AN OUTCROP–BASED DEPOSITIONAL MODEL FOR A SUBMARINE SLOPE SYSTEM, MAGALLANES BASIN, SOUTHERN CHILE

Slope depositional systems are generally fine grained and ancient systems typically are very poorly exposed, therefore most depositional models for these systems are based on seismic studies and observations of modern systems. Interpreted photopanoramas and detailed measured sections from seismic-scale outcrop panels provide the database for interpretation of the Upper Cretaceous Tres Pasos Formation as a submarine slope depositional system, adding much needed outcrop data to complement seismic and modern studies. Overlain by deltaic shallow-marine deposits, this upward shoaling formation presents a relatively complete and well-exposed record of the last phase of deep-water deposition in Magallanes foreland basin, southern Chile. Stacked, laterally offset turbidite channel-fills are intimately related to thick, tabular sand packages occurring down depositional-dip. Many of these sandstone bodies directly overlie slump deposits tens of meters thick and are interpreted as fills of slide evacuation scars. At least two mass failure deposits are laterally continuous for up to 10 km, and are both eroded and onlapped by turbidite sand packages up to 60 m thick. These reservoir-scale outcrops provide explicit evidence for a close relationship between slope failure and sediment distribution, and serve as an excellent database for development of models for deposition on the slope. These models will be useful as analogs for current exploration plays in rapidly deposited, delta-fed slope systems such as the Niger delta.