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Titel |
Environmental change during the Late Berriasian - Early Valanginian: a prelude to the late Early Valanginian carbon-isotope event? |
VerfasserIn |
Chloé Morales, Johann Schnyder, Jorge Spangenberg, Thierry Adatte, Stéphane Westermann, Karl Föllmi |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250037873
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Zusammenfassung |
The Valanginian period is well known for a positive excursion in marine and terrestrial δ13C
records, which has been interpreted as the consequence of a major perturbation in the global
carbon cycle (Lini et al., 1992; Erba et al., 2004). In contrast to the positive δ13C excursions
of the Early Aptian and latest Cenomanian, marine organic-rich sediments have only been
recognized from a few localities (van de Schootbrugge et al., 2003; Reboulet et al., 2003;
Gröcke et al., 2005; Westermann et al., in press). The δ13C excursion began in the late Early
Valanginian (campylotoxus ammonite zone) and gradually ended during the Late
Valanginian. It is associated with a phase of widespread carbonate-platform drowning on the
shelf (Föllmi et al., 1994) and a decline in calcareous nannofossils in the pelagic
realm (Erba et al., 2004). As a triggering mechanism, numerous authors invoke the
formation of the Parañà-Etendeka flood basalt. The correlation of this episode with the
Valanginian δ13C event depends, however, on the absolute ages attributed to the
Valanginian stage. The recent geological timescale by Ogg et al. (2008) shows that the
major eruptional phase occurred during the Late Valanginian. This may imply that
the late Early Valanginian δ13C event resulted from a combination of different
factors.
Important paleoenvironmental change occurred already in the latest Berriasian and
earliest Valanginian, prior to the positive δ13C excursion. An increase in nutrient input near
the onset of the δ13C excursion (campylotoxus ammonite zone), which may be considered as
a trigger of the carbon cycle perturbation, has been identified in different studies, (Hennig,
2003; Duchamp-Alphonse et al., 2007; Bornemann & Mutterlose, 2008). Heterozoan faunal
associations became dominant since the Early Valanginian on the northern Tethyan Helvetic
platform and may indicate the beginning of sea-water eutrophication (Föllmi et al., 2007).
Clay assemblages in the Tethys and Western European basins show that the climate
became more humid during the Late Berriasian (Hallam et al., 1991, Schnyder et al.,
2009).
The aim of this project is to precisely characterize and date paleoenvironmental and
paleoclimatic change during the latest Berriasian-Early Valanginian time interval in order to
decipher if they can be viewed as precursor events, linked with the late Early Valanginian
δ13C event. Three key sections have been studied: Capriolo (N Italy), Montclus (SE France)
and Musfallen (E Switzerland) located in the Lombardian and Vocontian basins and on the
Helvetic platform, respectively. Phosphorus and stable-isotope analyses have been
performed, in addition to clay-mineralogy and facies determinations. The three
sections show similar and comparable trends: The phosphorus content (in ppm) is
higher in Late Berriasian sediments (compared to Early Berriasian and Valanginian
deposits) and this period is also characterised by a decrease in δ13C values. This is
interpreted as the result of enhanced continental weathering, which would be coeval
with a change to a more humid climate during the Late Berriasian (Schnyder et al.,
2009).
References:
Bornemann, A. and Mutterlose, J. (2008). "Calcareous nannofossil and d13C records
from the Early Cretaceous of the Western Atlantic ocean: evidence of enhanced fertilization
accross the Berriasian-Valanginian transition." palaios 23: 821-832.
Duchamp-Alphonse, S., Gardin, S., Fiet, N., Bartolini, A., Blamart, D. and Pagel, M.
(2007). "Fertilization of the northwestern Tethys (Vocontian basin, SE France) during the
Valanginian carbon isotope perturbation: Evidence from calcareous nannofossils and
trace element data." Palaeogeography, Palaeoclimatology, Palaeoecology 243(1-2):
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Föllmi, K.B., Weissert, H., Bisping, M. & Funk, H. 1994: Phosphogenesis,
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N., Ploch, I. and Duchamp-Alphonse, S. "The Valanginian δ13C excursion may not be an
expression of a global oceanic anoxic event." Earth and Planetary Science Letters In Press. |
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