Palynological analysis of the La Anita and Cerro Fortaleza formations (Campanian), southern margin of the Viedma Lake, Santa Cruz Province, Argentina

Abstract

We present the palynological assemblages recovered from the upper part of the La Anita and Cerro Fortaleza formations (Campanian) from SW Patagonia, Argentina. A total of 73 continental species and 11 dinoflagellate cysts species were identified in this study. Continental species comprise 17 bryophytes and lycophytes, 20 ferns, 14 gymnosperms, 21 angiosperms, and 1 of uncertain affinity. The palynofloras are strongly dominated by gymnosperms, with angiosperms and ferns as secondary components. Cluster analysis employed to explore floristic similarities with Campanian–Maastrichtian palynofloras reveals two main groups: one grouping the palynofloras presented here and another grouping Campanian–Maastrichtian palynofloras from southern South America and the Antarctic Peninsula. The occurrence of spores attributable to Salviniales and Anemiaceae, along with pollen grains referable to Symplocaceae, Aquifoliaceae, and Arecaceae suggests a humid and temperate climate. The presence of Odontochitina porifera and Nelsoniella aceras suggests a late Santonian–early Maastrichtian age of deposition. In addition, continental palynological assemblages are consistent with the Campanian age established by radiometric dating. A comparative assessment of angiosperm diversity and abundance within these assemblages and published records indicates that angiosperms had not yet become the dominant floral component in southern Patagonia during the Late Cretaceous, in contrast to coeval floras at similar paleolatitudes in the Northern Hemisphere. However, further high-resolution palynological analyses are needed to refine our understanding of floristic composition, biogeographic patterns, and the time and mode of angiosperm diversification in southern Patagonia during the late Cretaceous.