DENDROLITIC MICROBIAL MAT BOUNDSTONES FORMED BY THE BRANCHING FILAMENTOUS CYANOBACTERIUM ORTONELLA, LATE CARBONIFEROUS (MOSCOVIAN) PARADOX FORMATION, SOUTHEAST UTAH
Microbial mat laminites are common in the carbonates of the lower Akah and Barker Creek oil and gas intervals in the lower Paradox Fm. and occur in 10-150 cm thick beds with crinkly laminae with peloids and micritic grain “bridging” crusts. In the lower-most Akah interval, distinctive grey and black microbial mat boundstones cap the subaerially exposed Sequence 2.9. At the base of this 20-30 cm thick bed are black dendrolitic “shrubs” or tufted mats composed of the acute-angle-branching micritized sheath molds (7-12 µ diameter ) of the cyanobacterium Ortonella. The outer wall of the shrubs is formed by 3-5 mm diameter “balls” of Ortonella, which stack to build shrubs ranging from 1-4 cm in height, 4-5 cm in diameter. Within the overlying microbial mat boundstones in the top 15 cm of the bed, 2-8 mm thick black to dark grey crinkly laminae are composed of multiple layers of erect 1-3 mm high Ortonella, an unidentified larger diameter branching microbial form, peloids, and micritized peloid clumps. Laminae contain distinct horizons of fibrous calcite cements, spar-filled fenestral porosity, mud cracks, soft sediment deformation and rip-up clasts.
Like the recently described modern dendrolitic microbial mat “shrubs” of Hamlin Pool, Australia, these Carboniferous dendrolites were formed by filamentous cyanobacteria in intertidal to seasonally supratidal environments. Unlike the Hamlin Pool dendrolites, the Ortonella-dominated microbialites were calcified, increasing the likelihood of preservation in more ancient strata on Earth, or similar environments on Mars.