Precambrian Cabinet in Devlin Hall

This website accompanies the Precambrian display cabinet found on the 3rd floor of Devlin Hall, just outside the Baxter Isotope clean lab. The overall focus is broadly geological evidence for life and changing Oxygen levels through geologic time.

A. Shark Bay stromatolite

Stromatolites are organo-sedimentary structures built by the trapping and binding of sediment by cyanobacteria. This one was collected in the 1960s from Shark Bay, Western Australia. The carbonate clastic source for the stromatolites comes from the local Hamelin cockle, Fragum erugatum, which can be seen around the base of the speciem on display in the cabinet. The green-gray coating seen here is the dried microbial layer of cyanobacteria.

Age: Recent

B. Cambrian stromatolite "Cryptozoön"

Maryville Ls - Conasauga Grp, Thorn Hill Section eastern Tennesseee

Age: middle Cambrian

C. Aspidella terranovica Billings 1972

Fermeuse Fm, Ferryland, Newfoundland

Age: 564 Ma (Ediacaran)

Our only examples of Ediacaran organisms from the department collections. These macroscopic "organisms" are problematic with respect to their position in the tree of life, although some paleontologists treat them as animals, they are lacking the basic features that all animals today possess with regard to cell development ant the presence of different tissue types.

D. Aspidella terranovica Billings 1972

Fermeuse Fm, Ferryland, Newfoundland

Age: 564 Ma (Ediacaran)

These particular forms are thought to be the attachement structures (holdfasts) of frond-like organisms that are missing from these particular beds.

E. Bitter Springs chert - 850 Ma

The sample is stained red from weathering - the black layering is chert, the silicified remains of microbial mats and mat fragments.

Microfossils in the Bitter Springs chert include possible eukaryotic algae (Glenobotrydion, above) but are best known for cyanobacteria, particularly members of the Oscillatoriaceae (right).

F. reticulate nicrobial mat- 944 Ma

This microbial mat is from the Diabaig Fm - the basal shale of the Torridonian Sequence from the Northwest Scottish Highlands. Phosphatic nodules recovered from the Diabaig contain Bicellum Braiseri - the oldest known organism that possesses two distinct cell types and a possible precursor to the Metazoa.

H. Gunflint stromatolite

Gunflint Formation, Schreiber Ontario, Canada

age: 1.88 Ga

Gunflintia (filaments) and Huroniospora (spheres) dominant the stromatolitc biofaces of the Gunflint Fm.

For more images of the microfossils found in the Gunflint Chert , go to The Gunflint Biota page

I. Belcher Island Stromatolite

McLeary Fm, Tukarak Island, Hudson Bay, Canada

age: ca. 2.0 Ga

some of the Belcher stromatolites are silicified and samples of chert taken from the interior of these specimens may show the ghostly remains of cyanobacterial sheaths. These are the photosynthetic organisms responsible for the trapping and binding of sediment that forms the stromatolitic structure. These microfossils are classified as Gunflintia minuta.

J. banded iron formation - bif

Kipalu Formation, Tukarak Island, Hudson Bay, Canada

age: ca. 2.0 Ga

G. banded iron formation - bif

Soudan Iron Formation, Marquette Range, Minnesota

age: ca.1.9 Ga

In this hand specimen the red bands are dominated by hematite (Fe2O3) and the silvery layers contain magnetite (Fe3O4). The clear and white portion are plain chert SiO2. The layers show a rather nice model of normal faulting.

K. Archaean banded iron formation – bif

Geology: Swaziland Supergroup, Barberton, South Africa

Age: 3.4 Ga

L. detrital pyrite in quartz pebble conglomerate

Geology: Rand Group, South Africa

Age: 2.97 Ga

Detrital pyrites formed in a stream beds are not stable above 0.001 PAL (Present Atmospheric Level of 20.8%), so the presence of rounded detrital pyrite grains in aqueously laden rocks is evidence of lower atmospheric oxygen levels during the Archaean.

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