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| Titel |
Historical shifts of the Rhone River and catastrophic flood events revealed by multi-proxy analysis of the Rhone prodeltaic sediments (Gulf of Lions, NW Mediterranean) |
| VerfasserIn |
Anne-Sophie Fanget |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055335
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| Zusammenfassung |
| The Rhone is the main sediment source to the shelf of the Gulf of Lions, with about 80% of
the total sedimentary input. During the last ca. 20 kyr, the retreat path of the river
in response to pulsed sea-level rise is marked by transgressive parasequences on
the middle/inner shelf. The late Holocene sediments are accumulated, along the
coastal zone, in the form of prodeltaic lobes in continuity with major deltaic lobes
recognized onshore. These prodeltaic lobes are linked to the eastward migration of Rhone
distributaries. They constitute expanded sedimentary archives of the post-glacial
environmental changes because of high sediment rate (more than 1 cm/yr, on an
average).
The present study is focused on the modern history of the subaqueous Rhone delta. In
particular we focused on the most recent Peygoulier (XVIIIth century) and Roustan lobes
(XXth century), that are part of the Grand Rhone system.
Core RHS-KS57 was retrieved from the Roustan prodeltaic lobe during the RHOSOS cruise
in September 2008. It has been used for multi-proxy analysis, in order to characterize
changes both in the continental and marine environments. Chronostratigraphy was
established on the basis of radionucleids and 14C dates. In addition, benthic assemblages
(ostracods and foraminifera) and organic and inorganic geochemistry were used for
characterizing paleoenvironmental changes, in order to link those to rapid climate
fluctuations.
Our work provides a detailed sedimentary history of prodelta lobes during the last four
centuries. Historical shifts of the Rhone distributaries can be identified on the basis of benthic
assemblages. The lower half of the core is marked by full marine and deep water ostracods
(Krithe sp., Cytheropteron rotundatum...) and by foraminiferal faunas living in relatively
stable environments (Valvulineria bradyana, Ammonia beccarii forma inflata, Hyalinea
balthica...). This fauna reflects a weak influence of the Rhone River and consequently a distal
source of sediment. The upper half of the core is characterized by dominance of estuarine
ostracods (Loxoconcha spp.) and by increase of foraminiferal faunas tolerant to stress
conditions and high riverine influence (Quinqueloculina lata, Ammonia beccarii forma
beccarii, Nonionnella turgida...). The gradual increase of the riverine influence indicates
a more proximal source and reflects the present situation, with the Rhone River
flowing into the Gulf of Lions through the Roustan channel, where the studied core is
located.
In addition the imprint of extreme climate events, i.e. chatastrophic floods, can be detected at
discrete levels. They are pointed out by the punctuated occurrence of freshwater ostracods
(Candona sp., Ilyocypris sp...) that correlate with increases of the grain-size and organic
carbon content. The traces of flood events match perfectly with the events documented in the
historical archives.
This project is partly funded by ANR Extrema (contract number: ANR-06-VULN-005).
RHOSOS Group members:A.S. Fanget1, M.A. Bassetti1, S. Berné1,2, A. Goineau3, C.
Fontanier3, G. Jouet2, D. Cossa4, M. Arnaud5, R. Buscail1, G. Maillet6, B. Dennielou2 & A.
Roubi2
1 CEFREM, University of Perpignan, Perpignan, France
2 Géosciences Marines, Ifremer, Plouzané, France
3 BIAF, University of Angers, Angers, France
4 LBCM, Ifremer, Nantes, France
5 IRSN, La Seyne-sur-Mer, France
6 LEESA, University of Angers, Angers, France |
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