geologictimepics

Geology and Geologic Time through Photographs

Archive for the tag “geologic time photos”

Rockin’ countertops–geologic time in our kitchens and bathrooms!

I stopped by a “granite” supplier yesterday –the kind of place that sells “granite” and “marble” slabs for countertops.  Besides the fact that almost none of the slabs were actually granite or marble, they were spectacular rocks that showed wonderful wonderful detail. I nearly gushed at the idea of taking a geology field trip there.  It’s local, and you seldom find exposures like this anywhere else!

slabs of polished rock at a "granite" warehouse --not sure if any of this is actually granite, but it all reflects geologic time.

slabs of polished rock at a “granite” warehouse –most of it’s not actually granite, but it all reflects geologic time.

Generally speaking, “granite” in countertop language means “igneous” or “metamorphic” –crystalline rocks that form miles beneath Earth’s surface and so require great lengths of time to reach the surface where they can be quarried.  When I first started this blog, geologic time with respect to igneous and metamorphic rocks were some of the first things I wrote about –it’s such pervasive and important stuff.

So the main point is that your friend’s kitchen with “granite” countertops surrounds you with geologic time every time you walk in there!

But check out that green polka-dotted rock on the right side of the photo.  Full of rounded cobbles –it’s a conglomerate, originating by sedimentary processes on Earth’s surface. Does it indicate great lengths of geologic time? A Young Earth Creationist might say it were a deposit of “the Flood” and end-of-story.

Here’s a closer look:

Polished conglomerate --individual cobbles are metamorphic rocks. The green color comes from the mineral chlorite.

Polished conglomerate –individual cobbles are metamorphic rocks. The green color of the background material comes from the mineral chlorite. That’s a penny (on the left) for scale.

The conglomerate is made of beautifully rounded cobbles and small boulders that are almost entirely metamorphic in origin.  Most of them are gneisses, which form at especially high grades of metamorphism, typical of depths greater than 8 or 10 miles!  After a (long) period of uplift and erosion, the rock was exposed to erosion, gradually breaking into fragments, which eventually became these rounded cobbles, and ended up in the bottom of a big stream channel or on a gravel bar somewhere.

But that’s not the end of the story, because this deposit of rounded cobbles itself became metamorphosed –so it had to get buried again. We know that because the rock is pervaded by the mineral chlorite, which gives the rock its green color.  Chlorite requires metamorphism to form.  Granted, the rock isn’t highly metamorphosed –there’s no metamorphic layering and chlorite forms at low metamorphic temperatures– but it’s metamorphic nonetheless, typical of depths of a few miles beneath the surface.

And if you look even closer, you can see some of the effects of the reburial pressures: the edges of some of the cobbles poke into some of the other ones. This impingement is a result of the stress concentrations that naturally occur along points of contact.  The high stress causes the less soluble rocks to slowly dissolve into the other, more soluble rock.

cobbles, impinging into each other. Stars on right photo show locations.

cobbles, impinging into each other. Stars on right photo show locations.

I’m already jealous of the person who’s going to buy this slab of rock. It tells a story that begins with 1) metamorphic rock forming deep in the crust, then 2) a long period of uplift and erosion to expose the rocks, then 3) erosion, rounding, and deposition of the metamorphic cobbles, 4) reburial to the somewhat shallow depths of a mile or two–maybe more, 5) more uplift and erosion to expose the meta-sedimentary deposit, 6) Erosion by human beings.

And me? Personally, I’d like to make a shower stall or a bathtub out of this rock –can you imagine???


Some links you might like:
a blog I like that’s about science and creationism
another blog about an ancient Earth and deep time
my original song “Don’t take it for Granite“. (adds some levity?)
Geology photos for free download.

