Palynostratigraphic study of the Early Cretaceous Río Mayer and Kachaike formations at the Quebrada El Moro Section, Austral Basin, southwestern Argentina

Abstract

Palynomorph assemblages have been recovered from the upper levels of the Río Mayer Formation and the basal levels of the Kachaike Formation exposed at the Puesto El Moro Creek, southwest of Santa Cruz Province, Argentina. Forty-five spore species and 25 pollen taxa (including six angiosperms) have been identified. The palynological assemblages of the upper levels of Río Mayer Formation are dominated by pteridophytic spores, while Classopollis is a common element. In the Kachaike Formation, the angiosperm pollen grains are more diverse and abundant than in the underlying unit, and Cheirolepidiaceae pollen continues to dominate. The presence of scarce angiosperm pollen, represented by Clavatipollenites sp., allows reference of the assemblage recorded in the upper levels of the Río Mayer Formation to the Aptian Antulsporites- Clavatipollenites Zone. In addition, the lower levels of the Kachaike Formation are referred to the late Aptian-early Albian, based on the presence of Asteropollis asteroides, Pennipollis peroreticulatus, Clavatipollenites sp. and scarce tricolpate pollen. From the three major stages of the early angiosperm evolution in southern South America that have been previously recognized, the palynoflora of the upper levels of the Río Mayer Formation can be referred to Stage I (late Barremian-Aptian), whereas the assemblages recognized in the Kachaike strata are comparable to Stage II (latest Aptian- earliest Albian).