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Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: clues from the central-western Tethys (Alano section, NE Italy)

Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: clues from the central-western Tethys (Alano section, NE Italy)
Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: clues from the central-western Tethys (Alano section, NE Italy)
We present a study focused on changes in calcareous nannofossil assemblages of the Alano section during the Middle Eocene Climatic Optimum (MECO). This warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the Chron C18r-C18n transition (ca. 40 Ma) and lasting ca. 500-600 kyr. Semi- quantitative analyses on calcareous nannofossil assemblages have been carried out. Our results show that the MECO interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa, suggesting a relationship between biotic changes and stable isotope shifts. Paleoecological studies at species level and/or based on morphometric criteria (i.e., small placoliths) sometimes show the opposite behaviour between changes observed at the genus level and those observed at lower taxonomic levels. For instance, a taxon thought to be better adapted to oligotrophic/warm waters, e.g. Sphenolithus, shows a prominent decrease if analyzed at genus level, but an increase was instead recorded for S. spiniger. Moreover, taxa preferentially thriving in eutrophic/cold waters, as for instance small reticulofenestrids, increase remarkably in abundance during this warming phase, while medium-large placoliths do not show any significant trend. An increase in reworked, mainly Cretaceous, specimens is also observed during the MECO. These lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make-up of the calcareous nannofossil assemblages. The increase in reworking may indicate an increase in terrigenous input, due to increased chemical weathering likely produced by an enhanced hydrological cycle.
0377-8398
22-31
Toffanin, Federica
6becc87c-6bd2-4a1d-b88a-1ee304e7554a
Agnini, Claudia
accab295-8795-4af8-943a-22d2d2afda89
Fornaciari, Eliana
a51ba751-92df-4550-a210-c0911b435595
Rio, Domenico
14427630-5fab-4d9c-bbdb-3c856c9a984d
Luca, Giusberti
a278728f-230b-4eee-a854-0c666ecd85b8
Luciani, Valeria
d37642c8-f55b-4a0d-ac77-85d155b63066
Spofforth, David J.A.
f852f47b-d21c-4ccc-8f07-bdaa677ee92d
Pälike, Heiko
b9bf7798-ad8c-479b-8487-dd9a30a61fa5
Toffanin, Federica
6becc87c-6bd2-4a1d-b88a-1ee304e7554a
Agnini, Claudia
accab295-8795-4af8-943a-22d2d2afda89
Fornaciari, Eliana
a51ba751-92df-4550-a210-c0911b435595
Rio, Domenico
14427630-5fab-4d9c-bbdb-3c856c9a984d
Luca, Giusberti
a278728f-230b-4eee-a854-0c666ecd85b8
Luciani, Valeria
d37642c8-f55b-4a0d-ac77-85d155b63066
Spofforth, David J.A.
f852f47b-d21c-4ccc-8f07-bdaa677ee92d
Pälike, Heiko
b9bf7798-ad8c-479b-8487-dd9a30a61fa5

Toffanin, Federica, Agnini, Claudia, Fornaciari, Eliana, Rio, Domenico, Luca, Giusberti, Luciani, Valeria, Spofforth, David J.A. and Pälike, Heiko (2011) Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: clues from the central-western Tethys (Alano section, NE Italy). Marine Micropaleontology, 81 (1-2), 22-31. (doi:10.1016/j.marmicro.2011.07.002).

Record type: Article

Abstract

We present a study focused on changes in calcareous nannofossil assemblages of the Alano section during the Middle Eocene Climatic Optimum (MECO). This warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the Chron C18r-C18n transition (ca. 40 Ma) and lasting ca. 500-600 kyr. Semi- quantitative analyses on calcareous nannofossil assemblages have been carried out. Our results show that the MECO interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa, suggesting a relationship between biotic changes and stable isotope shifts. Paleoecological studies at species level and/or based on morphometric criteria (i.e., small placoliths) sometimes show the opposite behaviour between changes observed at the genus level and those observed at lower taxonomic levels. For instance, a taxon thought to be better adapted to oligotrophic/warm waters, e.g. Sphenolithus, shows a prominent decrease if analyzed at genus level, but an increase was instead recorded for S. spiniger. Moreover, taxa preferentially thriving in eutrophic/cold waters, as for instance small reticulofenestrids, increase remarkably in abundance during this warming phase, while medium-large placoliths do not show any significant trend. An increase in reworked, mainly Cretaceous, specimens is also observed during the MECO. These lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make-up of the calcareous nannofossil assemblages. The increase in reworking may indicate an increase in terrigenous input, due to increased chemical weathering likely produced by an enhanced hydrological cycle.

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Published date: 23 July 2011

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Local EPrints ID: 194431
URI: http://eprints.soton.ac.uk/id/eprint/194431
ISSN: 0377-8398
PURE UUID: a7a3c152-6345-4586-bf5c-7ca7b5a90316

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Date deposited: 28 Jul 2011 09:15
Last modified: 25 Nov 2019 21:13

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