The Tres Pasos Formation, Chilean Patagonia: An Ancient Outcropping Slope Succession with Analog value for West African Slope Reservoirs

Michael R. Shultz
Chevron Texaco ETC, San Ramon, CA

The Upper Cretaceous Tres Pasos Formation, Magallanes Basin, southernmost Chile and Argentina represents the deposit of an ancient mixed-load slope depositional system. Regionally, the formation is characterized by a basal turbiditic sandstone unit up to two hundred meters thick overlain by up to one kilometer of mass transport complexes and concordant shale punctuated by channelized and sheet-like turbiditic sandstone units. Multiple scales of synsedimentary stratal failure, both catastrophic (slumping) and prolonged (growth faulting), lead to the development of complex slope topography that exerted a primary control on coarse-grained sediment dispersal networks, and deposition and preservation of sand-rich turbidite facies. Seismic-scale outcrop exposures of both fine- and coarse-grained strata allow for documentation of architectural relationships between stratal failure, associated mass transport complexes, and turbidite sandstone bodies (both channelized and sheet-like). Features exposed in the Tres Pasos Formation that make it a promising interval from which to derive outcrop analog information for west African slope petroleum reservoirs include: (1) sand-rich turbidite infill of slope topography created by catastrophic stratal failure; (2), ponding of turbidite sandstone bodies in growth fault-bounded slope mini-basins and thrust-fault (toe-thrust?) piggyback basins, and (3) control of mass transport complexes on turbidite channel-fill location and facies.