Kinematic Reconstruction of a Triassic Syndepositional Detachment Fault, Ischigualasto Provincial Park, Northwestern Argentina

Tony Albrecht
Miami University, Department of Geology
Oxford, Ohio
albrecal@muohio.edu

This project will document the deformation features and kinematic evolution of a Triassic-aged, shallow detachment fault preserved in the strata of the Ischigualasto Basin, NW Argentina. The Ischigualasto Basin is a continental back-arc rift in which > 4 km of fluvial and lacustrine strata were deposited. The Middle Triassic Los Rastros Fm. (230-233 Ma) is one of the primary stratigraphic units in the basin and consists of shallow lacustrine and fluvial deposits. The Los Rastros Fm. is overlain by fluvial deposits of the La Peña Mbr. of the Ischigualasto Fm. Detachment-related deformation features are exposed in both units in the Agua de la Peña Canyon. The detachment, ~15 km from the main basin bounding fault, is unique because it developed at shallow depths (< 30 m from surface). Paired extensional-contractional detachment systems are commonly associated with depositional loading and/or gravity gliding on basin-ward dipping horizons in passive margin strata, and are orders of magnitude larger. The principal process involved in the development of detachments is considered to be depositional loading or gravity gliding on low-angle, basin-dipping horizons, usually evaporites or over-pressured shales. Given the absence of evaporites, depositional loading and/or slip along an over-pressured horizon are the most likely causes of the detachment. This research will provide a small-scale analog for the kinematics of large-scale syndepositional detachment systems. Since there is no documentation of shallow detachments in rift basins, this project has the potential to break new ground regarding syndepositional deformation in extensional settings.