| Summary: | Hybrid event beds (HEBs) containing matrix (clay)-poor and overlying matrix-rich sandstone facies are increasingly recognised in deep-water systems and differ significantly from facies traditionally associated with sediment gravity flow deposition. HEBs are thought to reflect deposition from flows whose turbulence became increasingly suppressed due to the enrichment of cohesive clay within the flow. Conceptual and experimental work has stressed either the longitudinal or vertical redistribution of cohesive clay material within flows; resulting end-member models tend to envisage the development of discrete rheological zones along the flow vs. the progressive rheological evolution of the whole flow. HEBs are largely documented in the distal, unconfined regions of deep-water systems with only a few studies having considered their development in association with confining sea-floor topography. Prior to this work, no case studies existed from fully contained (ponded) basins. This work presents case studies of HEB-prone deep-water systems from unconfined(intra-Springar Sandstone, Norwegian Sea),confined (Mam Tor Sandstone and Shale Grit, N England and contained (Costa Grande Member, NW Italy) basins. Principal findings are: 1) Hybrid-flow development is complex in that a flow may become increasingly clay-rich and turbulence-suppressed in hindward regions whilst headward regions remain non-cohesive, and undergo downstream turbulence-enhancement driven by declining sediment concentration, 2) Styles of HEB suggest that flows can be characterised by both longitudinal and vertical redistribution of cohesive material, indicating that current models for hybrid flow are not mutually exclusive. 3) In confined or contained settings, HEBs are not always laterally-restricted or systematically variable in their depositional character with respect to confining topography as documented in previous studies. Thus, in topographically complex settings, confinement is not always the trigger mechanism for hybrid-flow development; prior development may occur in relatively distal confined settings where a greater flow run-out distance, and thus time for other mechanisms promoting flow transformation to operate, is achieved. 4) In contained settings complex patterns of flow expansion and confinement are interpreted to; a) prevent the development of slope-localised HEBs; and b) promote the development of relatively sandy HEBs.
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