Abstract

The Mid-Continent contains three primary carbonate sequences: (1) Sauk Cambro-Ordovician Arbuckle Group, (2) Tippecanoe Ordovician Viola Group and Siluro-Devonian Hunton Group, and (3) Kaskaskia Mississippian Osage-Meramec-Chester limestone sequence. The Pennsylvanian and Permian Absaroka sequence also contains significant carbonate cyclothems which are associated and subordinate to thick clastic deposits. Unconformities (and related conformities) are the boundaries that define carbonate depositional sequences and are the basis for the interpretations of sequence stratigraphy. A hierarchy of unconformities is worldwide, interregional, regional, subregional, and local according to their extent and hiatus or measurable time gap. Diagenesis associated with unconformity is both porosity destructive and constructive and, if developed on a large scale, can be recognized as karst terrain by large dissolution cavities, breccias, etc. The six most used methods for recognizing unconformity and related diagenesis are (1) outcrop and core analysis, (2) well log evaluation and correlation, (3) biostratigraphy, (4) seismic interpretation, (5) sequence evaluation, and (6) basin modeling. Carbonate reservoirs are often associated with unconformities worldwide and especially in the Mid-Continent. The recognition of key sequence boundaries, sequences, and associated diagenetic modifications can provide the basis for exploring any subtle traps.