Lower Jurassic deformation in the eastern Huincul High, Argentina

Abstract

Subsurface characterization of the structure and sedimentary sequences in the Agua del Cajón area was performed to understand the Lower Jurassic deformation across the eastern Huincul High. Integration of seismic, well data, and fossil fauna allowed establishing the Late Triassic rifting and Jurassic compressional evolution underwent for this area. Four Late Triassic - Early Jurassic extensional depocenters were recognized, being the most significant the Agua del Cajón and El Salitral depocenters. In general, all of them present an E-W to WNW-ESE orientation and are flanked by NNE to NE-trend transfer zones. The contractional structural style of the Agua del Cajón area consists of south-vergence reverse faults and folds with two primary trends: (i) E-W to WNW-ESE and (ii) NE-SW to NNE-SSW. According to the slip and uplift amount, the first-order structural feature in the study area corresponds to the S-verging, E-W Huincul fault. Geometries and patterns in the seismic reflectors evidence two compressional episodes from late early Toarcian to Callovian time. The first one is associated with the inversion of the previous master normal fault of the El Salitral and Agua del Cajón depocenters during the late early Toarcian. The inversion of the NE-SW synthetic normal fault associated with the El Salitral depocenter also occurred during the first deformation pulses favored by its perpendicular orientation to NW-SE Jurassic σ1. NE-SW fault associated with the Agua del Cajon inversion shows no evidence of inversion-related deformation mechanisms. Instead, the formation of this structure is related to the previous NE-SW transfer zone. After a tectonic quiescence period in late Toarcian – late Aalenian, the compressional activity continued during the late Aalenian and Bajocian evidenced by progressive unconformities into Jurassic sequences. This activity would have continued until Callovian times. These results are in agreement with previously reported evolution in the eastern-central Huincul High region. However, they indicate that the contractional intraplate deformation in the southern Neuquén basin would have begun during the late early Toarcian; this is older than previously proposed.