Evidence for Active Growth Faulting in the Terrebonne Delta Plain, South Louisiana: Implications for Wetland Loss and the Vertical Migration of Petroleum

Abstract

Two regional growth faults, the Golden Meadow Fault and the Lake Hatch Fault, were mapped in Terrebonne and Lafourche Parishes, Louisiana, utilizing over 3000 line kilometers of seismic data. The subcropping location of these faults identify major vegetation biozonations, new areas of wetland loss, and the position of transgressive lakes. The proposed mechanism governing these fault-related manifestations of subsidence involves the venting of fluid (and gas) from geopressured shales vertically up fault planes. Saline fluids and gases exiting a basin via growth faults provide accommodation space at depth, resulting in active, fault-induced subsidence in the down-thrown block. By contrast, areas along the fault trend where no fluids or gases were migrating would not result in an increase of accommodation space and would be considered inactive regarding faultinduced subsidence. The model that emerges is a growth fault trace that does not act in concert but more closely resembles a key-stepping system with sections alternating between active and inactive. These findings are relevant to the role of growth faults in subsidence-related coastal land loss and the vertical migration of hydrocarbons.