Plio–Pleistocene water cooling in the southeastern Pacific Ocean: Insights from paleoecology, marine sedimentary facies analysis, and Sr isotope stratigraphy at Coquimbo (∼30°S), Chile

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 (∼30°S), northern Chile, supported by 22 numerical ages from the last 6 Ma obtained through ⁸⁷Sr/⁸⁶Sr 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 (∼6–5.10 Ma) and Zanclean–Piacenzian (∼4.23–3 Ma) ages, whereas the last two occurred mainly on the foreshore during middle Calabrian (∼1.15 Ma) and late Calabrian–Chibanian (∼0.83–0.25 Ma). The most significant taxonomic changes are observed in the transition between the Pliocene and Pleistocene deposits (∼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 Niño Southern Oscillation (ENSO) climate system.