Cretaceous climatic reconstruction from Argentina based on palynological data

MERCEDES B. PRÁMPARO; BARBARA VENTO; NARVAEZ, PAULA; MEGO, NATALIA; PUEBLA, GABRIELA G.

Ghent

Simposio; 52 Annual Meeting AASP-The Palynological Society; 2019

Ghent University and The Palynological Society (AASP)

Paleoclimaticreconstructions have used different proxies as climate indicators. In thiscontext, palynomorphs play a crucial role for making inferences about pastclimate changes because of their presence and distribution during the geologichistory in almost all type of environments. Plants and palynomorphs are indirect data (proxy), whichhelp us to elucidate long-term climate changes. An analysis of the palynofloralcontent in each stratigraphic layer (sample) studied from a geological unit cantell us what types of plants were growing when sediments were deposited.Climatic inferences can be made based on the autoecology of fossil taxaassuming that are similar to those of their nearest living relatives. The Earlyto Mid-Cretaceous in the Southern Hemisphere is marked by strong floralprovincialisms as a response to the climatic conditions. Argentina has a widelatitudinal range within South America, with diverse cretaceous units yieldingpalynomorphs that represent different climatic conditions. The globalCretaceous climate was predominantly warmer than at present. More refinedpaleoclimate models, applied to the Cretaceous, highlight a progressive warmingfrom Aptian to Maastrichtian. Different theories about the climatic conditionsat this time were postulated. The main aim of this contribution is tounderstand climatic trends during the Cretaceous, based on the quantitativeanalysis of selected pollen and spores, considered as climate indicators, from17 geological units in Argentina. The evaluation of the palynofloras has beenundertaken mainly by reviewing published sources from cretaceous basins butalso with our own unpublished data, covering between 22° to 54° south latitude.The climatic trend during the Cretaceous showed that the Early Cretaceous was markedby aridity episodes with high values of Classopollisand Gnetales. The palynofloras from all the studied basins show a gradual ariditytrend during the Aptian-early Albian with some notorious peaks in Classopollis abundance including thoseassociations of high latitudes. There are evidences of an expanding warm aridbelt characterized by increased abundances of the drought-resistant coniferpollen Classopollis and gnetaleanpollen together with reduced free-sporing plants abundance, during theAptian-Albian at mid and low latitudes of Argentina. In contrast, the LateCretaceous showed warm and more humid conditions indicated by increasing valuesof free-sporing plants (especially Bryophytes and ferns) and palm pollengrains, comparedwith the Early Cretaceous palynofloras. From the Albian to the end of theCretaceous, the aquatic ferns became important components of the microflorasfrom South America, while indicators of aridity decrease until absence. Nevertheless,statistical data about Cretaceous palynofloras are still scarce and incomplete.Further quantitative analysis of palynofloras from Argentina, will be necessaryto understand better the climatic trends during the Cretaceous.