Wave-mud interactions over the muddy Atchafalaya subaqueous clinoform, Louisiana, United States: Wave-supported sediment transport

Near-bottom fluid-mud layers were observed during two experiments conducted on the muddy Atchafalaya inner shelf (subaqueous clinoform), Louisiana, United States. On the face of the subaqueous delta (4-7 m water depth, first experiment) fluid-mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages, and supported by near-bed wave-induced turbulence. The layers are episodic (lifetime of 9-12 h), form prior to significant postfrontal settling of sediment in the overlying water column, and flow seaward (downslope) at about 5 cm/s. Farther westward on the delta front (finer grain size, with negligible sand or coarse silt content, second experiment), similar wave-supported fluid-mud layers are observed to last longer (>2 days), show weaker alongshore (westward) flow of about 1-3 cm/s. The results suggest a sequence of near-bed sediment transport processes, triggered by frontal swell activity (bed liquefaction, resuspension and advection, modulated by the bathymetric characteristics of the clinoform) that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas.