Turbidite sands filling accommodation associated with supra-mass transport deposit topography: Outcrop examples from Western Argentina

Mass transport deposits (MTDs) generate topographic relief on their upper surfaces. The scale and geometry of the topographic features, and the interconnectivity of their sediment fill plays a crucial role in defining the characteristics of associated turbidite reservoirs. Turbidite sands may be ponded in isolated depocenters created by supra-MTD topography. The spacing and maximum thickness of ponded and isolated or tortuously interconnected sands are controlled by the dominant topographic wavelength and amplitude on the surface topography. Once the topography is filled to the saddles (the lowest point between adjacent topographic lows), the sand body forms a continuous sheet peppered with lacunae (‘holes’) marking the emergent heights (‘nunataks’). This is illustrated by confined turbidites over a 200-m thick MTD at Cerro Bola, Western Argentina. Field data differentiate ponded turbidites into a) Underfilled section; an isolated and laterally variable sand interval, confined by short-wavelength (tens to hundreds of meters) topography. Correlation of thicker beds suggests that larger flows were able to over-run at least the saddles in the topography, with only a small portion of the flow being captured in each low. b) Overfilled section; consists of a laterally continuous sand interval that covers the short-wavelength topography while progressively onlapping longer-wavelength (km-scale) features. Depositional facies may help to differentiate the confined/ponded stages, where local topography is still emergent, and thus to indicate the overall connectivity.