The presence of the messaoudensis-trifidum acritarch assemblage (Upper Tremadocian-Floian) in the Central Andean Basin, north-western Argentina: calibration with chitinozoans and graptolite zonation

RUBINSTEIN, CLAUDIA V.; DE LA PUENTE, G. SUSANA; TORO, BLANCA A.; SERVAIS, THOMAS B.

Acta Palaeontologica Sinica

Acta Palaeontologica Sinica

Lugar: Nanjing ; Año: 2007 vol. 46 p. 422 - 428

The presence of the messaoudensis-trifidum assemblage (Upper Tremadocian-Floian) in the Central Andean Basin, north-western Argentina, is reanalyzed. New records of this assemblage from different localities in the Cordillera Oriental and Sierras Subandinas, most of them accompanied by chitinozoans, are presented. A reassessment of the graptolite biostratigraphic scheme previously proposed for the Cordillera Oriental, allows to an accurate stratigraphical succession of  acritarchs of the messaoudensis-trifidum assemblage. This revision reduces the gap of diagnostic forms in the lower part of the Floian of the Cordillera Oriental, corresponding to the T. akzharensis graptolite Biozone. Some characteristic taxa of the messaoudensis-trifidum assemblage show a different distribution in the Floian of north-western Argentina, than that of western and southern Europe, where taxa corresponding to the sub-assemblage 5, equivalent to the phyllograptoides graptolite Biozone (time-slice. 2a) in north-western England, extend up to the bifidus Zone (TS. 2c). The lowest record of this assemblage in north-western Argentina, corresponds to Kiaerograptus and lower Araneograptus murrayi/pulchellus local biozones (probably equivalents to TS. 1b). In terms of palaeogeography, records of the messaoudensis-trifidum acritarch assemblage in north-western Argentina represent the lowest latitudinal occurrence from all the peri-Gondwanan localities.