Facies Development of Atchafalaya Delta, Louisiana: A Modern Bayhead Delta

Early studies of Atchafalaya delta focused on large-scale characteristics of accretion in Atchafalaya Bay. This study concentrates on sedimentation processes and stratigraphic as well as plan-view facies development in a rapidly prograding bayhead delta. Since initiation of subaqueous delta growth (early 1950s), the bay has become shallower with accumulation of progressively coarser grained sediment. Stratigraphic relationships indicate a buildup from the pre-1950 bay bottom through prodelta, distal bar, distributary-mouth bar, levee, back-bar algal flat, and channel-fill deposits. At the present stage of delta development, two distinct processes of subaerial growth are recognizable. Initial growth relates to channel extension, bifurcation, and development of sinuous overbank channels. A later, more mature response of lobe fusion and upstream lobe growth becomes dominant as progradation through bifurcation diminishes in older areas of the delta. Atchafalaya delta growth to 1982 serves as a well-documented sedimentary example for understanding bayhead deltas, which commonly form in protected environments.