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Lithostratigraphic analysis of the Chesterian Big Clifty Sandstone Asphaltic Complex at the Stampede Mine, Logan County, Kentucky


The Big Clifty (Jackson) Sandstone Member of the Golconda Formation is a Mississippian (Chesterian) heavy-oil reservoir in the southeastern portion of the Illinois Basin of Kentucky. Heavy-oil reservoirs, or asphalt-rock deposits, have been studied for over a century at the periphery of the basin from Grayson County in the northeast to Logan County in the southwest with asphalt-rock mining being most extensive in Edmonson County. Despite all of the 20th century development of this resource, there have been few detailed sedimentological or stratigraphic contextual studies, especially along the southwest terminus of the asphalt-rock outcrop belt such as in northern Logan County. This study offers a high-resolution facies analysis of the Big Clifty at the Stampede Mine, an open pit or strip mine being developed in asphalt rock by USA and Canadian investors in Logan County. Initial results of this study suggests that there is an interplay between tidally-influenced shallow marine facies and bitumen occurrence as well as depositional and diagenetic partitioning of the reservoir or asphaltic deposits. Calcite and pyrite are common minerals in the asphaltic deposits with calcite being the most important partitioning mineral. Depositional complexities related to changing marine accommodation are reflected in relatively muddy or shaley versus sandy deposits. Such heterogeneity poses a challenge to isopach mapping of high-quality bitumen percentage values. This integrated sedimentologic and stratigraphic study is however providing a unique core-calibrated solution for geophysical surveys being conducted both within an open mining pit directly atop the bitumen-rich deposits and atop approximately 10–15 meters of overburden rock and soil. Core descriptions, downhole geophysical logs, aerial geophysical surveys, and mine pit geological data are providing an unprecedented geological and geophysical dataset of an outcropping heavy-oil reservoir. Analogous geophysical studies, particularly those utilizing Electrical Resistivity Tomography (ERT), have been conducted in asphalt rock in Nigeria, but these lack the detailed geologic context which this study affords. This ongoing study is providing direction for mining operations including pit siting and blasting which relies heavily on identification of relatively mud-free sandstone tidal channels and their respective orientations.