Rock formations in Glacier National Park include thick layers of Proterozoic sedimentary rocks ranging from 800 to 1,600 million years in age, underlain by youger Cretaceous rocks (see Figure 1 below) (Raup, et al., 1983). The layers of Proterozoic rocks form the Belt Supergroup, which consists of mudstones (argillite and siltite), dolomite and limestone deposited near the margins of a Middle Proterozoic sea, interspersed with basaltic igneous intrusions (Earhart, et al., 1989). These sedimentary rocks have been slightly metamorphosed, but many of their original sedimentary features such as fossils, mudcracks and ripple marks are still visible (Raup, et al., 1983). Originally, the Belt Supergroup rocks were located to the west of their present position. Tectonic uplift about 70 million years ago caused these rocks to slide to the east along the Lewis Thrust Fault (Alt & Hyndman, 1973). As a result, today we find older rocks on top of younger rocks. As this thick rock layer slid eastward, the rocks deformed creating the Akamina syncline, the axis of which runs approximately through the center of the park and trends northwest to southeast approximately parallel to the Continental Divide (Whipple, 1992).
Sources: Andersen
& Borns, 1997; Harris & Tuttle,
1990; Raup, et al., 1983
Created March 12, 1999
by Karen A. Lemke (klemke@uwsp.edu). Last
updated February 23, 2006 by KAL.
The URL for this page is http:/www.uwsp.edu/acaddept/geog/faculty/lemke/gnp_vft/general_information/geology.html