STRATIGRAPHY OF THE MIOCENE/PLIOCENE PISCO FORMATION IN THE PISCO BASIN, PERU

The vertebrate fossils and the geology of the Miocene/Pliocene Pisco Formation have been the subject of investigation for several decades. Paleontology work has focused on systematics and evolution, with recent investigation of the taphonomy of the abundant whales. The Pisco Formation and associated formations have been interpreted as a series of transgression/regression cycles in shallow bays. Geologic sections have been measured at various places, but there has been no published stratigraphy for the formation as a whole. We have measured a complete section through the Pisco Formation on the west side of the Ica River, from the vicinity of Yesera de Amara to Cerro Blanco and Cerro Ballena. Correlation between prominent outcrops and lateral correlation from the measured section was done by walking out marker beds. Tentative correlation was also made to the west, across the modern dune field to Dos Quesos and Cerro Queso Grande. The Pisco Formation in the Pisco Basin is about 640 m thick, and shows pronounced facies changes with a nearshore-offshore trend over a few km. This area in the Pisco Formation, with its fairly continuous outcrop and abundant marine vertebrate fauna, has considerable potential for study of faunal changes from Middle Miocene into Pliocene.