Fern diversity and comparative analisis of the cretaceous formations in Argentina

MEGO, NATALIA; NARVAEZ, PAULA; PUEBLA, GRISELDA ; VENTO, BARBARA; PRAMPARO, MERCEDES

Congreso; XIV International Palynological Congress and X International Organisation of Paleobotany Conference; 2016

Asociacion Latinoamericana de Paleobotanica y Palinologia

The fossil record is relevant for biological reconstructions helping to understand the evolutionary processes ofthe biota worldwide. Fern spores and macrofossils have been widely recorded in different basins around theworld. Previous studies indicate that the fern flora was highly diverse during the early and mid-Cretaceous andunderwent a considerable decline in species number by the end of this period when the angiosperms becamedominant. The goal of this work is to analyze the Cretaceous fern distribution and diversity in Argentinabased on published spore and macrofossil 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 adistribution chart. A cluster analysis was performed to detect associations between paleofloristic locationsand the Jaccard index was used as a similarity measurement. The diversity comparative analysis results showthat the Kachaike Formation is the most diverse for the Lower Cretaceous and the Monte Chico Formation forthe Upper Cretaceous. The Order Schizaeales (including Lygodiaceae, Anemiaceae, and Schizaeaceae) containsthe higher number of species followed by the Marsileales (Marsileaceae). The Lower Cretaceous concentratesabout 68% of the fern diversity while the Upper Cretaceous the remaining 32%. The cluster analysis for theLower 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% ofspecies in common. For the Upper Cretaceous, the Allen (Campanian) and Jagüel (Maastrichtian) formationsalso from the Neuquén Basin share around 35% of the species. The higher diversity of fern spores duringthe Lower Cretaceous previously documented in other regions is confirmed in this work. The most diversecretaceous 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 onesor perhaps they have better lithologies for fossil preservation. Our results constitute a good contribution tounderstand the Cretaceous paleoclimatic and paleocologic conditions in this part of southern south America.