Abstract

In the Blanding sub-basin of the Paradox Basin, oil and gas are produced from numerous Upper Ismay (Desmoinesian) carbonate mounds. The mounds form linear, subparallel trends; are underlain by thickened sections of Hovenweep Shale; are flanked by thick salina anhydrites; and are overlain by thin upper Ismay sabkha deposits and marine carbonates of the basal Honaker Trail Formation. Correlative, but thinner, marine-shelf upper Ismay carbonates are underlain by thin Hovenweep Shale.

Based mainly on local mapping of thickness trends and serial stratigraphic cross sections, we propose that the anomalously thick upper Ismay carbonate mounds result from: 1) regional base-level changes, 2) differential subsidence during Hovenweep time due to salt movements, 3) loading of the salt by thickened Upper Ismay carbonates and evaporites, and 4) differential compaction of the evaporites surrounding the carbonate-mound masses during latest Ismay and earliest Honaker Trail deposition. This depositional model has implications for understanding and predicting the distribution of Upper Ismay carbonate mounds in the subsurface.