Resumen de The Bivalvia (Mollusca) from the Upper Miocene of the Sais Basin (southern Rifian Corridor, Morocco). Palaeobiogeography and palaeoecology

A. Lauriat-Rage, Amor Ben Moussa, J.-P. Piquet, J.P. Saint Martin

• español

  Las margas grises de la cuenca del Sais, datadas del Mioceno superior (Tortoniense-Messiniense), contienen una fauna de bivalvos muy diversificada. La fauna procede de siete localidades alineadas entre Fes al este y Meknes al oeste. Esta cuenca tiene mucha similitud con el Tortoniense mediterráneo (principalmente Italia, Grecia y Bulgaria) que contienen también Pecten seguenzai y Linga agassizi. El Corredor Sur Rifeño facilitó la comunicación entre el Mediterráneo y la cuenca del Sais, hasta que en el Messiniense se cerró el Estrecho de Taza. La comparación de la fauna de bivalvos entre el Mediterráneo y el Atlántico y la posición muy meridional de la Cuenca del Sais permiten concluir que existió un clima subtropical. La conservación de todos los fósiles bivalvos de concha calcítica y aragonítica de la Cuenca del Sais tiene interés paleoecológico. Los fósiles sufrieron un corto transporte por la acción de corrientes selectivas; representan los componentes de tanatocenosis procedentes de biotopos algo diferentes. Toda la fauna es de salinidad normal (no se ha reconocido ninguna especie salobre o lagunar) y se desarrolló en un medio somero (Infralitoral y parte superior del Circalitoral).

• English

  The grey marls of the Sais basin, Tortonian-Messinian in age, yielded rich and rather diverse faunas of bivalves. They come from seven localities which are approximately on a line between the Fes region, eastwards, to the Meknes region, westwards. This basin shows the closest affinities with the Tortonian of the Mediterranean (mainly Italy, Greece, Bulgaria) as shown by Pecten seguenzai and Linga agassizi. These relations were largely favoured by the Southern Rifian Corridor which enabled a direct connection between the Mediterranean and the Sais Basin, up to the closing of the Strait of Taza during the Messinian. Comparisons between the bivalve faunas of the Upper Miocene of the Mediterranean and Atlantic approaches, and because of the southern latitude of the Sais Basin, it may be inferred that the climate was subtropical. From a palaeoecological point of view, the bivalve faunas of the Sais Basin are of interest because all fossils, i.e. both aragonitic and calcitic ones, are well preserved. The fossils were transported on short distances by selective currents; they represent components of thanatocenoses which originated in slightly different biotopes. The fauna as a whole indicates a normal salinity (brackish and lagunal forms are lacking); it lived in shallow environments (infralittoral and upper circalittoral).