Eustelos gondwanicos de medulas diafragmadas e a sua posicao estratigrafica.

Abstract

Based on palynological studies, the Irati Formation is generally correlated with the Ecca and Raniganj formations of Africa and India, respectively, whereas studies on Gondwanic eusteles indicate similarities with a lower horizon corresponding to the White-Band of South Africa and Barakar of India. In a previous article, the solenoid biozone that emphasizes this result was discussed. Now a new set of fossil plants is distinguished whose biozone coincides approximately with that of the solenoid group and thus seems to present the same difficulty for correlation. The distribution of plants with pith diaphragms in sequences so far apart in Gondwana certainly implies the close likeness of unusual environmental conditions which also must have evoked adaptive responses in the vegetative body of the plants, such as xeromorphic adaptations for aeration or water storage in the anatomical plans peculiar to each genus, associated or not with sclerenchyma. The evidence therefore points to a set of highly specialized plants growing near small basins of restricted circulation under intermittent to markedly periodic conditions of scarce aeration or brackish or saline waters. -from English summary