May BRGS Meeting: Faulting in southeastern LA: its relationship to subsurface salt structures and expressions of these features in the coastal landscape

Join us Friday, May 9, 2025

as Dr. Nancye Dawers

presents

Faulting in southeastern Louisiana: its relationship to subsurface salt structures and expressions of these features in the coastal landscape

Abstract

The landscape of southeastern Louisiana is dominated by its low topographic relief and coastal wetland environments. Unique within this region is the area known as the Five Islands. Each of the “islands” is underlain by a pillar of diapiric salt that extends to the very near surface producing a topographic expression. From NW to SE these are: Jefferson Island, Avery Island, Weeks Island, Cote Blanche Island and Belle Isle. This presentation compares and contrasts these salt structures, and the subsurface and near-surface faulting that records their growth, with salt structures and faults underlying Terrebonne Bay.  In both Terrebonne Bay and the Five Islands, Neogene compression (through sediment loading) shortened the weak, viscous salt sheet. Belle Isle is used as a case study to show that this created salt ridges that helped initiate ascent of the diapirs. Patterns of wetland change may be affected by: depth to salt, the geometry of fault systems around and between salt structures, and whether the diapirs are still being sourced from a deep salt ridge. It may not be a coincidence that wetland gain in the Five Islands regions, i.e, at the Wax Lake delta, is occurring in close proximity to Belle Isle.

Biography

Nancye Dawers is a structural geologist in the Department of Earth and Environmental Sciences at Tulane University. She holds a PhD from Columbia University, an MS from the University of Illinois at Urbana-Champaign, and a BS from the University of Kentucky. Dr. Dawers joined the Tulane faculty in 2000; prior to that she was a Research Associate at the University of Edinburgh. Her interests range from brittle fault evolution to salt-fault interaction, and impacts of active subsurface geological processes on landscapes.