Tuesday, September 2, 2008

Glacier National Park Geology & Paleontology: Part 4 - Siyeh

*Please remember that all collecting of rocks, minerals, plants, fossils or cultural objects (i.e. arrowheads) from National Park Service land is illegal and punishable by a fine*


The Siyeh Formation (also known as the Helena Formation) is by far the best exposed formation in the park. This formation outcrops as one drives along the Going-to-the-Sun Road alongside the Garden Wall, up to the western flank of Going-to-the-Sun Mountain in the Saint Mary
Valley and in several other locations within the park, particularly in Two Medicine and the Many Glacier areas. This 1.1 Ga limestone formation also contains numerous fossils. Seven species of stromatolites have been described from the formation, along with filamentous microfossils and
puzzling “molar-tooth structures.”

Mound-, conical- and dome-shaped stromatolites are so abundant in the Siyeh (Helena) Formation that they are now often grouped in zones. These zones are typically somewhat continuous and have a general similar thickness. The Fentons worked extensively in the Siyeh
(Helena) and first described four subdivisions and stromatolite zones within the park. Some of these zones are so persistent that they are often called bioherms (Fenton and Fenton, 1933). Some of these well exposed zones can be seen at the foot of Grinnell Glacier (right), along the trail leading to Granite Park chalet (above left), and near Hole-in-the-Wall. Rezak (1957), and later with Ross (Ross and Rezak, 1959), redefine these into three zones. Afterward Horodyski (1985b, 1989) redefined the zones into cycles, specifically the Jacutophyton and Baicalia-Conophyton cycles. The Baicalia-Conophyton cycle is subdivided into six distinct units by Horodyski and composes 70% of the actual volume of stromatolites from within the Siyeh (Helena) Formation. Horodyski conducted thorough research on the Siyeh stromatolites, resulting in eight publications. Isolated stromatolite occurrences not associated with these cycles are also known from within the park.

A conical stromatolite, conophyton, from the Siyeh Formation.

Sedimentary structures, such as mud cracks, scour marks and load-casts are common in the Siyeh (Helena) Formation. Fenton and Fenton (1937) describe pelecypod burrows and trails near Dawson Pass. It is commonly believed that the remains described by Fenton and Fenton (1937) can be attributed to these non-organic remains. Microfossils have also been described from chert in the lower portions of the Baicalia-Conophyton cycles (Horodyski, 1985a).

The Siyeh (Helena) Formation also contains one of the strangest pseudofossils to be described from the park – the molar-tooth structure (right). These irregular patterns were first described by Bauerman (1885) and are thought to resemble the grinding surface on the molar teeth of
elephants. They have been considered to be organic in origin by several authors; an idea often contested. Daly hypothesized that these structures were the result of “secondary tectonic segregation” (Daly, 1912; O’Connor, 1972). Walcott (1914) described these structures as organic remains, believing them to be algal, and named three types, Greysonia, Copperia and Weedia. Fenton and Fenton (1937) and Rezak (1957) concur with Daly’s hypothesis, where O’Connor (1972) and Smith (1968) interpret them as having a syndepositional origin, as a direct result of algal activity (Horodyski, 1993b). However, Ross (1959) also attributed the structures to an organic source. Horodyski (1976b, 1983b, 1985a,b, 1989) interprets them as being produced as a result of calcite infill of open-space structures. Overall, the prevailing opinion regards these molartooth structures as inorganic remains.

Bauerman, H., 1885, Report on the geology of the country near the fortyninth parallel of north latitude west of the Rocky Mountains: Geological Survey of Canada, Report of Progress 1882–1884, Pt B, p. 1-42.

Daly, R.A., 1912, Geology of North American Cordillera at the forty-ninth parallel: Geological Survey of Canada, Memoir 38.

Fenton, C.L. and Fenton, M.A., 1933, Algal reefs or bioherms in the Belt series of Montana: Geological Society of America Bulletin, v. 44, p. 1135-1142.

