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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 4 | Copyright

Special issue: Climatic and biotic events of the Paleogene

Clim. Past, 12, 883-909, 2016
https://doi.org/10.5194/cp-12-883-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 11 Apr 2016

Research article | 11 Apr 2016

Stable isotope and calcareous nannofossil assemblage record of the late Paleocene and early Eocene (Cicogna section)

Claudia Agnini1,2, David J. A. Spofforth3, Gerald R. Dickens4,5, Domenico Rio1, Heiko Pälike6, Jan Backman5, Giovanni Muttoni7,8, and Edoardo Dallanave9 Claudia Agnini et al.
  • 1Dipartimento di Geoscienze, Università di Padova, Padua, Italy
  • 2Istituto di Geoscienze e Georisorse, CNR, Padua, Italy
  • 3Robertson, CGG GeoSpec, Llandudno, UK
  • 4Department of Earth Sciences, Rice University, Houston, Texas, USA
  • 5MARUM, University of Bremen, Bremen, Germany
  • 6Department of Geological Sciences, Stockholm University, Stockholm, Sweden
  • 7Dipartimento di Scienze della Terra “Ardito Desio”, Università Statale di Milano, Milan, Italy
  • 8ALP, Alpine Laboratory of Paleomagnetism, Peveragno (CN), Italy
  • 9Department of Earth and Environmental Sciences, Ludwig-Maximilians Universität München, Munich, Germany

Abstract. We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81m thick section of upper Paleocene–lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate δ13C profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in δ13C and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated δ13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the δ13C record at Cicogna, an interpretation supported by variations in bulk carbonate δ18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene–Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Toweius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in the relative and absolute abundances, even some minor changes, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although the linkages between variations in calcareous nannoplankton, changes in δ13C records and oceanography will need additional work.

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In this paper we present records of stable C and O isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages in a upper Paleocene-lower Eocene rocks now exposed in northeast Italy. Modifications of nannoplankton assemblages and carbon isotopes are strictly linked one to each other and always display the same ranking and spacing. The integration of this two data sets represents a significative improvement in our capacity to correlate different sections at a very high resolution.
In this paper we present records of stable C and O isotopes, CaCO3 content, and changes in...
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