Stable isotope and calcareous nannofossil assemblage records for the Cicogna section : toward a detailed template of late Paleocene and early Eocene global carbon cycle and nannoplankton evolution
Articolo
Data di Pubblicazione:
2015
Citazione:
Stable isotope and calcareous nannofossil assemblage records for the Cicogna section : toward a detailed template of late Paleocene and early Eocene global carbon cycle and nannoplankton evolution / C. Agnini, D.J.A. Spofforth, G.R. Dickens, D. Rio, H. Pälike, J. Backman, G. Muttoni, E. Dallanave. - In: CLIMATE OF THE PAST DISCUSSIONS. - ISSN 1814-9359. - 11:5(2015), pp. 4329-4389. [10.5194/cpd-11-4329-2015]
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 Cicogna
5 Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation
in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multimillion-
year time interval characterized by perturbations in the global carbon cycle and
changes in calcareous nannofossil assemblages. The bulk carbonate 13C profile for
the Cicogna section, once placed on a common time scale, resembles that at sev10
eral other locations across the world, and includes both a long-term drop in 13C, and
multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely
separated 13C records in marine sequences results from temporal changes in the carbon
composition of the exogenic carbon cycle. However, diagenesis has likely modified
the 13C record at Cicogna, an interpretation supported by variations in bulk carbonate
15 18O, 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 dierences before, during and after the Paleocene
Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit
20 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 aected nannoliths or holococcoliths
such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Spenolithus and
25 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 relative and absolute abundance,
even some minor ones, were globally synchronous. An obvious link is through climate
forcing and carbon cycling, although precise linkages to changes in δ13C records and
5 oceanographic change will need additional work.
Tipologia IRIS:
01 - Articolo su periodico
Elenco autori:
C. Agnini, D.J.A. Spofforth, G.R. Dickens, D. Rio, H. Pälike, J. Backman, G. Muttoni, E. Dallanave
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