Lower Proterozoic Girvanella Stromatolite

Massive Girvanella Stromatolites

Geologic Time: Lower Proterozoic (2.2 to 2.4 billion years old)

Size: 11.5 by 9.6 inches maximum

Fossil Site: Chocolay Group, Chocolay Hills, Northern Michigan

GirvanellaStromatolite is the oldest of all fossils, and with much labor (cutting and polishing), it is most beautiful. The banding that commonly appears in stromatolite is a record of the growth patterns of colonies of microorganisms, principally photosynthetic prokaryotes (e.g, cyanobacteria). The colors that are often expressed are the result of the interaction of biological and sedimentary processes, together with subsequent chemistry and mineral exchange. Note the contrast in the polished and unpolished sides in the first two pictures.

This stromatolite is at once, ancient (Lower Proterozoic), beautiful, and unusually colored. Coming from the Chocolay Group in an area know as the Chocolay Hills located southeast of Ishpeming, Michigan, it dates to some 2.2 to 2.4 Billion years old. This stromatolitic carbonate has been hand-polished to a mirror finish on one side exhibits a broad spectrum and intricate pattern of colors.

This is a rare form from the Northern Michigan locality known as Girvanella (denoting a form appearing as an individual growth colony of non-symmetrical, pseudo-spherical shape. Girvanella forms are rarely found in older stromatolite. Such a massive pseudo-sphere as seen here may have no precedent in the formation. The portion in the specimen that appears to be about one half the width colony is nearly a foot wide, implying a two-foot wide colony. This specimen is also interesting in that it exhibits both flat and wavy lamination outside the Girvanella form, and there are red blotches that are precipitated Rhodochrosite. Measuring 11 by 9.6 inches, such plates are exceedingly difficult to cut and polish.

Also see: Stromatolites Across Geologic Time

Click to enlarge

Fossil Mall Home
l Museum and Rare Fossils l Fossil Dealers l
Fossil Categories:
l Ammonites for Sale l Trilobites for Sale l Fish Fossils for Sale l
l Insect Fossils l Invertebrate Fossils l Plant Fossils l Stromatolites l
l Crinoids and Echinoderms Fossils l Dinosaur Fossils l Fossil Amber l