Subsurface Sequence Stratigraphy of the West Baden Group in Pike County, Indiana

The abundance of coarse-grained siliciclastics and lack of carbonate marker beds within the West Baden Clastic Belt has long posed a problem when correlating it litho-stratigraphically and sequence stratigraphically to the surrounding West Baden Group of the eastern Illinois Basin. Detailed analysis of well data surrounding a northward split in the clastic belt in Pike County, Indiana was conducted to determine the depositional processes responsible for its development as well as identify its formation boundaries and sequence stratigraphic context within the Illinois Basin. Analysis of well data suggests that sequence stratigraphic analysis, in combination with detailed correlation of geophysical log curve patterns, makes it possible to both identify and correlate West Baden Group stratigraphic formation and sequence boundaries within the clastic belt. The data also show that cyclic variation between fluvial and tidal depositional processes is present in what was previously understood as a solely fluvial system. This variation is related to correspondingly cyclic fluctuations in eustatic sea level and resulting sequence development. All formerly recognized sequence boundaries have been verified, with the addition of two new boundaries within sequence 6 of Nelson et al. (2002). The ability to identify the West Baden Group formations within the clastic belt and place them in context with the rest of the Illinois Basin permits better targeting of the Cypress Formation, one of the most prolific petroleum reservoirs in the Illinois Basin. The recognition of tidal processes in the development of the West Baden Clastic Belt in Indiana link it with deposition of the West Baden Group in the central Illinois Basin.