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Quaternary faulting in the southern Mississippi embayment and implications for tectonics and seismicity in an intraplate setting

Randel Tom Cox^*,1, Roy B. Van Arsdale^,1, James B. Harris^,2, Steven L. Forman^#,3, William Beard^#,4 and Joseph Galluzzi^#,5

¹ Department of Geological Sciences, University of Memphis, Memphis, Tennessee 38152, USA
² Department of Geology, Millsaps College, Jackson, Mississippi 39210, USA
³ Department of Earth and Environmental Science, University of Illinois, Chicago, Illinois 60607-2279, USA
⁴ Department of Geology, Millsaps College, Jackson, Mississippi 39210, USA
⁵ Department of Geological Sciences, University of Memphis, Memphis, Tennessee 38152, USA

The recently recognized Saline River fault zone in the southwestern Mississippi embayment (strike = 135°) is characterized by moderate historic seismicity. We document paleoseismicity (possibly strong) on the Saline River fault zone that is outside the known region of neotectonism in the northern embayment. Six surface faults were excavated within the Saline River fault zone, and all faults displace marine Eocene units and fluvial Pliocene–Pleistocene units; five show post-Wisconsin loess movement (thermoluminescence [TL] age = 23.6 ± 3 ka), and three deform middle to late Holocene eolian silt (TL age = 5.1 ± 0.6 ka and 3.6 ± 0.5 ka) as fault-tip flexures. Along the principal excavated fault, fault-plane braiding and plunging drag folding suggest a strong component of left slip, and subsidiary faults show both normal and reverse displacement (<1m) of Pliocene–Pleistocene, Wisconsin, and Holocene units. We interpret these faults as components of a left-slip flower structure. A shallow seismic reflection profile acquired across the principal fault and a subsidiary fault shows Eocene stratigraphy separated in a reverse sense below 120 m depth and separated in a normal sense above 120 m, supporting a strike-slip interpretation. In addition, the only focal plane mechanism available in the area indicates left slip with a small reverse component.

We conclude that the Saline River fault zone is a Paleozoic–Mesozoic basement fault zone reactivated as a left-slip system in a Quaternary east-west compressive stress field. Field evidence suggests that earthquakes with several meters of strike slip may be characteristic, and the width of a liquefaction field on the Saline River fault zone suggests an event of magnitude 5.5–6. Considering a similarity of strike and sense of Holocene movements of the Meers fault of southern Oklahoma and of the Saline River fault zone, there may be additional active fault zones that pose seismic hazards concealed by sediments in southern North America.

Key Words: active faults • eastern North America • geomorphology • Mississippi embayment • neotectonics • paleoseismicity • Quaternary • Saline River

This article has been cited by other articles:

				R. Csontos, R. Van Arsdale, R. Cox, and B. Waldron Reelfoot rift and its impact on Quaternary deformation in the central Mississippi River valley Geosphere, February 1, 2008; 4(1): 145 - 158. [Abstract] [Full Text] [PDF]

				Preliminary Assessment of Sand Blows in the Southern Mississippi Embayment Bulletin of the Seismological Society of America, June 1, 2004; 94(3): 1125 - 1142.

				R. T. Cox, R. B. Van Arsdale, and J. B. Harris Identification of possible Quaternary deformation in the northeastern Mississippi Embayment using quantitative geomorphic analysis of drainage-basin asymmetry Geological Society of America Bulletin, May 1, 2001; 113(5): 615 - 624. [Abstract] [Full Text] [PDF]