Fenton, C.L. and Fenton, M.A., 1937, Belt Series of the north: Stratigraphy, sedimentation, paleontology: Geological Society of America Bulletin, v. 48, p. 1873-1969.

Horodyski, R.J., 1976b, Stromatolites of the Upper Siyeh Limestone (Middle Proterozoic), Belt Supergroup, Glacier National Park, Montana: Precambrian Research, v. 3, p. 517-536.

Horodyski, R.J., 1983b, Baicalia-Conophyton stromatolite cycles in the Middle Proterozoic Siyeh limestone, northwestern Montana (abs.): Geological Society of America, Abstracts with Programs, v. 15, no. 6, p.

Horodyski, R.J., 1985a, Stromatolites and Paleontology of the Middle Proterozoic Belt Supergroup, Glacier National Park, Montana, in Whipple, J.W., O.B. Raup, Kelty, T., Davis, G., and Horodyski, R., eds., A field guidebook to the geology of Glacier National Park, Montana and vicinity: Society for Sedimentary Geologist (SEPM) midyear meeting field guide, 19 p.

Horodyski, R.J., 1985b, Stromatolites of the Middle Proterozoic Belt Supergroup, Glacier National Park, Montana: Summary and a comment on the Relationships between their Morphology and Paleoenvironment, in Toomey, D.F., and Nitecki, M.H., eds., Paleoalgology: Contemporary Research and Applications: Berlin-Heildelberg, p. 34-39.

Horodyski, R.J., 1989, Stromatolites of the Belt Supergroup, Glacier National Park, Montana, in Winston, D., Horodyski, R.J., and Whipple, J.W., eds., Middle Proterozoic Belt Supergroup, Western Montana: 28th International Geological Congress, Field Trip Guidebook T334, p. 27-

Horodyski, R.J., 1993b, Precambrian paleontology of the western conterminous United States and northwestern New Mexico, in Reed, J.C., ed., Precambrian of the Conterminous United States: Boulder, Geological Society of America, Geology of North America, v. C-2, p. 558-565
(microfiche appendix of 77 pages).

O’Connor, M.P., 1972, Classification and environmental interpretation of the cryptalgal organosedimentary “Molar-tooth” structure from the late Precambrian Belt-Purcell Supergroup: Journal of Geology, v. 80, p. 592-610.

Smith, A.G., 1968, The origin and deformation of some “molar-tooth” structures in the Precambrian Belt-Purcell Supergroup: Journal of Geology, v. 76, p. 426-443.

Rezak, R., 1957, Stromatolites of the Belt Series in Glacier National Park and vicinity, Montana: U.S. Geological Survey Professional Paper 294-D, p. 127-154.

Ross, C.P., 1959, Geology of Glacier National Park and the Flathead region, northwestern Montana: U.S. Geological Survey Professional Paper, 296, 125 p.

Ross, C.P., and Rezak, R., 1959, The rocks and fossils of Glacier National Park: The story of their origin and history: U.S. Geological Survey Professional Paper 294-K, p. 401-439.

Walcott, C.D., 1914, Cambrian Geology and Paleontology. Smithsonian Miscellaneous Collections, v. 64, no. 2, p. 77-156.


schreiber said...

I have visited this section 3 times- this is the best review that I have seen. Horodyski was a great scientist (too soon gone) and there is so much more to be seen. Equally interesting is the redbed and crossbedded sands of the Grinnell Formation... it is bright red but and somewhat boring but is full of desiccation surfaces, rippled beds (shallow water) and perfect salt casts. Someone showed me raindrops on one surface - funny, they were cubic (salt casts).
Sincerely B.C. Schreiber

ReBecca Hunt-Foster said...

Thank you, I appreciate your comments. I also love the Grinnell Formation and have even found some small stromatolites in it. I have seen some pretty large salt cast in the Grinnell as well! So many great things to see up there!