Photogeologic and field mapping of a 530 mi² area in southeastern Washington and southern Madison Counties, Arkansas, indicates that post-Atoka structural deformation occurred primarily through differential uplift of basement fault blocks. Northeast and east trending basement faults and fracture systems are present. Northeast trending features are related to the major fracture systems of the stable continental interior. They were initiated by shearing during Pre-Cambrian time and have subsequently acted as crustal zones of weakness along which mostly vertical movement has occurred. East trending basement faults may have originally developed as a result of tension between the stable Ozark uplift and the subsiding Arkoma basin during late Atokan time. Northeast and east trending faults join to form a mosaic of polygonal basement blocks. During post-Atoka uplift(s) of the Ozark region, each block behaved more or less independently. Normal faults and (more commonly) monoclinal draping occurred in the sedimentary rocks which overlie the marginal basement fault zones. Slight tilting and warping of the blocks created local homoclinal dips whose magnitude and direction may change abruptly at block margins. Structural highs occur at the most elevated margin or corner of each block. Horizontal compression during the Ouachita orogeny possibly accounts for several gentle east trending folds in the Pettigrew area. An anomalous dome structure near Witter may be related to a local high on the Pre-Cambrian basement surface.
Shinn, Mikel R.
"Structural Geology of the Brentwood-St. Paul Area, Northwest Arkansas,"
Journal of the Arkansas Academy of Science: Vol. 32
, Article 25.
Available at: https://scholarworks.uark.edu/jaas/vol32/iss1/25