Organic petrography of Mississippian and Devonian shales in east-central Kentucky

Abstract

The Devonian and Mississippian oil shales of east-central Kentucky are classified as marinites. The petrographic composition of the kerogen in the shales is complex, and significant amounts of macerals from all of the major groups are present. Unfigured alginite (lamalginite) and bituminite are the most abundant macerals present, followed by vitrinite and inertinite (fusinite and semifusinite). Figured alginite (telalginite) includes Leosphoridia and Tasmanites; a minor amount of sporinite (~1% or less) is also present. The maceral composition of the Cleveland and Sunbury Shale interval from a core taken in Fleming County, Kentucky was determined quantitatively. The liptinite suite in the Sunbury interval was dominated by bituminite, while the Cleveland contained higher proportions of alginite. The total amount of inertinite plus vitrinite was found to be relatively constant. Variations in maceral composition affect the scatter of Fischer assay oil yield versus organic carbon relations for Eastern US oil shale. The kerogen macerals were found to correlate selectively with certain trace elements (e.g. Cr, Cu, V and Zn), suggesting that the maceral composition may be related to shale provenance. Bituminite:alginite ratio was found to correlate selectively with trace element concentration and supports the concept that the organic precursors for this maceral were bacterial decay products.