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

Abstract

[1] 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.

Sources of Terrestrial Organic Carbon in the Mississippi Plume Region: Evidence for the Importance of Coastal Marsh Inputs

“…Although the sources to Atchafalaya and Mississippi River plumes are very similar, the dynamics of fluid muds (fine-grained suspensions at a density [10 g L -1 ; (Allison et al 2000;Kineke et al 2006a;Jaramillo et al 2009) outside the Atchafalaya vs. mobile muds outside the Mississippi (Corbett et al 2004) may provide different transport regimes for the terrigenous material received on each shelf. Most of the terrestrially derived organic carbon in fluid muds is transported along the coast close to the shore west of the Atchafalaya River, as opposed to the broader distribution of mobile muds in the Mississippi River shelf-slope region.…”

Impact of Hurricane Katrina (2005) on shelf organic carbon burial and deltaic evolution

“…Further, this deflation by successive storms over decades, is likely a major factor generating retreat of inactive Mississippi deltaic lobe headlands. While winter cold-fronts likely contribute to this erosion on the shoreface (<10 m), significant wave heights (<1-2 m) during these events are generally too small to generate resuspension at greater depths [Jaramillo et al, 2009]. Assuming a conservative 2 cm average shelf surface erosional deflation caused by Katrina for the area from the shoreline to the seaward edge of the erosional hiatal surface (∼40 m water depth), and from Southwest Pass to the edge of our study area (∼90.0W) in Figure 1 (2600 km 2 ), sediment yield at 1825 kg/m 3 would be ∼95 million tons.…”

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…sediment motion threshold, leading to the thick foreset deposition ( Fig. 6b; Kuehl et al, 1986Kuehl et al, , 1997Driscoll and Karner, 1999;Hernández-Molina et al, 2000a;Walsh et al, 2004;Swenson et al, 2005;Puig et al, 2007;Jaramillo et al, 2009;Sheremet et al, 2011;Mitchell, 2012;Mitchell et al, 2012;Qiu et al, 2014).…”