Stromatolites New and Old

Extremities: Geology and Life in Yellowstone and Implications for Other Worlds

STROMATOLITES

Stromatolites are petrified microbial mats, and show the same structures as living microbial mats (and sometimes even fossilized filaments of microbes). Large microbial mats are rare today, as they are food to many kinds of animals. But in Proterozoic and Archaean times, when there were no animals, microbial mats were everywhere and stromatilite fossils are abundant.


This diorama of microbial mat mounds is in the Museum of the Rockies. It is modeled after the microbial mounds in Shark Bay Australia (where the water is so hot and saline that few animals can live).		These cyanobacterial mat mounds are in the Octopus Springs channel. Although they are only a few centimeters across, their shape is identical to that of the Sharks Bay mounds.


A stromatolite fossil, now limestone rock, from late preCambrian rocks in Montana (the Belt series, for cognoscenti), in the Museum of the Rockies. This cut slab is a cross-section perpendicular to the original water surface. The flat layers are fossilized microbial mats, and the curved layers are fossilized mounds like those living today in Shark Bay (above).		Another stromatilite, also from the late preCambrian rocks of Montana, in Dr. Ward's collection. This rock surface is parallel to the original water surface, and so it shows the microbial mounds as circular features.

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