DEUNFFIA AND DOMASIA FROM THE SILURIAN OF BRAZIL: CHRONOSTRATIGRAPHIC IMPLICATIONS

This work is based on the palynological investigation of core samples from PETROBRAS deep well 1-AM-1-AM, ELECTRONORTE shallow drills SM 1015, SM 1018, SM 1044, SM 1048 from the Amazonas Basin (Autás-Mirim Formation, Trombetas Group), and an outcrop sample from the Parnaíba Basin (Tinguá Formation).

Acritarch assemblages from the Trombetas Group are cosmopolitan in character. They show close similarity to coeval assemblages from the United States, Canada, Argentina, Spain, the British Isles, Norway, Sweden (Gotland), Belgium, Poland, Turkey, Libya, and Saudi Arabia.

The present study enhances the distribution of two typical Silurian genera of acritarch in Brazil: Deunffia Downie 1960 and Domasia Downie 1960. The first one with the species D. brevispinosa and D. furcata and the second one with the species D. amphora, D. bispinosa, D. canadensis, D. limaciforme, D. rochesterensis, and D. trispinosa. All the species related were recovered from the Amazonas basin, and only D. limaciforme could be registered at Parnaíba Basin.

This two genera are important taxa defining the Llandovery-Wenlock interval, of incontestable chronostratigraphic value, since they are globally restricted to the Silurian. According to Cramer (1970); Le Hérrisé (1989) and Molyneux et al. (1996), these taxa increase in number near the Llandovery-Wenlock boundary, what is also confirmed in the present paper.