Fluorescent microscopy of particulate organic matter: Sparta Formation and Wilcox Group, South Central Louisiana

Abstract

Particulate organic matter (POM) isolated from core samples of mudstones in the Mid-Eocene Sparta Formation and the Late Paleocene-Early Eocene Wilcox Group in Louisiana was characterized using transmitted and fluorescent light microscopy and Rock-Eval pyrolysis. Observations of maceral fluorescence combined with programmed pyrolysis results better define source potential than visual examination using transmitted (white) light alone. Transmitted light microscopic characterization of POM indicates that amorphous macerals of mixed terrestrial and marine origin dominate samples from both the lagoonal and shelf depositional environments. Microscopic examination under fluorescent light indicates that some of the amorphous matter, including terrestrially derived material, fluoresces to some degree. Hydrogen Index values show a positive correlation with the total number of fluorescing particles in the isolate, as well as with the relative fluorescence levels. Comparison of Sparta and Wilcox samples indicates that significant changes occur in the assemblages at levels of thermal maturation associated with the onset of petroleum generation. Thermally mature samples contain a higher percentage of moderately fluorescent particles and lesser percentages of highly and weakly fluorescent particles. This phenomenon is readily apparent in specific particle types, namely amorphous nonstructured protistoclasts, miospores and dinoflagellate cysts.