Coal rank (vitrinite maximum reflectance) has been determined for coals in the Henderson basin, Rough Creek fault complex, and Webster Syncline of the western Kentucky part of the Eastern Interior basin (Henderson, Union, and Webster Counties). The samples represent major coals (Western Kentucky No. 6, No. 9, No. 11) as well as minor coals from several bore holes.

The rank increases from high volatile C in the Henderson basin to high volatile B and A in the Webster Syncline to the south of the Rough Creek fault complex. The rank decreases to high volatile C to the south across the central faults in the Moorman Syncline. Coals in a bore hole in a graben of the Rough Creek complex (Bordley quadrangle, Union County) display a variable rank gradient. Rank increases from the hvC (0.56%R) of the top coal (youngest known Paleozoic coal in Kentucky) to hvA (0.88%R) of coals 400 m below (still several hundred meters above the WK No. 9 coal). The coal 15 m below the top coal, however, has a reflectance of 0.86%R. Hydrothermal metamorphism is suspected as the cause of the rank anomaly. The relatively high rank of coals in the Webster Syncline may have bee influenced by the above event but in general the rank can be attributed to a higher paleogeothermal gradient in the syncline. The heat flow regime may have been influenced by the activity which produced the mineralization in the Fluorspar complex to the west. The fault zones to the north and south may have delineated the boundaries of the block subjected to higher heat flow.

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