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Posts Tagged ‘geology graduate school’

A couple weeks ago I wrote about how being in graduate school is an emotional roller coaster. It was kind of a negative post, because I was on the uphill side of a really sweet hill of said roller coaster. Yes, the semester is still winding down, but so is my to-do list. I am so much closer to only having teaching and research responsibilities in my life.

And it feels fantastic.

The Thanksgiving holiday certainly helped a ton as well. I am one seminar (which requires me to critically read a scientific paper in my field of research), 2 classes, and 1 final exam away from being alone with my research (and teaching, but that’s easy and fun).

As for my research, I’m focusing on “point counting” right now, which is difficult, but pretty straightforward. Basically, I’m looking at very thin slices of my rocks under a polarized light microscope.

microscope

I move the slide around in a grid pattern controlled by the microscope stage, and identify whatever lands under the cross hairs. I have to identify 500 “points” of the basic “framework grains” (the more common things found in sedimentary rocks like quartz, feldspar, and rock fragments), and keep track of them in a spreadsheet.

microscope

That’s it.

I mean, distinguishing between different rock types when all you have is a fragment the size of a fine grain of sand is often difficult. But after a while you get used to what certain things look like, and your options are just volcanic, metamorphic, and sedimentary (yes, you can have fragments of sedimentary rocks in a sedimentary rock, though they are generally more rare in sandstones, which is what I’m looking at). There are a few other things I have to identify, but I won’t bore you with the details.

Essentially, this is what’s ahead for me for the next two months of graduate school research.

This, and the Christmas/my birthday holiday of course! This is my giant skylight in the tunnel that is graduate school. It’s going to be a perfect time to recharge and relax and have some fun. Even if it is only 10 days. But I haven’t been home since March, and I’ve been working really hard, so I’m pretty sure I deserve this break.

The point of this post is to prove that graduate school is indeed a roller coaster of emotion. You’ll have weeks where everything piles up on top of you and you can’t even begin to think of a way to dig yourself out. Then you’ll have weeks where everything feels like it’s falling into place and you’re moving right along with the progress of your work.

Granted, things can change in an instant with a few simple words from your advisor, but this can be bad or good. Honestly, I was afraid to tell my advisor I’d be going home just for 10 days because I have very little work I can do remotely right now. After I told him, I realized it was a completely irrational fear. It’s only 10 days. It’s a freaking family holiday, and I didn’t leave town last year. I have no reason to feel guilty for doing this. He also didn’t seem to care AT ALL.

My advice to those of you starting graduate school or thinking about going back to school – it’s really hard, but it’s also very rewarding, and you will have your ups and downs. Know what you’re getting yourself into, and don’t beat yourself into the ground over nothing. And for those of you who are in the thick of it – if things are looking bleak, remember that they’ll probably change in a week or two, so try not to worry about it too hard. Just keep making progress.

You can do anything for a year, and you can do many things for two years. I can’t speak for PhD candidates, but this much I know about getting a two-year degree.

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I went fishing for the first time today, and I’d love to write about it because it was REALLY fun – but I only managed to get one photo, and I technically was in between casts, so I wasn’t really fishing. Just sitting on a boat looking cool with a dog. Oops. So stay tuned for a post about fishing later, after I’ve had a few goes at it (and taken some more photos!).

Instead, I’m going to attempt to explain sequence stratigraphy and my graduate thesis project to non-sedimentary geologists!

brace yourselves knowledge

First, some Geology 101:

Sedimentary rocks are rocks that are made up of sediment (gravel, sand, clay, mud, etc. derived from other rocks that were weathered and eroded). Water (and other things, like wind, but mostly water) moved this sediment around via rivers and waves and tides. Eventually, this sediment settles down for the long haul and slowly gets buried by more and more sediment. This burial causes the sediment to squish together and compact. At a certain point, the sediment “lithifies” and becomes a sedimentary rock. Welcome to my favorite part of the rock cycle.

