Abstract

The Crittenden County fault zone (CCFZ) is located near the southeast boundary of the Reelfoot rift in northeastern Arkansas. The southeastern boundary of the rift has been characterized as an 8-km-wide zone of down-to-the-northwest displacement. The CCFZ, however, shows significant down-to-the-southeast reverse faulting of Paleozoic and Cretaceous rocks and flexure and thinning within the Tertiary sedimentary section.

We discuss four of nine Mini-Sosie seismic reflection profiles, each 1 to 2 km long, acquired over the surface projection of the CCFZ and Reelfoot rift boundary. One second of two-way traveltime data was recorded, which corresponds to a maximum depth of approximately 1.2 km. Sedimentary layers between 50 and 800 m are well imaged; deeper strata are evident but not well imaged.

Well data at one site on the CCFZ indicate approximately 63 and 82 m of vertical displacement of Cretaceous and Paleozoic rocks, respectively. Proprietary seismic-reflection data show reverse displacement of these rock units, indicating compressional tectonics. From the Mini-Sosie profiles, we estimate structural relief across the CCFZ at the Paleocene (Fort Pillow Sand) level to range between 14 and 70 m. The overlying middle-to-late Eocene section shows a similar or slightly smaller amount of thinning, indicating that much of the movement on the CCFZ dates mid-to-late Eocene. Displacement, flexure, and thinning in the geologic section increases as the CCFZ converges with the Reelfoot rift boundary, in the southwest part of the area studied. Surface expression of the CCFZ has not been identified. Reflections from the Quaternary-Eocene unconformity, however, show warping, dip, or interruptions in places over the CCFZ, suggesting that the CCFZ may have experienced Quaternary or Holocene movement as well.

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