New Mexico Geological Society Annual Spring Meeting — Abstracts

The outstanding, primarily carbonate Franklin Mountains exposures of the Tobosa basin-related sediments (Ordovician-Devonian) reveal spectacular karsts that are analogous to synchronous Permian Basin producing horizons. Two major periods of subaerial karsting occur; they are: Post-El Paso Middle Ordovician (27 Ma) and Post-Fusselman Middle Silurian to Middle Devonian (40 Ma). Numerous other minor karsting events are recorded also.

Post-El Paso Group (Middle ordovician) karsting extends to depths down to approximately 1000 feet below the top of the group. This would include (in descending order) Florida Mountains, Scenic Drive, and McKelligon formations. The lower Scenic Drive arenaceous, supratidal to intertidal Black Band Dolomite Member contains early diagenetic dolomite that was resistant to karst solutional activity in comparison to adjacent, calcareous, shallow marine carbonates. The Black Band Dolomite, therefore, forms the roofs of the major caverns in the McKelligon Formation. In the correlative, subsurface Ellenberger Formation production of the Permian Basin (e.g., keystone, Andector, Emma fields) production is developed in cave roof fracture porosity and separately in lower collapse zone (cave-fill) porosity.

Post-Fusselman (Middle Silurian-Middle Devonian) karsting extended down to the caverns developed during the post-El Paso Group Karsting. The best karst feature are developed at the contact between the Fusselman (Crazy Cat Member) and the overlying Canutillo Formation. Permian Basin equivalent Fusselman production is best exemplified by cavern-size porosity developed on the Central Basin platform Dollarhide Field.