Geological Survey Professional Paper 294—D Stromatolites of the Belt Series in Glacier National Park and Vicinity, Montana

PREVIOUS INVESTIGATIONS

The precambrian stromatolites of the Belt series were first recognized by C. D. Walcott, and in 1906 he published photographs of an algal structure for which the name Cryptozoon frequens was proposed. (See pl. 20, fig. 6.) In 1914, Walcott published descriptions of several genera and species of Precambrian stromatolites. Many of Walcott's "algae" have since been considered to be of inorganic origin (Fenton and Fenton, 1936). However, later studies agree with Walcott's belief in the algal nature of several of the species he described, especially some of those he referred to the genus Collenia.

From 1911 to 1914, field parties of the Geological Survey under the supervision of M. R. Campbell made extensive geologic studies and mapped a large part of Glacier National Park. Although at first they did not recognize the stromatolites as organic structures, their many references to gnarly and concretionary limestones have been a great aid in locating outcrops of stromatolite beds.

Very little attention was given the stromatolites of the Belt series until the period between 1927. and 1936. During this time C. L. and M. A. Fenton devoted five field seasons to the study of the paleontology and stratigraphy of the Belt series. The results of their investigations were published between 1931 and 1943 in papers cited.

PRESENT INVESTIGATION

The present investigation was begun in 1951 as a part of a project on the Belt series of northwestern Montana, under the direction of C. P. Ross, and has continued to the present time. During the early stages of his mapping, Ross recognized that several beds in the Belt series of Glacier National Park, Mont., contained structures of probable algal origin. A few of the beds or zones appeared to be persistent over rather wide areas, and one zone in the Siyeh limestone was mapped. Later, a zone in the Missoula group was also mapped. Owing to the small map scale, it was not possible to map any of the other zones.

The primary purpose of the present investigation was to determine if these zones could be used as stratigraphic markers. In such a great thickness of strata, where the only basis for correlation has been lithology, the geologist would welcome any paleontologic aids to subdivision and correlation. Local datum markers would also be useful for correct interpretation of some of the more complex structural features involving rocks of the Belt series. In addition, an ecological study of the stromatolite beds could furnish information that might be used in interpreting the paleogeography of Belt time. These uses of stromatolites have been proved in the Glacier National Park region.

As a result of these studies it was found possible to group the several growth forms of the stromatolites into a fewer number of "specific" categories, to rearrange "generic" assignments more systematically, and to define the "genera" and "species" more precisely.

AREA OF INVESTIGATION

Most of the detailed work has been carried out in the Glacier National Park region, but a part of it has been done in other localities in northwestern Montana and northern Idaho. (See fig. 49.) Stromatolites were found at each locality. It appears that the Belt series in those areas is susceptible of subdivision on the basis of stromatolite zones.

FIGURE 49.—Map of northwestern Montana and adjacent States, showing area of investigation and localities mentioned in text.

In the Coeur d'Alene district, Idaho, stromatolites have been noted in the Prichard formation and the Burke formation. Possibly detailed work will uncover stromatolite zones that will be useful as key horizons in other formations of the district. In the vicinity of Troy and Libby, Mont., stromatolite beds occur in the Wallace and Striped Peak formations. Near Helena, Mont., the Helena limestone, Spokane shale, and the Greyson shale have yielded stromatolites. In the Big Belt and Little Belt Mountains stromatolites have been reported in the Spokane shale, Greyson shale, and Newland limestone.

ACKNOWLEDGMENTS

It is a pleasure to acknowledge my indebtedness to the many persons who have contributed to the successful completion of this investigation. M. E. Beatty, chief naturalist, and Don Robinson, assistant chief naturalist, were especially helpful in placing at my disposal the Park Service facilities at Glacier National Park. Arthur B. Campbell guided me to stromatolite localities in the Coeur d'Alene district, Idaho. Prof. Adolf Knopf of the University of California and Montis R. Klepper showed me exposures of stromatolites near Helena, Mont. During the 1952 and 1953 field seasons, Robert N. Oldale ably assisted me in the field. Prof. John L. Rich of the University of Cincinnati and Prof. Erling Dorf of Princeton University allowed me to examine type specimens in their museums. Robert N. Ginsburg showed me Recent stromatolites on some of the keys in Florida Bay. G. E. Lewis, Sergius Mamay, and J. Harlan Johnson have read the manuscript and contributed many valuable suggestions.