 

 

 

Geologic history of the western United States in a cliff face in Death Valley National Park

Of the many geologic events that shaped the western United States since the beginning of the Paleozoic Era, five really stand out.  In approximate chronological order, these events include the accumulation of tens of thousands of feet of sedimentary rock on a passive margin, periods of compressional mountain building that folded and faulted those rocks during much of the Mesozoic–likely driven by the accretion of terranes, intrusion of subduction-related granitic rock (such as the Sierra Nevada) during the Jurassic and Cretaceous, volcanic activity during the late Cenozoic, and mountain-building by crustal extension during the late Cenozoic and continuing today.  This photo on the western edge of Panamint Valley in Death Valley National Park of California, captures all five.

View of canyon wall on west side of Panamint Valley in SE California --part of Death Valley National Park.  See photo below for interpretation.

View of canyon wall on west side of Panamint Valley in SE California –part of Death Valley National Park. See photo below for interpretation.

The photograph below shows an interpretation.  Paleozoic rock is folded because of the Late Paleozoic-early Mesozoic compressional mountain-building; it’s intruded by Jurassic age granitic rock, an early phase of Sierran magmatism that took place just to the west; the granitic rock is overlain by Late Cenozoic basalt flows, and everything is cut by a normal (extensional) fault.  And there is also a dike that cuts the Paleozoic rock –probably a feeder for the basalt flows.

Interpretation of top photo.

Interpretation of top photo.

So this is all nerdy geology cross-cutting relations talk –but here’s the point: in this one place, you can see evidence for 100s of millions of years of Earth History.  Earth is old old old!  THAT’S why I love geology!

And for those of you who crave geologic contacts?  This photo has all three: depositional, between the basalt and underlying rock; intrusive, between the Mesozoic granite and the folded Paleozoic rock; fault, the steeply dipping black line between the basalt and the Paleozoic rock.  Another reason why I love geology!


click here to see photos and explanations of geologic contacts.
or click here for a slideshow of Death Valley geology.

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

San Andreas Fault

Here’s a view of the San Andreas fault and Pt. Reyes in northern California, looking northward.  The fault runs right up the narrow Tomales Bay–and in just a few miles, runs along the edge of San Francisco.

The San Andreas fault is amazingly well-studied –it’s probably the most-studied fault zone in the world.  After all, it is capable of generating huge earthquakes in heavily populated areas, so the more we know about it the better.

San Andreas fault and Tomales Bay

Aerial view of San Andreas fault and Pt. Reyes --just north of San Francisco. View is to the north. The fault runs down Tomales Bay, the narrow arm of the ocean that runs diagonally across the photo.

One thing we know about the San Andreas is that it generally moves in a side-by-side way (strike-slip) so that rock on the east side moves south relative to that on the west side.  And over time, the fault has moved the eastern rock more than 300km relative to the western rock.

Now, 300 km –that speaks to millions of years of geologic time.  We can measure the rate at which the Pacific Plate moves relative to the North American Plate –about 4.5 cm/year.  The San Andreas takes up most of that –but not all.  But if we assume it takes it all, we’re looking at a total of 300km at 4.5cm/year –so at least 6.6 million years.

Of course… if you think planet Earth is only 10,000 years old, that means the fault’s moved some 300 meters (3 football fields) every 10 years.  And considering that the displacement was about 6 meters during the M 8.3 1906 San Francisco Earthquake…that’s a lot of earthquakes in just a short period of time!

Or another way of putting it, if planet Earth were 10,000 years old AND the San Andreas fault formed at the very beginning, 10,000 years ago… then there must have been 50 of those San-Francisco-sized Earthquakes every ten years –or… 5 of those every year.  Yikes!

But of course… we know that the San Andreas isn’t as old as the planet.  It cuts that granite at Pt. Reyes… which is related to the Sierra Nevada granite –which is really pretty young –but older than 10,000 years by about 100 million.

click here if you want to see more photos of the San Andreas fault –with a map!

