Archive for the ‘Geology’ category

Molar Tooth Texture

August 12, 2010

Ok, so remember the weird rock I showed in my Galcier Park geology post? No? Here it is again:

This texture is called “molar-tooth” texture, because apparently someone thought it looked like the teeth of elephants. They must have been studying some weird elephants. It’s a very bizarre texture. It cuts across the layers of the rock as if it is related to fractures, but it is often deformed and squished as if it formed in wet sediment. In some places the minerals filling the fractures are broken up and collected as hard clasts, but it other places they clearly formed after the sediment was deformed.

The two leading explanations for this texture are bubbles and waves*. In the bubble model, the fractures form when gas is evolved in the gooey mud, and builds up enough pressure to propagate through the layers. Then once those voids are formed, fine-grained crystals fill them in. Sometimes, the overlying pressure of newer sediment compressed the voids before they are filled, causing them to accordion up into the contorted shapes we see today. In the wave scenario, pressure changes from powerful storm waves cause the sea floor to undulate, forming the fractures which are then filled in with minerals.

This texture has no modern-day analog because macroscopic life forms disrupt the mud before the mineralization can take place.It’s very unlikely that we would find this on Mars, but it is good practice for us martians to try to explain rocks we’ve never seen before!

*I’m sure I am completely oversimplifying, and likely mangling, these explanations.

The Geology of Glacier National Park: Part 1

August 7, 2010

Well, the field trip is over and I am happy to say that I was not eaten by any bears. They seemed much more interested in the huckleberries.

My adviser and two colleagues and a family of bears.

I am also happy to say that I know a little bit more about the geology of Glacier National Park (and about how to interpret sedimentary geology in general) than I did before I left. The park is famous for its large-scale geography of course: towering mountains and deep valleys carved by rivers of ice. Glaciers tend to form broad U-shaped valleys, while rivers and streams cut V-shaped valleys. Take a look at this picture and you can see glaciers have been involved, even though they are mostly gone now (and the few that remain are disappearing fast: there will be no more glaciers in the park by 2030).

Glacier National Park: soon to be known as "U-shaped Valley National Park".

Despite the spectacular views, we actually spent most of our time in the park with our backs to the vistas, staring intently at rocks that most visitors would pass by without a second glance. Most of the rocks in Glacier are Precambrian sedimentary rocks, deposited around 1.5 billion years ago. The world was a very different place back then, with essentially no oxygen in the atmosphere and no multicellular life. Without large life forms crawling around in the mud of the seafloor (a process called “bioturbation”), the physical processes that shape the sediments are nicely preserved, and I learned a lot about how to interpret their record.

For example, take a look at this ripple:

This symmetric ripple indicates back-and-forth flow of water over the soft mud.

A ripple means that the water was flowing and moving sediment, but you can actually learn more than that based on its shape. This ripple is symmetric, meaning that the water was flowing back and forth, rather than only in one direction. That tells us that it didn’t form in a stream, but more likely due to the movement of tides or waves.

Here’s another interesting feature:

You can see that the layers here aren’t parallel – there’s a lens of material with a relatively flat top, but a curved lower portion that cuts into the underlying layers. This is a little channel, carved into the lower sediments while they were still soft and filled with coarser material!

The coarseness of the sediment tells you a lot about the environment where it was dropped. It takes a much faster, more energetic flow to carry rocks than it does to carry sand. Silt and mud will stay suspended in all but the most tranquil of bodies of water, so what happened here?

This location is actually much younger cretaceous rock outside the park, where the ancient Precambrian mountains have been broken down and deposited in a floodplain. (lots of dinosaur bones have been discovered in other outcrops of this cretaceous rock, but alas, we didn’t find any) There has been some crazy deformation in this area, tilting the layers so that they are almost vertical, but you can still see striking evidence of different environments here. This spot actually shows another much larger example of a channel, filled with big green and red rocks. (The channel is the coarse layer behind the geologist in the picture that narrows as you go upward) The size of the rocks in this channel means the water must have been flowing pretty fast to move them. But you can see that other parts of the same outcrop are very different. The tan stuff is extremely soft, and when you crush it between your fingertips, it turns into a powder with grains far too small to see or feel.

