GONDWANICAS DEL PALEOZOICO SUPERIOR, ESPECIALMENTE ARGENTINAS

Carlos L. Azcuy

Abstract


The possible paleoecological significance of the Upper Paleozoic microfloras of Argentina are .analyzed. The following points have been taken into account: a) method limitations; b) criteria to value the information coming from Gondwana microfloras; e) known botanical affinity of some Argentine miospores, and d) preliminary results. In the fírst point, difficulties and limitations arise from the "dispersae" character of the palynomorphs, their antiquity, the use of the almost exclusively morfological characteristics in their classification and the latitudinal topical model of the climatic zone, used as a pattern in the paleoenvironments interpretation have been analyzed. These and other elements, such as the selective fossilization, the excessive or scarce representation of some plants derived from their productive capacity of polien and spores, and the change brought about because of the overmaceration or contamination have been discussed as agents of qualitative and quantitative modification of the fossil record and, in consequence, of its ecological significance. In the second point, reference has been made to the necessity of developing the information about the megafloras and microfloras arising from the Gondwana Continent, taking into account the climatic differences that existed during the Upper Paleozoic between the habitat of these taphofloras and the one of those coming from the equatorial bando The use of the multidisciplinary control is an arduous way but a sure one to the correct comprehension of the paleoenvironmental conditions that prevailed over the Southern Hemisphere. In thc third point, not only the information about the botanical affinities referred to some genus present in the Argentinian Gondwana assernblages, but other mofphological characteristics of paleoenvironmental undoubted significance have been brought in. These other features, however, are littIe used in the valoration of paleoenvironments. They are the thickness of the exine, its volume and the structures that serve the spread. The valoration of these characteristics has been set tentatively through arbitrary pararneters for the thickness and the volume; their paleoenvironmental interpretation has been partially in agreement with the significance attributed to some grains of pollen and spores. In the last point, the paleoecological significance of the four palynological asemblages between the (Mlddle Carboniferous and Middle Permian) in the Paganzo and Chaco-Paraná Basins, in the light of the evidences coming from the information considered above has been analyzed. Palynozone of Ancistrospora is developed in a wet environment of low grounds with prevailing pteridophytic vegetation and nor far away from elevated ones with forests of Cordaitales (and/or Coniferales). During the existence of Palynozone of Potonieisporites and Palynozone III, the climate still remained wet and the first Glossopteridales made their appearence origining an incipient and gradual Xeritization
as it seems to show Palynozone of Striatites. The increase of dryness caused an outstanding decrease of the pteridophytes that probably remained confined in the thicket forest of reduced to restricted environments.

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