Comparative structural analysis of inverted structures in the San Bernardo fold belt (Golfo San Jorge basin, Argentina): Inversion controls and tecto-sedimentary context of the Chubut Group

Abstract

The Golfo San Jorge Basin is one of the most important hydrocarbon-bearing basins of Argentina. Its position in the distal Patagonian Broken Foreland confers a particular structural architecture. Specifically, the western margin was affected by positive tectonic inversion, with higher degrees of inversion at the San Bernardo Fold Belt (SBFB). This paper synthesizes the comparative structural analysis of outcropped and buried inverted structures in the SBFB. The study areas are regionally distributed, and the geometric characterizations integrate field structural data, topographic trends, cutting records, borehole logs, and 2D-3D seismic data. The geometries of the studied inversion folds are poorly vergent and can be classified as asymmetric anticlines or pop-up growth folds. The architecture of the inverted fault system shows: along-strike variability in reverse displacement, inherited extensional growth-strata, selective inversion, oblique inversion, and heterogeneous deformation. Pre-inversion major controls include: 1) an extensional network linked to the fabric of the pre-rift basement, 2) a non-coaxial extensional phase during the early Upper Cretaceous times, and 3) a basin-scale paleohigh of crystalline rocks located to the east of the SBFB. The kinematic analysis evaluates the timing of the tectonic inversion phase, which is actually under discussion. Our results are consistent with a tecto-sedimentary context dominated by normal fault reactivations during the deposition of the basal units of the Chubut Group (Barremian-Albian), and a reverse-reactivation during the record of the Laguna Palacios Formation (late Upper Cretaceous). The geometric-kinematic characterization of the inverted structures at the SBFB contradicts many of the evidence that supports recently proposed geodynamic models for the Cretaceous evolution of Southern Patagonia.