ABSTRACT The Santiago Basin of the northern Peruvian sub-Andes is a structurally complex region related to a combination of thin- and thick-skinned deformation and the impact of salt tectonics during Andean deformation. Oil shows in this basin are very common, and even though the first exploration campaigns started in the 1940s, no commercially exploitable hydrocarbons have been discovered yet. We present three basin-scale structural transects and refined structural interpretations, based on vintage 2-D seismic data and well tops that help elucidate the relationships between thin-skinned and deep-seated, thick-skinned structures. Two dip sections were kinematically restored to the top of the Yahuarango formation, one of the youngest pre-Andean units. We calculated the depth to the intra-basement detachment to be approximately 20 km (12 mi), a value that correlates with other thick-skinned detachments and earthquake hypocenters from the region. We recognized a varied inventory of salt-related structures, which we interpret to be part of the approximately 800-km (500-mi)-long Peruvian Salt Belt. The onset of salt movement occurred soon after salt deposition, likely through sediment loading. Our data suggest that Miocene-Pliocene basin deformation starting at 5.3 Ma has been sustained until the present-day. Shortening ranges from 7.31 km (4.54 mi) to 7.56 km (4.70 mi) (5.9% and 6.1%, respectively), corresponding to Miocene-Pliocene deformation rates of 1.3–1.4 mm/yr. These values are significantly lower than those of adjacent regions in the sub-Andes. This may be related to the combined effects of pressure solution, strain accommodation, or deflection by crustal-scale faults farther west.

ABSTRACT The quartz-rich sandstones of the Upper Cretaceous Vivian Formation constitute the most important reservoirs in the prolific Marañón foreland basin of northern Peru. The Vivian sandstones are largely fluvial in the northeast and transition to a marine shoreface and open shelf in the west. The formation consists of two sand-rich units (Lower and Upper Vivian) with better reservoir characteristics in the Lower Vivian. Porosity versus depth analysis for the dominantly fluvial Vivian sandstones shows a simple trend of decreasing porosity with depth, with facies-dependent variations for wave-reworked facies. This simple linear trend (correlation coefficient R2 > 0.77) indicates that overburden stress is the dominant factor that determines the porosity reduction. Further west, in the wedge-top Santiago Basin, the Vivian sandstones exhibit anomalously low porosities at relatively shallow depths, a distinct diversion from the regional trend. The depth difference between these low porosities and the porosities of the regional trend was used as a proxy for the uplift that the basin has suffered during the Andean deformation in the latest Miocene. The resulting values (up to approximately 2600 m [8530 ft]) are consistent with uplift estimates derived from other methods and suggest that parts of the foredeep have been partially uplifted.