Revised stratigraphic framework of the Cretaceous in the Bajo Grande area (Argentinean Patagonia) inferred from new U–Pb ages and palynology

2016 
Abstract The revision of the stratigraphy of the Cerro Bayo in the Bajo Grande area (Argentinean Patagonia) and the new 206 Pb/ 238 U age of 116.85 ± 0.26 Ma constrain the dating of the Baquero flora, one of the most abundant Aptian floras of southern Gondwana. This flora, preserved in the Baquero Group, represents an extinct biome that flourished ca. 118 Ma ago and was affected by increasing regional volcanism during the subsequent four millions years. The outcrops of the Cerro Bayo are characterized by fluvio-lacustrine deposits divided into three facies associations that include nine lithofacies. The first palynological record for the locality confirms the correlation of the lower part of the outcrops with the Anfiteatro de Tico Formation (the oldest unit of the Baquero Group). The new radiometric age and stratigraphy support recognition of the Bajo Tigre Formation (the middle unit of the Baquero Group) in the area and date the earliest stage in angiosperm diversification in southern South America. Stratigraphic relationships among the Baquero, Chubut and Divisadero groups are briefly discussed.
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