INIBIOMA   20415
INSTITUTO DE INVESTIGACIONES EN BIODIVERSIDAD Y MEDIOAMBIENTE
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Paleofloristic and paleoenvironmental analyses of Sorocayense Group (Triassic) in northern Cuyo Basin, San Juan Province, Argentina
Autor/es:
BODNAR JOSEFINA; ARI IGLESIAS; CARINA COLOMBI
Lugar:
Mendoza
Reunión:
Congreso; 4th International Paleontological Congress; 2014
Institución organizadora:
IANIGLA CCT CONCIET Mendoza
Resumen:
The northern area of Cuyo Basin (west‐central Argentina) corresponds to Rincón Blanco half-graben, whose filling is arranged into Rincón Blanco and Sorocayense Groups. In the present study we propose a new sequence-stratigraphy of Sorocayense Group, reinterpret the paleoenvironments and organize and analyze the floristic composition of previous and new fossiliferous levels. On the basis of the new information, we adjust the geological correlation and age of the lithostratigraphic units. We defined three tectosedimentary sequences. The Basal Sequence represents the initial graben filling with pyroclastic flows, alluvial fan and ephemeral fluvial systems. The Middle Sequence, including Barreal and Cortaderita Formations, is characterized by sediment gravity flow deposits and high sinuosity gravel-sand meandering, anastomosed and high-energy sandy braided fluvial systems, with the development of ponds/lakes, vertisols and calcisols. The Upper Sequence, represented by Cepeda Formation, was deposited by distributary alluvial and ephemeral fluvial systems. We recognized eleven fossiliferous strata (EF), all of them identified in the Middle Sequence: EF1 and EF2 in Barreal Formation, EF3-EF7 in lower section of Cortaderita Formation, and EF8-EF11 in its upper section. EF1 is constituted by corystosperm stumps, equisetacean axes and osmundacean leaves. EF2 bears leaves of Dipteridaceae (Dictyophyllum spp.), Ginkgoales (Saportaea spp.) and Corystospermaceae (Zuberia spp.). EF3 contains trunks and leaves of Corystospermaceae (Rhexoxylon cortaderitaense, Johnstonia stelzneriana), equisetacean axes, and leaves of Dipteridaceae. The EF4, EF5, EF6 and EF7 are characterized by the presence of Corystospermaceae (R. cortaderitaense, Zuberia spp. Dicroidium spp.), Peltaspermaceae (Scytophyllum bonettiae, Lepidopteris stormbergensis), Cycadales (Pseudoctenis sp.), Ginkgoales (Sphenobaiera spp.), conifers (Cupressinoxylon zamunerae) and Gnetales (Yabeiella spp.). EF8 is distinguished by the occurrence of Corystospermaceae (Dicroidium spp.), Peltaspermaceae (S. bonettiae, L. stormbergensis, Pachydermophyllum papillosum), Ginkgoales (Sphenobaiera argentinae) and Gnetales (Yabeiella spp.). EF9, EF10 and EF11 only show corystosperm fossils (R. cortaderitaense). Previous authors assigned Barreal Formation to early Middle Triassic CSD Biozone; lower section of Cortaderita Formation to late Middle Triassic MBC Biozone and upper section of Cortaderita Formation to the Late Triassic OL Biozone. However, the paleofloras here studied exhibit diagnostic elements of MBC Biozone (i.e. Yabeiella mareyesiaca, Scytophyllum bonettiae, Rhexoxylon cortaderitaense) in both sections of Cortaderita Formation, and permit to assign both to Middle Triassic. Moreover, according to the new tectosedimentary interpretation, correlations with Rincón Blanco Group are more accurate, allowing us to infer that: Basal Sequence was accumulated during Early to Middle Triassic, the age of Middle Sequence is Middle Triassic and Upper Sequence was deposited in Late Triassic.