The relationship between morphology, microstructure, and microbiota in three vertically intergrading stromatolites from the Gunflint Iron Formation

Abstract

The microstructure in three silicified morphologically distinct and vertically intergrading stromatolites from the Aphebian (~2 Ga old) Gunflint Iron Formation of Ontario, Canada was found to be different for each stromatolite morphology studied; each in turn has a characteristic microbial composition. Non-columnar stromatolites that comprise the middle zone of the intergrading sequence contain a microstructure characterized by relatively thin laminae composed of a cyanophytic community dominated by the coccoid Huroniospora Barghoorn while the columnar stromatolites of the lower (small, frequently divergent branching columns) and upper zone (large, infrequently α- to β-parallel branching columns) have thicker laminae differing in shape and continuity, which were built by a filamentous cyanophyte-dominated community. 'Microstromatolites' referable to Frutexites Maslov are found in the middle non-columnar and occasionally in the lower parts of the upper columnar zone.In the stromatolites thus far examined from the Gunflint formation, the microbiota, microstructure, and macrostructure are all interrelated, the composition of the microbiota, the nature of the microstructure, and the resulting gross morphology of the stromatolite presumably were influenced or controlled by the microbiota.