A detailed field investigation along the intricately folded and faulted Frontal Ouachitas for the first time permits accurate sampling of sandstones encompassing the entire Jackfork section. The resulting petrographic information supplements paleocurrent studies and sedimentary structures in postulating a provenance and dispersal system. Rocks of the Frontal Ouachitas consist approximately 30 percent of sandstone deposited by mass flow or turbidity currents and 70 percent of shale, mostly contorted by downslope movement after deposition. Exposures along a southern belt consist of 75 percent of sandstone; only negligible amounts of gravity-deformed, argillaceous rocks are present in this southern belt.

Approximately 200 thin sections were analyzed from measured sections and isolated areas. Along the Frontal Ouachitas, the sandstone is predominantly fine-grained quartz arenite and wacke (range 0.07 to 0.31 mm; average 0.14 mm), high in polycrystalline quartz, and having less than 1 percent feldspar, 2.5 percent unstable rock fragments, a stable heavy-mineral suite, and varying amounts of matrix. These rocks are moderately sorted to moderately well sorted although pressure solution has masked and altered the original texture. Stylolites along bedding planes and sutured, interlocking grain contacts indicate considerable removal of silica by post-depositional means, a small amount remaining as quartz overgrowths. More argillaceous wacke shows highly corroded quartz grains due to local i creases in pH but with little grain interpenetration. Dominantly friable sandstone along the southern belt has comparable grain sizes but a marked increase in matrix and decreased post-depositional changes. The matrix probably reduced the flow of silica-removing waters, also forming a cushion that would reduce number of point contacts. Feldspar content may approach 10 percent but remains lower than that of the Stanley sandstone.

Basinal filling was mainly from the end (east), aided by sediment bypassing through the Illinois basin. A volcanic archipelago (Llanoria) probably contributed the feldspar. Rocks throughout the Frontal Ouachitas apparently were deposited along a steep, south-dipping, unstable slope. West-flowing, bottom-hugging turbidity currents concentrated the sand in the deepest part of the east-west trending Ouachita trough which today is exposed as the rocks of the southern belt. Care must be taken when interpreting sandstone-shale ratios in flysch basins where the greatest sand content is along the basin axis.

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