Abstract
Five instances of association between distinctive stromatolites and blue-green algal nannofossils are recorded from a 100-m sequence of carbonate rocks about 1.6 × 109 years old, along the south side of Paradise Creek, northwestern Queensland, Australia. No eukaryotes were identified in any of these systematically limited assemblages, although they are known from rocks as old as 1.3 × 109 years in eastern California. Thus, eukaryotes may not have appeared until after 1.6 × 109 years ago (but before 1.3 × 109 years ago). The associations observed would also be consistent with (but do not prove) a biotic influence on stromatolite morphology. As is usual among prePaleozoic forms described, the morphology of the nannofossils is very similar to living forms, displaying marked evolutionary conservatism. Primary orientation of stromatolitic laminae and columns is not invariably convex upward, as conventionally believed, but convex away from and parallel to the initial point or surface of attachment, which may be horizontal or even downward beneath overhangs.
Keywords: blue-green algae, carbonate rocks, nannofossils, orientation of laminae
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