Relation of Halokinesis and Associated Faulting to Subsidence and Land Loss in the Chenier Plains, Cameron Parish, Louisiana

Abstract

The greatest threat to coastal Louisiana is land loss. The major contributing factor for land loss is the poorly understood process of subsidence. Subsidence, controlled by several integrated factors that exert feedback on each other, makes an unequivocal recognition of its causes challenging. This study focuses on the relationship between tectonics and land loss, specifically faulting and halokinesis. Previous studies have used surface data to show that active faults have a relationship to subsidence. However, they were focused on the Mississippi Deltaic Plain, an area strongly affected by Holocene sediment compaction associated with Mississippi River Delta deposition. This study focuses on the Chenier Plain of southwestern Louisiana, a micro-tidal coastline influenced by low energy waves, but not affected by the compaction processes of the Mississippi River. We use subsurface data to establish fault location and geometry within the study area. Expansion indices were calculated from the well logs to compare strata expansion (growth) on the hanging wall vs footwall of the faults. Growth seen in the hanging wall implies an active down slip motion along the fault leading to subsidence of the downthrown area. The subsurface investigation is compared to surface satellite imagery gathered from 1984 to 2022. The surface data shows that the area downthrown of the identified faults has subsided, and what was once occupied by marsh vegetation, is now occupied by a large water body supporting the hypothesis of tectonically controlled land loss. Thus, the results gathered from this methodology demonstrates that deep fault activity linked to salt tectonics is a leading factor contributing to coastal subsidence land loss in all areas of coastal Louisiana, even those not subject to the influences of recent Mississippi River deposition.