Abstract

Understanding the oceanographic and environmental changes experienced on the South American Pacific coast during the Plio-Pleistocene transition and the influence of these variations on the evolution of marine ecosystems is particularly interesting to assess the effects of current global climate projections. We present a stratigraphic model of the marine sedimentary successions exposed in Coquimbo (similar to 30 degrees S), northern Chile, supported by 22 numerical ages from the last 6 Ma obtained through Sr-87/Sr-86 dating of fossil mollusk shells. This stratigraphic model, and paleoecological and sedimentary facies analyses allow us to interpret the paleoenvironmental evolution and depositional dynamics in the basin. The marine successions accumulated in four sedimentation episodes: the first two on the shoreface during Messinian-Zanclean (similar to 6-5.10 Ma) and Zanclean-Piacenzian (similar to 4.23-3 Ma) ages, whereas the last two occurred mainly on the foreshore during middle Calabrian (similar to 1.15 Ma) and late Calabrian-Chibanian (similar to 0.83-0.25 Ma). The most significant taxonomic changes are observed in the transition between the Pliocene and Pleistocene deposits (similar to 3-1.15 Ma), reflecting the shift from faunal associations typical of warm-temperate waters to others of cool-temperate water preferences. The faunal turnover identified in this study correlates well with two climatic transition pulses out of three previously recognized in the southeastern Pacific Ocean for the Plio-Pleistocene: one during the Piacenzian-Gelasian (3-2.4 Ma), marked by a decrease in water temperature and an expansion of upwelling zones in the Humboldt Current System; and the other during the Gelasian-Calabrian (2-1.5 Ma), which has been linked to the establishment of the current El Nino Southern Oscillation (ENSO) climate system.