SEDIMENTOLOGICAL RECOGNITION CRITERIA FOR CURRENT-WAVE-ENHANCED SEDIMENT GRAVITY FLOWS (CWESGFS)

Discoveries over the last ~ 20 years have demonstrated that if sufficient current and wave-orbital energies are present gravity flows can rapidly transport sediment across very low-gradient shelves (<12 m/km). These flows, termed current-wave-enhanced sediment gravity flows, or CWESGFs, play a key role in transporting large volumes of sediments offshore on low-gradient muddy shelves – a revelation that has important implications for how earth scientists interpret the muddy sedimentary record. Here we provide new sedimentological recognition criteria for CWESGF deposits by relating their formative hydrodynamics to their sedimentary products across the Southwest Louisiana subaqueous delta. We build on previous work from the Eel Shelf where the sedimentary structures produced by an ideal WESGFs were first described (basal crossbeds, intermediate planar interlaminations of clay and silt; topmost clay-rich drape). A new prismatic ternary diagram is introduced that visualizes how the overarching parameter wave period controls CWESGF stratigraphy. The combined effects of currents, gravity, wave orbital velocity, and wave period exert a strong control on CWESGF sedimentary fabric development. Together, these parameters can be used to construct a novel framework by which relationships among CWESGF formative conditions and subtle variations in the resultant sedimentary fabric may be further investigated. This framework also provides a tool which can be used, at least qualitatively, to help interpret the hydrodynamic conditions and better understand the environments of deposition of CWESGFs observed in the rock record. This is an important contribution as it may provide insights into paleo-depositional conditions represented by sedimentary structures in ancient fine-grained strata, and provide the basis for developing additional recognition criteria for CWESGFs, an important and diverse class of sediment gravity flows.