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 tectonic evolution of the Marañón Basin and its related basins, the Huallaga and Santiago Basins, in northern Peru, spans more than 250 m.y. of Mesozoic–Cenozoic subsidence. Basin evolution began with an initial rifting in the Late Permian–Early Triassic. This period of extension was accommodated by inherited structural inhomogeneities and a southwest-oriented extension, which dissected the Paleozoic sequences into a series of roughly northwest-southeast-trending grabens and half grabens filled with volcanic and continental-derived sediments. Fault-controlled subsidence was followed by regional postrift subsidence, and a thick section of Triassic to Jurassic marine to transitional sediments was deposited over the preexisting extensional features. These included one of the potential source rocks for the western part of the basin (the Aramachay Formation). The Late Jurassic to Early Cretaceous Jurua orogeny and later peneplanation produced a major regional unconformity. Subsequent Cretaceous sedimentation, mostly controlled by eustatic processes and related regressive–transgressive cycles, is composed of a thick section of continental to proximal and shallow marine deposits, comprising the main reservoirs and the main source rock for the basin, responsible for most of the oil discoveries in the northeastern region. Several compressional and structural inversion episodes, related with the subduction of the Nazca plate in Late Cretaceous and that culminated in the Miocene, have modified the basin and isolated the Huallaga and Santiago subbasins to the west, both structured by complex thrust systems. Cenozoic deposits constitute the foreland basin system infill and contain more than 4000 m (13,120 ft) of mostly fluvial and deltaic deposits with minor marine incursions. In the sub-Andean zone they constitute the “molasses” from the rising Andean cordillera to the west. This history of tectonic evolution is reflected in a complex structural framework in the western part and a well-developed foreland system to the east with a broad topographic high, known as the Iquitos Arch, which corresponds to the present forebulge.