REGIONAL JOINT ANALYSIS FOR THE BUFFALO NATIONAL RIVER AREA OF NORTHERN ARKANSAS: IMPLICATIONS FOR TECTONIC HISTORY AND LANDSCAPE INFLUENCE

Joints record past stress events, impart fracture permeability, and enhance physical and chemical erosion that contributes to landscape evolution, particularly in karst regions. We use relative field ages, stratigraphic and spatial analyses to examine a large joint population (n = 3744, 746 sites) recorded during geologic mapping of an 80-km-long, E-W-trending transect in the Buffalo National River area in northern Arkansas. Lying on the southern flank of the Ozark Dome, this area exposes gently dipping Ordovician, Mississippian, and Pennsylvanian sedimentary rocks broken by faults and open folds formed during N-S extension and subsequent local N-S shortening in the foreland of the Late Paleozoic Ouachita orogenic belt.

Six joint sets are recognized on the basis of orientation frequency. The highest frequency set strikes N (345-5 azimuth range), with subordinate NNW (325-340) and NNE (5-20) subsets. Other strong sets strike NE (40-65) and WNW (285-310), and a weak EW set (80-95) is recognized from age relations. Whereas N and NE sets are pervasive, the WNW set and NNE subset are relatively more common in the east and the NNW subset is more common in the west. Abutting relations between joints provide relative ages at 95 sites and indicate mixed ages among the N, NE, WNW, and EW sets. In the west, the EW set is oldest and locally bleached by fluids related to nearby Pb-Zn mineralization in Boxley Valley whereas successively younger abutting NE and N sets are unbleached. In the east, N, NE, WNW, and EW sets mutually abut and thus are broadly contemporaneous. Joints of the oldest EW set probably accompanied faulting and N-S extension of the Ozark Dome during mid- to late Pennsylvanian, but the extensive N set probably formed in late Pennsylvanian to Permian as compressive stresses propagated into the foreland as the Ouachita orogenic belt docked with Laurentia to the south.

Many linear segments of surface drainages in the present Buffalo River landscape parallel the major joint orientations, particularly within carbonate units. This correlation indicates that erosion and karst dissolution are enhanced by regional jointing.