This soft stuff could have been emplaced when the river carrying the larger rocks flooded its banks, dumping its sediment as it stagnated in the floodplains. This same process is why places like the Nile river valley are so fertile. It’s not a sure thing that the fine-grained stuff came from a flooding river though. It could also be fine ash from a volcanic eruption (a more likely scenario for Mars!).

There’s a lot more cool geology to show you from the park, but this post is long enough, so I will leave you with a puzzle. Take a look at this bizarre rock texture that we saw all over the park:

What is going on here?

What do you think it is? We were asked the exact same question by our field trip leader to get us to practice explaining completely unknown rock types, something that could very well happen on Mars. Stay tuned for my next post where I’ll attempt to explain what this texture is!

Big Sky Country

July 31, 2010

Well folks, I’m headed off to Big Sky Country tomorrow (aka Montana)! I’ll start the week at the MSL camera team meeting, where I will get all sorts of cool news about the MastCam, MAHLI and MARDI cameras which I will not be able to share with you.* After that, the lot of us will pack up and head to Glacier National Park to learn about the geology of the Belt-Purcell supergroup, and more generally, how to apply terrestrial geology to martian geology. I always enjoy field trips like this because I get to hike around on the rocks with a bunch of experts as well as many with less field experience, so there are lots of educational discussions. Also, did I mention the part where I get to drive and  hike around in spectacular scenery? Yeah. Times like this I’m reminded that my job Does Not Suck.

I’ll try to write a post or two about the trip once I actually understand the geology we’re going to see a little more. Hopefully the weather will cooperate and I’ll have some pretty pictures to share too!

*One of the difficulties with actually being involved in missions is that I can’t just write about all the cool stuff I hear about. I got scolded when this blog was just starting out for posting information before JPL or NASA had approved of it, so I tend to err on the side of caution now. It’s frustrating, but there’s nothing I can really do.

Big Pictures: Space Shuttle and Mount St. Helens

May 18, 2010

The Big Picture has been on a roll lately, with two sets of particular interest to planetary and space-types. First, is the feature on the final launch of the space shuttle Atlantis last week:

Second, today is the 30th anniversary of the explosive eruption of Mount St. Helens, and there are some amazing photos that show the devastating power of a volcanic eruption:

Carnival of Space 152

May 2, 2010

Welcome to The Martian Chronicles and the 152nd edition of the Carnival of Space! As always, we’ve got a great bunch of space-related posts from across the blogosphere, ranging from life on Mars to the age of the universe to Science Ninjas!

I’ll get things started with a pair of posts from right here at The Martian Chronicles. A couple weeks ago I went on a cool geology field trip in the El Paso/Carlsbad area along with a whole bunch of other martian and terrestrial geologists. Among other things, we learned that printed Mars panoramas make good raincoats, that graduate students are ideal for menial labor like counting hundreds of thousands of layers of rock, and that ancient reefs have a surprising amount to teach us about stratigraphy on Mars. Check out my summaries of Day 1 and Day 2 of the field trip! Day three is coming soon, with lots of pretty pictures of Carlsbad Caverns!

Speaking of rocks and Mars, Paul Scott Anderson at Planetaria has a post about another Mars meteorite that might have evidence of life! He includes a few very nice electron microscope images of the meteorite for your consideration. Personally, I’m not convinced, but I’m also not an expert on this corner of Mars science. Take a look for yourself!

Ian O’Neill at Discovery News also has been thinking about martian microbes, and whether germs from Earth might have hitched a ride on our rovers, set up camp on Mars and wiped out the locals. It would sure be disappointing if we discover life on Mars only to learn that someone at JPL forgot to wash their hands! Of course, there are also those who think we should stop bothering with all this planetary protection business and deliberately seed Mars with Earth life. What do you think?

While we’re on the topic of our potentially infectious little rovers, Stuart Atkinson has some beautiful pictures from the Opportunity rover. Oppy is slowly making her way across the Meridiani Plains, and has a tantalizing view of the distant hills that are her ultimate destination. As Stu says, “The far horizon is calling…

But this is the Carnival of Space, not the Carnival of Rocks and Bugs and Rovers, so let’s get on to the more “spacey” stuff! I’m a big fan of stuff, and so is Steve Nerlich at Cheap Astronomy! This week they have a great podcast about “stuff” in space and the surprisingly limited number of shapes in which it can be found.

