LATITUDINAL CHANGES IN THE MORPHOLOGY OF SUBMARINE CHANNELS: REEVALUATING THE EVIDENCE FOR THE INFLUENCE OF THE CORIOLIS FORCE

Published in "Latitudinal Controls on Stratigraphic Models and Sedimentary Concepts", SEPM Special Publication 108, September 2017, DOI: 10.2110/sepmsp.108. 02. Accompanying data and code available at https://github.com/zsylvester/channel_sinuosities. Abstract Using a script that automatically calculates sinuosity and radius of curvature for multiple bends on sinuous channel centerlines, we have assembled a new data set that allows us to reevaluate the relationship between latitude and submarine channel sinuosity. Sinuosity measurements on hundreds of channel bends from nine modern systems suggest that there is no statistically significant relationship between latitudinal position and channel sinuosity. In addition, for the vast majority of submarine channels on Earth, using flow velocities that are needed to transport the coarse-grained sediment found in channel thalwegs, estimates of the curvature-based Rossby number are significantly larger than unity. In contrast, low flow velocities that characterize the upper parts of turbidity currents in submarine channels located at high latitudes can easily result in Rossby numbers of less than one; this is the reason why levee deposits are often highly asymmetric in such channels. However, even in channels with asymmetric levees, the sinuosity of the thalweg is often obvious and must have developed as the result of an instability driven by the centrifugal force. Analysis of a simple centerline-evolution model shows that the increase in channel curvature precedes the increase in sinuosity and that low sinuosities are already associated with large curvatures. This suggests that the Coriolis effect is unlikely to be responsible for the low sinuosities observed in certain systems.Keywordssubmarine channels, Coriolis force, sinuosity, curvatureIntroduction Submarine channels are common—and often beautifully sinuous— geomorphic features of the Earth’s seafloor that serve as important conduits of sediment transport from rivers and shallow water to the continental slope and basin floor. In addition to their role in the large- scale redistribution of clastic sediment, they often correspond to locations of thick and relatively coarse-grained accumulations that can host commercially significant hydrocarbon reservoirs. Ever since it was recognized that these features exist \citep{Henry_W_Menard_Jr_2__1955} and that their planform patterns can be remarkably similar to the meandering shapes familiar from rivers \citep{Damuth_1983,Clark_1992} the assumption has been that the relevant physical processes are fundamentally the same across the globe and, therefore, there is no need for facies and architecture models of submarine channels that are specific for different latitudes. This line of thinking has been challenged by \citet{Peakall_2011}, who have looked at the relationship between submarine channel sinuosity and latitude and suggested that channels closer to the poles had lower peak sinuosities. They concluded that this is largely due to the Coriolis force having a stronger influence at high latitudes. Experimental work relying on a rotating flume tank showed that at low Rossby numbers (that is, when the Coriolis force is larger than the centrifugal force) turbidity currents do behave differently from the conventional model \citep{Cossu_2010,Cossu_2010a,Cossu_2012}. Building on these and similar experimental results, \citet{Cossu_2015} proposed that channel systems of the Cretaceous Cerro Toro Formation, exposed in southern Chile and deposited at high paleo latitude, display low sinuosity and an asymmetric stratigraphic structure due to the Coriolis effect.In a comment on the \citet{Peakall_2011} study, we have presented evidence that the apparent pole-ward decrease in submarine channel sinuosity is unrelated to the Coriolis force \citep{Sylvester_2013}. In the present article we expand on these ideas and present additional analysis (1) of an improved and more consistent channel sinuosity measurement and (2) of the magnitude of different forces as a function of channel size and flow behavior. In addition, we briefly discuss the impact of the Coriolis effect on overbank deposits, which is an important latitudinal effect in these systems.