Morphodynamics of Supercritical Turbidity Currents in the Channel-Lobe Transition Zone

Abstract

This study aims to resolve process-facies links at both bed and environmental scales for the channel lobe transition zone (CLTZ). Data comes from existing experimental and modern CLTZ studies and from new outcrop studies. The experiments show that the CLTZ architecture of supercritical turbidity currents is complex and different from their counterparts where flows are subcritical throughout. Supercritical CLTZ's are characterised by erosive channels formed by supercritical turbidity currents, by offset stacked lobes deposited from subcritical turbidity currents and by hydraulic jump related mouth bar deposits and upslope onlapping backfill deposits at the down slope end of the transition zone. Erosive channels and backfill features can be resolved by high resolution seismic data, yet evidence for supercritical flow must come from facies analysis of core data. Outcrop examples of the CLTZ from the Tabernas submarine fan (SE Spain) and the Llorenc ¸del Munt deep-water delta slope (N. Spain) are used to establish such links between seismic scale architecture and facies recognised in cores. The outcrops described here were mapped as transition zone, and show 100 m sized, spoon-shaped scours filled with sediment containing sandy to gravelly backsets up to 4 m in height. Their facies and architecture is indicative of deposition by hydraulic jumps, can be recognized from cores, and is a good proxy for further predicting CLTZ architecture constructed by supercritical turbidity currents.

Froude supercritical flow bedforms in deepwater slope channels? Field examples in conglomerates, sandstones and fine‐grained deposits

“…12 of Postma et al ., and fig. 47.4 of Postma et al ., ), where they are also interpreted as cyclic step deposits.…”

“…Paull et al ., , ) and along isolated volcanic islands (Babonneau et al ., ). Also, in ancient outcrops, abundant supercritical flow deposition has been linked to canyons on forearc continental margins (Ito et al ., ), canyon to channel‐lobe settings in tectonically active margins (Postma et al ., , ) and steep delta fronts (Massari, ; Lang & Winsemann, ; Fricke et al ., ). Modelling and experimental studies demonstrate that a slope steeper than 0·6 to 1·0° promotes turbidity currents to accelerate to supercritical flow (Komar, ; Pirmez & Imran, ; Sequeiros, ).…”

“…Understanding the occurrence of the erosive and powerful supercritical flows on deepwater slopes and sea floor is significant for risk mitigation on infrastructures, such as communication cables and production facilities for hydrocarbons (Barley, ; Hsu et al ., ; Hughes Clarke, ). Recognition of supercritical flow deposits has implications for the hydrocarbon reservoirs themselves, due to the distinct lithofacies distribution, depositional geometries and architecture discussed in this paper (see also Postma et al ., , , ; Spinewine et al ., ; Postma & Cartigny, ). Further distinction is likely to be caused by elevated avulsion rates (Hoyal & Sheets, ; Hamilton et al ., ).…”

“…From outcrop observations, tens of centimetres to tens of metres scale sedimentary structures and geometries have been interpreted as supercritical flow sedimentary structures in alluvial to deepwater settings, such as in slope to basin floor turbidite systems (e.g. Walker, ; Postma et al ., , , ; Ito et al ., ; Postma & Cartigny, ), glacial settings (e.g. Russell & Arnott, ; Duller et al ., ; Lang & Winsemann, ), deltas (Massari, ; Ventra et al ., ) and variable discharge fluvial systems (e.g.…”

Submarine Mass Movements and Their Consequences: Progress and Challenges

“…Outcrop investigations provide detailed insight into the kinematics (Ogata et al 2016) and internal mixing and structure (Sobiesiak et al 2016) of MTD. Sympathetic to these approaches are fine-scale sedimentological studies that provide a modern context of present day seafloor processes (Postma et al 2016;Sawyer and Hodelka 2016). The link between onland outcrop studies of MTD and detailed marine studies is one that deserves to be strengthened given the benefits of cross pollination between these disciplines.…”