New insights for the paleobiogeographic analysis of the Early Ordovician graptolite fauna of Northwestern Argentina.

VENTO, B.A.; TORO, B.A.; MALETZ, J.

La Plata

Congreso; 2° Simposio de bioestratigrafía y eventos del Paleozoico inferior. X Congreso Argentino de Paleontología y Bioestratigrafía. VII Congreso Latinoamericano de Paleontología.; 2010

Trichograptus dilaceratus (Herrmann), Acrograptus gracilis (Törnquist), Expansograptus urbanus (Monsen) and Corymbograptus v-fractus tullbergi (Monsen) are recognized and described in Argentina for the first time, reinforcing the graptolite faunal affinities with Baltoscandia. The studied specimens come from the Quinilican and Agua Chica sections, located at the northern extreme of the Aguilar Range in the Cordillera Oriental (Jujuy Province). The presence of Baltograptus vacillans (Tullberg), Acrograptus filiformis (Tullberg) and Expansograptus cf. holmi (Törnquist) allow to assign the studied levels to the Tetragraptus akzharensis biozone, which corresponds to the lower Floian. A multivariate analysis (mvsp) was used and the determination of faunistic similarities was made with the classic Jaccards’ index. The resulting affinity dendrogram shows stronger relationships between early Floian graptolite faunas from Northwestern Argentina and those coming from Baltoscandia. Great Britain is located in an intermediate position in the similarity dendrogram, and shows less affinity with northwestern Argentina. In addition, weak affinities with North American faunas are observed. The statistical analysis confirms the paleobiogeographic relationships previously established in other areas of the Cordillera Oriental, and supports the hypothesis that during the Early Ordovician, northwestern Argentina was located in middle to high latitudes, corresponding to the Atlantic Faunal Realm of cold water graptolite biofacies.