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Reconstructing Turbidity Current Processes During Submarine Slope Channel Evolution; An Integrated Experimental and Field Approach

Abstract

Submarine channel complexes may form significant sandstone bodies in the subsurface, which often have a complex architecture. Channel elements constitute the infill of submarine channels and form the building blocks of these channel complexes. The formation of a channel element starts with channel inception either by erosion or by deposition of confining topography, followed by infill and abandonment. A set of experiments was conducted to replicate the described life cycle and to monitor the flow conditions during this process. We present experiments of sand-laden turbidity currents, which flowed out on an unconfined slope. The flows were monitored using UVP sensors while the deposit geometry was mapped with a laser scanner. The deposits were sampled along the flowlines, as well as perpendicular to flowlines to uncover grain size partitioning of the coarse and fine-grained load as the flows evolved down-dip and differentiated laterally. The results show interaction between the evolving substrate morphology and the measured turbidity currents. In proximal locations, an initial phase of erosion results in the formation of a slope channel. The relief associated with this channel was enhanced by simultaneous aggradation of downslope elongated ridges which resembled levees. In more distal positions, channel inception took place through aggradation of levees laterally to a by-pass pathway. The relief created resulted in the focussing of currents as was shown by increase of axial and decrease of off-axis current velocities trough time. The decrease in off-axis current velocity was associated with increasingly fine-grained deposition and decrease in deposition rates on the levees. Deposition within the channel was rapid and limited to the final stage of evolution when basin-floor lobe deposition migrated upslope and backfilled the channel. A comparison between the experimentally created channel elements can be used to relate deposit geometry and facies to properties of the depositing currents. This may, in turn, allow inversion of flow properties from natural deposits. If successful, such a reconstruction enables a process-based prediction of lateral and downdip architecture and facies variability of channel-fill deposits. We have chosen the slope channels of the Chilean Tres Pasos slope system as a test case for the hypotheses formed in the laboratory. Preliminary results of the comparison between these natural and the experimental deposits will be shown.