Sub Period: None
Chalk Canyon Formation?
Collector: DPS Ammonite
Acquired by: Field Collection
Length: 9 "
This silicified lacustrine Miocene stromatolite is a trace fossil made by a gram-negative photosynthetic blue-green bacteria. The originally limestone stromatolite was formed as a bacterial mat trapped sediment and precipitated limestone as it grew from the lake floor towards the sun. It shows classic convex layering towards the top.
The stromatolites occur in tuffaceous and lime rich lake sediments that might be part of the Chalk Canyon Formation that is bounded on the bottom by basaltic lava and volcanic rich conglomerate and sandstone on the top. Locally numerous silicified casts and molds of reed like plants, their roots, and palm wood occur in the lacustrine sediments. Since the area is under possible scientific investigation I will not give a more specific locality. The Arizona Museum of Natural History has fossils from the site per my showing them the site.
The taxonomy is very unsettled as is the author of Cyanobacteria. Taxonomy per International Registry of Marine and Nonmarine Genera:
“The cyanobacteria are named under Botanical and Bacteriological Codes, and the usage of both systems at the same time causes considerable confusion as the rules of the Botanical Code are quite different from those of the Bacteriological one.”
Photo 1: detail of photo 2.
Photo 2: 9” wide polished cross section cut and polished courtesy of Stan Celestian.
Photo 3: 6” wide polished cross section of another side.
Photo 4: top of colony.
Photo 5: bottom of colony.
Fossil Cyanobacteria & stromatolite overview:
Interesting paper that suggest Cyanobacteria created calcified structures because of interactions with viruses:
White, R. A., 3rd, Visscher, P. T., & Burns, B. P. (2021). Between a Rock and a Soft Place: The Role of Viruses in Lithification of Modern Microbial Mats. Trends in microbiology, 29(3), 204–213. https://doi.org/10.1016/j.tim.2020.06.004