Quaternary Deformation Across the Proterozoic Alabama-Oklahoma Transform Imaged By High-Resolution Seismic Reflection Data

Abstract:

We hypothesize that Quaternary deformation in the Mississippi Embayment in the Central U.S. has been accommodated by faults additional to the New Madrid seismic zone, and that the location of these faults is strongly controlled by paleotectonic structures inherited from the long tectonic history of the North American continent. To test this hypothesis, a 950 km-long high-resolution multichannel marine seismic reflection section was acquired along the Mississippi River to identify and characterize zones of Quaternary deformation in this region.

Here we present three seismic profiles crossing the Alabama-Oklahoma Transform (AOT) that imaged significant faults. The northern profile images multiple faults striking northwest interpreted as the Arkansas River fault zone. The faults offset the reflectors from the tops of Cretaceous to the Eocene Cane River Formation and likely deform Quaternary strata in the upper 20-30 m. The central profile images a down-to-the-north normal fault, displacing the tops of Cretaceous and Paleocene Midway Group units by ~210 m and ~160 m, respectively, interpreted as the northern edge of the Monroe Uplift, a Late Cretaceous uplift caused by igneous intrusions. The southernmost profile shows a down-to-the-south displacement along a south dipping fault, which offsets the tops of the Cretaceous and the Paleocene-Eocene Wilcox Group ~125 m and ~32 m, respectively. Tilted reflectors in the uppermost Eocene and Quaternary strata suggest very recent activity of this fault.

The spatial coincidence of the imaged faults with the AOT strongly argues toward a reactivation of this paleotectonic structure in the present stress field. The new seismic data suggest that the AOT is a deformation zone, spanning as wide as ~80 km, that persisted as a weak zone of the lithosphere controlling the location of Tertiary and Quaternary deformation, as demonstrated by dipping reflectors immediately beneath the Mississippi River bottom, earthquake-induced sand blows, and near-surface faulting in the vicinities. The data also suggest that the AOT may have controlled reactivations of Triassic-Jurassic synrift basement structures, focusing the igneous intrusions during the Late Cretaceous.