Abstract: Vitrinite Reflectance and Solid Hydrocarbon Reflectance: Their Relationship in the German Zechstein

Martin J. Reinhardt, Silke Mehlhorn

The Upper Permian Formations of Northern Germany (Zechstein) mainly

consist of carbonates, anhydrites and salt. Maturity determinations on vitrinites cannot be carried out in these facies types because of the lack of this material. Therefore attempts have been made to use the reflectivity of the frequently occurring solid hydrocarbons as a rank parameter. The importance of a correlation between solid hydrocarbon and vitrinite reflectance in carbonate of sequences without vitrinites is obvious. However, a correlation between vitrinite and bituminite-reflectivity becomes problematical due to two different populations of solid hydrocarbons with varying reflectivity alternating over short depth intervals.

The rocks examined consist of an organic-rich stylolite/solution seam subfacies and an organic-poor "matrix" subfacies. The former contains consistently lower reflecting bituminite than the latter (ca. 1.0-2.0% VR vs 2.5-3.5% VR). The lower reflecting population of the solution seams is the more realistic value, as corroborated by other maturity parameters. The higher reflecting family is found commonly as pore-filling intergranular bituminite in a lithology dominated by anhydrite. In contrast, the lower reflecting family is found in the organic-rich clay and carbonate mineral dominated subfacies. In addition to these well defined subfacies related bituminite populations, fracture filling bituminites are also found. These probably are migrabituminites and can contain one or the other ype of bituminite.

Several possible mechanisms for the formation of these different reflecting bituminite populations (thermochemical sulfate reduction, different source rocks, disproportionation) will be discussed.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994