ARCHEAN PLUMOSE MICROBIALITES: THREE DISTINCT GROWTH MORPHOLOGIES & ECOLOGICAL IMPLICATIONS

Microbialites can have complex morphologies that preserve clues to ancient microbial ecology. However, extracting and interpreting these clues is challenging due to both the complexity of microbial structures and the difficulties of connecting morphology to microbial processes. Fenestrate microbialites in the 2521 ± 3 Ma Gamohaan formation, South Africa, include plumose microbialites, which are composed of surfaces called supports and zones of dense organic inclusions. Three-dimensional reconstruction of plumose microbialites has led to identification of three distinct growth structures: 1) Supports with an Organic Rich Zone (ORZ); 2) Supports without ORZ; and 3) domes. Three-dimensional analysis of plumose microbialites shows that dome sides dip 25º to 45º, supports with ORZ dip 55º to 70º and supports without ORZ dip 80º to 90º, resulting in a 15º dip gap in dip between domes and supports with ORZ and a 10º dip gap between supports with and without ORZ. Results suggest that the three distinct growth structures grew in fundamentally different ways and require a subdivision of the growth environments within the microbial structures. In modern microbialites, different organisms preferentially live on and produce different morphological elements. By analogy, we predict that the microbial communities forming the three components of plumose microbialites were ecologically distinct.