Lithofacies analysis of the Simpson Group in south-central Kansas

Abstract

The Simpson Group, a sequence of Middle Ordovician clastic rocks and sandy carbonates, was studied in the subsurface of south-central Kansas. An analysis of lithofacies based primarily on well cuttings permitted the construction of a stratigraphic framework of six informal units. The McLish formation corresponds to the lowermost two of these units and the Bromide formation to the remaining four. Statistical moments of gamma-ray logs were used to characterize the shale content and variability with depth within the Simpson Group. The moments were interpolated between wells and transformed to polynomial trends of estimated shale content in the three dimensions of geographic location and depth. A series of cross sections through this regional three-dimensional model outlines the geometry of major shale and nonshale units. The well cuttings confirm the validity of these patterns and provide more detailed and conventional geologic information for use in their interpretation.