# Morphosedimentary behaviour of the deltaïc fringe in comparison to the relative sea-level rise on the Rhône delta

Serge Suanez, Mireille Provansal

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Serge Suanez, Mireille Provansal. Morphosedimentary behaviour of the deltaïc fringe in comparison to the relative sea-level rise on the Rhône delta. 1995 Annual meeting International Geological Correlation Program IGCP Project 367 "Late Quaternary coastal records of rapid change: Application to present and future conditions", ORSTOM, Universités d'Antofagasta et de Chile Santiago, Nov 1995, Antofagasta, Chili. pp.111-112. hal-05115524

HAL Id: hal-05115524

https://cnrs.hal.science/hal-05115524v1

Submitted on 28 Jun 2025

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# ABSTRACTS

1995 Annual meeting
International Geological Correlation Program

Project 367
Late Quaternary coastal records of rapid change:
Application to present and future conditions

Antofagasta, Chile, 19-28 November 1995

IUGS
UNESCO
P

Project 367

Edited by

LUC ORTLIEB

CUSTOM

1995
# MORPHOSEDIMENTARY BEHAVIOUR OF THE DELTAIC FRINGE IN COMPARISON TO THE RELATIVE SEA-LEVEL RISE ON THE RHONE DELTA

Serge SUANEZ & Mireille PROVANSAL

Lab. de Géographie Physique (URA 903), Institut de Géographie, Université de Provence

For the first time original maregraphic data obtained in the Camargue area have been analysed (maregraph of the "Grau de la Dent" installed by the "Compagnie du Salin du Midi"). The long term series (about one hundred years) has been compared with the data recorded in the Marseille area (PIRAZZOLI, 1986; BLANC et al. 1990). The results show that relative sea-level rise was different at each of the sites. In the Camargue, the relative rise in sea level is equal to 2.1 mm/year, in Marseille 1.1 mm/year (figure 1).

The secular trend obtained shows a value similar to those described in the literature (PIRAZZOLI, 1986; GORNITZ et al., 1982, 1987; BLANC et al., 1990; WIGLEY et al. 1992). The difference of 1 mm/year is attributed to subsidence movements that affect the Rhone delta principally localized along the littoral fringe. They can be explained, in part, by man's intervention in morphosedimentary processes of the delta system. Nevertheless, this value is also close to the plurimillennium estimation obtained in the eastern part of deltaic fringe from the study of the archeological sites (L'HOMER, 1992) and focuses on the long term geological forcing agent.

The sediment supply is an important factor in setting off the impact of relative sea-level rise. The study of the sedimentation behaviour focused on the mi-secular evolution of the deltaic coast (figure 2) using imagery processing and the recent accretion pattern of the beaches using the ¹³⁷Cs dating method. The global sediment budget over the last fifty years is positive but the analysis by different sectors shows that the eastern part of the mouth of the Rhone has prograded while the wertem part has eroded (figure 3). Cores were taken on the beaches on either side of the mouth of the Rhone. The chronology has been estimated by ¹³⁷Cs isotope analyses. The results show that the deposit is recent for the two sectors studied (after 1950). A minimum value of the rate of sedimentation equal to +1 cm/year is suggested. Nevertheless the concentration of ¹³⁷Cs seems to indicate that the sedimentation rate could be higher than 1 cm/year in the eastern part.

The morphosedimentary behaviour shows that the eastern part of the mouth of the Rhone delta is not threatened by the relative sea level rise. The evolution of the coast in this area shows that the supply of sediment seems to be enough to offset the rise of sea level. The western part remains vulnerable.

## REFERENCES

BLANC, J.J., FAURE, H. (1990) - La remontée récente du niveau de la mer. Exemples de Marseille, Gênes et Venise (Méditerranée), Géologie Méditerranéenne, Tome XVII, n°2, pp.109-122.

GORNITZ, V, LEBEDEFF, S, HANSEN, J. (1982) - Global sea level trend in the past century, *Science*, 215, pp. 287-289.

GORNITZ, V, LEBEDEFF, S. (1987) - Global sea-level changes during the past century, *The Society of Economic Paleontologist & Mineralogist, Speciale Publication* 41, pp.3-16.

L'HOMER, A. (1992) - Sea level changes and impacts on the Rhone delta coastal lowlands, in *TOOLEY, M.J., JELGERSMA, S. (1992) - Impact of sea-level rise on european coastal lowlands*. Edit. Blackwell, UK, pp.136-152.

PIRAZZOLI, P.A. (1986) - Secular trends of Relative Sea-Level (RSL) changes indicated by tide gauge records, *Journal of Coastal Research*, SI, N°1, pp.1-26.

WIGLEY, T.M.L., RAPER, S.C.B. (1992) - Implications for climate and sea level of revised IPCC emissions scenarios, *Nature*, Vol.357, pp.293-300.
<figure><img src="image_1.png" /><figcaption>FIGURE 1 - Secular trend analysis of the R-S-L-R using linear regression</figcaption></figure>

<figure><img src="image_2.png" /><figcaption>FIGURE 2 - Location map of the studied area</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>FIGURE 3 - Evolution of the global sediment budget by different sectors</figcaption></figure>