POST-EOCENE DEFORMATION OBSERVED IN SEISMIC-REFLECTION PROFILES ACROSS THE SOUTHWESTERN BLYTHEVILLE ARCH AND CROWLEYS RIDGE, ARKANSAS
WILLIAMS, R.A., STEPHENSON, W.J., and ODUM, J.K., U.S. Geological Survey, Denver Federal Center, MS966, Box 25046, Denver, CO 80225, firstname.lastname@example.org; GOMBERG, J., U.S. Geological Survey, Univ. of Wash., Dept. of Earth and Space Science, Johnson Hall, Rm 63, Box 351310, Seattle, WA 98195-1310, email@example.com
Two new east-west trending high-resolution minivibe P-wave reflection profiles, located in the New Madrid seismic zone in northeastern Arkansas about 70 km northwest of Memphis, TN, reveal details of an anticline beneath Crowleys Ridge and a buried monocline in the post-Paleozoic deposits near Harrisburg and Lepanto, Arkansas, respectively. These profiles, which are higher resolution (144 channels/sweep at 5-m intervals) than previously acquired in this area, are part of a planned continuous transect that eventually will span the Reelfoot Rift in a study of regional deformation patterns. Preliminary results from Crowleys Ridge, an anomalous topographic high on an otherwise flat Mississippi embayment surface, are consistent with previous COCORP and USGS reflection data and strongly suggest that the 50-m high topography of the ridge is caused by post-Eocene tectonic uplift related to near vertical ridge-bounding faults. The Paleozoic-Cretaceous sequence is upturned about 50 m on both sides of Crowleys Ridge, an amount roughly equal to the height of the ridge. No seismicity has been recorded in this part of Crowleys Ridge since 1974. In contrast, the Lepanto profile images a monocline in Paloezoic and younger reflectors within a seismically active area on the eastern margin of the buried Blytheville Arch. The maximum amplitude of the west-side-up monocline, observed on the Paleozoic through Eocene reflector sequence, is about 100 m. This sequence is also an interval of constant thickness from about 800 to 300 m depth. Above the Eocene section, and possibly into the Quaternary, the sediments thicken east of the monocline, suggesting a late Eocene to possibly Quaternary period of growth for this monocline. It is not clear at this stage of interpretation if the current seismicity near Lepanto is related to ongoing deformation of this monocline.