The southernmost record of tropical angiosperm pollen in the Early Cretaceous of Patagonia, Argentina

BARREDA, V. Y ARCHANGELSKY, S

Gramado, Brasil

Otro; 11º Reunión de Paleobotánicos y Palinológos; 2004

UNISINOS

The presence in the austral tip of South America of angiosperm genera of the Afropollis-Schrankipollis group and Brenneripollis peroreticulatus invites to reevaluate the currently accepted boundaries between Early Cretaceous palynological provinces in the light of the distribution of these key taxa. The material was recovered from the Kachaike Formation at the Bajo Comisión section in Santa Cruz province. Angiosperms are poorly represented in these palynological assemblages dominated by gymnosperm pollen and bryophyte-pteridophyte spores. This sequence is dated in the Albian to Early Cenomanian. The basal levels include sediments of a nearshore marine environment in which chlorantaceous pollen of Clavatipollenites and Asteropollis is found. Grading to deltaic and fluvial environments that characterize the middle-upper levels the first eudicots were identified: Cupuliferoidaepollis, Retitricolporites and Tricolporoidites, together with the Afropollis - Schrankipollis group. These grains are mainly zonosulculate of radial or bilateral symmetry and a sexine that is mostly detached from the nexine. They are related to the Winteraceae, a family now represented in the Patagonian flora, and seem to have a very restricted stratigraphical distribution. In addition, B. peroreticulatus, a type having affinities with Alismatales, species of Retimonocolpites, and a monoaperturate (ulcerate) tetrahedral tetrad comparable to modern members of the Winteraceae, were also recognized. These records suggest that a diversified angiosperm community was living during the Albian-Cenomanian in Patagonia, including basal groups related to Chloranthaceae, southern hemisphere elements allied to Winteraceae, aquatic to semi aquatic herbs of the Alismatales together with diversified eudicots of uncertain affinities. A global temperature increase and generalized Albian-Cenomanian transgressions were probably responsible for the diversification and southward radiation of these tropical elements, reaching the marginal area of the Patagonian province.