Bioturbation and event preservation in Mississippi Delta sediments following 2005 Hurricanes Katrina & Rita

The present paper examines the sedimentary record present in a modern system, the Mississippi River Delta, following the 2005 hurricane events: Katrina and Rita. The objective of this research is to determine the nature of event bed preservation in a modern sedimentary environment; as well as challenging the current ichnofacies models, usually based on ancient systems. The data used were X-radiographs of sediment cores retrieved by R/V Cape Hatteras in the Northern Gulf of Mexico, close to Southwest Pass within the Mississippi Delta System. The X-radiographed cores showed multiple hurricane event beds (tempestites) recorded in both cores examined, with several pulses of wave-enhanced sediment gravity flows (WESGFs). These WESGFs exhibit a tri-partite subunit assemblage, a consequence of the evolution of the hurricanes, that was previously described by Macquaker et al. (2010); and that correlates well with similar tempestites present in ancient deposits. Finally, the present paper describes a trace fossil assemblage that aligns with the newly suggested Phycosiphon ichnofacies (MacEachern and Bann, 2020), exhibiting Chondrites, Skolithos and Phycosiphon in beds of varying low to medium bioturbation indices, with some escape burrows. This line of evidence supports the affinity of Phycosiphon ichnofacies to supply-dominated prodeltaic shelves, with rapid and recurring high-deposition events that limit colonization, characteristics that define the Mississippi River Delta System.