Abstract: Depositional and Diagenetic Environment of the Sonora Sands, Ozona Field, Crockett County, Texas

STROUD, JOHN, and R. NOWELL DONOVAN

The Sonora sands were deposited on the southern margin of the Ozona arch within the Permian Val Verde basin, a north-west trending peripheral foreland basin. Sandstone deposition in the eastern part of the basin took place during the final episode of the Marathon orogeny during the middle Wolfcamp. Sediment transport into the area by fluvio/deltaic systems was initially from the east, rotating to the northwest through time and onlapping underlying Pennsylvanian strata. The Sonora sands were deposited as submarine fans in and along two large north-south trending submarine erosional pathways that were carved into the underlying Strawn topography by a catastrophic shelf margin slumping episode. Slope-onlap and upward-fining stratigraphic patterns suggests a sea level lowstand during which sand-rich basin-floor submarine fans were overlain by turbidite slope wedges. Sonora facies are stacked submarine fans and mud/sand-rich turbidites with incomplete Bouma sequences that are distal in the upper packages and proximal in the older Sonora intervals. Slump, debris-flow deposits and fan-lobe deposits are common. The sands are fine to medium grained sublitharenites and litharenites with grain rimming siderite. Siderite enhancement is concentrated along the onlap surface with some linear distribution throughout the sand intervals. Although primary porosity is limited due to cementation by mixed layer clays, sandstone porosity range from 2-7%. Fractures in the Sonora sands are common and may affect reservoir properties; they are short, healed, random strikes with limited vertical conductivity.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma