On May 7th I lead two fossil hunters to an accessible fossil locality in Murray County, Georgia. The locality is part of the Conasauga Shale Formation. This rock unit runs through Georgia, Alabama, and Tennessee. It is made of shales and mudstones that were deposited during the Cambrian Period (~541-485 million years ago). During this time, Northeast Georgia was under a shallow sea known as the Iapetus Ocean. This ancient sea was located deep in the Southern Hemisphere. Animals living in these waters included sponges, brachiopods, hyoliths, and the famous trilobites.
The most abundant fossils in this portion of the Conasauga Formation are the shed exoskeletons of trilobites. Trilobites are arthropods that were very common animals during the Paleozoic Era (~550-250 million years ago). The trilobites found in Murray County, Georgia died from rapid mudflows that came from a deep marine basin and anoxic (lacked oxygen) environment. Because of this, the trilobite fossils from this site are preserved very well and occur in body clusters with halos of iron oxide surrounding their bodies.
We began to plunge down a hill under a bridge where the outcrops are exposed to the surface. The exposures lie right near the Conasauga River (where the rock unit received its name). It didn’t take long to split the mudstone and come across the remnants of ancient Georgia’s inhabitants. The most common species of trilobite found in the outcroppings is Aphelaspis brachyphasis. They are so common that this locality has been referred to as the Aphelaspis Biozone. There are other species that were found such as agnostids like Glyptagnostus reticulatus which serves as an index fossil for the middle Cambrian and Agnostus inexpectans.
Agnostids are very small and only occur in rocks from the Cambrian and Ordovician period. Paleontologists have debated whether agnostids are even part of the class Trilobita at all. Agnostids had a head and a tail body parts with two or three thoracic segments. They also have have no eyes which suggest they lived in deeper waters where light did not penetrate the ocean. A lot of the trilobites that we found were disarticulated but some specimens recovered were complete molts. We all came back with well-preserved and numerous specimens.
Every Semester, the University of Massachusetts Amherst Department of Geosciences offers the class Introduction to Geology. The course is designed for undergraduate students who need science credits for their degree, but it is also a required course for our geoscience undergraduate majors. The course has a lab that complements and expands on topics that are covered in lecture, such as plate tectonics, igneous, metamorphic, and sedimentary rocks, river dynamics, topography, and the history of how the Connecticut river valley was formed. The labs are run by four to five teaching assistants, graduate students who are pursuing their master’s or PhD degrees. We take the students on two field trips as part of their labs: the first trip is to look at geologic features in the valley leftover from the glaciers, and the second to look at the major rock formations in the valley.
This post is about the glaciation that ended around 20,000 years ago, and the imprint the ice and ice melt left on this area of western Massachusetts. This time of huge ice sheets that covered northern North America, Europe, and Asia is referred to as the Last Glacial Maximum. In North America, the glaciation is referred to as the Wisconsin Glaciation. The glaciers that covered North America reached their maximum southern extent about 26,000 years ago, after which the ice began to melt and retreat back to the north. At the glacier’s maximum extent, Massachusetts was totally covered by ice. Estimates based on how thick the ice was range from 1 to 2 kilometers (0.62-1.24 miles)! That’s a ton of ice! Because ice is very heavy, it depressed the Earth’s crust below it. In southern New England, the ice is estimated to have depressed the Earth’s crust down by about 50 meters (~165 feet; Oakley and Boothroyd, 2012). Once the ice melted, the crust of the Earth began to pop back up. This phenomenon is called isostatic rebound. Satellites that measure the rate of isostatic rebound indicate that parts of Greenland and Canada, where the ice was thickest, are still popping back up today.
Back at a more local scale, there are several features around UMass Amherst that we, the graduate students that teach the Introduction to Geology labs, can identify that were created as a direct result of the glaciers in this area. I’m going to take you on our glacial field trip virtually, so that you, too, can get a first-hand look at the types of geologic features the glaciers left behind! First, a fun aside: There are several large boulders all over campus that, at first glance, look like they were placed in specific locations for an aesthetic affect. Upon closer inspection, the boulders are made from a certain rock type that occurs in our valley. Glaciers, and ice, act as bulldozers, and have no problem picking up and carrying huge chunks of rocks. These boulders, then, were picked up from the nearby hills and deposited all over the valley, with some ending up on our campus! These boulders aren’t part of our field trip, but are neat nonetheless.
