Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: Temporal evolution of sedimentation along an active margin

We present an integrated geochronological and sedimentological study that significantly revises the basin and magmatic history associated with lithospheric thinning in southern coastal Peru (15-18 degrees S) since the onset of subduction at similar to 530 Ma. Until now, estimating the age of the sedimentary and volcanic rocks has heavily relied on paleontologic determinations. Our new geochronological data, combined with numerous field observations, provide the first robust constraints on their chronostratigraphy, which is discussed in the light of biostratigraphical attributions. A detailed review of the existing local units simplifies the current stratigraphic nomenclature and clarifies its absolute chronology using zircon U-Pb ages. We observe that the Late Paleozoic to Jurassic stratigraphy of coastal southern Peru consists of two first-order units, namely (1) the Yamayo Group, a sedimentary succession of variable (0-2 km) thickness, with apparently. no nearby volcanic lateral equivalent, and (2) the overlying Yura Group, consisting of a lower, 1-6 km-thick volcanic and volcaniclastic unit, the Chocolate Formation, and an upper, 1-2 km-thick sedimentary succession that are in markedly diachronous contact across the coeval arc and back-arc. We date the local base of the Chocolate Formation, and thus of the Yura Group, to 216 Ma, and show that the underlying Yamayo Group spans a >110 Myr-long time interval, from at least the Late Visean to the Late Triassic, and is apparently devoid of significant internal discontinuities. The age of the top of the Chocolate Formation, i.e. of the volcanic arc pile, varies from similar to 194 Ma to less than similar to 135 Ma across the study area. We suggest that this simplified and updated stratigraphic framework can be reliably used as a reference for future studies. (C) 2013 Elsevier Ltd. All rights reserved.