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| Titel |
Carbon stable isotopes and ammonite biochronostratigraphy across the Sinemurian-Pliensbachian boundary in the Lusitanian Basin, Portugal |
| VerfasserIn |
Luís V. Duarte, Maria José Comas-Rengifo, Ricardo L. Silva, Ricardo Paredes, Antonio Goy |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087953
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| Publikation (Nr.) |
 EGU/EGU2014-2011.pdf |
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| Zusammenfassung |
| Here, we present an integrated stratigraphical study across the Sinemurian-Pliensbachian
interval cropping out into the Portuguese reference section of S. Pedro de Moel
(Lusitanian Basin). Characterized by marl-limestone alternations belonging to the
Água de Madeiros Formation (subdivided into Polvoeira and Praia da Pedra Lisa
members), this unit is particularly dominated by organic-rich facies (black shales)
and represented by a large diversity of benthic and nektonic macrofossils. Using
this stratigraphic and sedimentary setting, we developed a high-resolution carbon
isotopic study, involving new ammonite biochronostratigraphic precisions and other
palaeontological data. The analysis of the collected ammonite specimens facilitated the
characterization of Oxynotum and Raricostatum chronozones and the definition of
Raricostatum, Macdonnelli and Aplanatum subchronozones to accurately identify the
Sinemurian-Pliensbachian boundary in the western Iberian margin. The characterization of
the carbon isotope evolution in bulk carbonate (δ13Ccarb) was performed in 351
samples, representing the Oxynotum – earliest Jamesoni chronozone interval. In this
interval, the carbon-isotope values exhibited a large range of results, varying between
+2.85o(Oxynotum Subchronozone) to strong negative values observed in some limestone
beds from the Raricostatum Subchronozone (lowest reaching -6.7 ), a variation
clearly controlled through lithological and facies changes. Despite these strong
anomalous isotopically light values (below -1), clearly associated with organic
matter degradation and early diagenesis, the δ13Ccarb curve shows a long-term
negative trend across the Oxynotum to the early Taylori subchronozone interval. This
tendency is reversed around 5 meters above the Sinemurian-Pliensbachian boundary,
and the δ13Ccarb value becomes positive with the absence of organic matter and
argillaceous sediments in the series (in the limestones of Praia da Pedra Lisa Member).
Rather than a global event, as recently recognized for the Late Sinemurian, the
δ13C curve recorded across the Sinemurian-Pliensbachian of the western Iberian
margin is controlled through internal depositional conditions in the Lusitanian Basin. |
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