Palynofacies describes the total acid-resistant organic matter content of sedimentary rocks within a specific sedimentary environment (Combaz, 1964). Palynofacies analysis involves the identification of palynomorphs, plant debris and amorphous particles, their absolute and relative proportions, size spectra and preservation states (Tyson, 1995). When integrated with sedimentological and stratigraphic data, palynofacies adds a unique and significant aspect to paleoenvironmental interpretations. When integrated with geochemical information, it helps develop a greater understanding of a source rock, its quality, and the expected (or observed) hydrocarbon phase (gas versus oil). Palynofacies and its identified components is not to be confused with kerogen, which is a geochemical term referring to organic matter that is non-soluble in an organic solvent. Palynofacies refers to ALL organic components in a given sedimentary rock sample, whereas kerogen limits the organic matter to that which is non-soluble. Unfortunately, these two terms have been greatly confused and co-mingled over the years creating debate among palynologists, organic petrographers, and geochemists.

The visual identification and characterization used in palynofacies analysis is through reflected light microscopy with organic matter strewn on a thin section. The organic matter is liberated from the rock matrix through acid digestion: no other chemical processes are performed since this may affect both the content and visual aspect of the organic matter. For most studies, a semi-quantitative assessment of the palynofacies components is performed, and the terms abundant, frequent, common, and rare are adequate in describing the organic assemblage. For additional paleoenvironmental detail, 300 counts are performed of the organic matter components present.

In a broad sense, palynofacies components can be separated into marine and non-marine constituents, which can give a broad sense of hydrocarbon phase: for the most part, non-marine organic matter will result in gas, whereas marine organic matter will result in oil. The exceptions are non-marine lacustrine paleoenvironments where lacustrine algae will mature and subsequently produce oil. Important terrestrial components include pollen, spores, and algae, which can further be separated from the palynofacies assemblage to produce a palynology slide: these can then be analyzed further for chronostratigraphic interpretation. In the palynofacies assemblage, the color of pollen/spore can be utilized to determine maturation: the lighter the color of the pollen/spores, the less mature the rocks, and the darker the pollen/spores, the higher the maturity, which can be confirmed through vitrinite reflectance (%R_o) and geochemical analyses (e.g., RockEval/T_max).

Case studies demonstrating the significance of palynofacies analyses will be discussed. For example, palynofacies analyses assisted in understanding why wells completed in the Niobrara Formation in a Wyoming field were producing different hydrocarbon phase from the same formation. Differences in the abundances of marine versus non-marine palynofacies components helped define parts of the field that were gas-prone, whereas other areas with abundant marine organic matter were oil-prone.

REFERENCES CITED
Combaz, A., 1964, Les palynofacies: Revue de Micropaléontologie, v. 7, no. 3, p. 205–218.
Tyson, R. V., 1995, Abundance of organic matter in sediments: TOC, hydrodynamic equivalence, dilution and flux effects, in R. V. Tyson, Sedimentary organic matter: Organic facies and palynofacies: Springer, p. 81–118.