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

Abstract

Mass transport deposits (MTDs) generate topographic relief on their upper surfaces. The scale and geometry ofthe topographic features, and the interconnectivity of their sediment fill plays a crucial role in defining thecharacteristics of associated turbidite reservoirs. Turbidite sands may be ponded in isolated depocenters createdby 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), thesand 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 datadifferentiate 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 thatlarger flows were able to over-run at least the saddles in the topography, with only a small portion of the flowbeing captured in each low. b) Overfilled section; consists of a laterally continuous sand interval that covers theshort-wavelength topography while progressively onlapping longer-wavelength (km-scale) features. Depositionalfacies may help to differentiate the confined/ponded stages, where local topography is still emergent, and thus toindicate the overall connectivity.