Stratigraphical, sedimentological and palaeofloristic characterization of the Sorocayense Group (Triassic) in Barreal depocenter, San Juan Province, Argentina

BODNAR JOSEFINA; IGLESIAS, ARI; CARINA COLOMBI; DROVANDI, J.M.

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Lugar: Santiago de Chile; Año: 2019 vol. 46 p. 567 - 603

0718-7092

Abstract. The northern area of Cuyo Basin (west‐central Argentina) corresponds to the RincónBlanco half-graben, whose filling is arranged into the Rincón Blanco and Sorocayense groups. Inthe present study, we propose a new stratigraphic scheme for the Sorocayense Group in the Barrealdepocenter (San Juan Province), revise the palaeoenvironmental interpretations, and organize andanalyse the plant assemblages of previous and new fossiliferous levels. We defined the followingthree tectosedimentary sequences. The basal sequence represents the initial graben filling withpyroclastic flows, alluvial fan, and ephemeral fluvial systems, and is arranged in a new unit, theCerro Colorado del Cementerio Formation. The middle sequence, including Barreal and Cortaderitaformations, is characterized by sediment gravity flow deposits and different fluvial systems, withdevelopment of floodplains with vertisols and calcisols, and temporal ponds/lakes. In turn, theCortaderita Formation was divided into the following lithostratigraphic members: Don Raúl and LaEmilia. The upper sequence, represented by Cepeda Formation, was deposited by distributaryfluvial and ephemeral fluvial systems. Twelve fossiliferous strata (EF) were recognized, which wereall identified in the middle sequence: EF1 to EF3 in Barreal Formation, EF4 to EF8 in Don RaúlMember, and EF9 to EF12 in the La Emilia Member, both of Cortaderita formation. Thetaphocoenosis found in the Barreal and Cortaderita formations were dominated by corystosperms,with conifers, cycadales, and peltasperms as subordinate forms. The available evidence from thetaphofloras, palaeosols and palaeonvironments indicate the development of seasonal subtropicalclimates, which vary from arid or semi-arid in the basal sequence, sub-humid to semi-arid in themiddle sequence, and arid or semi-arid in the upper sequence. On the basis of the new information,geological correlation and age of the lithostratigraphic units were accurately re-evaluated. Based onthe palaeofloristic content and the correlation with the Rincón Blanco Group, it is possible to inferthat the basal sequence was accumulated during late Early Triassic-early Middle Triassic, themiddle sequence during the Middle Triassic, while the upper sequence was deposited in the earlyLate Triassic.