Relationships Between Channel Hydraulics and Lobe Geometry on Experimental Submarine Fans

Abstract:

Submarine fans are complex sea-floor landforms built over a variety of time and space scales from turbulent instability on the low end up to basin-scale filling on the upper end. The intervening intermediate scale is often a source of eventual lithologic heterogeneity as many depositional lobes are built through time and space as building blocks for the larger landform. Here we take an experimental approach toward investigating submarine fan evolution and the preserved architecture by addressing the question: What is the relationship between the formative hydraulics and preserved sedimentary product of intermediate-scale, i.e., avulsion-scale, features? Experiments offer the ability to dictate boundary conditions as well as monitor the evolution of the flow field, here through image-based particle tracking techniques, and of the sediment bed. Our experimental approach consists of using saline density currents with crushed melamine plastic sediment to build submarine fans with supercritical distributaries. These fan systems experience avulsion cycles characterized by: (1) channel incision and basinward extension, (2) channel stagnation and lobe aggradation, (3) hydraulic jump formation upstream of the lobe that then retreats updip, and (4) flow avulsion. Hydraulic jump formation is an important part of these cycles in that the jump region becomes a significant locus of deposition. We found there exists a relationship between the upstream hydraulic properties, namely the denismetric Froude number, and depositional lobe thickness. This occurs because of consistent relationships between Froude number and the sequent depth ratio. This also leads to other relationships in the planform that can be tied to hydraulic variables. In this way there exists the potential to invert upstream hydraulic data from preserved depositional features created within avulsion cycles.