Formation and stability of oxygen‐rich bubbles that shape photosynthetic mats

Abstract

Gas release in photic-zone microbialites can lead to preservable morphological biosignatures. Here, we investigate the formation and stability of oxygen-rich bubbles enmeshed by filamentous cyanobacteria. Sub-millimetric and millimetric bubbles can be stable for weeks and even months. During this time, lithifying organic-rich laminae surrounding the bubbles can preserve the shape of bubbles. Cm-scale unstable bubbles support the growth of centimetric tubular towers with distinctly laminated mineralized walls. In environments that enable high photosynthetic rates, only small stable bubbles will be enclosed by a dense microbial mesh, while in deep waters extensive microbial mesh will cover even larger photosynthetic bubbles, increasing their preservation potential. Stable photosynthetic bubbles may be preserved as sub-millimeter and millimeter-diameter features with nearly circular cross-sections in the crests of some Proterozoic conical stromatolites, while centrimetric tubes formed around unstable bubbles provide a model for the formation of tubular carbonate microbialites that are not markedly depleted in (13)C.

Oxygen-Dependent Morphogenesis of Modern Clumped Photosynthetic Mats and Implications for the Archean Stromatolite Record

“…An even more direct record of oxygenic photosynthesis may occur as 0.1-1 mm scale fenestrate textures at the tips or within the laminae of regularly laminated stromatolites and tubular microbialites. Briefly noted as "lenticular fenestrae" in modern stromatolites from Yellowstone National Park (YNP; [16]), these textures were recently described in much more detail, discussed as biosignatures of oxygenic photosynthesis and contrasted to the more common fabric-destroying fenestrae produced during extensive organic decay [17][18][19]. With possible exceptions [10,16,20], analogous fenestrate textures are yet to be identified or confirmed in Archean stromatolites.…”

Fossils of Putative Marine Algae From the Cryogenian Glacial Interlude of Mongolia

“…The presence of cellular material inside the warts, as well as their darkened, concave tops negate any interpretation of these structures as gas bubbles produced by microbial mats (e.g., Bosak et al 2009Bosak et al , 2010. In addition, MOWS consist of discrete structures that are not internally laminated, a characteristic typical of disrupted or eroded microbial mats (Riding 2000).…”

The Tooth of Time: Conrad Gebelein

“…On the one hand, she has grown ordinary stromatolites with metabolically-ancient, anoxygenic bacterial phototrophs, proving that stromatolites per se are not diagnostic of cyanobacteria (Bosak et al 2007). On the other hand, she has replicated the disturbed apical zone characteristic of certain conical stromatolites (Conophyton) by the inflation and bursting of bubbles of dioxygen, produced strictly by cyanobacteria (Bosak et al 2009(Bosak et al , 2010. The significance of this discovery for the problematic origin of oxygenic photosynthesis now depends on the range of Conophyton in the Archean stratigraphic record.…”