The southern sub-Andean fold-thrust belt of Bolivia and northwestern Argentina is constructed from a ~10-km (~6-mi) thick stratigraphic pile of post-Ordovician to Neogene deposits that have been shortened above a detachment located in Silurian to Upper Ordovician horizons. Hydrocarbon accumulations in this fold-thrust belt include a variety of plays, with reservoirs ranging in age from Devonian to Neogene. Giant gas fields, however, are restricted to deep structures involving Devonian reservoirs. Exploration for this play relies on structural models, as seismic imaging is challenged by geological and topographical conditions.

Duplex systems seem to be the dominant thrust system type, including passive, active, and composite roof-thrust geometries. Pure structural wedges are common either in structural plunges or early stage structures. The main controlling factor for the development of duplexes and structural wedges is the presence of two major detachments, the basal detachment, mainly located along the Silurian Kirusillas Formation and the Devonian Los Monos Formation. Once duplex horses, or wedges, start developing in the lower structural level, the overpressured Los Monos Formation is passively uplifted and lithostatic pressure decreases. As this happens, the overpressure increases significantly, triggering pseudoplastic deformation within the Los Monos Formation, which results in the classic complexities of the southern sub-Andean belt.

Regional variations in the Silurian–Devonian stratigraphic package seem to be an important control on modes of deformation. Overall structural complexities in the lower structural level increase toward the most distal parts of the Silurian-Devonian basin, with additional detachments developed in the Icla Formation, and a marked decrease in the thickness and mechanical strength of the quartzite packages of the Devonian section. This results in complex and unpredictable trap geometries and a more challenging exploration for the deep plays.