The stratigraphic record of sediment gravity flow transformations in submarine slope settings

Sediment gravity flows are sensitive to changes in seafloor topography and substrate character. Flows in mud-prone submarine settings with inherited topography can undergo rapid and significant changes in character as cohesive forces increase relative to turbulent forces. The resulting flow transformations have been shown to generate distinctive deposits in distal submarine fan settings, which challenged existing models of sediment gravity flow processes. However, the present understanding of the stratigraphic distribution and lateral variability of flow transformation deposits in submarine slope settings remains poorly understood. This thesis presents new process-based conceptual models which account for different flow transformations in a variety of submarine slope settings. Outcrop, core, and photogrammetric model datasets from the Karoo Laingsburg depocentre (South Africa), the Peninsular Ranges Forearc (Mexico), and the Aínsa depocentre (Spain), reveal a range of bed types that record the evolution of flow transformations and complex interactions with different topographic configurations. Mixed grain-size bedforms demonstrate spatio-temporal flow transformations from turbulent to laminar states, and are common in incised slope valley-fills and canyon-fills, in terrace deposits and internal levées, and in channel mouth settings. The length scales of the bedforms point to rapid and abrupt flow transformations (100s of metres). These bedforms show that flow transformations and transitional flow behaviours can be used to support interpretations of submarine slope settings where abrupt losses in confinement, and/or changes in gradient, force flows to entrain mud and decelerate. Sand-rich hummock-like structures, and associated mixed grain-size bedforms, are interpreted as combined flow deposits, resulting from reflection, deflection and ponding processes, which can be used as a criterion to interpret flow confinement and the presence of erosional and depositional relief. The documented deposits of flow transformations characterise heterogenous successions that vary substantially with respect to slope position, degree of confinement and tectonic setting. Therefore, this work unlocks key insights into sediment gravity flow transformations and provides criteria to support palaeogeographic reconstructions, modelling hydrocarbon reservoirs and evaluating the potential for deep-water sediments to sequester pollutants and organic carbon.