Geologic Publications for Mount Rainier
The lithostratigraphy and depositional environments of the Pella Formation (Mississippian) in Keokuk and Wapello Counties, southeastern Iowa
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Scott R. Beason
The Compass: Journal of Earth Sciences, Sigma Gamma Epsilon
35 to 44
The Pella Formation is the uppermost Mississippian rock formation in Iowa, cropping out mainly in the southeastern part of the state. It typically consists of a relatively thin (<2 m) basal limestone that is overlain by thicker (up to 7.5 m), highly fossiliferous marl. The Pella Formation rests unconformably on the "St. Louis Formation," the upper part of which is nonmarine limestone and plant-bearing sandstone. The upper contact of the Pella Formation is a major erosional unconformity corresponding to the Mississippian-Pennsylvanian systemic boundary. Carbonate petrography of the lower part of the Pella Formation enabled identification of distinct brachiopodal and oolitic lithofacies that are locally correlatable. Bioclasts increase in diversity up-section and quartz sand decreases in abundance up-section, suggesting that at least the lower part of the formation is a deepening-upward succession in which restricted marine and then normal marine conditions became established during transgression. The unconformity between the upper Pella Formation and overlying Pennsylvanian rocks is rarely exposed in outcrops because it occurs within relatively nonresistant beds that are eroded and covered by vegetation. The unconformity is well preserved in a core from Wapello County. Uppermost Pella beds in the core are deeply weathered and rubbly, and are interpreted as a coarse residual paleosol.
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In Text Citation:
Beason (2007) or (Beason, 2007)
Beason, S.R., 2007, The lithostratigraphy and depositional environments of the Pella Formation (Mississippian) in Keokuk and Wapello Counties, southeastern Iowa: The Compass: Journal of Earth Sciences, Sigma Gamma Epsilon, Vol. 80, No. 2, pp. 35-44.