Jones, T.D.; (2008) The response of low-latitude calcareous phytoplankton to global change through the Eocene-Oligocene transition. Doctoral thesis , University of London.

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Abstract

This thesis documents the response of calcareous phytoplankton assemblages to major changes in global climate during the Eocene-Oligocene transition (EOT) at three low-latitude sites Tanzanian Drilling Project (TDP) Sites 12 & 17 (southern coastal Tanzania), Deep Sea Drilling Site 242 (Mozambique Channel, western Indian Ocean) and St Stephens Quarry (Alabama, USA). High-resolution nannofossil count data from all three study sites clearly indicate a major change in coccolithophore assemblage compositions directly coincident with the first step change in the positive oxygen isotope (d180) shift into the early Oligocene Glacial Maximum (EOGM). This is followed by continued shifts in coccolithophore assemblages in the vicinity of the Eocene-Oligocene boundary to reach new "Oligocene" assemblage compositions before the second step in duO and peak glacial conditions of the EOGM. At all sites there is a marked increase in the abundance of Cyclicargolithus floridanus (>5um) and to a lesser extent Sphenolithus predistentus, combined with a general loss of warm-water and oligotrophic taxa including Calcidiscus protoannulus, discoaster and holococcolith species. This consistent pattern of biotic change, from sites with varying species compositions and preservation states, indicates a large and geographically widespread perturbation in the low-latitude surface water environment and is consistent with new trace metal paleothermometry that indicates a significant, 2-3 C, cooling of surface waters in the earliest stages of the EOT. An exceptionally-well preserved and highly diverse nannofossil assemblage from late Eocene-early Oligocene (nannofossil zones NP19/20 to NP21 Martini 1971) sediments of coastal Tanzania is described and its implications for the Cenozoic history of the coccolithophores is discussed. This consists of a total of 114 species-equivalent morphotypes, one new genus (Pocillithus), six new species (Reticulofenestra macmillanii, Blackites culter, Rhabdosphaera suptilis, Orthozygus occultus, Orthozygus arms, Pocillithus spinulifer) and a previously unknown Paleogene deep-photic zone assemblage including representatives of the extant genera Gladiolithus, Algirosphaera and Acanthoica.

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