Bottom currents, submarine mass failures and halokinesis at the toe of the Sigsbee Escarpment (Gulf of Mexico): Contrasting regimes during lowstand and highstand conditions?

In this study we explore the role of sediment supply, halokinesis and deep ocean circulation in promoting margin instability. The analysis was carried out on multibeam and high-resolution seismic data that allowed the imaging of mass failure deposits and current-driven depositional features along a portion of the lower continental slope and upper continental rise of the Sigsbee Escarpment (Gulf of Mexico). Different styles of deposition have been recognised during sea level lowstand (LST) and highstand (HST) conditions, due to alternating bottom current activity and salt tectonics. Lowstands are characterized by a reduced intensity of the Loop Current, as underlined by the lack of current-driven erosional features. On the contrary, highstands show a strengthened Loop Current that generates a fast bottom current circulation, as suggested by the presence of extensive furrow fields on the modern sea floor and on the Marine Isotope Stage 5e palaeo-sea floor horizon. Increased sediment load combined with changes in the intensity of deep water circulation are also responsible for the instability of the Sigsbee Escarpment, triggering mass failure phenomena with distinct morphology, size, location and timing of emplacement. Type 1 mass transport complexes (MTCs) form on the upper continental rise during sea level fall, and are genetically linked to the growth of deep water sediment drifts. Type 2 MTCs develop during sea level lowstands and originate along the slope of the Sigsbee Escarpment, triggered by oversteepening generated by halokinesis. Type 3 MTCs form during sea level rise to highstand conditions and mostly consist of debris flow deposits, generated in the lower portions of the Sigsbee Escarpment and then accumulated in the upper continental rise.