Sedimentary Control on Early Diagenesis in Shallow-marine Carbonates: Control on Fracturation (Madison Formation)

The carbonates of the Madison Formation outcrop in the core of the Laramide fold of Sheep Mountain (Wyoming). The sedimentation is organized in stacked meter-scale fining-up cycles, illustrating a repetitive evolution from (1) a "deep" subtidal environment (mid ramp system), to (2) a subtidal environment subjected to storm reworking, and finally (3) a quiet lagoon environment separated from the open marine setting by migrating oolithic shoals. The diagenetic evolution is controlled by the initial sedimentary facies: (1) mudstones present an intense early dolomitization; (2) oolithic grainstones display isopachous marine calcite cements; (3) mud-supported facies (wacke- to packstones) are poorly impacted by early diagenesis (little early dolomitization of the carbonate mud). The multi-scale characterization of the fracture network reveals a strong control by the coupled depositional pattern and diagenetic imprint.