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The morphology and shallow structure of the Peru continental margin has been mapped using bathymetric and seismic reflection profiles from lat 6°S to 16°S. Other geophysical and geologic data are used to constrain interpretations of the margin’s deeper structure and to relate the offshore to the onshore Andean geology.

Two prominent structural ridges, subparallel to onshore Andean trends, control the distribution of the offshore Cenozoic sedimentary basins. The Coastal Cordillera, which surfaces north of lat 6°S and south of lat 14°S, can be traced onto the offshore as an Outer Shelf High (OSH); it is evidently cored with Precambrian and Paleozoic metasediments and crystalline rocks. A series of shelf basins is situated between the Coast Range/OSH and the Andean Cordillera: from north to south, these are the Sechura, Salaverry, and East Pisco Basins. A second set of upper-slope basins flanks the Coast Range/OSH to the southwest, limited seaward by an Upper-Slope Ridge (USR) of deformed sediment: from north to south, these are the Trujillo, Lima, and West Pisco Basins. The Yaquina Basin lies within divergent arms of the USR. The shelf and upper-slope basins are set on continental massif. An anastomosing network of elongate ridges and ponded sediments is the surficial expression of the subduction complex, which apparently begins just seaward of the USR.

The effect of the late Paleocene/Eocene Andean orogeny has been extrapolated offshore as a distinct interface of seismic velocity in the Salaverry Basin. Though Cenozoic marine sedimentation in the shelf basins did not begin until after this event, sedimentation in the upper-slope Trujillo Basin may have been more continuous through the early Tertiary. In the Trujillo Basin, the bulk of the nearly 4 km thick sedimentary section is of Paleogene age, while in the adjoining upper-slope Lima Basin to the southeast, the bulk of the nearly 2 km thick sedimentary section is of late Miocene or younger age. Apparently, post-Oligocene tectonism caused uplift, deformation, and a gross reduction of sedimentation in the Trujillo Basin; this event is evidenced by boundaries of differential structural deformation in seismic reflection profiles. In middle to late Miocene time, while orogenic activity affected the inland Andean Cordillera, the upper-slope Lima Basin subsided and began its depositional record. Unconformites in shelf basins apparently reflect the inland tectonism at this time.

The boundary between the Lima and Trujillo Basins, and between the contrasting styles of upperslope tectonic movement, is near lat 9.5°S, coincident with the present day intersection of the Mendaña Fracture Zone with the continental margin.

A final phase of upper-slope deformation closed the Pliocene. Like earlier tectonic activity, the major break in structural style of this epoch occurs near lat 9.5° S: compressional faulting and folding characterize the younger sediments of the Trujillo Basin, while the Lima Basin appears as a broad, open syncline, distrubed only in its southernmost occurrence.

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