Sedimentary rocks are conglomerates (gravel-sized sediment held together by smaller sediment), sandstones (basically sand that has become a rock via the process described above), shales (really fine grained stuff, generally too small to see without some kind of magnifier), and mudstones (the finest grained sediment).

The type of sedimentary rock you’re looking at, the size of the sediment grains, and any sedimentary structures that were preserved (like ripples, crossbeds, planar beds, etc,) can tell you what kind of environment the sediment was deposited in. Composition of the sediment grains (minerals and rock fragments) can also help, but sometimes the grains are too small to determine that without a microscope. You might imagine that a sedimentary rock created by a lake (mostly very fine-grained sediments like mud and clay) would be very different from one created in a beach environment (mostly sand), which would in turn be very different from a rock from a river environment (gravel and pebbles). Of course, all of these environments can be variable, but I’ll get to that in a minute.

seds

 

Stratigraphy is the study of these sedimentary deposits/rocks, and how they are layered.

One more thing before we start putting things together into sequence stratigraphy. Over time, sea level around the world rises and falls for a variety of reasons. Sometimes it’s climate – either global (eustatic) or local. Sometimes it’s caused by plate tectonics – the movement and interaction between crustal plates.

Now, let’s put these concepts together:

I’ve talked about depositional environments, and I’ve talked about sea level change. At the most basic level, putting these two concepts together is sequence stratigraphy. Burial is what ties them together.

I’m going to put this into context with a coastline, because that’s what I work with, and that’s what makes the most sense to me. On a coastline you might have the river meeting the ocean, a beach, a tidal flat, and the deeper, offshore environments.

Imagine you’re on a beach, and sea level begins to rise. Pretend you can breathe under water/sediment, and you’re immortal, so you can totally watch things change on a geological time scale.

First, your beach sand would get buried by finer grained sand from the tidal flat, and as the water continued to get deeper, the beach sediment deposit and the tidal flat deposit would get buried by the deep offshore deposits (really fine muds with maybe a little really fine sand).

That, my friend, is a sequence. If you cut a slice into the sediment right where you were standing when sea level began to rise, you would see this stratigraphic sequence, and the sediment would be getting finer closer to the top. We call this a “transgressive” cycle, because the shoreline is “transgressing” across the land – it is moving landward. Also, the furthest the shoreline extends at the end of transgression creates a surface called the “maximum flooding surface” – hopefully this seems pretty obvious: as sea level rises, you are flooding the environments that were there before sea level began to rise.

Now, pretend you are still standing in the same place on that beach (now buried under quite a lot of sediment), and sea level begins to drop. You might see the return of tidal flat deposits, and eventually you’d see the beach again, and if sea level drops far enough, you might even see the river environments at the very top. This is what we call a “regressive” cycle – the shoreline is regressing away from the land and moving seaward.

If you were to step back and take a slice out of this whole sequence I have described – from the first beach deposit to the fluvial deposit, and then studied how these depositional environments changed laterally and vertically, you would be studying sequence stratigraphy.

Of course, it is a TON more complicated than this, especially since these processes are often erosive, so you don’t always get a perfect sequence that records an entire cycle of sea level rise and fall, but hopefully you get the idea. There are also these things called “significant surfaces” (the maximum flooding surface is one of them), which help us define sequences. They are usually created by some form of erosion – either transgressive or regressive, but involve some kind of shift in either the direction or speed of sea level rise or fall.

One important aspect of sequence stratigraphy is the source of sediment, and this is where the focus of my thesis project lies. You can hopefully imagine that river sediments come from somewhere upstream, while beach or tidal flat deposits might be sourced from somewhere else on the coastline, or they might get sediment from the ocean. Sediment comes from all over the place.

In my field area, the previous graduate student identified three different sources of sediment. I’m going to be looking at the composition of all the sandstones (sorry, sand can be found in many different environments, try not to thing about it too hard) in my rock formation and comparing them to see if there are significant differences between these different sources – and if the sands from the same source have similar compositions. Again, it’s a bit more complicated than that, but that’s the general idea. Also there are GREEN minerals in my sandstones (not a common sedimentary mineral color). I get to identify them – I’m pretty stoked.

