none 10.1144/0016-76492007-039 Geological Society of London Geological Society of London 1881 34549850 44798 2024072301351900630 10.1144 2024-07-23T10:06:09Z 2008-10-21T17:55:07Z 17 Journal of the Geological Society JGS 0016-7649 2041-479X 10 12 2007 12 2008 165 6 LUCA RAGAINI Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria, 53, 56126 Pisa, Italy (e-mail: ) CLAUDIO DI CELMA Dipartimento di Scienze della Terra, Università degli Studi di Camerino, Via Gentile III da Varano, 1, 62032 Camerino (MC), Italy GINO CANTALAMESSA Dipartimento di Scienze della Terra, Università degli Studi di Camerino, Via Gentile III da Varano, 1, 62032 Camerino (MC), Italy Although results have been controversial, understanding the tropical Pacific climatic state during the Pliocene warm interval ( c . 4.5–3.0 Ma) is crucial if insight is to be gained into the dynamic processes of present and future global warming. In the multi-proxy effort to reconstruct ancient climates, a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature-sensitive marine molluscs. Shallow-water strata of the Mejillones Peninsula, northern Chile (23°S), contain dense faunal assemblages in which molluscs exclusive to, or characteristic of, Pliocene deposits ( Chlamys simpsoni , Chlamys vidali , Chorus blainvillei , Concholepas nodosa , Fusinus remondi , Herminespina mirabilis ) coexist with surprisingly abundant and varied populations of extant warm-water species ( Bulla punctulata , Cerithium stercusmuscarum , Olivella sp., Turbo cf. fluctuosus , Anomia peruviana , Argopecten ventricosus , Donax peruvianus , Dosinia ponderosa , Mexicardia procera , Undulostrea megodon ), most of which have their current southern zoogeographical limit at 6°S. These tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures (SST) along the northern Chile coast were at least 2 °C warmer in the mid-Pliocene than at present, and that these very different conditions lasted long enough to allow stable colonization of the area. 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