Reassessment of the Early–Middle Eocene biomagnetochronology based on evidence from the Gorrondatxe section (Basque Country, western Pyrenees)

Abstract

Thirteen Lower–Middle Eocene (Ypresian–Lutetian) successions, including the Gorrondatxe section in the western Pyrenees, show biomagnetostratigraphic correlation schemes that do not agree with the current standard framework. The main discrepancy concerns the position of the boundary between planktonic foraminiferal Zones P9 (=E7, approximately) and P10 (=E8, approximately), which was thought to occur within calcareous nannofossil Subzone CP12a and at the boundary between magnetic polarity Chrons C22n and C21r. However, in the differing correlation scheme the boundary between Zones P9 (=E7) and P10 (=E8) occurs close to the base of Subzone CP13a and to the boundary between Chrons C21n and C20r. An attempt at a new Ypresian–Lutetian boundary biomagnetochronology is made based on data from the Gorrondatxe section, which shows that the boundary between Zones P9 (=E7) and P10 (=E8) is 3.1 Myr younger than hitherto considered. Therefore, the duration of the Early Eocene, most commonly defined according to this planktonic foraminiferal zonal boundary, has generally been underestimated over the last four decades.

Review and revision of Cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale

“…For example, detailed biostratigraphic investigations from Ceara Rise Pearson and Chaisson, 1997;Turco et al, 2002), equatorial Pacific Ocean (Wade et al, 2007), Indian Ocean (Hancock et al, 2002) and the Gorrondaxte and Agost sections in Spain (Payros et al, , 2009Larrasoaña et al, 2008;Ortiz et al, 2008) have resulted in revision of the calibrations of numerous bioevents. Most of these changes are small and incremental in nature, but some (e.g., the revision of the lower-middle Eocene by Payros et al, 2007) are major developments. This accumulated new information presents the opportunity for a reassessment of the planktonic foraminiferal calibrations and to incorporate developments and amendments to the existing biostratigraphic zonal scheme.…”

“…In a detailed magnetobiostratigraphic study of an expanded lowermiddle Eocene succession from the western Pyrenees, Payros et al (2007) examined the divergence of planktonic foraminiferal Zones P9 and P10 and the standard zonation (BKSA95). Unlike BKSA95 which places the boundary between planktonic foraminiferal Zones P9 and P10 within calcareous nannofossil Zone NP14 (Subzone CP12a) and magnetic polarity Chron C22n/C21r boundary, they found the boundary to occur within Zone NP15 (=Zone CP13) and Chron C20r.…”

Microbiostratigrapy of the Paleocene-Lower Eocene Sequences in the Bibi Hakimeh 2 Subsurface Section Located in the SW of Iran

“…The cross-sections were examined from a fossil content viewpoint and the biozonation of the Bibi Hakimeh subsurface/subterranean section was determined through the identification of the specific microfossils, their appearance/shape, emergence and decline period. Various sources such as Postuma [9], Loeblich and Tappan [10], Olsson [11], Berggren [12], Berggren and Pearson [13], Payros [14], Wade [15] were employed in the identification of the foraminifera's microfossils. The latest Wade [15] Biozonation was used in the determination of the biozonation and was compared with the older Wynd [6] version performed on the Pabdeh Formation.…”

“…This zone is of the lowest-occurrence zone type and covers the interval between the lowest occurrence of Acarininacuneicamerata (LO) and the lowest occurrence of Turborotalia frontosa (LO) [14].…”

“…This zone is of the lowest-occurrence zone type and covers the interval between the lowest occurrence of Turborotalia frontosa (LO) and the lowest occurrence of Guembelitrioidesnuttalli (LO) [14]. In the Bibi Hakimeh section the lower boundary of this biozonewas determined by the lowest occurrence of the Turborotalia frontosa species at a depth of 2086 m while the upper boundary is established by the lowest occurrence of the Guembelitrioidesnuttalli of the Middle Eocene age though it does not fall within the study area.…”