Carbonate Petrology of the Silurian Wink Formation, Howard County, TX

KOHL, MICHAEL L., Department of Geosciences, Texas Tech University, Lubbock Texas

Wenlock flooding of the karsted surface of the Llandovery Fusselman Formation in West Texas initiated deposition of the argillaceous carbonates that comprise the Wink Formation of the Wristen Group. A core from the Cobra Frazier #1 well in Howard County, Texas, includes approximately 60 feet of Wink carbonates that grade upward into the highly argillaceous Frame Formation. The core ranges in age from early Wenlock to early Ludlow, based on conodont data.

    The Wink was deposited as argillaceous skeletal mudstones and wackestones initially in a deep ramp setting that later (late Wenlock-Ludlow?) became a basinal setting. Karsting features (fracture and collapse breccias) are present throughout, and Middle to Late Devonian conodonts in the karst fill indicates that karsting occurred a significant time after deposition. Karsting was followed by two diagenetic dolomitization events and an epithermal event. The first event resulted in the dolomitization of the karst fill throughout the core. The second event is concentrated in the lower Wink, and dolomitized the micrite and skeletal fractions. These diagenetic events produced a sucrosic dolomite with some fracture and vuggy porosity, in the lower Wink. The epithermal event precipitated baroque dolomite in most of the fracture and vuggy porosity, and subsequent precipitation of calcite filled much of the intercrystalline porosity. These events caused a significant loss of porosity and permeability, which resulted in the Wink present in the Cobra Frazier to be uneconomic as reservoir rock.