New precisions concerning the angiosperm record in the Baqueró Group, Patagonia, Argentina

LLORENS, MAGDALENA; PASSALÍA, MAURO GABRIEL; PEREZ LOINAZE, VALERIA SUSANA; VERA, EZEQUIEL IGNACIO; CESARI, SILVIA NÉLIDA; LIMARINO, CARLOS OSCAR

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

Conicet Mendoza - International Palaeontolocial Association

The Baqueró Group, located in the Argentinian Patagonia, with its diverse, exquisitely preserved, and accurately dated megafloristic and palynologic remains, is one of the most relevant units for the study of the early diversification of angiosperms in southern Gondwana. The floristic and environmental framework in which the diversification of early flowering plants took place is accurately contextualized by the extensive knowledge of non-angiosperm floral components and sedimentological data. The Baqueró Group comprises three units, i.e. Anfiteatro de Ticó, Bajo Tigre and Punta del Barco formations, deposited during an interval constrained between 118.23 ± 0.09 and 114.67 ± 0.18 Ma (late Aptian). The lower and upper units contain remains of flowering plants, whereas deposits of the Bajo Tigre Formation are devoid of them. Angiosperm leaves from the basal Anfiteatro de Ticó Formation include a festooned brochidodromous morphotype (Nymphaeaphyll morphotype) and a variety of micromesophyll, lobate serrate morphotypes with craspedodromous venation. In all cases, the leaves are characterized by multistranded veins, a feature considered a symplesiomorphy within the group. The only possible angiosperm megafloristic record from the Punta del Barco Formation consists of nanophyll leaves with incised laminae and actino to palinactinodromous venation. The palynological assemblages studied from the Anfiteatro de Ticó Formation are characterized by eight types of angiosperm pollen grains, referred to the genera Clavatipollenites, Retimonocolpites and Jusinghipollis, with some species exclusive from this unit. The Punta del Barco Formation yielded five types of angiosperm pollen, referred to Clavatipollenites and Retimonocolpites. Among them, Clavatipollenites sp. B, Retimonocolpites sp. B and Retimonocolpites sp. C are exclusive from this unit. Differences in pollen richness along the Baqueró Group may reflect adverse environmental conditions towards the top of the unit, which are in accordance with observed lithological features. Nevertheless, according to the new data presented herein, and especially from the palynological record, it results evident that the diversity of early angiosperms in Patagonia during the late Aptian, was higher than previously thought.