Regional Stratigraphy Field Trip
Stratigraphy of Central Montana. A trip back through geologic time. Pleistocene river channel
at Sand Coulee cutoff. Outcrops of sedimentary rocks ranging from 100 million years (m.y.) at
Belt to 500 m.y. at Monarch. Mississippian fossil locality. A 2 billion year gap (disconformity)
in the geologic record in Belt Creek Canyon. 2.64 billion year old metamorphic rocks with 1.8
b.y. old intrusion near Neihart. Belt Supergroup. Memorial Falls.
Route: Great Falls, Belt, Monarch, Neihart, Kings Hill, White Sulphur Springs
Table 1. The sequence of formations under the Highwood Mountains is:
| Period |
Age |
Group |
Formation |
Localities |
| Eocene |
53-48
m.y. |
|
Lava flows |
Highwood Mtns. |
|
56 |
|
Wasatch
conglomerate |
Highwood Mtns. |
| Cretaceous |
78 |
Montana |
Judith River
formation |
Highwood Mtns. |
|
|
" |
Clagett shale |
|
|
82 |
" |
Eagle sandstone |
Square Butte, White
Cliffs of Missouri River |
|
|
" |
Telegraph Creek
shale |
|
|
|
Colorado |
Marias River shale |
|
|
95 |
" |
Blackleaf
formation |
Belt Butte |
|
115 |
|
Kootenai formation |
Belt Armington
Raynesford |
Table 2. The sequence of formations in Kibbey Canyon (between Raynesford and Monarch) is:
| Period |
Age |
Group |
Formation |
Characteristics |
| Cretaceous |
115
m.y. |
|
Kootenai
Formation |
sandstone, shale, redbeds |
| Jurassic |
148 |
|
Morrison
Formation |
coal, grey mudstone |
|
152 |
Ellis |
Swift Sandstone |
yellow sandstone |
|
|
" |
Piper Shale |
|
|
165 |
" |
Rierdon Shale |
|
| Mississippian |
320 |
Big
Snowy |
Heath Shale |
|
|
|
" |
Otter Shale |
grey shale |
|
|
|
Kibbey
Formation |
red beds, gypsum |
|
330 |
Madison |
Mission Canyon
Limestone |
massive limestone, karst |
Table 3. The sequence of formations in the Monarch area is:
| Period |
Age |
Group |
Formation |
Lithology |
| Mississippian |
330
m.y. |
Madison |
Mission
Canyon
Limestone |
massive limestone, karst |
|
350 |
" |
Lodgepole
Limestone |
massive limestone, fossils |
|
|
|
|
|
| Devonian |
360 |
|
Three Forks
Shale |
|
|
370 |
|
Jefferson
Dolomite |
dolomite |
|
|
|
Maywood
Shale |
|
| Cambrian |
510 |
|
Pilgrim
Limestone |
flat-pebble conglomerate |
|
|
|
Park Shale |
|
|
525 |
|
Meagher
Limestone |
mottled limestone |
|
|
|
Wolsey Shale |
|
|
550
m.y. |
|
Flathead
Sandstone |
dark red sandstone, source of
Monarch Sandstone-a
decorative building stone |
| Archean |
2.64
b.y. |
|
Basement
complex |
meta-gabbro dated at 2640
m.y. |
Table 4. Starting at Neihart and extending across western Montana, the Belt Supergroup of
Proterozoic (Precambrian) age sedimentary rocks is found beneath the Cambrian-age Flathead
sandstone and the highly metamorphic basement rocks. The lower Belt formations were
deposited during the period of 1.48 to 1.44 billion.years ago. The sequence of Belt formations
found between Neihart and White Sulphur Springs is:
| Period |
Age |
Group |
Formation |
Lithology |
| Cambrian |
530 m.y. |
|
Flathead |
sandstone |
| Proterozoic |
1.44 b.y. |
Belt |
Spokane |
shale |
| " |
|
" |
Greyson |
shale |
| " |
|
" |
Newland |
limestone |
| " |
|
" |
Chamberlain |
shale |
| " |
<1.58 b.y. |
" |
Neihart |
quartzite |
| " |
1.86 b.y. |
|
Pinto diorite |
intrusion |
| Archean |
>1.86 b.y. |
|
gneiss |
metamorphic
basement |
Concepts: stratigraphy, Archean, Proterozoic, Paleozoic, Mesozoic, brachiopods, bryozoa, horn
coral, crinoids, limestone, dolomite, unconformity, disconformity, regional metamorphism,
retrograde metamorphism, Belt Basin, Helena Embayment, aulochogen
Guidebook
Guidebook to the Stratigraphy of Central Montana.. The 85 page geology guidebook describes
the geological features seen on the field trip and the geologic setting in which they occur.
Links to Related Sites
- A "Geologic History of the Western U.S." is a website with a series of pairs of maps showing
the both the tectonic features and distribution of sedimentary rocks (on the left side) and the
paleogeography (on the right side) for the period of 600 million years ago to the present. The
environmental and tectonic setting for the periods listed above can be seen on these maps.
Visit the website of Prof. Ron Blakey, scroll down to "Teaching and Other Activities", click
on "Historical Geology", scroll down to "Graphics" and click on "Geologic History of the
Western U.S."
- Visit the University of California Museum of Paleontology to learn more about
- Historical narratives of mining districts on this field trip
Return to Table of Contents
Last Updated October 31, 2000 by David Baker