The Continental Cenomanian of Patagonian: A comparison between the fosil vertebrate faunas of the Rio Limay Subgroup (Neuquén Group) and the Bajo Barrreal Formation (Chubut Group).

CANALE, JUAN I.; IBIRICU, LUCIO M.; HALUZA, ALEJANDRO ; CASAL, GABRIEL A.

San Juan

Congreso; Congreso Latinoamericano Paleontologia de Vertebrados; 2011

 Cenomanian continental sediments are well represented in Patagonia, with two major stratigraphic units, particularly regarding the extent and fossiliferous richness of their outcrops. On one hand in Neuquén and Río Negro Provinces it outcrops the Río Limay Subgroup, which is composed by Candeleros and Huincul formations, and on the other hand the Chubut Province present extensive outcrops of the lower member of Bajo Barreal Formation. These units have yielded a large number of vertebrate fossils, showing remarkable faunal similarities. The hypothesis of faunal relationships between those stratigraphic units was tested using an UPGMA cluster analyses (Sokal and Michener, 1958) based on Bray-Curtis distance coefficient (using Jaccard and Simpson similarity coefficients). In this analysis were included other stratigraphic units of Neuquén Group (Río Neuquén and Río Colorado Subgroups) and Allen Formation (Garrido, 2011). Likewise, the as well as levels preliminarily assigned to the upper member of the Bajo Barreal Formation exposed in the southeastern region of Lago Colhué Huapi were included (Casal et al., 2006; Casal et al., 2007). Results showed that, these previously-mentioned levels previously mentioned presents a strong grouping with the Allen Formation in particular, and post-Turonian units analyzed in general. These analysis shows, from the evidence that comes from the fossil record, the marked difference between the faunal associations found in both members of Bajo Barreal Formation, which agrees with previous proposals about an important diacronism within this Formation (Casal et al., 2007). Cenomanian units analyzed display a strong clustering, characterized by the presence of basal coelurosaurs (Aniksosaurus Martínez and Novas, 2006, and related forms), rebbachisaurids and basal titanosauriforms (Andesaurus Calvo and Bonaparte, 1991). In addition, they are separated from the rest of the post-Turonian units, which present moderate to strong clustering between them. This pattern suggests that faunal associations of wide geographical distribution in Patagonia suffered a significant turnover, probably related to an extinction event at the Cenomanian-Turonian period (Coria and Salgado, 2005).