COMPACTION OVER PENNSYLVANIAN PARADOX BASIN BIOHERMS AS A MODEL FOR FOLDS IN THE THUNDER SPRINGS MEMBER OF THE MISSISSIPPIAN REDWALL, LIMESTONE, GRAND CANYON, ARIZONA

Bioherms in the Pennsylvanian of the Paradox basin have been extensively studied and revisited for almost 70 years due to their exceptional outcrop exposures and economic importance. Previous work focused on the porosity evolution, sequence stratigraphy and biotic composition. An overlooked aspect of these carbonate buildups is their influence on the geometry of overlying beds which amplify both the apparent vertical and horizontal extent of the buildup through the compaction. This is especially well developed over the largest bioherms (13-20m thick) exposed in the Goosenecks of the San Juan River in the Barker Creek interval of the Paradox Formation.

Analogous processes may control the mysterious “folds" formed in the Mississippian (Kinderhookian) Thunder Springs Member of the Redwall Limestone in the Eastern Grand Canyon reported but not explained by Mckee and Gutshick (1969) and observed by thousands of visitors to Marble Canyon every year. These apparent buildups and compactionl features are similar in scale and geometry to those of the Pennsylvanian described above. Ongoing fieldwork on the portion of Marble Canyon where the Thunder Springs Member emerges from the subsurface allows access and inspection of the base of these features. Above the top of the underlying Whitmore Wash Member, flat bottomed carbonate build-ups with very recrystallized bryozoan (bafflestones?) are 10 to 90 meters long and 5 to 20 meters high. Overlying strata of typical cherty Thunder Springs Member form larger antiform features over these build-ups with draping, but no onlapping geometries. These features deform the entire thickness of the Thunder Springs Member until they are “healed” by prograding crinoidal grainstone facies of the overlying lower Mooney Falls Member. Identifying these processes and features these two locations has implications understanding aquifers, reservoirs and their seismic signatures.