Cretaceous climatic reconstruction from Argentina based on palynological data

NARVÁEZ, P.L; VENTO, B.; PUEBLA, G.G.; PRÁMPARO, M.B.; MEGO, N.

Ghent

Congreso; 52nd Annual Meeting. AASP - The Palynological Society; 2019

AASP - The Palynological Society

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 type of environments. Plants and palynomorphs are indirect data (proxy), which help us to elucidate long-term climate changes. An analysis of the palynofloral content in each stratigraphic layer (sample) studied from a geological unit can tell us what types of plants were growing when sediments were deposited. Climatic inferences can be made based on the autoecology of fossil taxa assuming that are similar to those of their nearest living relatives. The Early to Mid-Cretaceous in the Southern Hemisphere is marked by strong floral provincialisms as a response to the climatic conditions. Argentina has a wide latitudinal range within South America, with diverse cretaceous units yielding palynomorphs that represent different climatic conditions. The global Cretaceous climate was predominantly warmer than at present. More refined paleoclimate models, applied to the Cretaceous, highlight a progressive warming from Aptian to Maastrichtian. Different theories about the climatic conditions at this time were postulated. The main aim of this contribution is to understand climatic trends during the Cretaceous, based on the quantitative analysis of selected pollen and spores, considered as climate indicators, from 17 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the palynofloras has been undertaken mainly by reviewing published sources from cretaceous basins but also with our own unpublished data, covering between 22° to 54° south latitude. The climatic trend during the Cretaceous showed that the Early Cretaceous was marked by aridity episodes with high values of Classopollis and Gnetales. The palynofloras from all the studied basins show a gradual aridity trend during the Aptian-early Albian with some notorious peaks in Classopollis abundance including those associations of high latitudes. There are evidences of an expanding warm arid belt characterized by increased abundances of the drought-resistant conifer pollen Classopollis and gnetalean pollen together with reduced free-sporing plants abundance, during the Aptian-Albian at mid and low latitudes of Argentina. In contrast, the Late Cretaceous showed warm and more humid conditions indicated by increasing values of free-sporing plants (especially Bryophytes and ferns) and palm pollen grains, compared with the Early Cretaceous palynofloras. From the Albian to the end of the Cretaceous, the aquatic ferns became important components of the microfloras from 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 necessary to understand better the climatic trends during the Cretaceous.