Role of Upper-Flow-Regime Bedforms Emplaced by Sediment Gravity Flows in the Evolution of Deltas

Abstract

Upper-flow-regime bedforms and their role in the evolution of marine and lacustrine deltas are not well understood. Wave-like undulations on delta foresets are by far the most commonly reported bedforms on deltas and it will take time before many of these features get identified as upper-flow-regime bedforms. This study aims at: (1) Providing a summary of our knowledge to date on deltaic bedforms emplaced by sediment gravity flows; (2) illustrating that these features are most likely transitional upper-flow-regime bedforms; and (3) using field case studies of two markedly different deltas in order to examine their role in the evolution of deltas. The study combines numerical analysis with digital elevation models, outcrop, borehole, and high-resolution seismic data. The Mazzarrà river delta in the Gulf of Patti, Italy, is selected to show that upper-flow-regime bedforms in gullies can be linked to the onset, growth, and evolution of marine deltas via processes of gully initiation, filling, and maintenance. Ice-marginal lacustrine deltas in Germany are selected as they illustrate the importance of unconfined upper-flow-regime bedforms in the onset and evolution of distinct delta morphologies under different lake-level trends.

Bedforms and sedimentary structures related to supercritical flows in glacigenic settings

“…If deposits of cyclic steps and antidunes occur in the same depositional system, cyclic-step wavelengths are one order of magnitude larger than antidune wavelengths (Fig. 12A), matching the results of numerical simulations by Kostic (2014) and Kostic et al (2019).…”

“…In glacilacustrine settings, very rapid high-magnitude lake-level falls may occur due to the opening of outlet channels (Winsemann et al, 2011(Winsemann et al, , 2018. The initial valley incision may relate to the formation of (neterosional) cyclic steps (Strong & Paola, 2008;Winsemann et al, 2011Winsemann et al, , 2018Muto et al, 2012;Kostic et al, 2019). Examples of such incised valleys related to lake-level falls include symmetrical to slightly asymmetrical bedforms (wavelength of ca 60 to 90 m) associated with isolated scour fills and interpreted as representing cyclic steps or antidunes (Winsemann et al, 2011(Winsemann et al, , 2018Kostic et al, 2019).…”

“…The initial valley incision may relate to the formation of (neterosional) cyclic steps (Strong & Paola, 2008;Winsemann et al, 2011Winsemann et al, , 2018Muto et al, 2012;Kostic et al, 2019). Examples of such incised valleys related to lake-level falls include symmetrical to slightly asymmetrical bedforms (wavelength of ca 60 to 90 m) associated with isolated scour fills and interpreted as representing cyclic steps or antidunes (Winsemann et al, 2011(Winsemann et al, , 2018Kostic et al, 2019). Scours infilled by gravelly backsets occur along erosional surfaces related to forced regression and point to deposition in the hydraulic-jump zone of cyclic steps (Fig.…”

Retreat Pattern of Glaciers Controls the Occurrence of Turbidity Currents on High‐Latitude Fjord Deltas (Eastern Baffin Island)

“…Cyclic steps are sediment waves that migrate upstream and are formed by turbidity currents that recurrently undergo hydraulic jumps (Kostic et al, ). These types of sediment waves are known to be present on active delta slopes (Clare et al, ; Fricke et al, ; Hughes Clarke, ; Kostic et al, ; Normandeau et al, ); their presence indicates active processes (e.g., Hughes Clarke, ; Normandeau et al, ; Smith et al, ). Therefore, the presence of sediment waves indicates that turbidity currents occur on the delta slopes (i.e., active deltas) although their frequency is unknown.…”

Towards adopting open and data‐driven science practices in bed form dynamics research, and some steps to this end

“…Bed forms are ubiquitous features in shallow and deep‐water environments, having a strong influence on flow properties, sediment transport, and biota distribution. They are also of great value for the interpretation of stratigraphic records, which are used as proxies for determining the nature, direction, and strength of palaeoflows (DeCelles et al ., 1983; Dasgupta, 2002; Kostic et al ., 2019). As such, a better understanding of their dynamics is of relevance for engineers, stratigraphists, geomorphologists, and planers (ASCE, 2002; Best, 2005).…”