This study integrates the geological and geophysical data for Peru's Andean foothills to define the main structural features in the basement and the source of the gravity and magnetic anomalies. It also provides a regional structural interpretation and estimates the potential sedimentary thicknesses in the basins.

The Sub-Andean and foreland basins are the largest basins explored for oil in Peru, covering approximately 370,000 km², yet most of them remain frontier basins. This investigation is based on some of the most recent geological and geophysical data available in the area, including six gravity surveys, twelve aeromagnetic surveys, over 2,500 km of seismic reflection lines, geological information for 185 oil wells, electrical logs for 27 oil wells, and regional geology.

The seismic interpretation was based on the kink area balancing method and showed three types of structural styles: a) thin-skinned thrust faults in the foothills, b) basement-involved reverse faults in the Ucayali basin, and c) tectonic inversion in the foreland basins.

To obtain the maximum information from the potential fields, horizontal gradient, 3D Euler deconvolution, and analytical signal (not presented) in this study) techniques were applied to the data. Reduction to the pole and the equator were tested for the total magnetic field to reduce the low magnetic latitude problem. Downward continuation of the total field was applied before merging the data to minimize problems with differences in flight elevations.

Gravity anomalies delineate the boundaries of the basins and, in some cases, great intra basement igneous bodies. In areas with detailed gravity data, there is a good correlation between Andean structures and the gravity field. For instance, anticlines and salt diapirism can easily be identified with gravity in the Huallaga and Ucayali basins. This investigation also showed a higher linear correlation between depths to the top of the Cushabatay Fm. (Albian - Aptian) and residual gravity in the Maranon basin. In the foothills, low gravity anomalies correspond to higher sedimentary thicknesses or salt bodies. High relative gravity anomalies correspond to sequence repetition by thrust faulting and basement-involved thrusting.

The magnetic field correlates with early Paleozoic basement structures and contacts. In areas where the magnetic anomalies follow Andean structures, the basement controls the morphology of the Andean structures. High frequency anomalies are related to the Brazilian and Guiana shields, and low frequency anomalies to the Amazon basin. The magnetic lows in the southern area are related to basaltic sills and dikes, which have been observed along the rivers. Important basement contacts and faults were identified in the northern area using the Euler Deconvolution method.

Gravity and magnetic anomalies delineate important basement structures, including the Purus high, the Inuya-Jurua high, the Pisco-Jurua fault, the Contaya arch, and the Iquitos arch.