AN ANALYSIS OF WHETHER THE DEEP-SEATED MAGNOLIA GROWTH FAULT IN SOUTHEASTERN LOUISIANA HAS AFFECTED HOLOCENE STRATIGRAPHY AND GEOMORPHOLOGY

Growth faults in southern Louisiana are a fundamental structural element of the northern Gulf of Mexico Salt Basin and deep subsurface data shows that they have been locally active through much of the Cenozoic. The Magnolia fault is a down-to-the-south, deep-seated listric fault that terminates into salt diapirs at both ends. Previous work has suggested that the Magnolia fault has been recently active and caused rapid local subsidence and land loss in the Lake Hermitage area west of the Mississippi River in Plaquemines Parish, Louisiana. Evidence from oil and gas industry 3-D seismic data, well logs, and biostratigraphy indicates the fault has slipped intermittently since the Miocene with a clear increase in fault throw with depth as well as an expansion of stratigraphic intervals from the footwall to the hanging wall. Similar to other regional growth faults in southern Louisiana the upward, projected surface trace of the Magnolia fault spatially coincides with an abrupt, linear boundary between emergent wetlands and open water. To investigate whether a correlation exists between deep-seated growth faults and subsidence at this location, high-resolution near-surface geologic data was collected and analyzed in combination with existing deep subsurface data. Thirteen vibracores and 10 2-D Chirp lines were acquired across the projected surface trace to examine whether stratigraphic evidence exists indicating recent (Holocene) motion where the fault is projected to rise from the subsurface. Each vibracore was stratigraphically described in detail and a shallow chronostratigraphic framework is being constructed using radiocarbon dated material. A shallow litho- and chronostratigraphic framework should provide a clear indication of whether Holocene sedimentation patterns were affected by slip along the deep-seated fault.