A radar "image" of an asteroid and its two tiny moons. Credit: NASA / JPL / GSSR / Emily Lakdawalla

While we’re on the topic of stuff and its various shapes, I should point out that radar is a great way to find out the shape of stuff in space like asteroids. If you’ve ever seen one of the “images” of an asteroid taken by a telescope like Arecibo and wondered how a radar antenna can be used to take a picture, then wonder no longer! Just take a look at Emily Lakdawalla’s post about radar imaging and all your questions will be answered.

If radar images are not your cup of tea, then maybe you’d prefer to learn about an old-school optical telescope: the Radcliffe 1.9 meter telescope. Markus shares the joy of handling the massive old wrought iron telescope in this post at Supernova Condensate.

Not a fan of old school ‘scopes? Well, perhaps I can interest you in some futuristic  Hypertelescopes? Next Big Future also has some cool posts about even more far-out ideas like Dyson Swarms and Dyson bubbles and “statites” – structures that hover above a star by balancing its gravitational force with its radiation pressure.

We’re a long way from that level of engineering, but solar sail technologies are getting more advanced. Centauri Dreams has a post about the Japanese IKAROS mission: an interplanetary solar sail that also uses its sail as a solar panel to generate electricity! I hadn’t heard of this mission, but it sounds really cool!

Whether you’re talking about star-enveloping Dyson spheres or relatively simpler missions, you have to wonder what drives exploration, particularly since big steps forward like the Apollo program come so rarely. Well, 21st Century waves talks about the idea that what we’re really dealing with is a chaotic system in this post on how complexity drives exploration.

Of course, sometimes it’s just the brilliance of one person that makes the difference, and lights the path forward, and Robert Goddard is a great example. Over at Music of the Spheres, there’s a great post about Goddard that takes a look as some of his earliest thoughts on space and also some of his inventions, which are now available online thanks to Google Patents.

Weird Sciences contributed three posts this week: First up, some thoughts on why Stephen Hawking is wrong about aliens and the threat they pose. Also, some thoughts on the implications of self-replicating machines. And third, visualizing the fourth spatial dimension.

Speaking of weird, what does Weird Warp have for us this week? Why it’s a nice, informative (and actually not very weird!) post all about the ins and outs of comets, everyone’s favorite icy visitors to the inner solar system.

While we’re back on the subject of “things that are in the inner solar system”, let’s take a look at Astroblogger Ian Musgrave’s post about how to use the moon to find stuff in the night sky. Ian even provides some scripts for the free programs Celestia and Stellarium!

Once you have rounded up your friends and family and taken them on a tour of the night sky using the moon as your guide, you’re bound to start getting pelted with questions. Luckily, “We are all in the gutter” has started a new “how do we know” feature. Their first post in the series is an answer to the question: “How do we know how old the universe is?” Do you have other “how do we know”-type questions? Contact the “We are all in the gutter” folks and get your answer!

Our penultimate post is from Steinn Sigurdsson, who reports on the unfortunate incident of the Nuclear Compton Telescope: a balloon-borne telescope that crashed in Australia during an attempted launch earlier this week. Condolences for those on the telescope team; it’s painful to watch so much work fall apart at its culmination.

And finally, on a (much) lighter note, what you’ve all been waiting for. Toothpaste ingredients! Which of course, logically, lead us to discover Amanda Bauer’s secret alter ego: the Science Ninja. This post makes me wish that a) all products had ingredient lists like the one on that toothpaste, and b) that I, too, was a science ninja.

Update: one late addition to the carnival! Nancy Atkinson at Universe Today is working on a series of posts entitled “13 Things that Saved Apollo 13“. The main article has link to the rest of the articles. Very interesting stuff!

Update 2: One more latebreaking addition! Out of the Cradle has a nice review of the book “The Big Splat, or How the Moon Came to Be”.

