Paleoecological and paleobiogeographic considerations of Ordovician graptolites from the Cordillera Oriental, Jujuy province, Argentina

Abstract

We analyse new paleoecological data from South American graptolite records to understand the patterns that influence the space-tempo distribution of the group. A cluster analysis including taxa from the Baltograptus cf. B. deflexus and Didymograptellus bifidus Zones is carried out to evaluate the paleogeographic relationships between north-western Argentina and the other regions in the world. Three different biofacies were recognised in the Acoite Formation. The first biofacies takes place in the lower part of the unit, corresponding to pelitic levels (Tetragraptus phyllograptoides and Tetragraptus akzharensis Zones), and it is represented by pandemic forms. The other two biofacies belong to the endemic or neritic shallow water environments, and develop in deposits corresponding to the middle part of the Acoite Formation (bottom of the Baltograptus cf. B. deflexus Zone) in the Sierra de Aguilar, and in the upper half of the unit exposed in the Los Colorados area (D. bifidus Zone), respectively. The statistical analysis highlight the paleobiogeographic relationship between north-western Argentina and south-western China during the middle-upper Floian (Baltograptus cf. B. deflexus and D. bifidus Zones), and it supports the hypothesis that during the Early Ordovician north-western Argentina was located in the middle to high latitudes, included in the cold water faunal realm.