geologictimepics

Geology and Geologic Time through Photographs

Archive for the category “mountains”

Geologic Time in a mountainside –the Wallowa Mountains from Joseph, Oregon

Joseph, Oregon is a wonderful place for geology.  The town sits right at the foot of the Wallowa Mountains in the northeastern corner of Oregon.  The mountains rise some 4-5000′ abruptly from the valley floor along a recently active normal fault.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

In the mountains, you can see some bedrock relations that speak to great lengths of geologic time.  An erosional remnant of the Columbia River Basalt Group caps Sawtooth Peak in the photos below; it sits directly on granite of the Wallowa Batholith –and just a little bit south, on the next peak, the granite intrudes Martin Bridge Limestone!  So, from oldest to youngest, the rock units are the Martin Bridge Limestone, the Wallowa granite, the Columbia River Basalt.

Sawtooth Peak (right) capped by Columbia River Basalt.  Beneath it is granite of the Wallow Batholith --and off to the left, are the bedded rocks of the Martin Bridge Limestone.

Sawtooth Peak (right) capped by Columbia River Basalt. Beneath it is granite of the Wallowa Batholith –and off to the left, are the bedded rocks of the Martin Bridge Limestone.  See below for labels.

Rock units and contacts described in the text

Rock units and contacts described in the text

Never mind that we know the Martin Bridge Limestone is Triassic –so more than 200 million years old –and that the Wallowa Batholith formed at different times between 140 to about 120 million years ago –and that the basalt is about 16 million years old.  You can throw out radiometric dating, but even so, you’re looking at a great span of geologic time.  The limestone first had to be deposited, layer after layer –and then buried –and then intruded at a depth of 5-8 km by the granite –which THEN had to get uplifted to Earth’s surface so the basalt could flow over it.  After THAT, it all had to get uplifted to its present elevation along the normal fault just south of town and much of the basalt had to erode away.

Honestly, we have influential people in this country who spout off things like the Earth is only 6000 years old.  They also deny the overwhelming evidence for climate change.  I guess I should stop writing now before I get too worked up!


More photos of the Wallowas at Geologic Photography.

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.

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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

young and old, close and far

Here’s a photo of the Three Sisters Volcanoes in Oregon –looking northward.  The oldest volcano, North Sister, erupted more than 100,000 years ago and so is considered extinct.  Because no lava has erupted there in so long, erosion has cut deeply into the volcano.  By contrast, South Sister, the closest volcano on the left, most recently erupted only 2000 years ago and is much less eroded.

And then there are the stars –you can see the Big Dipper on the right side of the photo.  The closest star in the Big Dipper is some 68 light years away.

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You can see more photos of Oregon by typing the name “Oregon” into the search function on my website at http://www.marlimillerphoto.com/searchstart.html

Great Unconformity –in the Teton Range, Wyoming

As it turns out, the “Great Unconformity”, the contact between Cambrian sedimentary rock and the underlying Precambrian basement rock, is a regional feature –it’s not only in the Grand Canyon, but found all over the Rocky Mountain West –and for that matter, it’s even in the midwest.  As an example, here are a couple photos from the Teton Range in Wyoming.

The yellow arrow points to the contact between the Cambrian Sandstone and underlying Precambrian metamorphic rock... the Great unconformity.

This top photo shows the Grand Teton (right) and Mt. Owen (left) in the background… in the foreground, you can see a flat bench, which is underlain by flat-lying Cambrian sandstone.  Below that are darker-colored cliffs of Precambrian metamorphic rock.  The unconformity is right at their contact (arrow).

Also notice that the Grand Teton and Mt. Owen are made of metamorphic (and igneous) rock –but they’re much much higher in elevation than the sandstone.  That’s because there’s a fault, called the “Buck Mountain fault” that lies in-between the two.  The Buck Mountain fault moved the rock of the high peaks over the ones in the foreground during a mountain-building event at the end of the Mesozoic Era.  Because the metamorphic and igneous rock is so much more resistant to erosion than the sandstone, it stands up a lot higher.

Precambrian metamorphic and igneous rock of the Teton Range and overlying sedimentary rock.

This lower photo shows the view of the Teton range from the top of the sandstone bench (appropriately called “Table Mountain”).  As you look eastward towards the range, you can pick out the Buck Mountain fault (between the metamorphic and igneous rock of the high peaks) and the Cambrian sedimentary rock (the layered rocks).  Significantly, the Cambrian rocks, just like in the Grand Canyon, consist of sandstone, overlain by shale, overlain by limestone.

And geologic time… remember… for the sandstone to be deposited on the metamorphic or igneous rock, the metamorphic and igneous rock had to get uplifted from miles beneath the surface and exposed at sea level.  And since then, it’s been uplifted to the elevation of The Grand Teton (13370′) and Mt. Owen (12, 928′) !

Click here to see more photos of unconformities.
or… click here to see a geologic map of Grand Teton National Park, Wyoming.

Metamorphic Rock

Metamorphic rock, just its very existence at Earth’s surface, signifies great lengths of geologic time –on the order of millions of years.

