Sedimentology and Stratigraphic Architecture of a Mass Transport Deposit Dominated Submarine Slope Environment: The Sierra Contreras, Tres Pasos Formation, Chile

Armitage, Dominic A.¹, Brian W. Romans¹ (1) Stanford University, Stanford, CA

The Cretaceous Tres Pasos Formation, Magallanes Basin, Chile, represents the deposit of a submarine slope system. The formation is approximately 1500 m thick where exposed in the Ultima Esperanza district of southernmost Chile and is characterized by a basal turbiditic sandstone. Restored orientations of flow structures display a north – south facies evolution. The lateral and vertical evolution of the proximal Tres Pasos Formation can be studied in the excellent outcrop exposures at the Sierra Contreras. The Sierra Contreras records the three-dimensional facies evolution and interaction of channelized to unconfined turbiditic sandstones and mass transport deposits.

Several architectural styles of conformable turbidite deposition over mass transport deposits are recognized at the Sierra Contreras. These are expressed by a lower MTD unit overlain by an infilling to amalgamating sheet-like lower sandstone unit. Stratigraphically above these lower sandstones is an upper MTD unit. Within this upper MTD is a listric failure plane defined by syn-sedimentary slumping that is overlain by confined to channelized turbiditic sandstones. A down dip evolution of the mass transport deposits can be traced along the west face of the Sierra Contreras from the listric failure plane showing a transition from slump to slide to flow.