Sequence stratigraphy is like studying history, but it’s history of the earth rather than of people, and that’s what I love about it. Sequences of depositional environments is very intuitive to me. Plus, looking at things in a powerful microscope (a few different kinds actually), is really fun.

microscope

That thing up in the right corner that looks like plaid? That’s called “tartan twinning.” It’s a potassium feldspar grain. It GREW like that. Plaid is found in nature, guys. Chew on that.

If you’re curious, or you need me to explain something differently, please feel free to leave questions in the comments, and I’ll do my best to help you understand! This stuff comes as second nature to me (and I already find it fascinating), so it’s difficult (as any specialty can be) to break it down and keep it interesting. I hope you at least learned something about sedimentology by reading this post.

bill nye dropping science

 

Fun fact: “Sedimentology” is not recognized by computer dictionaries. My entire area of study does not exist to technological devices.

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Yes, I mean actual diamonds. I cut rocks with diamonds. Be jealous.

Ok, so they’re REALLY tiny (microscopic, even), and they’re synthetic, so it sounds a lot cooler than it actually is.

Oh, who am I kidding, cutting rocks is one of the best things about being a geologist. Especially when you’re cutting sedimentary rocks with a diamond rock saw – it’s like slicing butter with a hot knife. If someone ever asks you if you want to try cutting a rock, just say yes.

Last Friday I got to cut some rocks as part of my thesis work. I’m going to attempt to explain my thesis project in non-geologist terms in a later post, but right now I just want to brag about cutting rocks and feeling a little bit like a god while doing so. This particular batch of rocks were all from a fresh rock core (someone drilled a tube into the subsurface and pulled out a cylinder of rock – essentially). The core was also thankfully already sliced in half. You might imagine that flat edges would make rock cutting much easier, and you’d be right.

photo 1

This is what the rocks looked like before I started slicing them, except for the 2 at the top. The goal is to cut a thin section “blank.” They go by many names (billet, chip…), but the piece you cut before it gets shaved down enough that light can pass through it under a microscope. They’re roughly 1″ x 1 & 7/8″ and about half an inch thick. Then we send them off to a lab where everything is standardized and we get a bunch of perfect thin sections returned like magic. And then I have to count 70,000 individual grains, among many other things. But I’m getting ahead of myself.

photo 4

The rock saw! It’s basically stationary, and you put your rock on the rack, and move the rack under the blade. That chip sitting on it is a typical thin section blank. Fun fact: it’s pretty difficult to cut yourself on this blade, even though it’s designed to cut rocks. It’s actually pretty blunt – about 1/16″ thick. I meant, don’t get your finger trapped between the rock and the blade, but you could probably hold your finger right on the blade as it spins and it wouldn’t cut you.

photo 3

Look! I’m doing science! Literally just sliding the rock into the blade, and it just cuts. You gotta go slow, so you don’t fracture the rock or damage the blade. But not THAT slow. At least, not with sedimentary rocks. We were able to cut about 15 samples in about 3 hours – and that includes refilling water buckets and labeling everything. I have to cut about 85 more though… going to be a busy few weeks.

photo

In the end, this is what we had left. I failed to take a photo of any of the actually blanks, because… I have no excuse, it just didn’t happen.

Honestly, I am just really excited to get this part done. Microscopes are fun. Probably I’ll change my mind about this after I spend many hours staring down into them, but rocks look really cool in thin section. I’ll hopefully post some photos of that when I get around to that process. My project is mostly a sedimentary petrology deal (petrology = looking at rocks under a microscope and identifying minerals and figuring out where the sediment came from), and I am just really anxious to get to the data collection part. Collecting and preparing samples is only fun for the first few days, in my opinion.

photo 5

Then there are the big cabinets in the lab that just say “ACID” on them in giant red letters…

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