The lower member of the Pennsylvanian Atoka Formation exposed in the Ouachita Mountains of Oklahoma and Arkansas is part of a thick (more than 10,000 m or 32,800 ft) turbidite sequence deposited in a remnant ocean basin (the Ouachita geosyncline) during the Carboniferous. Paleocurrent data indicate a predominantly longitudinal sediment dispersal pattern westward down the basin axis.

Nine lithofacies are recognized: massive, amalgamated sandstones (A1), graded, matrix-supported sandy mudstones (A2), six different types of classic turbidites (C1, C2, C3, D1, D2, and D3), and chaotic deposits (F) including debris flows. These occur in two principal lithofacies associations, both representing deposition in an areally extensive, sand-rich, channelized deep-sea fan environment. Lithofacies association 1 consists of packages of lithofacies A1 (and to a lesser extent A2 and C3) 1-30 m (3-98 ft) thick, interbedded with intervals comprised of lithofacies A2, C1, C2, C3, D1, D2, and D3, in which the sandstone:shale ratio is generally high (amalgamated to 1:5). Thickening- and thinning-upward sequences are arranged symmetrically about the lithofacies A1 packages, producing s acked symmetrical sequences 1 to 20 m thick. Lithofacies association 2 consists of lithofacies C3, D1, D3, and minor amount of D2, arranged in symmetrical as well as individual thickening- and thinning-upward sequences 1-40 m (3-130 ft) thick. The sandstone:shale ratio is highly variable (amalgamated to 1:50). Although thickness trends in this lithofacies association can be highly complex, thinning-upward sequences (10-40 m or 33-130 ft thick) are prominent. Slumped chaotic deposits (lithofacies F) are intercalated throughout both lithofacies associations. Common crevasse splays that develop into new channel segments, and filling of distributary channels are the inferred processes involved in the development of the two lithofacies associations.

The absence of deposits of major depositional lobes and the extensive development (both vertically and laterally) of a channelized (distributary channel) fan environment suggest that current submarine-fan models are not generally applicable to this deposit.

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