Synsedimentary broken‐foreland tectonics during the Paleogene in the Andes of NW Argentine: new evidence from regional to centimetre‐scale deformation features

Abstract

Unravelling the spatiotemporal evolution of the Cenozoic Andean (Altiplano-Puna) plateau has been one of the most intriguing problems of South American geology. Despite a number of investigations, the early deformation and uplift history of this area remained largely enigmatic. This paper analyses the Paleogene tectono-sedimentary history of the Casa Grande Basin, in the present-day transition zone between the northern sector of the Puna Plateau and the northern part of the Argentine Eastern Cordillera. Our detailed mapping of synsedimentary structures records the onset of regional contractional deformation during the middle Eocene, revealing reactivation of Cretaceous extensional structures and the development of doubly vergent thrusts. This is in agreement with records from other southern parts of the Puna Plateau and the Eastern Cordillera. These observations indicate the existence of an Eocene broken foreland setting within the region, characterized by low-lying compressional basins and ranges with spatially disparate sectors of deformation, which was subsequently subjected to regional uplift resulting in the attainment of present-day elevations during the Neogene.

Miocene to Quaternary basin evolution at the southeastern Andean Plateau (Puna) margin (ca. 24°S lat, Northwestern Argentina)

“…Accordingly, between <14.5 Ma and >12.4 Ma, the Los Patos Conglomerate was deposited on an erosional palaeotopography carved into the underlying, deformed Palaeocene units of the Salta Group (del Papa & Petrinovic, ). Outcrops of the Middle Eocene Casa Grande Formation (reviewed in Montero‐López et al., ) near the eastern margin of the SAC area (along the Muñaño Fault) document a depositional environment in this region at least until the Middle Eocene and consequently imply a hiatus between both units of up to 23 Myr. This setting requires that the Early Miocene SAC area – similar to the neighbouring Pastos Grandes Basin in the south or the Salinas Grandes and Casa Grande basins in the north at that time – was still part of a fluvially connected and externally drained broken foreland system that did not promote deposition in isolated basin centres as observed today (Montero‐López et al., ).…”

“…Following Cretaceous‐Early Palaeogene extension and thermal subsidence, associated with the deposition of the Salta Group (Marquillas, del Papa, & Sabino, ), sedimentation in the region of the present‐day SAC area resumed during the Late Eocene with sands and conglomeratic redbeds of the Casa Grande Formation (Hongn et al., ; Montero‐López, del Papa, Hongn, Strecker, & Aramayo, ; Steinmetz & Galli, ). These beds were most likely deposited in a fluvially connected, but largely broken foreland basin related to spatially distributed surface uplifts that mark the onset of Andean shortening in an area that includes the present‐day eastern Puna Plateau margin (del Papa et al., ; Hongn et al., ; Jordan & Alonso, ; Montero‐López et al., ; Payrola, Powell, del Papa, & Hongn, ; Steinmetz & Galli, ).…”

“…Following Cretaceous‐Early Palaeogene extension and thermal subsidence, associated with the deposition of the Salta Group (Marquillas, del Papa, & Sabino, ), sedimentation in the region of the present‐day SAC area resumed during the Late Eocene with sands and conglomeratic redbeds of the Casa Grande Formation (Hongn et al., ; Montero‐López, del Papa, Hongn, Strecker, & Aramayo, ; Steinmetz & Galli, ). These beds were most likely deposited in a fluvially connected, but largely broken foreland basin related to spatially distributed surface uplifts that mark the onset of Andean shortening in an area that includes the present‐day eastern Puna Plateau margin (del Papa et al., ; Hongn et al., ; Jordan & Alonso, ; Montero‐López et al., ; Payrola, Powell, del Papa, & Hongn, ; Steinmetz & Galli, ). Further insights regarding the earlier morphotectonic evolution of the region comes from thermochronological and tectono‐sedimentary studies, which have shown that most of the SAC‐bounding ranges experienced exhumation, deformation, and presumably to some degree surface uplift during Middle Eocene to Early Oligocene times (Andriessen & Reutter, ; Deeken et al., ; del Papa et al., ; Hongn et al., ; Letcher, ; Payrola et al., ; Pearson et al., ; 2012).…”

Fracture network analysis of Yacoraite Formation in the Tres Cruces sub-basin, northwestern Argentina

“…Although some controversy persists regarding the beginning of the formation of the Andean foreland basin, several studies suggest that deformation has been propagating eastward in pulses since at least the middle Eocene (e.g. Salfity and Marquillas, 1994;Oncken et al, 2006;Hongn et al, 2007;Payrola et al, 2009;Montero-López et al, 2018).…”

“…The Eocene contractional phase is widely recognized in the Puna/southern Altiplano, the Eastern and Western Cordilleras, where it represents the first stage of Andean short-ening (Coutand et al, 2001;del Papa et al, 2004;Elger et al, 2005;Hongn et al, 2007;Oncken et al, 2006;Payrola et al, 2009;Montero-López et al, 2018). The principal event involving shortening and uplift in Central Andes occurred during the Miocene (Oncken et al, 2006;Payrola et al, 2009).…”