Genesis of bedding-parallel gypsum veins (beef) in a tectonically relaxed basin: Insights from the Malargüe Group (Cretaceous-Paleogene), Neuquén Basin, Argentina

Abstract

We conducted a structural analysis of deformation structures developed in the Corral gypsum quarries, hosted within the Allen Formation (Malargüe Group; Cretaceous–Paleogene boundary) in the Neuquén Basin, Argentina. Our results reveal a diverse suite of deformation structures, including normal faults, bedding-parallel boudins and stylolites, and bedding-parallel gypsum veins (“beef”). From a geometric and dynamic perspective, bedding-parallel gypsum veins are not compatible with the development of normal faults (and related structures), highlighting the complexity of the governing mechanical processes. To explain their formation, we invoke three main sources of stress: gravitational (overburden loading), fluid overpressure, and, to a lesser extent, tectonic stresses. This framework allows us to account for the coexistence of normal faults and bedding-parallel gypsum veins in a tectonically relaxed basin. These processes might have act together producing cycles of faulting and formation of gypsum veins. Although this mechanism provides a plausible explanation for the observed structures, they should be regarded as a conceptual model that requires further testing in other evaporitic successions. Additionally, this case study highlights that evaporitic rocks, which commonly act as low-permeability barriers to fluid flow, may become mechanically compromised during the early stages of burial, with repeated cycles of fracturing and mineral sealing progressively modifying their geomechanical behavior.