Neogene calcareous nannofossils: western Mediterranean biostratigraphy and paleoclimatology

Abstract

Six sites (974–979) in the western Mediterranean were investigated during Leg 161. Calcareous nannofossils are mostly abundant and well preserved in sediments recovered at all six sites, allowing detailed stratigraphic resolution. The Neogene intervals cored in Holes 974B and 975B range from upper Miocene (Messinian; Zone NN11) to upper Pliocene (Gelasian; Zone NN19A). In Hole 976B, the Neogene sequence cored ranges from middle Miocene (Serravallian; NN7) to upper Pliocene (Zone NN19A). A disconformity exists in the upper Miocene (indicated by the absence of Zones NN9 and NN10) and in the Pliocene (indicated by the absence of Zones NN13–NN17). The Neogene stratigraphic interval in Hole 977A ranges from middle or upper Miocene (Zone NN7–NN11) to upper Pliocene (NN19A). A brief hiatus occurs at the Zone NN13/NN14 boundary. The sedimentary sequence cored in Hole 978A terminated in the upper Miocene (Zone NN11). All NN11 to NN19A zones are present. Hole 979A terminated in the middle Pliocene (Zone NN16A). All Pliocene zones from NN16A to NN19A are present, although a brief Zone NN17 intrazonal hiatus is inferred based on foraminifer and nannofossil co-occurrences. The ratio of warm-water Discoaster brouweri to cool-water Coccolithus pelagicus was used to assess changing Pliocene surface-water temperatures. All holes show a dramatic cooling beginning by Zone NN18 in the late Pliocene. Relatively cool periods also occur during the early Pliocene in early Zone NN12 and in late Zone NN13. Generally warm-water intervals occur in most holes in the early Pliocene in the late Zone NN12-early Zone NN13 and NN15 intervals and in the middle Pliocene in Zones NN16A and NN16B. The warmest period in the Pliocene was a brief interval in the middle Pliocene from late Zone NN16A to latest Zone NN16B (about 3.0 Ma to 2.6 Ma).