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| Titel |
Benthic foraminiferal assemblages: a clue to the palaeoecology and palaeoenvironment of the Pliensbachian- Toarcian transition of Peniche (Lusitanian Basin, Portugal) |
| VerfasserIn |
Patrícia Rita, Matías Reolid, Luís V. Duarte |
| 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 |
250102533
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| Publikation (Nr.) |
 EGU/EGU2015-1856.pdf |
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| Zusammenfassung |
| The Lower Jurassic of the Peniche region (Lusitanian Basin, Portugal) constitutes one of the
most worldwide references concerning the stratigraphy of the Lower Toarcian. In fact, the
Peniche Section is the unique candidate to the Toarcian Global Boundary Stratotype Section
and Point and records some important evidences about the palaeoenvironmental perturbations
associated to the Toarcian Oceanic Anoxic Event (T-OAE) (e.g. Hesselbo et al., 2007).
Despite the large number of micropaleontological studies developed in this section (e.g.
ostracods, calcareous nannofossils), any relevant study of benthic foraminifera has been
presented, even to the whole basin scale. Thus, based on a detailed stratigraphic
analysis that includes 39 marly samples of the Emaciatum (= Spinatum) – Levisoni (=
Serpentinum) ammonite zone interval (around 37 m thick), the aim of this work is the
study of the foraminiferal assemblages from the Pliensbachian-Toarcian boundary
and across the T-OAE. The results and main conclusions of this preliminary study
show three different stages: 1) The uppermost Pliensbachian (Emaciatum Zone)
is characterized by foraminiferal assemblages with high diversity and abundance
(foram/g) dominated by Marginulina, Lenticulina, Dentalina and Ammobaculites,
suggesting well-oxygenation and nutrient availability. 2) The beginning of the Toarcian
(Polymorphum Zone) evidences a drastic decrease of the diversity and abundance of the
foraminiferal assemblages. 3) This trend continues in the Levisoni Zone with decreasing
diversity and abundance (some barren samples are recorded), but opportunistic
forms such as Epistomina and Lenticulina, occasionally proliferate. This evolution
suggests a clear perturbation in the palaeocological conditions at the sea-bottom
during the Early Toarcian, feature that is observed in other basins (see Reolid et al.,
2012). The fluctuations of foraminiferal assemblages recorded across the studied
interval seems to correlate with the previous sequence stratigraphic interpretation of
the series (e.g. Duarte, 2007) and the proliferation of opportunistic forms in some
levels could be a reflex of the turbiditic sedimentation that took place in this area
during this period (Wright & Wilson, 1984), which promotes the oxygenation of the
sea-bottom.
References
Duarte, L.V. (2007). In R. B. Rocha (Ed.): The Peniche section (Portugal). Contributions
to the definition of the Toarcian GSSP. International Subcommission on Jurassic
Stratigraphy, ISBN 978-972-8893-14-9, 17-23;
Hesselbo, S. P., Kenkyns, H. C., Duarte, L.V., Oliveira, L. C. V. (2007). Carbon-isotope
record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine
carbonate (Lusitanian Basin, Portugal). Earth and Planetary Science Letters, 253:
455-470.
Reolid, M., Sebane, A., Rodríguez-Tovar, F. J., Marok, A. (2012). Foraminiferal
morphogroups as a tool to approach the Toarcian Anoxic Event in the Western
Saharan Atlas (Algeria). Palaeogeography Palaeoclimatology Palaeoecology, 323-325:
87-99.
Wright, V.P. & Wilson, R.C.L. (1984). A carbonate submarine-fan sequence from the
Jurassic of Portugal, Journal of Sedimentary Petrology, 54: 394-412. |
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