Trench-forearc interactions reflected in the sedimentary fill of Talara basin, northwest Peru

ABSTRACT Exceptional exposure of the forearc region of NW Peru offers insight into evolving convergent margins. The sedimentary fill of the Talara basin spans the Cretaceous to the Eocene for an overall thickness of 9000 m and records within its stratigraphy the complicated history of plate interactions, subduction tectonics, terrane accretion, and Andean orogeny. By the early Tertiary, extensional tectonism was forming a complex horst and graben system that partitioned the basin into a series of localized depocentres. Eocene strata record temporal transitions from deltaic and fluvial to deep‐water depositional environments as a response to abrupt, tectonically controlled relative sea‐level changes across those depocentres. Stratigraphic and provenance data suggest a direct relationship between sedimentary packaging and regional tectonics, marked by changes in source terranes at major unconformities. A sharp shift is recognized at the onset of deepwater (bathyal) sedimentation of the Talara Formation, whose sediments reflect an increased influx of mafic material to the basin, likely related to the arc region. Although the modern topography of the Amotape Mountains partially isolates the Talara basin from the Lancones basin and the Andean Cordillera to the east, provenance data suggest that the Amotape Mountains were not always an obstacle for Cordilleran sediment dispersal. The mountain belt intermittently isolated the Talara basin from Andean‐related sediment throughout the early Tertiary, allowing arc‐related sediment to reach the basin only during periods of subsidence in the forearc region, probably related to plate rearrangement and/or seamounts colliding with the trench. Intraplate coupling and/or partial locking of subduction plates could be among the major causes behind shifts from contraction to extension (and enhanced subduction erosion) in the forearc region. Eventually, collisional tectonic and terrane accretion along the Ecuadorian margin forced a major late‐Eocene change in sediment dispersal.