Palynological, megafloral and mesofossil record from the Bajo Grande area (Anfiteatro de Ticó Formation, Baqueró Group, Upper Aptian), Patagonia, Argentina

Abstract

The late Aptian flora of Baqueró is one of the best known and accurately dated Cretaceous plant associations from Gondwana, recognized for their well-preserved fossil remains. The Cerro Bayo (Bajo Grande area, Argentinean Patagonia) is one of its classical locations and includes the northernmost fossiliferous outcrops of the Baqueró Group, which belong to the Anfiteatro de Ticó Formation. It yields diverse and numerous plant megafossils and reproductive structures with associated pollen. We report a complete systematic study of a palynological association with 124 species, including 26 that are identified for the first time in the unit. This allowed the first record of three major botanical groups not reported before (i.e., lycophytes, hornworts and angiosperms), as well as algae and fungal spores. The same fossiliferous levels also yielded megafloral remains and the first record of a mesofossils assemblage for the Baqueró flora. By integrating all these floristic data sources, relative abundance analyses, and sedimentological data it is possible to propose a paleoenvironmental reconstruction of the Bajo Grande area during the late Aptian: a diverse forest growing in a temperate to warm climate with subtle variations between those associations from floodplains with water instability within a delta and those that grew into a more stable area out of the flooding influence. Thus, the presumed xeromorphic features identified in the Cerro Bayo flora (sunken stomata, papillae, epicuticular waxes) may have been related to contemporaneous volcanic activity recorded in Patagonia rather than to dry conditions.