Hydrodynamic controls on muddy sedimentary-fabric development on the Southwest Louisiana subaqueous delta

This study examines the sedimentary products of current-wave-enhanced sediment gravity flows (CWESGFs) on the muddy Southwest Louisiana (SWLA) subaqueous delta where the combined effects of gravity, currents, and wave orbital velocity exert a strong control on sedimentary-fabric development, and contribute to development of a muddy inner-shelf clinothem. CWESGF microstratigraphy from the SWLA subaqueous delta displays an overall structure similar that is similar to the tripartite layering of WESGFs previously documented on the Eel Shelf, where wave-enhanced sediment gravity flow deposits were first described (basal crossbeds, intermediate planar interlaminations of clay and silt; topmost clay-rich drape). However, on the SWLA subaqueous delta, a shorter wave period appears to impart more rapid alternations in turbulent and laminar conditions than for the Eel shelf, reducing the prominence of the intermediate planar laminations that are thought to develop during laminar flow conditions only. A novel framework for relating the sedimentary products of CWESGFs to interacting unidirectional, wave-driven, and gravity-driven flow is used to place our results in a global context, with respect to other modern examples. This is an important contribution as it may provide insights into paleo-depositional conditions represented by sedimentary structures in ancient strata, and provide the basis for developing additional recognition criteria for CWESGFs, an important and diverse class of sediment gravity flows.