Sand pipes in eolian deposits as recorders of Andean deformation in the Miocene Angastaco Formation, northwest Argentina

Abstract

The aim of this paper is to describe and interpret clastic injectites structures recognized in the eolian deposits of the Tin Tin Member of the Angastaco Formation (Oligocene to Middle Miocene). The Angastaco Formation is part of the Andean foreland basin sedimentation in the Eastern Cordillera of northwestern Argentina. The structures appear in stratal intervals 4.8–8.6 m thick that are interpreted as fluvial-eolian and eolian environments. Clastic injectites are composed of sand pipes that pass upward to inverted cone, and clastic dikes. Synsedimentary faults and bending of laminae, as well as breccias, were observed associated with the clastic injectites. Sand pipes and clastic dikes are tentatively interpreted as the result of liquefaction and fluidization and upward injection of sediment that occurred during active migration of the dune field. Based on 1) vertical repetition of deformed intervals, 2) sedimentary structures comparable to those formed by liquefaction in recent earthquakes, 3) evidence for a shallow water table and for the active tectonism during deposition of the Angastaco Formation, we infer a seismic trigger for the formation of the sand pipes and clastic dikes.