Carboniferous Rocks of the Ouachita Mountains, Arkansas: A Study of Facies Patterns along the Unstable Slope and Axis of a Flysch Trough

Carboniferous Stanley-Jackfork rocks in the Ouachita Mountains constitute a flysch facies with unique lithologic associations, bedding characteristics, and sedimentary structures that differ according to position in the basin and geologic age. Field and laboratory studies confirm the presence of recurring rock types that can be differentiated into proximal turbidite facies, distal turbidite facies, pelagic facies, and disturbed beds. The proximal turbidite facies (fluxoturbidites) include either thick sandstones with scour-and-fill bedding or even-bedded turbidite sandstones with thin, interbedded mudstones. The distal turbidite facies consists of sandy and shaly flysch in which individual beds generally contain the sedimentary structures of a complete Bouma sequence. Laminated sandstones dominate sandy flysch, whereas shales exceed siltstones and sandstones in shaly flysch. The pelagic facies includes shales, ferruginous siltstones, siliceous shales, and impure cherts, all commonly associated with distal turbidites. Disturbed bedding is present with greatest frequency at the base and on the flanks of unstable slopes along an east-west–trending trough of abyssal plain character. The type of disturbed bedding was dependent upon the kind of material moved, its state of consolidation, and the distance of travel. Highest sand-shale ratios parallel the axis of the trough, whereas more shaly slope deposits are frequently disturbed. In the Mississippian rocks, paleocurrent mean (323°) for feldspathic Stanley turbidites suggests dominance of a southeastern provenance. Jackfork paleocurrents with considerable variation average 260° in lower Jackfork and 266° in upper Jackfork turbidites. In any vertical succession, these turbidites have noticeable variation in textures as well as compositions. The interpretation is that point sources from the northeast and the southeast fed clastics into the trough. The Pennsylvanian Atoka clastics principally entered from the northeast.