Algal reefs or bioherms in the Belt Series of Montana

Fenton, Carroll Lane; Fenton, Mildred

In a discussion of Belt formations and fossils in Glacier National Park, Montana, the writers described and illustrated thick, compact beds formed by the supposed alga, Collenia. Similar deposits, also of Proterozoic age, have been described by Twenhofel and by Moore, and figured by Walcott. They, and later formations of kindred nature, have been discussed by Cumings, who designates them as "biostromes", in distinction from true lenticular or ridgelike reefs, for which he uses the term "bioherm" of Cumings and Shroek---designations adopted in this paper. Though described examples are not numerous, biostromes appear to be common in Proterozoic deposits and are present in those of the Archeozoic as well. With the doubtful exception of the Kona dolomites described by Twenhofel, however, no references were found to bioherms in rocks of Proterozoic age. Indeed, several paleontologists have suggested that organisms did not acquire the ability to build mound- or ridge-shaped deposits before Paleozoic time. Special interest, therefore, attends the discovery of indubitable Proterozoic reefs at a horizon 19,000 to 20,000 feet below the known summit of the Belt series. The purposes of this paper are (1) to describe these reefs and associated sediments, and (2) to discuss their bearing on hypotheses of the nature of Collenia and similar supposed algae.

Algal reefs or bioherms in the Belt Series of Montana

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