The first stop on our field trip is right on campus, behind our football stadium. Here, there is a small creek with about 5 feet of the upper part of the soil profile exposed. But there’s something special about the soil here: it is unlike anything found in other places of the world: varves! Varves are alternating bands of dark and light-colored clay layers that made up the bottom of a lake that used to cover the valley. The lake was created once the glaciers began to melt, leaving more parts of Massachusetts exposed. The meltwater from the glaciers flowed via river into the Connecticut River Valley, and became dammed here. This created Glacial Lake Hitchcock. The varves are remnants of the sediment that collected on the bottom of this lake. Varves are awesome because they record climate changes on a seasonal basis! The dark bands contain finer clay particles, and are deposited during the winter months when there is less sediment being brought into the lake by the river (during the winter months, there is less glacial melt, and thus less water flowing in the rivers). Lighter varve bands are usually made of coarser (or larger) grains and are deposited during the spring and summer months when glacial melting increases, bringing more water and thus sediments into the lake. By counting the pairs of dark and light varves, scientists can estimate how old Glacial Lake Hitchcock was. Varves from the lake were counted by scientists at UMass Amherst, and they found that the lake was around for at least 4,000 years, from 17,5000 to 13,5000 year ago (Rittenour et al., 2000)!
After checking out the varves, our second stop is a kettle hole a few miles from campus. A kettle hole is a depression in the Earth formed from a chunk of ice that broke off from the retreating glacier. The ice chunks become buried by glacial outwash, or the mix of water and sediment that spreads across the land as the glacier melts. Thus, the ice chunk is completely buried by sediments. After some time, the chunk also melts, which then creates the kettle hole. These features are prominent throughout New England, and are usually small in size.
The third stop on our glacial field trip is to the Sunderland Delta. A delta is a place where a river meets a larger body of water, like a large lake, ocean, or sea. Some rivers flow fast, and some flow slower. In general, the faster a river flows, the more sediment it can move and carry. I mentioned earlier that the glacier began to melt back, and that melt water was transported by a river into Glacial Lake Hitchcock. The river was quite large, and had the ability to move sand-sized sediment. But where the river met the calm waters of the lake, it lost its velocity, and thus its ability to carry sediment. The sediment was then ‘dropped’ at the mouth of the river where it emptied into Glacial Lake Hitchcock. This dropped sediment formed a delta, or an area where fine-grained sand was deposited. This sand accumulated over thousands of years. Today, these sand deposits that make up the delta are mined by humans for use in concrete and manufacturing. There are several open mining pits around the university, but one in particular preserves the features of the delta, namely topset and foreset beds of sand. When the river gets close to the larger body of water, it begins to slow down. The loss of velocity leads to the river dropping some of its sediment it is transporting. This sediment is laid down in thin sheets that lie flat. These sediments form topset beds. Where the river meets the body of water, it is slowed even more, and the rest of the sediment it carries is dropped. These particles form a slope down into the lake, and make up the sloping foreset beds.
Once the students understand how the Sunderland Delta was formed, we then move downhill to our fourth stop: a trout hatchery right down the road. This, by far, is the coolest stop, as it contains a unique geologic feature: a natural spring! At our first stop, you saw that the base of Lake Hitchcock was composed of very fine sediment called clay and silt. Clay and silt grains are flat, and when they are compressed over time, they don’t allow water to pass through very quickly. In the introduction paragraphs of this post, I also explained how the Earth’s crust underneath New England, including Massachusetts, popped back up, or rebounded, after the overlying weight of the glaciers was gone. When the land began to rebound, that caused the clay layers of the lake to crack. When this happened, the groundwater that was stored deep in the sediment under the clay was able to come to the surface. Here, at the trout hatchery, is one of the places the groundwater is able to come to the surface via cracks and conduits in the thick clay layers! It can be seen bubbling to the surface continually throughout the year. The video below shows the spring in action:
The water stays a constant temperature year round because it originates from so deep within the sediment. The constant temperature and clarity of the water is great for raising trout, because the water rarely, if ever, freezes during the winter and is never too hot during summer months! The trout that are raised at the hatchery are released into local streams and rivers so that fishers do not over-fish the local populations. This stop is one of my favorites, as it is an excellent example of how geology and biology go hand-in-hand, and how the geologic processes of the past are relevant and useful today.
Our fifth and final stop is just down the road from the trout hatchery. The feature here is not as impressive or obvious after the large delta feature and the natural spring, but it records an important phenomenon related to the retreat of the glaciers nonetheless. On the side of the road is a small hill that most local folks pass by probably everyday. This hill is covered in trees and vegetation, and one might totally overlook it quite easily. But if you stop and dig down 4-5 inches through the roots and topsoil, you’ll hit sand! This small hill is, in fact, a sand dune that was formed from winds towards the end of the Last Glacial Maximum.
