A 571 million‐year‐old alkaline volcanic lake photosynthesizing microbial community, the Anti‐atlas, Morocco

Abstract

The Ediacaran period coincides with the emergence of ancestral animal lineages and cyanobacteria capable of thriving in nutrient deficient oceans which together with photosynthetic eukaryotic dominance, culminated in the rapid oxygenation of the Ediacaran atmosphere. However, ecological evidence for the colonization of the Ediacaran terrestrial biosphere by photosynthetic communities and their contribution to the oxygenation of the biosphere at this time is very sparse. Here, we expand the repertoire of Ediacaran habitable environments to a specific microbial community that thrived in an extreme alkaline volcanic lake 571 Myr ago in the Anti‐atlas of Morocco. The microbial fabrics preserve evidence of primary growth structures, comprised of two main microbialitic units, with the lower section consisting of irregular and patchy thrombolytic mesoclots associated with composite microbialitic domes. Calcirudite interbeds, dominated by wave‐rippled sandy calcarenites and stromatoclasts, fill the interdome troughs and seal the dome tops. A meter‐thick epiclastic stromatolite bed grading upwards from a dominantly flat to wavy laminated base, transitions into low convex laminae consisting of decimeter to meter‐thick dome‐shaped stromatolitic columns, overlies the thrombolitic and composite microbialitic facies. Microbialitic beds constructed during periods of limited clastic input, and underlain by coarse‐grained microbialite‐derived clasts and by the wave‐rippled calcarenites, suggest high‐energy events associated with lake expansion. High‐resolution microscopy revealed spherulitic aggregates and structures reminiscent of coccoidal microbial cell casts and mineralized extra‐polymeric substances (EPS). The primary fabrics and multistage diagenetic features, represented by active carbonate production, photosynthesizing microbial communities, photosynthetic gas bubbles, gas escape structures, and tufted mats, suggest specialized oxygenic photosynthesizers thriving in alkaline volcanic lakes, contributed toward oxygen variability in the Ediacaran terrestrial biosphere.

Blooming of a microbial community in an Ediacaran extreme volcanic lake system

“…Our study shows that P is absent or below detection in the carbonate samples, which if present should have been accumulated as abundant apatite carbonate minerals, but was instead co-enriched with Fe present principally as hematite 30 , 69 in most of the epiclastic samples (Supplementary Table 1 ). A well-supported positive linear correlation between Fe 2 O 3 and P 2 O 5 in the epiclastic deposit (Supplementary Fig.…”

“…In this regard, petrographic studies show that the microbialites preserve pristine carbonate phases and primary microbial fabrics 69 . However, they are slightly affected by early diagenesis, including dissolution and filling vugs with botryoidal and blocky/drusy mosaic calcite and late silicification 30 . The concentration of As in the studied microbialites presents a diffused pattern observed mainly within the mesoclots affiliated with the thrombolitic and composite microbialites, being concentrated within fine-grained clotted micrite (Fig.…”

“…Here, we combine high-resolution multiproxy geochemistry to a sequence of well-preserved microbialites in a continuous sedimentary profile of an Ediacaran alkaline lake ecosystem from Morocco's Anti-Atlas 30 , to demonstrate a strong link between changing environmental chemistry and the assemblage, organization, and succession of a rare extremophilic microbial community. We identify and characterize the discrete biogeochemical intervals that drove their spatial and temporal differentiation into distinct assemblages.…”