geologictimepics

Geology and Geologic Time through Photographs

Archive for the tag “glacial geology”

Glacier National Park –Proterozoic rock and fossil algae

Glacier National Park’s one of my favorite places.  It’s soaring cliffs, waterfalls, and colors are positively amazing –especially the colors.  Green green vegetation, and red, white, green, and tan rocks.

To think that these mountains were carved from sedimentary rock that was deposited at sea level and now host glacial cirques and valleys, and even a few remaining glaciers… The rocks are part of the so-called “Belt Supergroup”, which was deposited probably in a large inland sea over what is now much of western Montana, northern Idaho, eastern Washington, and southern BC and Alberta.

Peaks of Glacier National Park and St. Marys River.

Peaks of Glacier National Park and St. Marys River.

And the rocks are really old–radiometric dating has them as between about 1.4 and 1.5 BILLION years old.  Even without that knowledge though, you can guess they’re pretty old because, just about everywhere, they host fabulous sedimentary features like cross-beds, ripple marks, and mudcracks.  The sediments were deposited before critters were around to stir up the sediment.

Belt sedsrs pic

There are some fossils though: stromatalites, which are basically fossilized algae.  The algae grew as mats on the ocean floor, and because they were kind of sticky, trapped carbonate sediment.  Then they grew over the sediment –and then trapped more.  And more –until they created a mound, which in cross section looked like the photo just below –and in plan view, looked like the bottom photo.

cross-sectional view of a stromatalite in the Proterozoic Helena Formation, Glacier NP.

cross-sectional view of a stromatalite in the Proterozoic Helena Formation, Glacier NP.

Stromatalites of the Helena Formation as seen in plan view.

Stromatalites of the Helena Formation as seen in plan view.


for more photos of Glacier National Park, type “Glacier National Park, Montana” into the  geology photo search.
Or click here for a freely downloadable geologic map of Glacier National Park.

Glacially carved granite in Rocky Mountain National Park, Colorado

This landscape is so smooth and rounded that you can easily imagine the ice that must have covered it some 20,000 years ago.  And the ice must have been deep!  Look halfway up the mountain in the foreground on the left; it shows a distinct change of rock weathering akin to a bathtub ring–and the ring persists around much of the photo.  It likely marks the upper surface of the ice at maximum glaciation.

140809-94
Upper Glacier Gorge, a glacial cirque in Rocky Mountain National Park, Colorado.  View of the Spearhead (left) and McHenry’s Peak (just behind)

Like most landscapes, this one’s pretty young–and those glacial effects are even younger.  When compared to the age of the rock, it seems almost insignificant.  The granite bedrock, which is granite, is 1.4 billion years old!  Elsewhere in Rocky Mountain National Park, the granite intrudes even older metamorphic rock –1.7 billion years old.  Just .3 billion years older.  I think we forget that “just .3 billion years” is 300 million years –about the same length of time as the entire Paleozoic!  And the Pleistocene Epoch, during which the glaciers grew?  It started some 2 million and ended about 10,000 years ago

Granite sill intruding gneiss, Colorado.
1.4 billion year old granite intruding 1.7 billion year old gneiss in Rocky Mtn National Park.


images can be downloaded for free at marlimillerphoto.com

Post Navigation

<span>%d</span> bloggers like this: