Eléments de chronologie depuis 125 000 ans (Acides aminés et 14C) au Maroc atlantique (région de Rabat-Skhirat).

OCCHIETTI, Serge; PICHET, Pierre; RAYNAL, Jean-Paul; DEBÉNATH, André; DAUGAS, Jean-Pierre; EL HAJRAOUI, Addeljalil

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OCCHIETTI, Serge
GEOTOP, UQAM CP 8888 Centre-ville, Montréal, Québec, Canada H3C 3P8

PICHET, Pierre
GEOTOP, UQAM CP 8888 Centre-ville, Montréal, Québec, Canada H3C 3P8

RAYNAL, Jean-Paul
De la Préhistoire à l'Actuel : Culture, Environnement et Anthropologie [PACEA]

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Communication dans un congrès avec actes

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Colloque international L'homme préhistorique de Témara et ses contemporains du bassin méditerranéen depuis 100 000 ans, Témara, 21-23 septembre 1992, pré-actes, Colloque international L'homme préhistorique de Témara et ses contemporains du bassin méditerranéen depuis 100 000 ans, Témara, 21-23 septembre 1992, pré-actes., 1992, Rabat. 1992

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Abstract

En accord avec des datations au 14C, trois amino-groupes caractérisent le dernier cycle cli-matique : groupe associé au stade isotopique 5 (AIle/Ile = 0,540 ± 0,125 pour Patella), groupe associé aux stades 4, 3 et 2 (AIle/Ile ...Read more >

English Abstract

As part of a joint Morocco-France research project, a collaborative dating program has been held since 1987 with Canadian researchers of GEOTOP. Most of the Atlantic coast of Morocco has been continuously uplifted since the Pliocene. Because of favorable diagenetic conditions, a sequence of seashore morphostratigraphic units records the past climato-eustatic high stands along the rising coast. Due to the regional mean temperature (18-19 °C) and the intermediate high thermal history of Morocco, racemization ratios in molluscs are sufficiently high to establish a good zonation scale from the last cycle sites. The lithostratigraphic and archaeological framework of the last climatic cycle has been established within the project and supported by numerical chronology data. Using this framework and additional classical and AMS 14C datings on the same sample units used for amino acid analysis, a preliminary amino acid zonation for the last climatic cycle along the northern part of the Atlantic coast of Morocco has been proposed. <br />Patella from 9-12 m marine high stands yield AIle/Ile ratios of 0.8 ± 0.2 which are significantly greater than ratios of the last climatic cycle. <br />The last cycle can be divided into three informal amino groups which should be later subdivided in aminozones. The O (for Ouljian) group is related to the marine high stand(s) of isotopic stage 5. Patella racemisation mean ratio is 0.540 ± 0.125. The S (for Soltanian) amino group is roughly correlative to stages 4-3-2. Epimerisation ratios are comprised between 0.4 and 0.2 from Patella and from Helix (when sampled in caves). The H amino group is related to the marine and continental Holocene units. Epimerisation ratios are lower than 0.2 when the shells are sampled in caves. <br />The Morrocan sequence of the Plio-Pleistocene paleoshores is apparently the most varied and best preserved along the eastern facade of the Atlantic Ocean. Three amino groups related to high-sea-level events are unequivocally distinguished according to Patella racemisation ratios. Amino zonation can be applied as a tool independantly from morphostratigraphic criteria and local tectonics. In reference to the Eutyrrhenian and Neotyrrhenian events in the Mediterranean Sea, possible intermediate high-sea-level events might potentially be identified within the 0-0.540 range of Patella racemisation ratios during the past 125 ka. Events during Soltanian might be chronologically identified either, particularly during the poorly known lower part of this stage. Measuring of the AIle/Ile ratios is a rapid way to check the age homogeneity of a shell collection or to select samples close to the limit of 14C dating.Read less <

Keywords

Maroc

littoral atlantique

grottes

abris sous roche

Atérien

Epipaléolithique

Néolithique

aminochronologie

datations

English Keywords

Morocco

Atlantic Coast

Caves

Shelters

Aterian

Epipalaeolithic

Neolithic

Aminochronology

Absolute Datings

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