic carbon, the kerogen has to be isolated by acid maceration, and the traditional maturity assessment via vitrinite reflectance is sometimes hampered by the small amount of vitrinite exposed on polished plugs. This study presents an additional route of maturity estimation via Raman spectroscopy that is advantageous especially when only a small amount of vitrinite is available. Previous studies for maturation assessment based on Raman spectroscopy were mostly carried out on organic-rich rocks, prepared as whole-rock blocks. In this work we developed a maturity assessment based on Raman spectra obtained on isolated kerogen dispersed on strew mounts, as prepared for palynofacies analysis and spore coloration index, rendering additional information without further preparation. These strew mounts display a wider area for analysis per gram of isolated kerogen when compared to polished plugs, increasing the probability to find phytoclasts in scarce populations. The proposed method was developed regarding oil prospection, calibrating the Raman spectrometer with organic matter from rocks with vitrinite reflectance between 0.3 and 2.1%. A set of Raman parameters was combined using multilinear regression. Cross validation of the proposed regression showed that the spectral parameters of translucent phytoclasts resulted in a maturity estimate that correlated well with the vitrinite reflectance.