ORIGIN OF DISHARMONIC FOLDING: REVISITED

Viele (1995) looked at the disharmonic folding pattern in the Central Ouachita Mountains and concluded that the "lower deck" represented an earlier stage of deformation in an accretionary wedge and that the "upper deck" consists of sediments that prograded across a quiescent accretionary wedge. Late Carboniferous thrusting subsequently deformed both. Recent mapping between the Boktukola and Octavia faults provides insight into this contact. Outcrops were located with DGPS, coupled with remotely sensed imagery. These data were overlain on a digital elevation model utilizing GIS, producing 2D and 3D surfaces. The discontinuity between the decks is well exposed at Big Eagle Creek. At road level, the younger shales of the Stanley Formation are gently dipping towards the west, while in the creek steeply dipping, thin, tightly folded turbidite beds are apparent. A zone of extremely fissile shale extends ~3 m from road to creek level. This fabric is believed to record significant flattening, although no strain markers have been found. A ~1 m brecciated zone separates these cleaved rocks from the steeply dipping and tightly folded rocks below. This contact is interpreted to be a low angle fault. The fault trace (Buffalo fault) was mapped across the area. It follows the broad fold patterns of the Boktukola syncline and Nanichito anticline. The Boktukola fault appears to truncate the Buffalo fault but the latter may be a splay. The proposed Buffalo fault is a low angle thrust fault whose footwall contains high frequency, highly strained, east-west trending structures similar to the Benton uplift of Arkansas, in contrast to the open structures of the hanging wall, characteristic of the Boktukola syncline. No evidence for an unconformity was observed. These data do suggest an earlier folding history preserved in the footwall rocks. Assuming the entire sequence is allocthonous and displaced over the basement sequence of the Broken Bow uplift, then these early structures probably reflect deformation in the accretionary wedge.