Microbial vs Environmental Influences on the Morphology of Late Archean Fenestrate Microbialites

Stromatolite morphology is the most abundant record of Archean life, but interpretations of the role of microbial communities in stromatolite growth are difficult because stromatolites are the result of complex interactions among abiotic and biotic processes. Archean fenestrate microbialites are a group of structures in which the roles of biotic and abiotic processes can be constrained more than in most stromatolites. Fenestrate microbialites from the 2.52 Ga Gamohaan and Fairfield formations, South Africa, the 2.6 Ga Bulawayo greenstone belt, Zimbabwe, and the ~2.8 Ga Steep-rock greenstone belt, Ontario, each contain two morphologically distinct microbial communities that grew contemporaneously. One community grew as very fine, filmy laminae, and the other grew as wider, often vertically oriented “supports”. The distinction of filmy laminae and supports persists with various microbialite structures over hundreds of millions of years and with two carbonate precipitation styles. Comparisons of these microbialites imply that the growth structure was determined by the microbial communities, and the timing and location of carbonate precipitation influenced preserved morphology.