Phew! Well, that does it for this week’s Carnival of Space! It’s been a wild ride, as always. Thanks again to Fraser for letting me host, and thanks to all the space bloggers who contributed!


MarsSed 2010 Field Trip Day 2: Stromatolites, Gypsum and Layers

April 29, 2010

We started off Day 2 of the field trip by driving up onto the eroded rocks of what used to be the tidal flats of the ancient reef, between the shore and the continental shelf. The closest modern-day analog to the rocks that we visited is the Persian Gulf, where you have an arid climate and deposition on the shelf and down into the deeper ocean basin. In the tidal flats and lagoons of the ancient sea where the rocks that we visited formed, the water was only a few meters deep, and was a nice place for blue-green algae to grow. You might think that a bunch of single-celled organisms wouldn’t leave much of a mark in the geologic record, but you would be wrong!

The wavy layers in the carbonate rocks here are stromatolites - fossil backterial mats that grew in the shallow tidal flats and lagoon behind the ancient reef.

In fact, cyanobacteria growing in tidal flats tend to form thick, wavy mats that are then preserved and fossilized, forming “stromatolites”. Stromatolites are among the oldest evidence of life on the Earth. We spent quite a while discussing the stromatolites here, and particularly learning how to tell the difference between wavy layers that are biogenic and those that are due to things like sand ripples or deformed layers that were originally flat. The variation of the layer thickness is the first hint: stromatolites tend to be thicker in low points and thinner in high points. If the waviness was due to the deformation of originally flat layers, there shouldn’t be a change in thickness between highs and lows. Another hint is if you can tell that the waviness forms domes rather than parallel ridges, and especially if you find isolated domes or columns. It’s difficult to form an isolated dome-shaped ripple, but that’s exactly what you get when mounds of cyanobacteria are growing.

Modern stromatolites growing in Shark Bay, Australia. Original image by Paul Harrison.

After looking closely at stromatolites, we drove closer to what was the ancient shore and encountered an abrupt transition to layered gypsum and silt beds deposited as the near-shore pools periodically dried out. This area was used as the “slow-motion” field test for Mars Science Laboratory in 2007. The science teams essentially practiced by sending someone out here to take pictures and samples, and the team tried to understand the site without any other information. For our field stop, we took a look at some infrared maps of the minerals in the area, and then climbed a nice exposure of them.

We climbed "Tepee Hill", a nice exposure of gypsum and mudstone layers deposited in the evaporative shelf lagoon.

In the afternoon, we drove to “Last Chance Canyon” to admire an excellent exposure of the inclined beds that characterize the transition from the continental shelf to the ocean basin. The curves of the canyon let us see the tilted layers from different angles to get a good three-dimensional feel for the stratigraphy. We spent a while sitting up on one side of the canyon and sketching the opposite side and then hearing from our expert guides about all the subtle details that we amateurs had missed in our sketches.

The upper layers here are flat-lying, but below them, the layers begin to dip down to the right. These dipping beds were deposited on the slope of the shelf margin. Don't be fooled by the diagonal dark green vegetated stripes that go from upper right to lower left - those are fractures in the rocks where plants have taken hold.

It started to rain while we were studing the outcrop, but lucky for one member of our group, he was carrying the large canvas print-out of the Burns formation, a well studied section of rocks on Mars. Turns out it makes a decent cloak.

Our penultimate stop of the day was not listed in the guidebook but was pretty interesting. We took a look at some of the carbonate layers that had curious features called “tepee structures”. The leading theory for how these structures form is that, when carbonate deposits dry out, new minerals form and cause the layers to expand, causing them to buckle upward. There’s still a lot of debate about how they formed, however. They’re interesting to us martians because in an overhead view, the buckled zones form polygons, and there are polygonal features all over on mars.

A good example of a "tepee structure" is visible in the rocks here, just right of center. Geologists aren't completely sure how they form but the leading theory is that it has something to do with the rocks expanding as they dry out and new crystals form.

Our final stop was also not listed in the guidebook. We decided that since we had been talking about the ancient reef so much that we should take a look at it. Within the carbonates of the reef we found a lots of interesting fossils, including a texture that looked like miniature stromatolites, large spiral shells, and crinoid remains.

