Did the huge (~1,000 km3) and relatively recent Massingill-Walker Slump come from the Mississippi Canyon or from very large slide scars on the NE Gulf of Mexico continental slope?

The Massingill Walker Slump is an extremely large (~1,000 km3) mass flow deposit in the NE Gulf of Mexico. The slump comprises at least two major lobes, and is overlain by only a few tens of centimetres of postglacial (Zone Z) hemipelagic drape. It is therefore a relatively recent feature. The slump is traditionally inferred to have originated in the Mississippi Canyon, based on a high backscatter trail that leads from the canyon mouth to the slump deposit [1]. Recent work has shown that the continental slope immediately above the slump contains several extremely large slide scars of unknown age [2]. Although available seismic data suggest that the slump deposit does not continue all the way to these scars, these slide scars represent a second potential source for the Walker-Massingill Slump. The most recent channel on the Mississippi Fan has been plugged by a debris flow deposit that is over 100 m thick in DSDP cores [3]. The distal parts of the most recent fan lobe contain thin debris flow deposits with a complex frond-like plan form [4]. This contribution will analyse the source and timing of the Walker-Massingill Slump, and how the slump is (or is not) related to the thick debrite that plugs the main fan channel and the thin debrites at the fan fringe. In the longer term, we hope that the Massingill-Walker slump can provide insight into the factors that trigger very large submarine landslides. The timing of ocean warming and rapid sediment loading was sometimes decoupled during the late Quaternary in the NE Gulf of Mexico. It may therefore be possible to constrain their relative importance for triggering very large slope failure in this location. [1] Walker, J.R., & Massingill, J.V., 1970, Slump features on the Mississippi Fan, northeastern Gulf of Mexico: Geological Society of America Bulletin, v. 81, p. 3101-3108. [2] McAdoo, B., et al., 2000, Submarine landslide geomorphology, U.S. continental slope. Marine Geology, 169, 103136. [3] Normark, W.B., et al., 1986, Summary of drilling results for the Mississippi Fan and considerations for applications to other turbidite systems, Initial Reports of the Deep Sea Drilling Project: v. 96, p. 425-436. [4] Twichell, D.C., et al., 1992, Characteristics of a sandy depositional lobe on the outer Mississippi fan from SeaMARC 1A sidescan sonar images. Geology. 20, 689692.