Geology of the Big Clifty formation in the Wheatonville consolidated oil field in Gibson County, Indiana
The Wheatonvilie Consolidated Oil Field lies in Onion and Barton Townships of Gibson County, Indiana. Oil is produced from a sandstone reservoir commonly referred to the "Jackson Sand". The Jackson Sandstone is here informally adopted as member rank of Big Clifty Formation. The Stephen sport Group includes the Big Clifty and is Late Mississippian (Chesterian) in age.Within the area of the field, the Big Clifty Formation has been mapped between the underlying Beech Creek Limestone and the overlying Harvey Limestone. The lower contact of the Big Clifty appears to be sharp. The upper contact of the Big Clifty intergrades with at least one thin limestone tongue of Haney which pinches out laterally into the uppermost shales of the Big Clifty.The Big Clifty Formation includes sandstone, siltstone, shale, and mudstone with minor amounts of sandy limestone. A typical sequence from top to bottom includes:dark gray shale; thin red mudstone; gray shale; limey siltstone; very fine-grained white sandstone interbedded with gray shale; well sorted, fine-grained, white sandstone; and thin black shale. The percentage of sandstone within the Big Clifty Formation varies laterally significantly.The thickness of the Big Clifty Formation ranges from 64 feet to 97 feet. The formation dips to the southwest at a rate of approximately 29 feet per mile and lies 940 feet below the surface within the northeast portion of the study area.The areas containing high concentrations of sandstone form two elongated trends. The sandstone trends strike N35°E. The axes of the trends lie approximately 1 mile apart. The sandstone bodies are approximately 3/4 of a mile across and 5 miles long. These sand bodies range in thickness from 20 feet to 64 feet.The sandstone bodies may represent tidally influenced shallow marine offshore bars. Cross laminations and very fine grained clastics indicate a low velocity aqueous environment. The elongate shape of the sands indicate bar deposits and the sandy limestones indicate a marine environment.