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Abstract: Petrology and Diagenesis of Deep-Water Sandstones, Ouachita Mountains, Arkansas and Oklahoma

Robert C. Morris, Kenneth E. Proctor, Michael R. Koch

The Stanley and Jackfork Groups of the Ouachita Mountains consist of 18,000 ft (5,500 m) of interbedded sandstones and shales deposited during the Late Mississippian and Early Pennsylvanian. This flysch facies is dominated by a succession of westerly directed, deep-marine fans built up by turbidity currents and sandy-debris flows. Interest in their hydrocarbon potential has led to study of textures, compositions, and diagenetic alterations of these sandstones.

The Stanley sandstones are generally feldspathic and quartz wackes. Most are poorly sorted; mean grain sizes are the very fine sand range, with an average of 8% feldspar and 14% matrix. They have an average of 5% silica cement, but many specimens contain none. Porosities range from 0.5 to 26% and permeabilities from 0.05 to 23 md. Jackfork sandstones are predominantly quartz arenites, which tend to be moderately to poorly sorted, with mean grain sizes in the fine to very fine-sand range. They contain an average of 2% feldspar, 5% matrix, and 9% quartz cement. Porosities range from 0.5 to 14% and permeabilities from 0.05 to 9 md.

Pressure solution, silica cementation, and calcitization of plagioclase have acted to reduce the reservoir potential. Corrosion and dissolution of framework grains of quartz, feldspar, and garnet have increased secondary porosity. The presence of halloysite and kaolinite distinguishes permeable sandstones affected by surface leaching from sandstones unaffected by leaching. The sandstones display a random variation in porosity and permeability both laterally and vertically. Thick-bedded, scoured proximal turbidites and sandy debris flows commonly have the most favorable textures. Characteristics associated with the retention of favorable reservoir potentials include poor sorting, small mean-grain sizes, and high matrix content. Well-sorted quartz arenites are poor reservoirs because th ir pores were filled completely with silica cement.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado