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AGU: Paleoceanography

 

Keywords

  • Mio-Pliocence boundary
  • integrated stratigraphy
  • Atlantic Morocco

Index Terms

  • Geomagnetism and Paleomagnetism: Magnetostratigraphy
  • Oceanography: Biological and Chemical: Stable isotopes (0454, 1041)
  • Paleoceanography: Astronomical forcing
  • Paleoceanography: Micropaleontology (0459, 3030)
  • Information Related to Geologic Time: Neogene

Abstract

PALEOCEANOGRAPHY, VOL. 21, PA3011, 27 PP., 2006
doi:10.1029/2005PA001193

No major deglaciation across the Miocene-Pliocene boundary: Integrated stratigraphy and astronomical tuning of the Loulja sections (Bou Regreg area, NW Morocco)

E. van der Laan

Institute of Paleoenvironments and Paleoclimate Utrecht, Utrecht University, Utrecht, Netherlands

E. Snel

Institute of Paleoenvironments and Paleoclimate Utrecht, Utrecht University, Utrecht, Netherlands

E. de Kaenel

De Kaenel Paleo Research, Neuchâtel, Switzerland

F. J. Hilgen

Institute of Paleoenvironments and Paleoclimate Utrecht, Utrecht University, Utrecht, Netherlands

W. Krijgsman

Paleomagnetic Laboratory “Fort Hoofddijk,”, Utrecht, Netherlands

An integrated high-resolution stratigraphy and orbital tuning is presented for the Loulja sections located in the Bou Regreg area on the Atlantic side of Morocco. The sections constitute the upward continuation of the upper Messinian Ain el Beida section and contain a well-exposed, continuous record of the interval straddling the Miocene-Pliocene (M-P) boundary. The older Loulja-A section, which covers the interval from ~5.59 to 5.12 Ma, reveals a dominantly precession-controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the Mediterranean; the high-resolution and high-quality benthic isotope record allows us to trace the dominantly obliquity-controlled glacial history. Our results reveal that the M-P boundary coincides with a minor, partly precession-related shift to lighter “interglacial” values in d18O. This shift and hence the M-P boundary may not correlate with isotope stage TG5, as previously thought, but with an extra (weak) obliquity-controlled cycle between TG7 and TG5. Consequently, the M-P boundary and basal Pliocene flooding of the Mediterranean following the Messinian salinity crisis are not associated with a major deglaciation and glacio-eustatic sea level rise, indicating that other factors, such as tectonics, must have played a fundamental role. On the other hand, the onset of the Upper Evaporites in the Mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage TG12 and TG11, suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase. Finally, the Loulja-A section would represent an excellent auxiliary boundary stratotype for the M-P boundary as formally defined at the base of the Trubi marls in the Eraclea Minoa section on Sicily.

Received 14 July 2005; accepted 29 December 2005; published 22 August 2006.

Citation: van der Laan, E., E. Snel, E. de Kaenel, F. J. Hilgen, and W. Krijgsman (2006), No major deglaciation across the Miocene-Pliocene boundary: Integrated stratigraphy and astronomical tuning of the Loulja sections (Bou Regreg area, NW Morocco), Paleoceanography, 21, PA3011, doi:10.1029/2005PA001193.

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