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| Titel |
Astrochronology of the Pliensbachian–Toarcian transition in the Foum Tillicht section (central High Atlas, Morroco) |
| VerfasserIn |
Mathieu Martinez, Stephane Bodin, Francois-Nicolas Krencker |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106964
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| Publikation (Nr.) |
 EGU/EGU2015-6649.pdf |
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| Zusammenfassung |
| The Pliensbachian and Toarcian stages (Early Jurassic) are marked by a series of carbon cycle
disturbances, major climatic changes and severe faunal turnovers. An accurate knowledge of
the timing of the Pliensbachian–Toarcian age is a key for quantifying fluxes and rhythms of
faunal and geochemical processes during these major environmental perturbations. Although
many studies provided astrochronological frameworks of the Toarcian Stage and the Toarcian
oceanic anoxic event, no precise time frame exists for the Pliensbachian–Toarcian transition,
often condensed in the previously studied sections. Here, we provide an astrochronology of
the Pliensbachian–Toarcian transition in the Foum Tillicht section (central High Atlas,
Morocco). The section is composed of decimetric hemipelagic marl-limestone alternations
accompanied by cyclic fluctuations in the δ13Cmicrite. In this section, the marl-limestone
alternations reflect cyclic sea-level/climatic changes, which triggers rhythmic migrations
of the surrounding carbonate platforms and modulates the amount of carbonate
exported to the basin. The studied interval encompasses 142.15 m of the section, from
the base of the series to a hiatus in the Early Toarcian, marked by an erosional
surface. The Pliensbachian–Toarcian (P-To) Event, a negative excursion in carbonate
δ13Cmicrite, is observed pro parte in this studied interval. δ13Cmicrite measurements
were performed every ~2 m at the base of the section and every 0.20 m within
the P-To Event interval. Spectral analyses were performed using the multi-taper
method and the evolutive Fast Fourier Transform to get the accurate assessment of the
main significant periods and their evolution throughout the studied interval. Two
main cycles are observed in the series: the 405-kyr eccentricity cycles is observed
throughout the series, while the obliquity cycles is observed within the P-To Event, in the
most densely sampled interval. The studied interval covers a 3.6-Myr interval. The
duration of the part of P-To Event covered in this analysis is assessed at 0.70 Myr.
In addition, the interval from the base of the Toarcian to the first occurrence of
the calcareous nannofossil C. superbus has a duration assessed from 0.47 to 0.55
Myr. This duration is significantly higher than most of assessments obtained by
former cyclostratigraphy analyses, showing that previous studies underestimated the
duration of this interval, often condensed in the Western Tethys. This study shows
the potential of the Foum Tillicht section to provide a refined time frame of the
Pliensbachian–Toarcian boundary, which could be integrated in the next Geological Time
Scale. |
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