That concludes Day 2 of the field trip! Day 3 was a visit to Carlsbad Caverns – stay tuned for lots of pretty pictures!

MarsSed 2010 Field trip – Day 1: Guadalupe Mountains and Evaporites

April 26, 2010

Hello everyone, I’m back from the MarsSed 2010 meeting in ElPaso! The meeting was great: it was small and focused on sedimentology and stratigraphy on Mars, with lots of room for discussion. Even better, there were plenty of terrestrial geologists attending, and their comments were extremely helpful for me, and probably many other Martians who lack a geology background.

After two and a half days of presentations and discussion (and a lot of learning on my part), we headed off on our field trip to the Guadalupe Mountains!

We started off in a salt flat graben with a lovely view of the Guadalupe mountains. What’s a graben, you say? It is a low-lying block of land, bordered by parallel faults. If you have heard of the “basin and range” region of the southwestern US, then the basins are graben. The mountain ranges are also called “horsts”.

A nice diagram of horsts and graben. This is how the "basin and range" area of the southwest formed.

The graben that we stopped in was a salt flat, where gypsum and halite are left behind when water collects in the lowlands and then dries out.

A view of the Guadalupe Mountains from the salt flat.

From our vantage point, we studied the nicely exposed mountains and compared them to a detailed cross-section of the area. The rocks of the mountains were once a large carbonate reef on a continental shelf. When sea level was high, thick carbonate beds were deposited on the slope of the continental shelf, and when sea level fell, sand and silt from the continent  were transported across the reef and deposited in the floor of the ocean basin. Here is a nice illustration that we found at one of the national park exhibits on the last day that really helped clear things up for me.

A diagram showing the relationship between the geographic setting and the underlying stratigraphy of the shelf and reef.

Here we are on the salt flat taking our first look at the stratigraphic cross section of the Guadalupe mountains. The mountains are off to the right, outside the field of view of this picture.

You may wonder what the relevance of ancient ocean reefs are for a bunch of Mars scientists. Fair enough. Nobody claims that we would find a big carbonate reef on Mars. Believe me, scientists have been searching for carbonates on Mars for decades. Recently, some small amounts have been detected, but nothing comparable to a huge reef. We were instead studying the reef as an example of a well-understood stratigraphy on Earth, and trying to learn how that stratigraphy was deduced. One of the main lessons was that not everything starts as a flat-lying layer! In fact, the edge of the reef appears to form a nearly horizontal layer, but it is actually made up of multiple sequences building outward into the basin. It just seems to form a layer because the reef always forms at the edge of the continental shelf. You can sort of see this “fake” layer in the pictures above. It is dark blue in the colorful cross section and is the light-toned band in cross section in the artist’s impression.

After discussing the cross section in some detail, and particularly admiring the large, inclined beds of the reef that were exposed in the mountains, we moved on to take a look at the deposits that filled the ancient Delaware basin when the sea began to dry out. The deposits have a very striking light and dark banding:

Layered evaporite deposits in the Castile Formation in the Delaware Basin. The light layers are gypsum, formed during the summer when evaporation rates were high, the dark layers are carbonate formed in the winter when evaporation was slower.

The light layers are gypsum and the dark layers are carbonate. The current theory is that each couplet represents one annual cycle: gypsum was deposited in the summer when evaporation was rapid, and carbonates were deposited in the winter. Apparently some poor graduate student counted all 260,000 couplets, which implies that it took about that many years to fill the basin with evaporites.

Something similar may have happened in the Mediterranean Sea more recently. It is thought that occasionally, the ocean level drops to the point where the Mediterranean is cut off from the Atlantic, and begins to dry out, depositing similar salts on its floor.

The relevance to Mars in this case is a lot more clear. There is evidence that many large craters were once filled with water. Now they are bone-dry, so presumably big evaporite deposits should be common on Mars! There are nice big stacks of hydrated sulfates at the bottom of Valles Marineris which might be remnants of such a deposit that precipitated out of a body of water in the canyon.

Stay tuned for Days 2 and 3 of the field trip! If you’re really interested, I suggest that you check out the awesome field guide that was made especially for our trip.


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