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| Titel |
Ecological and evolutionary response of Tethyan planktonic foraminifera to the Middle Eocene Climatic Optimum (Alano di Piave section, NE Italy) |
| VerfasserIn |
V. Luciani, C. Agnini, E. Fornaciari, L. Giusberti, D. Rio, D. J. A. Spofforth, H. Pälike |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028444
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| Zusammenfassung |
| The transient (ca. 500 kyr) climatic warming event at ca. 40 Ma, known as Middle Eocene
Climatic Optimum (MECO), significantly interrupted the overall cooling trend of the Middle
Eocene. Originally documented in several deep sea sites at the Southern Ocean (Bohaty and
Zachos, 2003), now it appears to be recorded worldwide by pronounced changes of the δ13C
and δ18O values and coeval oscillations in global CCD (Tripati et al, 2005). Information on
the planktonic foraminiferal response to this event is so far lacking. Here we present a
detailed planktonic foraminiferal analysis of the MECO interval from a marginal
basin of the central-western Tethys (Alano di Piave section, northeastern Italy).
The expanded and continuous Alano section provides an excellent record of this
event and offers an unique opportunity to better understand the role of climate upon
calcareous plankton evolution. The initiation of the MECO occurs within magnetochron
C18r at ca. 40.5 Ma with minimum δ18O and δ13C values achieved at the base of
C18n.2n ca. 40.13 Ma, which are interpreted to represent peak warming conditions.
Two sapropel-like, organic-rich intervals coincide with the major change in δ13C
record at Alano (Agnini et al., 2007a; Spofforth et al., 2008). The MECO event
correlates the E12 (P13) and lower E3 (P14) planktonic foraminiferal zones. The
high-resolution quantitative planktonic foraminiferal analysis performed on both >38
μm and >63 μm fraction reveals pronounced and complex changes indicating a
strong environmental perturbation that parallels the variations of the stable isotope
curves. These changes are primarily represented by the marked increase in abundance
of the eutrophic subbotinids and of the small, low-oxygen tolerant Streptochilus,
Chiloguembelina and Pseudohastigerina, by the consistent and significant entrance of the
eutrophic opportunist triserial Jenkynsina and of Pseudoglobigerinella bolivariana,
typical species of high-productivity, upwelling areas. The environmental variations
related to the MECO thus induced a pronounced shift from oligotrophic to eutrophic,
opportunist, low-oxygen tolerant planktonic foraminiferal assemblages suggesting
increased nutrient input and surface ocean productivity. These results are supported by
the increase of calcareous nannofossil eutrophic indicators and by the occurrence
of radiolarians as well. These observed changes show certain analogies with the
PETM event recorded in the same area (Agnini et al., 2007b; Luciani et al., 2007).
Our data indicate that the definitive decline in abundance of the large acarininids
occurs within the MECO just following the major δ18O negative excursion. These
warm-indices muricate forms dominated the Eocene greenhouse planktonic foraminiferal
assemblages and became extinct near the middle/late Eocene boundary. Remarkably, our
data highlight that the evolutionary appearances of two species belonging to the
Turborotalia cerroazulensis lineage (T . cerroazulensis and T . cocoaensis) occur in
correspondence to the MECO event. Furthermore, the total range of the marker Orbulinoides
beckmanni at Alano is almost perfectly coincident with the major oxygen isotope
excursion corroborating the hypothesis that this peculiar species might represent
for the MECO an equivalent of the PETM excursion taxa (see also Edgar et al.,
2007).
References
Agnini, C., D. J. A. Spofforth, E. Fornaciari, L. Giusberti, L. Lanci, V. Luciani, G.
Muttoni, P, and D. Rio, 2007a. Is the Middle Eocene Climatic Optimum (MECO) recorded in
the central-western Tethys? Eos Trans. AGU, 88(52) Fall Meet. Suppl., Abstract
OS11A-0188.
Agnini,C., Fornaciari, E., Rio, D., Tateo, F., Backman, J., Giusberti, L., 2007b. Responses
of calcareous nannofossil assemblages, mineralogy and geochemistry to the environmental
perturbations across the Paleocene/Eocene boundary in the Venetian Pre-Alps. Marine
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