The Gunflint microbiota |
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| Authors: | Stanley M Awramik Elso S Barghoorn |
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| Institution: | 1. Department of Geological Sciences, University of California, Santa Barbara, Calif. 93106 U.S.A.;2. The Biological Laboratories, Harvard University, Cambridge, Mass. 02138 U.S.A. |
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| Abstract: | The microbiota of the Gunflint Iron Formation (～2 Ga old) is sufficiently great in diversity as to represent a “benchmark” in the level of evolution at a time only somewhat less than intermediate between the origin of the earth and the present.To date, thirty entities from these ～2 Ga old microfossiliferous cherts have been described and all but two systematically categorized. From our continuing detailed study of the Gunflint microbiota (ESB for over 20 years) and, in light of our recent investigations on blue-green algal cell degradation, we conclude that: (1) A considerable number of the taxa systematically described are either of doubtful biological origin, doubtful taxonomic assignment, and/or morphologically indistinguishable from previously described Gunflint microorganisms, (2) The microbiota is wholly prokaryotic.At present, we recognize sixteen taxa falling within three categories: (1) blue-green algae (6 taxa; e.g. Gunflintia minuta); (2) budding bacteria (4 taxa; e.g. Eoastrion simplex); and (3) unknown affinities (6 taxa; e.g. Eosphaera tyleri). Organisms of undoubted eukaryotic affinities have yet to be found in the Gunflint.The Gunflint assemblage includes a high percentage of morphologic entities of obscure taxonomic position.Recently, Walter (1975) and Knoll and Barghoorn (1975) reported Gunflint-type microbiotas of approximately the same age as the Gunflint from two localities in Australia. The dominant morphotypes of the Gunflint microbiota appear to be cosmopolitan and the striking similarity of the three assemblages may strengthen the potential of ancient microbiotas for use in Precambrian biostratigraphy. |
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