DETRITAL ZIRCON GEOCHRONOLOGY AS APPLIED TO THE EVOLUTION OF THE PETROLEUM-RICH TALARA BASIN, NORTHWEST PERU

Detrital zircon geochronology, a well-established technique in basin analysis, is recently showing applications to reservoir characterization. Uranium-lead ages obtained by single zircons help discriminate source terrane and tectonics as well as the timing and configuration of basin fill, all useful in predicting the quality of possible reservoirs. The Eocene stratigraphy of the petroliferous Talara Basin, in northwest Peru, records fluvial to deep-marine deposition into the Andean forearc. Subsidence of the basin in the lower and middle Eocene corresponds to high convergence rates between the Nazca and South American plates, and an abrupt deep-water event in the middle to late Eocene may signal a change in convergence direction. Volcanic activity is not well recorded in the basin, however, and the timing of uplift of the Amotape Mountains to the east, related to the nature of convergence, is also unconstrained. Detrital zircon geochronology of sandstones from five key formations throughout the sedimentary section helps to constrain both problems and to characterize non-Andean or non-Amotape sources that may have contributed to the Talara Basin. With the exception of the mid-stratigraphy Cabo Blanco Formation, all formations show a progressively younger suite of Tertiary zircons, indicating fairly continuous volcanic activity in that part of the Andes during the Eocene. There is a consistent volcanic/plutonic gap between 65-70 Ma, and post-Jurassic magmatism appears to begin at 90-95 Ma in the region. All formations tap source terranes containing abundant Paleozoic and Proterozoic zircons that fit established ages for the nearby Amotape and southwest Ecuadorian metamorphic terranes. There is no match between Talara zircons and Amazon craton ages, suggesting isolation of the forearc from the craton to the east throughout filling of the Talara basin. Finally, established depositional ages for both the Pale Greda and Verdun Formations will need to be revised based on the maximum depositional ages constrained by young detrital zircons.