Stromatolites of America

It is common to think of Australia when stromatolites are mentioned owing to the famous Shark Bay living stromatolites, as well as the bacterial microfossils and molecular fossils found in inland Australia that date to before 3 billion years ago. In fact, however, American North, South and Central) has numerous outcrops of stromatolites spanning across the continent as well as geological time. Older stromatolites are particularly abundant in the Northern states of Wisconsin, Michigan and Minnesota dating from about the upper Archaean to the Lower Proterozoic, including expansive banded iron formations that stand as testament to the rusting of the earth.

The American stromatolites image gallery below has specimens that have been cut and polished to a mirror finish. While rough stromatolites are generally dull and unremarkable in appearance, the fine polishing renders the inherent beauty of the oldest fossils on earth, including a myriad of colors and much variation in form genera and lamination structure.

Phanerzoic Stromatolites: Paleozoic
Yelma digitata Lower Cambrian Arbuckle Mountains, Oklahoma		Girvanella-like form genera Lower Cambrian Chambliss Limestone, Marble Mountains, California
Girvanella form genera Lower Cambrian Carrea Formation, Racheal, Nevada; adjacent to Area 51		Middle Cambrian Marjum Formation, Milliard County, Utah From the famous Cambrian trilobite locality
Cryptozoan rosemontensis Lower Ordovician (495 million years old) Oneota Formation, Monroe County, Wisconsin By this time in geological history, microbial communities consisted of complex consortia of both prokaryotic and eukaryotic forms with diverse metabolic needs, and competition for resources and differing motility among them made for an intriguing microcosm of interacting life, some autotrophic, some chemotrophic and some heterotrophic.		Somphospongia sp. Carboniferous Jackson County, Kansas By the time it was formed, the cyanobacterial organisms and their stromatolitic reef systems were becoming quite restricted on earth, having retreated to environments less favorable to other marine life (including other microorganisms, algae and animals) with which they competed or from which they suffered predation.
Cryptozoan sp. Lower Ordovician (495 million years old) Oneota Formation, Appleton, Wisconsin The form genera of the laminae is rather unusual having resemblance to cauliflower. The pattern is very attractive.	Brecciated Basal Stromatolites Blue Agate Lower Ordovician (495 million years old) Oneota Formation, Buffalo County, Wisconsin	Girvanella Form Genera Silurian - (420 million years old) Salina Formation, Wood County, Ohio The oval to circular structures in these images are bacterial fossil nodules, referred to as Girvanella.	Meteorite Impact Fallback Breccia Ordovician Stromatolites Lower Ordovician (495 million years old) Oneota Formation, Glover's Bluff, Wisconsin These stromatolites were formed during the Glover's Bluff meteorite strike during the Ordovician
Phanerzoic Stromatolites: Mesozoic
	Oncolite Upper Cretaceous Lady of Angels Lake, near Ascension, State of Chihuahua, Mexico Of interest from a scientific perspective is the young age. This dinosaur-age, Cretaceous stromatolite was formed long, long after stromatolite-building organisms had to compete with other life forms, and hence had become uncommon on earth, similar to modern times. The microorganism(s) that form this stromatolite is unknown. Perhaps it was photosynthetic cyanobacteria, other prokaryotic bacteria, Eukaryotic algae (often considered a simple plant), or perhaps some combination of these types of organisms competing to survive in a not-so-friendly aquatic environment.
Phanerzoic Stromatolites: Cenozoic
	Chlorellopsis sp. Middle Eocene Green River Formation Tipton Shale Member Green River Basin, Wyoming Specimen has been polished by wind and sand. May be of algal biogenic origin.	Chlorellopsis sp. Eocene Green River Formation, Colorado Interestingly, this Cryptozoon type stromatolite was very likely to have been built by plant-like green or red, algae (Chlorophycophyta), as opposed to cyanobacteria (that are Eubacteria). It is hypothesized that red and green algae appeared some 800 million years ago having acquired chloroplasts from eukaryotes through endosymbiosis to carry out photosynthetic metabolism using sunlight for their energy needs.

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