--> Complexities of Submarine Channel Overbank Architectures as a Result of Simultaneous Activity Within Adjacent Channels: Example From the Modern Gioia Basin Turbidite System, Tyrrhenian Sea, Italy

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Complexities of Submarine Channel Overbank Architectures as a Result of Simultaneous Activity Within Adjacent Channels: Example From the Modern Gioia Basin Turbidite System, Tyrrhenian Sea, Italy

Abstract

Sediments deposited in overbank areas adjacent to submarine channels record the history of turbidity current activity within the channels. Overbank areas include levees, which decrease in height away from the channels that they confine, often with predictable thickness decay. The modern turbidite system in the Gioia Basin (Sicilian margin of the Tyrrhenian Sea, Italy) consists of three different levee-bound slope channels with separations up to 10 km. Two of these channels are sub-parallel while the third is roughly perpendicular to the others. We have used CHIRP sub-bottom profiles and multi-beam bathymetric data to interpret the distribution of near-surface acoustic facies across this part of the Sicilian margin. These facies have been mapped and calibrated using shallow cores (gravity, piston and box cores). The cores were correlated using sedimentary logs and magnetic susceptibility measurements. The integrated interpretation of the available data reveals complex geometries and facies relationships that would be difficult to identify in outcrop or the subsurface. The magnetic susceptibility measurements of the cores show that the upper five metres of sediment on the levees of two of the three channels have similar signatures. This indicates that these two channels have a similar record of activity, implying simultaneous turbidity currents in both channels. The acoustic facies distribution and bathymetry show interactions between overbank flow from the three separate channels. This interaction creates complex topography, including sediment waves and scours that modify the levee/overbank geometries, and divert sediment to depositional areas further from the channel. Further complexity is introduced where the levee of the third channel, which runs perpendicular to the other two, is filling one of the other channels. Sediment-draped abandoned channels and levees also occur in the overbank areas, adding further complexity. Modern seafloor data show the interactions between multiple synchronously active channels and their levees, and reveal how the architecture of levees may depart from established thickness decay models. Channels that are in close proximity but which are active at different times can add to the complexity of the stratigraphic record. Awareness of these potential complications is vital when interpreting subsurface data.