Fern diversity and comparative analysis of Cretaceous formations in Argentina

VENTO BÁRBARA; PRÁMPARO MERCEDES; NARVÁEZ PAULA LILIANA; PUEBLA GRISELDA; MEGO NATALIA

Salvador

Congreso; XIV International Palynological Congress - X International Organisation of Palaeobotany Conference; 2016

IFPS ? International Federation of Palynological Societies, IOS ? International Organisation of Palaeobotany and ALPP ? Asociación Latinoamericana de Palaeobotánica y Palinología

The fossil record is relevant for biological reconstructions helping to understand the evolutionary processes of the biota worldwide. Fern spores and macrofossils have been widely recorded in different basins around the world. Previous studies indicate that the fern flora was highly diverse during the early and mid-Cretaceous and underwent a considerable decline in species number by the end of this period when the angiosperms became dominant. The goal of this work is to analyze the Cretaceous fern distribution and diversity in Argentina based on published spore and macrofossil records. A total number of 38 formations were considered in this study. They belong to seven basins distributed throughout the country (Salta Group, San Luis, Neuquén, Chubut River Area, San Jorge, Deseado Massif, and Austral). Presence-absence of species was included in a distribution chart. A cluster analysis was performed to detect associations between paleofloristic locations and the Jaccard index was used as a similarity measurement. The diversity comparative analysis results show that the Kachaike Formation is the most diverse for the Lower Cretaceous and the Monte Chico Formation for the Upper Cretaceous. The Order Schizaeales (including Lygodiaceae, Anemiaceae, and Schizaeaceae) contains the higher number of species followed by the Marsileales (Marsileaceae). The Lower Cretaceous concentrates about 68% of the fern diversity while the Upper Cretaceous the remaining 32%. The cluster analysis for the Lower Cretaceous determined that the higher similarity index on fern composition is between the Mulichinco (late Valanginian) and La Amarga (Barremian-Aptian) formations from the Neuquén Basin, with 38% of species in common. For the Upper Cretaceous, the Allen (Campanian) and Jagüel (Maastrichtian) formations also from the Neuquén Basin share around 35% of the species. The higher diversity of fern spores during the Lower Cretaceous previously documented in other regions is confirmed in this work. The most diverse cretaceous fossil association in terms of ferns belong to the Austral Basin located in southernmost Argentina. This may be due to different causes: patagonian basins have been most widely studied than the northern ones or perhaps they have better lithologies for fossil preservation..Our results constitute a good contribution to understand the cretaceous paleoclimatic and paleocologic conditions in this part of southern South America.