Consider this rock, high in the Teton Range of Wyoming.

Folded gneiss, formed at depths of 10 km or more, high in the Teton Range of Wyoming.

This is a metamorphic rock called gneiss –in a lot of ways, it’s like granite, because it contains a lot of the same minerals –but gneiss forms because an older rock (in this case, probably a granite) was heated to high enough temperatures that its minerals recrystallized into new minerals.  And most metamorphism also involves high pressures, so all the new crystals form in a particular arrangement (as opposed to granite, in which the crystals are randomly arranged) –that’s how the layering (called “foliation”) forms in metamorphic rocks: the recyrstallization of new minerals under pressure.

Close-up view of gneiss, showing crystals that formed in the same orientation, as a result of recrystallization while under directed pressure. The layering is called "foliation"

But the key thing here, is that metamorphic rocks form WITHIN the Earth, at depth –and just like granite, require uplift and erosion to get to the surface.  This gneiss formed at depths of 10 km or more and was then uplifted to its present elevation, nearly 4 km above sea level.  –which requires time.

click here to see more photos of metamorphic rocks
click here to see a geologic map of Grand Teton National Park, Wyoming.

Cambrian rock

–the last posting, (March 21) had a photo of granite of the Cretaceous Sierra Nevada Batholith intruding Cambrian sedimentary (now metamorphosed) rocks.  These photos show more Cambrian rock.  The Cambrian Period (542-488 million years ago) is the bottom of the Phanerozoic Eon –and one reason Cambrian rocks are significant, is that they are the oldest rocks to contain shelly fossils.  Older rocks, called “Precambrian” may contain fossil impressions or fossilized algae, but don’t contain any shells.

At the risk of being too repetitive (see post March 13) the upper photo shows Cambrian limestone in the Death Valley region –there are thousands of feet of Cambrian Limestone in the Death Valley region.   The lower photo shows Cambrian sandstone, shale, and limestone overlying tilted Precambrian sedimentary rock in the Grand Canyon.

My point is that the Cambrian section is traceable over great distances.  That’s important, because the base of the Cambrian provides a common datum over much of the western US –certainly from the Sierra Nevada to Death Valley to the Grand Canyon –but in later posts, you can see that it’s also in Colorado, Wyoming, Montana… and so on!

Cambrian limestone in the Nopah Range, SE Californi

Thousands of feet of marine limestone make up many of the mountain ranges in the Death Valley area of SE California. Click here to see a geologic map of Death Valley National Park...

The photo above shows the Cambrian Bonanza King Formation (gray) on top the Cambrian Carrara Fm (orange).

And the photo below shows the near-horizontal Cambrian and younger rocks of the Grand Canyon over tilted Precambrian sedimentary rock.  It’s really thin here… the Cambrian only goes up through the arrow.

Cretaceous batholiths and roof pendants

The photos from the last posting were from the Sierra Nevada Batholith –called a “batholith” because it consists of many many smaller intrusive bodies that collectively define a much larger intrusive complex that doesn’t even have a well-defined root.  As it turns out, the Sierra Nevada are one of several really large batholiths that intruded the crust of the Pacific Margin during the Cretaceous Period, about 80-100 million years ago.

Granitic Batholiths of Cretaceous age in western North America.

And along the east side of the Sierra Nevada, we can see the original rock into which the granite of the Sierra Nevada intruded.  This original rock consists of older sedimentary and volcanic rock–that dates from the Cambrian Period through the Jurassic– much of which was metamorphosed by the heat from the intruding granite.  The photo below shows the Cretaceous granite below (light colored rock) and the dark-colored sedimentary (now metamorphic) rock above.  These older rocks that are intruded by the granite are called “roof pendants” because they show the roof of the batholith.

Cretaceous granite intruding Cambrian metasedimentary rock, Sierra Nevada Range.

And as far as geologic time goes, this photo shows us that the granite, discussed in previous posts, is younger than the sedimentary rock that overlies it.

And click here to see a photo of glaciated granite in Yosemite National Park.

 

Granite

That’s actually the moon at the end of the crack in this rock…

granite and moon, Sierra Nevada, California.

A typical exposure of granite --coarse grained with an interlocking, random assortment of crystals. Click here to search for geology pictures by keyword.

And the rock is a pretty typical example of granodiorite… which is a lot like granite, except it has a little less silica.  See yesterday’s post about igneous rocks if you’re interested.

It turns out that most of the Sierra Nevada Range in California, including Mt. Whitney (the conterminous US’s highest peak) is made out of granodiorite.  And if you consider that most of the magma cooled and crystallized at a depth of 10km, and now resides about 4km ABOVE sea level, we’re looking at millions of years to accomplish this uplift.

Here’s Mt. Whitney at sunrise… It’s the peak just left-of center.  From this view, you can see that the rock of this part of the Sierra Nevada Range is all pretty much the same: granodiorite.

Mt. Whitney and Sierra Nevada, California at sunrise. Mt. Whitney's elevation is 14, 505' above sea level, the highest spot in the conterminous US. The rock in this photograph is almost entirely granodiorite.

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