Oligo-Miocene sedimentary and tectonic evolution of the northeastern sector of the Ñirihuau Basin, North Patagonian Andes

SANTONJA, CAMILA; BECHIS, FLORENCIA; SURIANO, JULIETA

New Delhi

Congreso; 36th International Geological Congress; 2022

The Ñirihuau basin is located between 41° and 43° S at the eastern side of the Patagonian Andes. Its filling consists of a thick sequence of Oligo-Miocene volcanic rocks (Ventana Formation) followed by Miocene volcaniclastic, clastic and carbonatic, mainly continental rocks (Ñirihuau and Collón Curá Formations). There is no generalized consensus about the origin of the basin. Some authors mentioned it as a typical foreland basin, others assigned a transtensional origin (pull-apart basin), or an extensional origin followed by a compressive regime.Its infill in the northeastern sector records, in the Ñirihuau Formation, the transition of different tectonic regimes. Based on a paleoenvironmental and provenance analysis performed on this unit along a section that follows the Las Bayas creek, and taking into account the regional geologic characteristics and the structural features that characterized the study area, we propose a model for the evolution of this basin sector, identifying the synrift, sag and foreland basin stages.The unit starts with very coarse alluvial deposits which rapidly pass into lacustrine facies with extensional synsedimentary features, representing synrift deposits and the later sag stage. Towards the top of the unit, there is a big change in sedimentation with the sudden development of high energy sandy fluvial systems. This forced regression is interpreted as the beginning of the foreland basin stage, with the uplift and deformation of the fold and thrust belt to the west. This tectonic switching is also marked by the changes in the provenance sources and supported by structural data. (Abstract No: 8305-7485)