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.