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Redefinition of the Ilerdian Stage (early Eocene)

Pujalte, V.; Baceta, J. I.; Schmitz, Birger LU ; Orue-Etxebarria, X.; Payros, A.; Bernaola, G.; Apellaniz, E.; Caballero, F.; Robador, A. and Serra-Kiel, J., et al. (2009) In Geologica Acta 7(1-2). p.177-194
Abstract
The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO's of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a... (More)
The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO's of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a "silver spike" to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp-Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy. (Less)
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keywords
P-E boundary, CIE, Larger foraminifera, Ilerdian stage, Silver spike, Pyrenees, Tremp-Graus Basin
in
Geologica Acta
volume
7
issue
1-2
pages
177 - 194
publisher
Institut de Ciències de la Terra "Jaume Almera" (CSIC)
external identifiers
  • wos:000263906300011
  • scopus:62249109382
ISSN
1695-6133
DOI
10.1344/105.000000268
language
English
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yes
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9fbe5286-71d5-400f-9917-0cc2de33a721 (old id 1404874)
date added to LUP
2009-06-10 15:53:50
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2017-10-22 04:19:41
@article{9fbe5286-71d5-400f-9917-0cc2de33a721,
  abstract     = {The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO's of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a "silver spike" to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp-Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy.},
  author       = {Pujalte, V. and Baceta, J. I. and Schmitz, Birger and Orue-Etxebarria, X. and Payros, A. and Bernaola, G. and Apellaniz, E. and Caballero, F. and Robador, A. and Serra-Kiel, J. and Tosquella, J.},
  issn         = {1695-6133},
  keyword      = {P-E boundary,CIE,Larger foraminifera,Ilerdian stage,Silver spike,Pyrenees,Tremp-Graus Basin},
  language     = {eng},
  number       = {1-2},
  pages        = {177--194},
  publisher    = {Institut de Ciències de la Terra "Jaume Almera" (CSIC)},
  series       = {Geologica Acta},
  title        = {Redefinition of the Ilerdian Stage (early Eocene)},
  url          = {http://dx.doi.org/10.1344/105.000000268},
  volume       = {7},
  year         = {2009},
}