Columnar stromatolites from the Early Proterozoic Schmidtsdrift Formation, Northern Cape province, South Africa - Part I: systematic and diagnostic features

Abstract

Main articleThe Schmidtsdrift Formation (Transvaal Dolomite) is a Lower Proterozoic stromatolite-bearing carbonate unit. A good succession of columnar stromatolites occurs along the Boetsap River (Northern Cape Province). Using the method of serial sections to draw the gross morphology of columns and following the actual classification based on a succession of different characters, many new groups and forms have been found : Topinamboura insulata is a bulbous column with wart-like projections spreading out everywhere on the smooth surface. Radiatina isotropa presents closely packed radiating columns forming compact bioherms. The small rhythmically superposed columns of Tibia cristata, Tibia plumata and Sapinia fucoides offer tiny bushy columns with a constant crestal zone, a very unusual feature, giving an angular ,shape to the laminae. Some of the stromatolites belong to previously described groups, from the same area as Katernia africana or Katernia perlina new form, which present true bushy columns forming thin biostromes; or, from other parts of the world, as Pilbaria boetsapia and Pilbaria inzeriformis, two new forms, attributed to a Lower Proteroroic group described in Australia. Besides description of morphologies and mode of occurrences, detailed studies of lamina microstructures have been carried out. Very interesting fabrics have been described but, until now, no true organic remains (cells) have been found. The conclusions emphasize the importance of detailed systematic description of stromatolites in order to make a biostratigraphical model of the Lower Proterozoic and to clear up confusions with Upper Proterozoic stromatolites which also present varied assemblages of ramified stromatolites.Non