Abstract

The subaqueous muddy clinoform located on the southwest Louisiana shelf is known to be deposited under the combined influences of high sediment supply from the Atchafalaya River and local hydrodynamic conditions. Using high-resolution swath sonar survey and sediment core data (²¹⁰Pb radiochemistry, grain size, and x-radiography) we examined the sedimentological character and clinoform mechanics that (1) operate to maintain equilibrium clinoform morphology; and (2) operate on the foreset beds, influencing long-term clinoform progradation. Our results indicate that the sedimentological characteristics of the southwest Louisiana clinoform are broadly consistent with other subaqueous deltas found on shallow continental shelves (e.g., Amazon and Gulf of Papua). On many of these other systems however, sediment transfer between the topset and foreset regions of the clinoform is thought to primarily occur through the action of hydrodynamic fluid-mud flows. While these types of flows do operate in our study area we also observe widespread low-gradient mass-failure events which are evidenced by scarping and channels visible on the seabed. This previously unexplored mechanism appears to be important for explaining the rapid transfer of large volumes of riverine-derived sediment to the southwest Louisiana clinoform foresets and as well as for maintaining equilibrium clinoform morphology.