Pennsylvanian System

Type locality, history of name, and related nomenclature: The Staunton Formation was named by Cumings (1922, p. 525) for rocks exposed near Staunton, Clay County. As defined by Cumings, this formation consisted of the interval from the disconformity above Coal II to the disconformity above Coal IV (Survant Coal Member) and therefore also included the Seelyville Coal Member and the Colchester Coal Member. As restricted by Wier (1960), however, the Staunton Formation consisted of those rocks in the interval between the disconformity above Coal II and the disconformity above the Seelyville. Still later, the upper boundary of the Staunton was changed to the top of the Seelyville (Wier and Gray, 1961), and the lower boundary was changed to the top of the Minshall Coal Member (Hutchison, 1976, p. 18). The Perth Limestone Member, which formerly belonged to the underlying Brazil Formation, was therefore reassigned to the Staunton Formation. In the same report by Hutchison, the poorly defined and miscorrelated Coal II was abandoned as a stratigraphic name.

Description: The Staunton Formation consists of 75 to 150 feet (23 to 46 m) of sandstone and shale and as many as eight coalbeds. These coalbeds are generally of little areal extent and variable in quality and thickness. Three lithologies characterize the roof of the coals: (1) black fissile shale overlain by limestone, (2) gray soft silty or sandy shale and interbedded fossiliferous shale or limestone, and (3) gray massive to shaly hard to friable sandstone. The floor of the coals is underclay, clay shale, or sandy shale. The four named members of the Staunton are the Perth, Holland, and Silverwood Limestone Members and the Seelyville Coal Member. The Perth limestone lies at or near the base of the Staunton, the Silverwood and Holland limestones are in the middle part of the formation, and the Seelyville, a commercially mined coalbed, is at the top of the formation.

Correlation: The Staunton Formation is considered to consist of basal rocks of the Desmoinesian Series in Indiana and is recognizable throughout the Indiana coalfield. Probable equivalents of the Staunton Formation are the uppermost part of the Tradewater Formation and the lowermost part of the Carbondale Formation of western Kentucky and part of the Spoon Formation of Illinois. According to Shaver and Smith (1974, p. 18) and Shaver (1984), the Atokan-Desmoinesian series boundary should be placed at the base of the Staunton Formation, that is, below the Perth Limestone Member in western Indiana and the limestone next above the Buffaloville Coal Member (Brazil Formation) in southern Indiana. This limestone contains microfaunas characterized by an unidentified species of Fusulinella, F. iowensis, and the ostracod Amphissites centronotus.