Fern diversity and comparative analysis of Cretaceous formations in Argentina

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

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 biologicalreconstructions helping to understand the evolutionary processes of the biotaworldwide. Fern spores and macrofossils have been widely recorded in differentbasins around the world. Previous studies indicate that the fern flora washighly diverse during the early and mid-Cretaceous and underwent a considerabledecline in species number by the end of this period when the angiosperms becamedominant. The goal of this work is to analyze the Cretaceousfern distribution and diversity in Argentina based on published spore andmacrofossil records. A total number of 38 formations were considered inthis 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 paleofloristiclocations and the Jaccard index was used as a similarity measurement. Thediversity comparative analysis results show that the Kachaike Formation is themost diverse for the Lower Cretaceous and the Monte Chico Formation for theUpper Cretaceous. The Order Schizaeales (including Lygodiaceae, Anemiaceae, andSchizaeaceae) contains the higher number of species followed by the Marsileales(Marsileaceae). The Lower Cretaceous concentrates about 68% of the ferndiversity while the Upper Cretaceous the remaining 32%. The cluster analysisfor the Lower Cretaceous determined that the higher similarity index on ferncomposition is between the Mulichinco (late Valanginian) and La Amarga(Barremian-Aptian) formations from the Neuquén Basin, with 38% of species incommon. For the Upper Cretaceous, the Allen (Campanian) and Jagüel(Maastrichtian) formations also from the Neuquén Basin share around 35% of thespecies. The higher diversity of fern spores during the Lower Cretaceouspreviously documented in other regions is confirmed in this work. The mostdiverse cretaceous fossil association in terms of ferns belong to the AustralBasin located in southernmost Argentina. This may be due to different causes:patagonian basins have been most widely studied than the northern ones orperhaps they have better lithologies for fossil preservation. Our resultsconstitute a good contribution to understand the Cretaceous paleoclimatic andpaleocologic conditions in this part of southern south America.