More Evidence for Young Tectonism Along the Saline River Fault Zone, Southern Mississippi Embayment

Within the southern Mississippi embayment the 315-striking Saline River fault zone (SRFZ) was recently recognized from linear river segments, aligned epicenters, fault and fold exposures, sand blows, seismic reflection profiles, and trench investigations. In our latest work, shallow S-wave reflection profiles were acquired across the SRFZ within a sand blow field in Holocene alluvium at the southeastern limit of the mapped SRFZ. Along the central part of the SRFZ our field surveys of linear river segments subparallel to the SRFZ reveal that these segments are associated with faulting, fracturing, and folding of Eocene, late Pleistocene, and Holocene strata. In addition, we used logs of coal exploration holes to map shallow Eocene structure across the central SRFZ. In the SE of our study region, two S-wave reflection profiles (parallel and overlapping) were acquired along a 0.6 km N-S transect of the fault zone in NE Ashley County, AR. They reveal the SRFZ has a flower structure geometry with both positive and negative elements. The Eocene/Quaternary contact is clearly seen at 0.3 s (30 to 40 m depth). Several faults cut through the Quaternary section, and Quaternary and Eocene strata are folded harmonically. A fault in the overlap zone can be shown to strike 289 deg. New luminescence (IRSL) dates constrain a significant sand blow episode near this locality to between 7690 and 5725 yrs BP and a later significant episode to younger than 6845 yrs BP, consistent with previous results of middle to late Holocene sand venting here. In the central portion of the SRFZ, previous investigations of a linear river segment revealed a faulted anticline deforming alluvium younger than 720 years old. Our latest river surveys reveal that other linear river segments are associated with fractures and folds in Eocene substrate and young alluvium. Some oblique structures suggest a subsidiary strike-slip array. Shallow subsurface structure in Eocene strata mapped from coal exploration logs across the central portion of the SRFZ in Cleveland County, AR suggest a restraining-bend anticline/horst near the site of a moderate 1911 earthquake and the young river-bank anticline. This positive structure strikes NE, at a high angle to the SRFZ strike. Growing geologic, geomorphic, and geophysical evidence documents young tectonism in the southern Mississippi embayment, specifically in association with the SRFZ. Characterization of the SRFZ and any similar fault zones is crucial to understanding the seismotectonics and seismic hazard of the southern midcontinent.