Fossils of Glacier National Park, stromatolites of the Belt Supergroup

Feinberg, David

Several fossilized life forms have been recognized within the strata of the Precambrian Belt Supergroup at Glacier National Park, Montana. These fossils occur as individual and colonial cyanophytes (blue-green algae) and bacteria. The colonial bluegreen algae occur most commonly as stromatolites and are by far the most abundant fossil types in the Beltian rocks. Some stromatolite biostromes form significantly thick and extensive units which can be traced throughout the area. There are at least eight zones of stromatolites which are useful in the regional correlation of strata in the Glacier Park area. These zones can be used as marker horizons within the strata because of their widespread consistency of position within the rock units over large areas. Each zone varies in composition,thickness, growth morphology, growth sequences and aerial extent. These thick and extensive stromatolite sequences make up the majority of the fossil mass of the Beltian rocks. However, a variety of other small assemblages can be found within the park which are limited to a variety of small, localized growth habitats. The variety of stromatolite forms has led some to believe that each "is formed by an individual biological cyanophyte species,while others believe that the different forms represent a single (or a few) species which grew under differing environmental circumstances. It is these stromatolites which will be the main topic of this report, while the other fossil types will be discussed in brief, in the last chapters. Numerous fossils of more advanced plants and animals can be found in the much younger cretaceous rocks on the east side of the park. Organic debris, seashore creatures and even dinosaur fossils can be found in these dark sandstones and shales. These rocks are in thrust fault contact with the older, overlying Belt Supergroup and make up many of the low rolling hills on the east side of the park. These rocks are relatively less resistant to erosion and therefore do not make up any bold outcrops in the park. These rocks can be examined in good detail in road-cuts along Two Medicine Ridge, near East Glacier Park. These cretaceous fossiliferous rocks are not discussed in any detail in this report.

Fossils of Glacier National Park, stromatolites of the Belt Supergroup

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