MICROFOSSILS IN MICROPHYTOLITES OF THE PALEOPROTEROZOIC GUNFLINT FORMATION, SOUTHERN CANADA

Silicified microphytolites of the Osagia group from the Paleoproterozo ic (Lower Proterozoic) Gunflint Formation of southern Canada (ca. 1.9 Ga) contain well preserved remnants of microorganisms represented by f ilamentous forms of genus Gunflintia (G. minuta, G, grandis), which co mpose accumulations (mats) along the Osagia lamination patterns, and b y less frequent coccoidal Huroniospora sp. scattered inside the mats. The filamentous forms seem to be remnants of oscillatoriacean or nosto calean cyanobacteria, and the latter ones are those of unicellular chr oococcalean cyanobacteria. The same microfossils were found in the sem i-rounded flattened fragments of stromatolitic laminae, well rounded p ellets, and some small columnar stromatolites occuring in the samples studied. Siliceous matrix of the samples contains the scarce planktoni c microfossils only. The predominant representatives of genus Gunflint ia inside Osagia, as well as their occurrence mode, support the earlie r suggestion that filamentous hormogonian cyanobacteria took part in t he formation of concentrically laminated microphytolites and composed dense mats on their surfaces. Microfossils from the Osagia group are t axonomically identical to those found earlier in silicified stromatoli tes of different morphology from the Gunflint Formation, but proportio ns of the present taxa are different.