WHAT’S GOING ON TECTONICALLY IN THE MISSISSIPPI EMBAYMENT DURING EOCENE? (Invited Presentation)

The Mississippi Embayment (ME) is a shallow Cretaceous/Paleogene basin developed by reactivation of the Cambrian Reelfoot Rift (RFR) involving igneous intrusion along rift faults, uplift, cooling and subsidence. Prior to Cretaceous, the RFR was compressed during Late Paleozoic Alleghenian/Ouachita orogenies, and a structural high is retained beneath the ME basin. Currently, the ME is in ENE/WSW compression, and several faults related to the RFR are seismogenic. Depending on strike, these faults show reverse, dextral, or sinistral slip. How long the ME has had the current state of stress is poorly understood, but several lines of evidence suggest a more significant episode of ENE/WSW compression in Late Eocene. First, Martin and VanArsdale (2017) report that displacement on eastern RFR margin faults changes from right-transtension to right-transpression in Late Eocene. Second, Vanderlip et al. (2021) describe compressional thrusting and folding on the eastern RFR margin that is constrained by stratigraphy primarily to Late Eocene. The thrust has 55 m of throw and a net slip of ~0.5 km. Third, the Kilmichael Structure (KS) in the eastern ME is stratigraphically constrained to the Late Eocene. The KS overlies the southern continuation of the NW-striking White River fault zone and has characteristics of a restraining bend uplift including reverse faults, folds, and large-scale sediment diapirs. Fourth, submarine mass wasting and sand intrusions record strong seismicity during Eocene in the SW ME. It is unclear how Late Eocene deformation in the ME is related to major tectonic events. Candidate events include the Laramide orogeny in the western US (but it was near its end) and the Middle/Late Eocene Cuba/Bahaman plateau collision.