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3-D Seismic Interpretation and Geologic Evolution of an Intraslope Basin, Talara Basin, Deepwater Peru


The middle slope of offshore Peru (500 to 2000m water depth) consists of a series of intraslope basins filled with Eocene (?) deepwater deposits. The region has an especially complex structural and stratigraphic history during the Cenozoic. The basins vary in their structural styles, indicating complex tectonics likely associated with the Andean subduction. The Peruvian slope is a frontier exploration area with several major geologic structures with seismic flat spots and amplitude anomalies, indicating good exploration potential. The study focuses on one instraslope basin in the middle slope off northern Peru, which is an extension of the shallow-marine and continental world-class Talara Basin. Interpretation is based on 215 km2 of 3-D seismic data. The area consists of an extensional intraslope basin that forms a half graben, which is bounded to the east by a major north-striking normal growth fault and regional structural highs to the west and south. Three prominent anticlines trend W/NW within the basin, and each anticline has seismic flat spots, suggesting the presence of hydrocarbons in the area. The strata filling this basin represent mid-slope turbidite systems deposited within a confined basin during syndepositional growth on different structures. Eight major depositional sequences have been identified. Each sequence comprises a series of stacked channel-levee and lobe deposits that vary in thickness, and onlap onto local growing structural highs. The local paleo-bathymetric highs and lows all shifted position through time, indicating the syndepositional growth of the structures. The intraslope basin was primarily dextral (?) transtensional in nature during its evolution, but had, at least, two discrete phases of dextral (?) transpressional movement causing the structural inversion. Substantial deformation and complicated structural geometries result from the transpression. The three anticlines have stratal thickening at the apexes, indicative of inversion that occurred along listric décollement surfaces that present at different depths. The later structural inversion placed deepwater sands in the crest of the folds.