The "Second" Frontier sandstone along the Moxa arch, southwestern Wyoming, forms a progradational sequence of marginal-marine and paralic to fluvial deposits that host important gas reservoirs. Thickness trends indicate that the paralic or fluvial sands had different immediate sediment sources than underlying marginal-marine sands did. Environmental interpretations imply that both deltaic and interdeltaic sedimentation controlled the distribution of sand deposits. Storage capacity mainly is in secondary "intergranular" pores, many of which formed by dissolution of calcite replacements of interstitial clay.

The development and preservation of secondary porosity entailed a complex diagenetic paragenesis that was controlled by deep burial and compaction, by compositional and textural variations imparted by depositional environments, and by position on structure. Best effective porosity is in thick deposits of medium to coarse-grained paralic or fluvial sandstone that contained, prior to dissolution, less than 60% chert and from 10 to 30% interstitial clay, calcite, and other unstable components. Other effective porosity is in fine to medium-grained marginal-marine sandstone that likewise contained appreciable unstable constituents. The smectite content and ordering of mixed-layer illite-smectite are related to permeability (IM ordering and more smectitic clay in more permeable sandstone; I II ordering and less smectitic clay in less permeable sandstone). Many of the diagenetic reactions, as growth of authigenic albite and recrystallization and authigenesis of clay, entailed components that already were available in the sandstone. Some diagenetic products suggest local kinetic controls that operated in realms nearly as small as single pore volumes.

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