NEW PRECISIONS CONCERNING THE ANGIOSPERM RECORD IN THE BAQUERÓ GROUP, PATAGONIA, ARGENTINA

LLORENS, M.; PASSALIA, M.G.; PÉREZ LOINAZE, V.; VERA, E.; CÉSARI, S.; LIMARINO, C.O.

Mendoza

Congreso; 4th International Paleontological Congress; 2014

International Paleontological 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 forthe study of the early diversification of angiosperms in southern Gondwana. The floristic andenvironmental framework in which the diversification of early flowering plants took place isaccurately contextualized by the extensive knowledge of non-angiosperm floral components andsedimentological data. The Baqueró Group comprises three units, i.e. Anfiteatro de Ticó, Bajo Tigreand Punta del Barco formations, deposited during an interval constrained between 118.23 ± 0.09and 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 basalAnfiteatro de Ticó Formation include a festooned brochidodromous morphotype (Nymphaeaphyllmorphotype) and a variety of micromesophyll, lobate serrate morphotypes with craspedodromousvenation. In all cases, the leaves are characterized by multistranded veins, a feature considereda symplesiomorphy within the group. The only possible angiosperm megafloristic record fromthe Punta del Barco Formation consists of nanophyll leaves with incised laminae and actino topalinactinodromous venation. The palynological assemblages studied from the Anfiteatro de TicóFormation are characterized by eight types of angiosperm pollen grains, referred to the generaClavatipollenites, Retimonocolpites and Jusinghipollis, with some species exclusive from this unit. ThePunta del Barco Formation yielded five types of angiosperm pollen, referred to Clavatipollenites andRetimonocolpites. Among them, Clavatipollenites sp. B, Retimonocolpites sp. B and Retimonocolpitessp. C are exclusive from this unit. Differences in pollen richness along the Baqueró Group mayreflect adverse environmental conditions towards the top of the unit, which are in accordancewith observed lithological features. Nevertheless, according to the new data presented herein, andespecially from the palynological record, it results evident that the diversity of early angiospermsin Patagonia during the late Aptian, was higher than previously thought.