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4 - CHRONOLOGY MEASUREMENT RESULTS
Three dating methods were used, giving 19 age results
at the Fort Oued Noun section: 14C method on 8 samples
of charcoal and Melanopsis; Optically Stimulated Luminescence
(OSL) on quartz grains from 6 sediment samples,
and Uranium/Thorium (U/Th) method on 5
samples of travertines (tab. 1, 2, 3 and fig. 4).
4.1 - 14C DATES (tab. 1 and fig. 4)
The samples were collected from layers 21 to 35 in
the upper part of Unit 2. All but 3 came from channel
sandy facies within the Unit. Three samples came from
the top layer 35 (massive sandy silts).
Radiocarbon analysis was performed by β-counting
(using conventional method employing CO2 gas
proportional counters) at the L.S.C.E. of Gif-sur-
Yvette. Results are presented as conventional 14C
ages. All samples were prepared following the standard
procedure (Délibrias, 1985). The shells were
mechanically cleaned of adhering contaminants.
Leaching with dilute HCl was used to remove the portions
of the shell matrix suspected to have been affected
by exchange reactions (Vita-Finzi & Roberts,
1984). However, Melanopsis shells are very thin and
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N°Gif Layer Reference Material Conventional
Age Y. B.P.
Delta
13C
Minimum14C
Y.B.P. age(1)
11487 35 ON99/11-3 Melanopsis 18 970+/–230 –6,13 ≥ 18 510
11486 33 ON99/11-2 Melanopsis 21 130+/–350 –5,33 ≥ 20 430
11488 35 ON99/11-4 Melanopsis 21 400+/–230 –6,23 ≥ 20 940
11758 35 ON8/3/02 Melanopsis 22 100+/–370 ≥ 24 000
11485 29 b ON99/11-1 Melanopsis 24 100+/–630 –7,29 ≥ 24 000
11212 21 OA98/11-9 Melanopsis >24 000 –7,82 ≥ 24 000
11648 31 ON11/22a Charcoal 27 820+/–580 –24,85 27 820+/–580
11650 31 ON22/2aval Charcoal 28030+/–530 –26,06 28 030+/–530
Tab. 1: 14C Dates of Fort Oued Noun section.
(1): Minimum 14C Y.B.P. age, except for charcoal samples
Fig. 4: Fort Oued Noun: Stratigraphic location of dated samples.
1 = Conglomerate; 2 = Angular schist gravel; 3 = Travertine; 4 = Sand; 5 = Silt; 6 = Calcrete; 7 = Cambrian bedrock (schist); 8 = Progressive limit
of layer.
Fig. 4 : Fort Oued Noun : position stratigraphique des échantillons datés.
1 = Conglomérat ; 2 = Gravier de schiste anguleux ; 3 = Travertin ; 4 = Sable ; 5 = Limon ; 6 = Croûte calcaire ; 7 = Substratum cambrien schisteux ; 8
= Limite de couche progressive.