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Thin sections of black chert from two 'localities at the base of the upper Precambrian Paraopeba Formation (Bambui Group) near Brasilia in south-central Brazil contain abundant microfossils. Although supposed Precambrian rnicrofossils have been recorded previously from Precambrian rocks (summarized in FAIRCHILD and DARDENNE, in prep.), the following preliminary study marks the first time that well-preserved, morphologically diverse rnicrofossils have been reported from indisputably Precambrian rocks in Brazil. These rnicrofossils occur in silicified, branched, columnar stromatolites from 3040 km north of Unai, Minas Gerais, and about 100 km to the northwest in silicified, flat-Iaminated dolostone 30 km west-southwest of Sao Gabriel, Goias. Solitary and colonial forms predominate at both localities, with the Sao Gabriel assemblege being the better preserved, more diverse, and more abundant assemblage. These discoveries are important because (1) They provide a standard of comparison for past and future rnicrofossil fmds in the Brazilian Precambrian; (2) They may further elucidate the relationships between biological content and columnar stromatolite morphology, thereby facilitating insight into the possible reasons for the apparent "evolution" of stromatolites; (3) Together with stromatolite data (see FAIRCHILD and DARDENNE, in prep.), they may help us to better date "and correlate the Bambu! Group and make better paleoenvironrnental and paleogeographical interpretations of these strata. On a broader scale, the Unai and Sao Gabriel rnicrofloras represent additional valuable evidence for deciphering the early evolution of the algae and for testing Precambrian biostratigraphic schemes (see SCHOPF, 1977).

First report of well-preserved precambrian microfossils in Brazil (Paraopeba formation, Bambuí Group, near Brasilia)