Paleokarstic Features and Their Relationship to Cementation History, Burlington-Keokuk Limestone, Middle Mississippian, Central Missouri

Lawrence D. Daniels, William J. Meyers

Various paleokarstic features, large scale to microscopic in size, are present in the upper Burlington-Keokuk Formation below the pre-Pennsylvanian unconformity in central Missouri. Solutional cavities of widely varying size and morphology are infilled with various sediment types including shale, peat, detrital quartz sand, residual chert, reworked limestone sediment and dolomite clasts, and pore-filling calcite cement. Wavy horizontal solution seams and solution-enlarged vertical fractures contain sandstone, shale, chert, and reworked limestone sediment. Chert nodules, apparently rotated from their original position, are commonly present in association with these features.

The petrography of the paleokarstic features integrated with a regionally consistent luminescent zonal sequence in calcite cement provided new evidence for the timing of these cements. First-generation nonferroan cement predates the major period of karstification, whereas second-generation ferroan and third-generation calcite cement postdate the karstic event. Therefore, the karstification may have occurred while the limestone was relatively porous. Cement in cavity fills, host limestone, and overlying Pennsylvanian strata suggest karstification is post-Mississippian but no later than the Desmoinesian. A post-Desmoinesian age is indicated for second- and third-generation cements, previously believed to be Mississippian. The postkarstification timing for second-generation ferroan and t ird-generation calcite cement and the fact that they postdate a major regional compaction event suggest that they may have precipitated under burial conditions. Stratigraphic information constrains the amount of overburden as less than 1 km. Minor barite and sphalerite mineralization, believed to be Late Pennsylvanian or Early

Permian, postdates calcite cementation and places a minimum age on the cement. Because some cavity fills contain considerable amounts of second- and third-generation cements, the study suggests that some solutional porosity created during karstification may temporarily survive subsequent sedimentation and burial. If this karstification occurs early in the cementation history of the rock, extremely favorable reservoir conditions should result.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.