ANALYSIS OF JOINTS IN THE ARKOMA BASIN AND SOUTHERN OZARK DOME

Geologic structures in the Ouachita fold and thrust belt, the Arkoma Basin, and the southern Ozark dome in northwestern Arkansas reflect the timing and directions of paleostress episodes during the late Paleozoic Ouachita Orogeny. We computed summary statistics on more than 35,000 strikes for near-vertical joints (dips > 70°) measured primarily by the U.S. and Arkansas Geological Surveys during geologic mapping in the Arkoma basin and southern Ozark dome. The Mississippian and Pennsylvanian strata cut by this joint system generally have shallow dips throughout the region. The overall distribution of joint strikes is distinctly trimodal. Mean strikes and circular variances (in parentheses) for the three joint sets are: J1, 52° (0.022); J2, 280° (0.029); and J3, 350° (0.045). J1 and J2 joints cut Chesterian to Atokan strata of the southern Ozark dome north of the Mulberry fault. These joints are parallel to and evidently coeval with a number of high-angle normal and oblique-slip faults that accommodated downwarping of southern Laurentia early during the Ouachita orogeny (the D2 phase of Hudson and Turner, 2022). J1 is related to NE-trending faults, including the Compton, Ponca, and Mill Creek zones, while J2 is related to NW-trending faults, including the Indian Creek, St. Joe, and Maumee zones. J3 joints are present throughout both the Ozark dome and the Arkoma Basin. In the Arkoma Basin, J3 joints strike near-perpendicular to gentle, east-trending folds in Desmoinesian strata and are interpreted as a response to NNW-directed compression (the D3 phase of Hudson and Turner, 2022).