Outcrop 12. Tres Pasos Formation Mass Transport Deposit Topography, Sierra Contreras

Abstract

Abstract Outcrop accessibility: difficult Outcrop Coordinates: 50.8859°S, 72.6545°W Refer to outcrop 12 on location map At Sierra Contreras, deep-water slope depositional relationships between fine-grained mass transport deposits (MTDs) and overlying turbiditic sandstones can be assessed. The lateral continuity of sandstone-rich reservoir-scale bodies was dominantly controlled by original seafloor topography, related to the morphology of underlying MTDs. Overlying sandstone beds pinch-out and lap onto the relative topographic highs of the MTDs. Turbidite architecture evolves to more laterally continuous, sheet-like deposits as a result of depositional smoothing of MTD relief and diminished confinement (Shultz et al., 2005; Armitage et al., in press). Small-scale MTD topography, characterized by several meters of vertical relief, was associated with local pockets of accommodation where sands were ponded. These small-scale surface irregularities are inferred to have been associated with the rugose tops of viscous MTDs. Meso-scale MTD topography (10 to several 10s of meters relief) was created by coherent rafted sandstone blocks resting on top of, or within the upper portion of MTD deposits; it is onlapped by overlying sandstone beds. This topography can laterally compartmentalize significant packages of sandstone. The largest scale of topography identified (several hundred meters horizontally and vertically) resulted from individual mass-wasting events (e.g., outsized block emplacement) creating topographic relief at the time of deposition. Topographic features at this scale can laterally divide large-scale sediment gravity flow pathways, leading to significant compartmentalization of sandstone bodies. The size and abundance of rafted blocks in MTDs increases vertically in the outcrop suggesting