Constructional process of relatively high-relief crescent-shaped bedforms in submarine channels by gravelly sand-laden flows: analysis of the ancient case study of the Guredin palaeo-bedforms

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Ramon Lopez Jimenez 


The channel-fills of the Miocene Alikayasi submarine channel system in the south of Turkey offer an extraordinary opportunity to improve our understanding of the physical properties of gravity-driven gravelly sand-laden flows and their resulting deposits on the seafloor. This study describes and analyses a particular area of an ancient channel-fill that is interpreted as the preserved deposits of relatively high-relief crescent-shaped bedforms consisting of conglomeratic sands (named the Guredin palaeo-bedforms). The mechanism of formation of these types of bedforms in submarine channel systems is largely speculative and normally explained by the ‘cyclic step paradigm’. A comparative analysis of the Guredin palaeo-bedforms with experimental flume studies and data from modern analogues supports a new model for the construction of relatively high-relief crescent-shaped bedforms. This model proposes the formation of this type of bedform as the result a two-stage process: 1) the formation of a crescent-shaped scour by an erosional hydraulic jump (from the abrupt transition from supercritical to subcritical flow regimes), and 2) the entry of a hyperconcentrated basal flow with a basal traction carpet, which develops a separation bubble in the scour that sorts out clasts and controls their deposition (creating the final dune-like crescent-shaped morphology). This new model deals with critical questions in the design of classification systems of bedforms for gravity-driven sediment-laden flows as well as with regard the dynamics and structure of the flow events that occur in submarine channels transporting gravelly sands.



Earth Sciences, Physical Sciences and Mathematics, Sedimentology


turbidites, Submarine channels, submarine canyon, bedforms, crescent-shaped bedforms, cyclic steps, gravity-driven flows, hydraulic jumps, knick-points, scours, sedimentary architecture, sediment-laden flows


Published: 2018-06-27 10:27


CC BY Attribution 4.0 International

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