The coals of the Upper Mansfield, Brazil, and Lower Staunton Formations (Atokan, Pennsylvanian) in Indiana (Illinois Basin) are characteristically thin and discontinuous. As a result, problems with correlation and identification of the seams have persisted for both researchers and industry. These discrepancies affect coal exploration, mine planning, and subsequently coal-fired utility customers when trying to compare coal quality characteristics beyond local mining areas. This study presents exploration and operational examples demonstrating some of the correlation problems associated with the coals of the Upper Mansfield, Brazil, and Lower Staunton Formations.

Application of regionally applied nomenclature assumes that coal seams are continuous and correlative, although, in fact, exploration drilling shows that very frequently these coals are discontinuous in nature with local depositional controls (mini-basins). As a result, miscorrelations of seams at similar stratigraphic horizons, but with different lithologic, coal quality, and enclosing strata characteristics, can occur. An example of this type of problems is the correlation of the Danville and Hymera Coal Members of the Dugger Formation to the Upper and Lower Millersburg Coals. Based on exploration boreholes, mine scale observations, coal quality, and petrographic data, this study suggests that: 1) the coal mapped as the Upper Block Coal Member of Parke, Clay, Greene, and Owen Counties may in fact be the same seam as the Lower Block Coal Member of Daviess County; and 2) the Lower Block coal of Parke, Clay, Greene, and Owen Counties is not present south of the Switz City area of central Greene County, Indiana.