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Changes in calcareous nannofossil assemblages across the Paleocene/Eocene transition from the paleo-equatorial Pacific Ocean

Record type: Article

Quantitative analyses of selected calcareous nannofossils in deep-sea sections recovered from the paleo-equatorial Pacific (ODP Leg 199) provide new information about biostratigraphy, biochronology and the evolutionary history of calcareous nannofossils across the Paleocene/Eocene transition interval. The sediment cores from ODP Leg 199 represent the first continuous Paleocene/Eocene boundary sections ever to be sampled in the central equatorial Pacific Ocean. Calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as Ericsonia, Discoaster, Fasciculithus, Rhomboaster and Tribrachiatus. Focus is given to the evolution of the Rhomboaster–Tribrachiatus lineage in the lower Eocene interval at Site 1215, and on the stratigraphic relationship of these taxa relative to species in the genus Fasciculithus. Critical intervals of North Atlantic DSDP Site 550 have also been re-examined. The Tribrachiatus digitalis morphotype was described at Site 550 from an interval affected by down-hole contamination, partly originating from within the Tribrachiatus orthostylus range. The T. digitalis morphotype represents an evolutionary transitional form between T. contortus and T. orthostylus, entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species. The subzonal subdivision of Zone NP10 hence collapses. Lithological and colour variability reflecting orbital cyclicity occur in the lower Eocene of Site 1215, permitting a relative astronomical age calibration of the Tribrachiatus taxa. The distinct Rhomboaster spp.–Discoaster araneus association also occurs in the paleo-equatorial Pacific Ocean, together with a marked decrease in diversity of Fasciculithus spp. Site 1220 reveals a short peak abundance of Thoracosphaera spp. just above the P/E boundary interval, which probably reflects a stressed surface water environment.

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Citation

Raffi, I., Backman, J. and Pälike, H. (2005) Changes in calcareous nannofossil assemblages across the Paleocene/Eocene transition from the paleo-equatorial Pacific Ocean Palaeogeography, Palaeoclimatology, Palaeoecology, 226, (1–2), pp. 93-126. (doi:10.1016/j.palaeo.2005.05.006).

More information

Published date: 2005
Keywords: Calcareous nannofossils, Biostratigraphy, Biochronology, Cyclostratigraphy, Paleogene, Milankovitch

Identifiers

Local EPrints ID: 17464
URI: http://eprints.soton.ac.uk/id/eprint/17464
ISSN: 0031-0182
PURE UUID: 66b1a010-755b-4771-82a5-3ce752527e7c

Catalogue record

Date deposited: 28 Sep 2005
Last modified: 17 Jul 2017 16:38

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Contributors

Author: I. Raffi
Author: J. Backman
Author: H. Pälike

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