Constraining the Formation of Submarine Gullies on Continental Slopes

Abstract:

Submarine gullies are ubiquitous on continental slopes and steep areas of seafloor worldwide, but their role in sediment transport remains unresolved. Direct observation of flows in the submarine realm is rare and expensive, but by analyzing basic geometries of gullies in the sedimentary record, it is possible to gain insight into the behavior of the flows that formed them. In shallow 3D seismic reflection data from the Taranaki Basin, New Zealand, we document gullies preserved in a Pliocene-Pleistocene progradational margin sequence. These gullies commonly form aggradational complexes hundreds of meters thick, showing alternating periods of erosion, inactivity, and roughly self-similar aggradation in response to slope sedimentation. Erosional phases speak of modification by energetic turbidity currents, whereas sediment drapes point to extended periods of flow quiescence and hemipelagic deposition.

We pair these observations with morphometrics of over 600 gullies in seafloor bathymetry from continental margins worldwide. The slopes of these modern gullies and interfluves are both well described by a power-law decay with along-profile distance. The decay of slopes with distance (concavity) obtained from power-law relationships for interfluves and gullies are well correlated, although gullies attain higher slopes and are slightly more concave than neighboring interfluves.

The self-similar growth of gullies in the subsurface and the strong similarity between gully and interfluve profiles in all datasets suggests a link between the evolution of gullies and of the slopes on which they form. We conclude by presenting a conceptual model in which gully and slope morphology are tightly coupled.