Fossils

Stromatolites are fossilized algae mounds.

NPS photo.

The fossil resources preserved in Glacier give a glimpse into the beginning of life on our planet and help to tell the deep history of the park.

Some of the oldest fossils in the park are found on the park’s east side, near Apikuni Falls. These fossils are found in the Altyn Formation, which is composed of nearly 1.5-billion-year-old limestone and dolomite rock. Here we find massive beds of stromatolites, which are fossilized algae mounds. Outcrops of them can also be seen at Logan Pass, Grinnell Glacier, and along the western side of Going-to-the-Sun Road.

Sometimes referred to as "sliced cabbage" because of their appearance, stromatolites formed in the bottoms of shallow, warm seas and are responsible, through photosynthesis, for the oxygen-rich atmosphere we live in today. Composed of layers of blue-green algae, stromatolites form a wide variety of shapes: conical, stratiform, branching, domal, and columnar.

During the Precambrian Era (4,500 to 500 million years ago), stromatolites were abundant and widespread, forming reef-like structures known as bioherms. Today, similar living stromatolites are known from tidal channels in the Exuma Cays, Bahamas, and in Australia's Hamelin Pool at Shark Bay.

 

Are stromatolites Glacier's only fossils?

Stromatolites aren't the only fossil present in Glacier, but they are the most commonly found. There are many others in the park that span the geologic record and are far less evident in terms of location, quantity, or size. Older sediments contain Horodyskia monilifomis, a multicellular organism resembling a string of beads and considered by some researcher to be an important evolutionary link to eukaryotic life, which includes plants, animals, and fungi. Cretaceous period sediments include mollusks, bivalves, gastropods, and plants. Rocks from the Paleogene and early Neogene periods contains petrified wood and fossilized gastropods, mammals, fish, insects, mollusks, and plants.

In Glacier, paleontology hasn't been the main focus of geological research—there is still a lot to learn. While the fossilized microorganisms, small mammals, and insects may lack the glamour of dinosaurs, there is no question these fossils are important to the development and understanding of all life as we know it today.

Why are stromatolites here?

The ancient Belt Sea covered parts of present-day eastern Washington, northern Idaho, western Montana, and nearby areas in Canada. This includes the area now known as Glacier National Park. Blue-green algae, or cyanobacteria, thrived in shallow parts of the Belt Sea and played a significant role in the formation of the carbonate rocks of the park. Limestone and dolomite are examples of the carbonate rocks that are found today. Stromatolites are the remains of these cyanobacteria.

How do stromatolites form?

Starting as a small clump of blue-green algae, stromatolites grow by catching sediments moving in the water around them. With each new layer of sediment, grows a new layer of algae trapping the sediment in between. Repeated over and over, this expands the mat of algae until it resembles a column or cone. Today, these fossils can take on various shapes and sizes, but often resemble sliced cabbage, the cross-section of a jawbreaker, or swirls of water.

How do stromatolites impact Glacier's geology?

As some of the earliest forms of photosynthetic life, stromatolites began to change the world around them. Sunlight allows algae to consume carbon dioxide from seawater and release oxygen in the process. There are two important results from this process:

1. When algae removes carbon dioxide from the seawater, fine particles of calcium carbonate are formed from a chemical reaction. Removal of carbon dioxide from seawater caused the formation of large quantities of calcium carbonate, which contributed to the great thickness of carbonate rocks in the park.
2. Oxygen is released into the atmosphere. This was a major factor in producing the oxygen-rich atmosphere that allowed development of oxygen-consuming life forms on Earth like gastropods, mammals, fish, insects, mollusks, and plants, all seen within some of Glacier's younger rock layers.

 

Glacier's rocks are either very old or relatively young. Precambrian, Cretaceous, and Tertiary age rocks are exposed within the park, along with the much younger Quaternary sediments. Missing from the park is an incredible gap of time—over 800 million years!

The compression and uplift that built the Rocky Mountains caused a huge fault, known as the Lewis overthrust. This movement pushed older rocks up and over the top of younger ones. Consequently, the Paleozoic geological era, with its spectacular trilobites, mollusks, giant ferns, and dinosaurs, has been eroded from the upper layers of Glacier's rocks, or is buried far below a two-mile-thick slab of very old Precambrian rock that is exposed.

 

 

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  Geologic Formations

  Glacier's sedimentary rock banding represents many ages.

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  Glacial Geology

  Once you know what to look for, viewing Glacier's landscape can seem like reading a textbook on the geologic effects of glaciation.

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  Mountains

  Glacier's impressive mountains are a story of pressure, folding, uplift, and erosion.