Cores from 13 upper Smackover wells in the Paup Spur field, Miller County, Arkansas, and adjacent areas have been studied to define depositional facies from sedimentary structures and carbonate textures. A depositional model is developed from these data. Petrographic studies of thin sections show the relation of diagenetic events to facies, and help unfold the history of porosity development.

The vertical succession of facies in the upper Smackover Formation may be interpreted as an upward-shoaling sequence. From the base, burrowed and oncolite-bearing pelmicrite is overlain by burrowed and bimodally cross-bedded oosparite and pelsparite. These in turn are overlain by algal biolithite and pelsparite. Shale and anhydrite of the Buckner Formation overlie the upper Smackover. Contacts between all facies are gradational.

A depositional model based on this vertical sequence consists of low-energy peloidal carbonate mud deposited seaward of a moderate to high-energy oolite and pelletal-shoal complex. Bimodal cross-bedding indicates tidal influence on the shoal. Landward of the shoal complex, algal mats and peloidal mud were deposited in a low-energy intertidal environment. Farther landward, sabkha evaporites of the Buckner Formation were deposited.

Porosity is highest in the cross-bedded oosparite and pelsparite facies (greater than 25%), where molds of oolites and pellets are the principal pore types. In the algal biolithite facies, porosity reaches 15% and is principally moldic, interparticle, and fenestral pore space. Some interparticle porosity in the algal facies may result from dissolution of anhydrite cement.

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