Great Unconformity in Montana –and rising seas during the Cambrian

Here’s yet another picture of the Great Unconformity –this time in southwestern Montana.  Once again, Cambrian sandstone overlies Precambrian gneiss.  You can see a thin intrusive body, called a dike, cutting through the gneiss on the right side.  You can also see that the bottom of the sandstone is actually a conglomerate –made of quartzite cobbles derived from some nearby outcrops during the Cambrian.

Great unconformity in SW Montana.

Photo of Cambrian Flathead Sandstone overlying Proterozoic gneiss in SW Montana.

 

And that’s me in the photo.  My left hand is on the sandstone –some 520 million years or so old; my right hand is on the gneiss, some 1.7 BILLION years old.  There’s more than a billion years of missing rock record between my two hands.  Considering that the entire Paleozoic section from the top of the Inner Gorge in the Grand Canyon to the top of the rim represents about 300 million years and is some 3500′ thick… yikes!

And… just like in the Grand Canyon and elsewhere, there is Cambrian age shale and limestone above the sandstone.  This rock sequence reflects rising sea levels during the Cambrian.  It’s called the “Cambrian Transgression”, when the sea moved up onto the continent, eventually inundating almost everywhere.  If you look at the diagram below, you can see how this sequence formed.

Marine transgression

Sequence of rock types expected during a transgression of the sea onto a continent.

If you look at time 1, you can see a coastline in cross-section, with sand being deposited closest to shore, mud a little farther out, and eventually carbonate material even farther out.  As sea levels rise (time 2), the sites of deposition for these materials migrates landward, putting mud deposition on top the earlier sand deposition and so on.  At time 3, the sequence moves even farther landward, resulting in carbonate over mud over sand.  If these materials become preserved and turned into rock, they form the sequence sandstone overlain by shale overlain by limestone –just what we see on top the Great Unconformity.

 

 

 

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.

Great Unconformity –Grand Canyon, Arizona

So just like intrusive igneous rocks, metamorphic rocks require great lengths of time to accomplish the uplift and erosion in order to be exposed at Earth’s surface.

So what do we make of this photograph?  It shows a sequence of sandstone, shale, and limestone sitting on top metamorphic rock (called the “Vishnu Schist”) in the Grand Canyon.  The sandstone was deposited right on top the schist.

Great unconformity, Grand Canyon, Arizona

Sequence of Cambrian sandstone (the ledge across the middle of the photo), shale (the overlying slopes) and limestone (the upper cliffs) deposited on top the Vishnu Schist in the Grand Canyon.

 

Since sedimentary rocks, like sandstone, shale, or limestone, are deposited at Earth’s surface –and metamorphic rock forms beneath the surface, this photo shows that BEFORE the sedimentary rocks were deposited, the metamorphic rock (schist) had to have been uplifted and exposed.  So all the time required to bring the schist to the surface had to take place before the sandstone was even deposited.

The surface of contact between the sandstone and the schist is called an unconformity because it is here that we see evidence for a great deal of missing rock record.  The sandstone must be much younger than the schist –for the very reason that the schist first had to get uplifted and exposed at the surface before the sandstone was deposited on top of it.  So… because the sandstone is so much younger, but it was deposited right on top the schist, there must be a gap in the rock record between them … an unconformity.

And here is where we see evidence for even LONGER periods of time.  Overlying the sandstone?  Thousands and thousands of feet of more sedimentary rock.  And much of that sedimentary rock was marine… formed at sea level.  It is now over a mile above sea level.

And the schist itself?  The people who’ve studied it have determined that much of it was originally volcanic –which means that it originally formed at the Earth’s surface.  So… over geologic time, it must have been buried to the depths needed to turn it into a metamorphic rock BEFORE it was uplifted and exposed.

So… how old is Earth?  Some say 6 or 10,000 years… I think we’re looking at 10s of millions in this photo.  And if we consider the numerical ages for these rocks, 1.7 billion is the age of metamorphism of the schist –its original volcanic rock must have been older!

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