Age of settlement and accumulation rate of submarine “coralligène” (−10 to −60 m) of the northwestern Mediterranean Sea; relation to Holocene rise in sea level |
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| Authors: | Stephane Sartoretto Marc Verlaque and Jacques Laborel |
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| Institution: | LBMEB, C.N.R.S. Faculté des Sciences de Luminy, Route de Luminy, 13288, Marseille, cedex 9, France |
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| Abstract: | Morphological and chronological studies have been carried out on coralline algal buildups (“coralligène”) situated between 10 and 60 m depth near Marseilles, and in Corsica (France). Despite the presence of occasionally sizeable quantities of iron hydroxide, these constructions prove to be a reliable material for radiocarbon dating. Ages obtained using this method range from 640±120 yrs B.P. (Corsica, Scandola Natural Reserve, ?15 m) to 7760±80 yrs B.P. (Marseilles, Grand Congloue, ?52 m). Internal erosion surfaces within the buildups give evidence of discontinuous development. The accumulation rate of the coralligène constructions is very low (0.006–0.83 mm yr?1 according to the depth and time period). The higher values (0.53–0.83 mm yr?1) were recorded for the deeper constructions. They correspond to a period between 8000 and 6000 yrs B.P. After 6000 yrs B.P., the only appreciable accumulation rates (0.11–0.42 mm yr?1) were recorded for constructions situated between 10 and 35 m depth, whereas the accumulation rates of deep coralligène (> 50 m) appear to be low or zero. The age of the large constructions (overhang:  80 cm in width) is positively correlated with depth (r = 0.95; p < 0.005). Their development occurred during the Flandrian transgression. The oldest structures, today situated at 50 to 60 m depth, started to develop when water depth was probably no greater than 10 to 15 m. Apart from in strongly shaded fissures on rocky coasts and areas subjected to heavy sedimentation, the main framework building algal species was initially Mesophyllum lichenoides (Ellis) Lemoine, a high tolerant species to light, hydrodynamic energy and temperature. With the rise in sea level, the coralligène structure gradually became available to other less tolerant algal species (Lithophyllum, Lithothamnion), and the crustforming population diversified. Because of the good preservation of coralligène structures, the reliability of radiocarbon dating and the correlation between the age and bathymetric position of the large coralligène structures (except in areas of heavy sedimentation and fissures in shallow rocky coasts), these buildups are considered to be of use as biological indicators of variations in sea level. |
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