Evidence of Paleokarstic Phenomena and Burial Diagenesis in Ordovician Arbuckle Group of Oklahoma

Mark Lynch, Zuhair Al-Shaieb

Numerous cores of Ordovician-age Arbuckle Group carbonates from Oklahoma were examined for evidence of paleokarstification. This investigation emphasizes the prominent role that karstification and deep burial diagenesis play in the establishment of Arbuckle reservoirs.

Cores from various localities in south-central and north-central Oklahoma display surprisingly similar suites of karstic and diagenetic phenomena. Vadose dissolution tubes, solution-enlarged fractures, collapse breccias, and vugular porosity, where present, are considered evidence of karstification. Primary speleothemic precipitates were not readily observed; either they were not present or were obscured by later hydrothermal dolomitization.

A complex history of exposure and subsidence is recorded in these rocks. Immature karst profiles may have subsided at rapid rates under conditions that prevented low-temperature phreatic cementation, thus preserving the open pore network of the karst profile. Deep burial diagenesis is evidenced by the appearance of highly ferroan baroque dolomite cement partially or entirely occluding vugular and fracture porosity. In addition, host-rock carbonates were extensively replaced by typical thermal xenomorphic dolomite. Cathodoluminescent microscopy indicates that the hydrothermal dolomite is uniform in composition and was precipitated under highly reducing conditions. Dolomite cementation was arrested when oil migrated into the remaining pore space. A complex multistage fracture network is present in cores from the Healdton oil field. Early fracture systems are healed by highly ferroan, dull luminescent baroque dolomite, and later fractures are cemented with nonferroan, brightly luminescent cement.

AAPG Search and Discovery Article #91025©1989 AAPG Midcontinent, Sept. 24-26, 1989, Oklahoma City, Oklahoma.