The late Valmeyeran Pella beds of southeastern Iowa are elevated formally to the rank of formation. A type section and several reference sections are designated.

The Pella Formation consists of a distinctive series of carbonate strata containing seven lithofacies representing fluctuations in environment near mean sea level within the Genevievian Sea, the last sea to inundate parts of Iowa during the Mississippian. The facies are basal sandstone-siltstone, carbonaceous shale, ostracod biomicrite, packed oomicrite, fossiliferous micrudite, shaly micrite, and packed biomicrudite. They possess properties indicative, both independently and collectively, of supratidal, intertidal, and subtidal environments.

A striking similarity can be noted between the shallow- and deep-water phases of Pella deposition and the regressional-transgressional phases in the Illinois basin during the late Valmeyeran. At least two complete cycles of change from supratidal to subtidal to supratidal environments are evident. It is probable that the two areas were connected across the Mississippi River arch, and that the shallow-water phases of Pella deposition correspond to the Spar Mountain, Joppa, and Rosiclare regressive sedimentation in the Illinois basin.