Paleogene foreland basin in theValles Calchaquíes, NW of Argentina

FERNANDO HONGN; CECILIA DEL PAPA; JAIME POWELL; PATRICIO PAYROLA BOSIO; IVÁN PETRINOVIC; RICARDO MON

Cenozoic Geology of the Central Andes of Argentina

SCS Publisher

Lugar: Salta; Año: 2011; p. 189 - 209

Sedimentologic-stratigraphic, paleontologic and structural detailed surveys on the well-exposed Cenozoic successions of the Valles Calchaquíes region have revealed key features for understanding the Paleogene Central Andes evolution in NW-Argentina. Our work has documented several Eocene fossiliferous sections showing unconformable relationships with the underlying Salta Group and evidences of syndeformational deposition such as progressive unconformities (e.g. La Poma-Saladillo, Cerro Tin Tin, Luracatao). Our data along with those ones offered by other research-groups have sensibly incremented the Eocene foreland record, what displays some particular characteristics, among them: Most of the Paleogene faults were west- or bivergent, affected the Neoproterozoic-Lower Paleozoic basement defining a thick-skin deformation and followed a rather unsteady propagation path. Evidences of Eocene deformation and sedimentation indicate the Cenozoic shortening in NW-Argentina is older than supposed in classical proposals on Andean evolution proposing that crustal shortening was delayed until the Late Oligocene-Miocene due to southward deformation migration from the Peruvian and Bolivian Andes. Eocene deposits are analyzed in the foreland basin system framework. Basement blocks with different grades of exhumation compartmentalized the Eocene foreland thus it evolved as a broken foreland from its initial stages. Tectonic inversion and reactivation of both Lower Paleozoic basement heterogeneities and normal faults related to Cretaceous rift enhanced the definition of the broken foreland and retrovergent structures. The easternmore recognized Eocene structures (La Poma-Saladillo and Tin Tin) were west-vergent so that the Eocene deformation front should be even more eastward. The precise localization of this front is basic for assessing the eastward reach of the Eocene shortening and for determining if the Eocene deformation zones along the Puna and its transition to Cordillera Oriental form part of the wedge-top zone. The wedge-top zone is a rather particular one because of its wide (nearly 300 km from the Cordillera Domeyko till the Cordillera Oriental western border) and dominant west- and bivergent faults that in some examples (North Calchaquí and Luracatao valleys) can be preliminary interpreted as incipient intermontane basins. In the same way, the precise definition of the wedge-top will permit to explore and define the foredeep and forebulge areas.