The Drum limestone is an algal build-up and oolite complex formed as a E-W belt at the shelf edge of the Pennsylvanian northamerican mid continent. The Drum formation lies on an erosive surface and formed in two depositional stages separated by an unconformity, resulting in a lower regressive and an upper transgressive unit. The diagenetic story of the Drum oolite is closely related to its depositional story. The main controls on the deposition and diagenesis of the Drum limestone were inherited topography, which controlled facies distribution and depositional sites, and relative sea level changes, influencing sedimentary processes