Biozonación paleoflorística y cronoestratigrafía del Triásico argentino

Abstract

A paleobotanical biozonation and a chronostratigraphic chart for the continental Triassic of Argentina are proposed. The biostratigraphic study was based on the multivariate analysis of 218 taxa distributed in 15 lithostratigraphic units and 134 taxa from 28 paleocommunities. The biostratigraphic analysis was also supported on the Permian or Jurassic lineage of several species, their acme, the temporal turnover and the evolution of the paleofloras. This information was evaluated together with the stratigraphic location of the fossiliferous horizons, the geochronologic information and the relationship between paleocommunities and sedimentary facies and environments. Five biozones were defined: 1. Dictvoptiullum castellanosii, [ohnsionia stcizneriana and Saportaea dichotoma Biozone (CSD), Represented by a mixed forest and identified in the Barreal and lschichuca Forrnations. 2. Yabeiella marefesiaca, Scytophylllll11 bonettiae and Protoptvflloctadoxvion cormderitacnsis Biozone (MBC). Mixed forests recognized in the Potrerillos, Cortaderita (lower section) and El Alcázar Formations. 3. Ynbeiella brackebuschiana, Scytophylllll11 neuburgianum and Rhexoxvlon piatnítzkui Biozone (BNP). Mixed forests, identified in the Vera, Potrerillos and Ischigualasto Formations, and in the El Tranquilo Group. 4. Dicroidium odontopteroides and D. lancijolium Biozone (OL). Represented by a herbaceous and shrub-like paleocornmunity, defined in the Cacheuta Formation and in the upper section of the Cortaderita Formation. 5. Dictyop/¡ylllll11 tenuiserraium, Linguijoliuni arctum and Protocircoporoxylon nuirionoensis Biozone (DLM). Deciduous and mesoxerophytic forests, identified in the Los Colorados and Río Blanco redbeds, the Paso Flores Formation and the Tronquimalal Group. The following local stages are defined on the bases of biozone chronology, analysis of the main stratigraphic unconformities and evolution of the basin infill: Barrealian (Early to Middle Triassic), Cortaritian (late Middle to early Late Triassic) and Flarian (upper Late Triassic).