Fluorescence alteration of oil inclusions under ultraviolet irradiation

The fluorescence colors of oil inclusions can be influenced by many geological factors including thermal maturity. However, the ultraviolet (UV) irradiation during laboratory process can also induce a significant alteration in fluorescence spectra of oil inclusions, which is seldom considered when using fluorescence to classify oil inclusions. Four oil inclusions from the Maokou Formation in the central Sichuan Basin, China were performed continuous UV irradiation. Their fluorescence spectra were recorded over time. The vapor / liquid phase ratio was measured by a confocal laser scanning microscope (CLSM). The results reveal a generally irreversible alteration of oil inclusion fluorescence spectra. lambda(max) shows long-time stable and instant mutation, whereas QF-535 and Q(650/500) exhibit monotone increasing trend. Recorded. max can represent the original based on spectral shape analysis, however, recorded QF-535 and Q(650/500) require a regression model to predict original values. Besides, there is a potential change in vapor / liquid ratio of oil inclusion after long and intense UV irradiation. The conclusion is that the thermal maturity determination by fluorescence spectra of oil inclusions should be used with care, because the spectra are easily altered during petrography study before being recorded.

Automated summary

The fluorescence spectra of oil inclusions can be significantly altered by UV irradiation during laboratory process. Therefore, the influence of UV irradiation should be considered when classifying oil inclusions based on fluorescence.