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Paleoclimatic reconstructions have used different proxies as climate indicators. In this context, palynomorphs play a crucial role for making inferences about past climate changes because of their presence and distribution during the geologic history in almost all types of environments. Argentina has a wide latitudinal range in South America, with diverse cretaceous units yielding palynomorphs that represent different climatic conditions. The Cretaceous was a time when climate conditions showed some special variations. Different theories about the climate conditions at this time were postulated. The main aim of this contribution is to understand climate trends during the Cretaceous, based on the quantitative analysis of selected pollen and spores, considered as climate indicators, from different geological units in Argentina. The evaluation of the palynofloras has been undertaken mainly by reviewing published sources from cretaceous basins but also with our own unpublished data. The climatic trend during the Cretaceous showed that the Early Cretaceous is marked by aridity episodes with high values of Classopollis and Gnetales. In contrast, the Late Cretaceous showed warmer and more humid conditions indicated by increasing values of free-sporing plants (especially Bryophytes and ferns) and palm pollen grains, and the decrease until their absence of the aridity indicators.

-VERRUCATE TRILETE SPORES FROM THE LAGARCITO FORMATION (ALBIAN?) SIERRA DE GUAYAGUAS, SAN JUAN PROVINCE: ARGENTINA. BIOSTRATIGRAPHIC ANALYSIS. A detailed study of the systematics of 13 species of verrucate trilete spores recovered from the Lagarcito Formation is presented. Taxonomic studies of these types of spores with great morphological diversity are very important as they constitute a useful contribution for the clarifi cation of many misidentifi cations usually very common within this morphologic group. The Lagarcito Formation is part of the El Gigante Group, formed by continental sediments of fl uvio-deltaic origin deposited in an extensional basin. The material was collected in a section exposed in the eastern side of the Sierra de Guayaguas, southeast of the San Juan province and corresponds to shallow lacustrine sediments. The following species are described and illustrated: Within the palynofl ora the verrucate trilete spores are abundant and correspond to the fern families: Lycopodiaceae, Selaginellaceae, Cyatheaceae, Osmundaceae, Dicksoniaceae and Schizaeaceae, indicative of local humid conditions near the lacustrine bodies. Based on the analysis of the occurrence and biostratigraphical value of the studied species in different Lower Cretaceous basins in Argentina and other related places, an Aptian-Albian range is concluded for the verrucate spore association recovered from the Lagarcito Formation. The present systematic study provides also new insight to the vegetal diversity developed during the Early Cretaceous in central-western Argentina.