When the glacier that covered Massachusetts began to melt back, the Earth was beginning to warm up. The area to the south of Massachusetts was becoming warmer, but on top of the glacier to the north, the air temperature was still very cold. This difference in air temperature, or temperature gradient, created strong winds that blew from the warmer regions towards the colder regions. This phenomenon happens today at the beach: during the day, the wind blows towards the ocean from the hot land; but at night, the wind direction changes as the land cools down until it is cooler than the ocean water. The beach is also characterized by sand dunes,which are the products of these strong winds depositing small sand grains behind the beach. Just like at the beach, the strong winds moving towards the glacier picked up small sand grains and deposited in the valley near UMass, where they are still visible today!
The features that we show our undergraduate students and that are explained here are just a few features in our valley that are leftover from the massive glaciers that once covered the land. All around New England, there is evidence of the heavy ice that was once here not too long ago: exposed rock where the glaciers scraped away soil; glacial striations, or scratches, in the exposed rocks from the glaciers moving over them; and potholes in the bedrock near the rivers, where melted water mixed with larger pebbles and boulders under the ice to carve out rounded holes in the rocks. If you’re ever in New England, keep your eyes peeled for evidence of the glaciers; it’s literally everywhere!
Oakley, B. A., and Boothroyd, J. C., 2012. Reconstructed topography of Southern New England prior to isostatic rebound with implications of total isostatic depression and relative sea level. Quaternary Research 79, 110-118.
Rittenour, T. M., Brigham-Grette, J., and Mann, M., 2000. El-Nino Like Teleconnections in New England during the Late Pleistocene. Science 288, 1039-1042.
I was recently one of fifteen participants in a workshop. Most participants in this workshop are graduate students or recent graduates studying paleontology or biology. The workshop is a month long with very few days off. We had one two day weekend and decided it would be fun to be tourists and go to St. Augustine! St. Augustine is a very old city that is on the eastern coast of Florida and is home to Castillo de San Marcos National Monument.
We were incredibly excited to realize that much of the local stone work was sourced from local rock. This rock is called coquina. Coquina is a sedimentary rock that is made up of shell fragments! The coquina is from the Anastasia Formation that was deposited in the Late Pleistocene (around 2.5 to 0.012 million years ago). We spent a lot of time with our faces pressed into walls looking at what shelly creatures were preserved in the wall. The National Park Service has a nice write up explaining how creating the fort out of coquina was incredibly beneficial, click here to read more. Essentially, the rock did not break when the opposing forces began firing weapons and at the fort. Instead, the rock absorbed the shock and compressed when hit with cannon fire!
We spent time exploring the fort, which had an amazing amount of rooms with some extraordinary details preserved. When I say the entire fort was made of coquina, I mean the entire thing. It was one of the most incredible things I have ever seen! There were rooms with barrel vaulted ceilings, tall arch like ceilings, some with carvings in the walls, and much more.
After visiting the fort we spent time around the city exploring and being tourists. Then we decided to venture out to the beach. Remember, paleontologists study ancient life. This means many of us have training in biological sciences and get really excited about animal life! We got to the beach and some people hopped right into the water while others sat on the beach and read or took a walk along the beach. May and I decided to walk along the beach and we eventually came to these large pillars supporting a boardwalk.
These pillars were completely covered in sea creatures! Mostly oysters, other small clams, snails, and barnacles! Most notably were the large barnacles that were a beautiful pink/purple color! Barnacles are related to crabs and lobsters but look so very different. It is absolutely astounding that these creatures can be cemented to the pillars and live for periods during high tide. Not all of the animals were still alive that were on the pillars, especially those that were quite high up.
This is a great example of how we can better explore the world around us through the lens of different sciences! Geology that contain biological remains and lots of living organisms on the beach!
A year ago I got the chance to visit the Grand Canyon National Park. I had been there once as a toddler, but of course I didn’t remember it, so I was very excited to have the opportunity to go again now, especially since I’ve been studying geology for a few years. The Grand Canyon is like Disneyland for geologists. There are SO many cool geologic processes and so much geologic time represented there (click here for a fun read on the geology).
We were staying in Flagstaff, AZ for a conference, but my colleague and I had a free day before it started and since the Grand Canyon is only an hour and a half away we decided to just hop in the car and go. We started off early in the morning so we could try and beat the heat. When we arrived we headed straight to the rim.
It was one of the most exciting moments of my life. I had seen pictures of the canyon, but nothing prepared me for what it was actually like to stand there in person. We walked up to the rim with our eyes on the ground so we would see it all at once. When we got close enough we looked up and were utterly speechless for at least a minute. It was so worth it. The Grand Canyon is so big. Like, SO BIG. Apart from all the cool geology, it is a really amazing view.
One of the coolest things about the Grand Canyon (besides the size) is how you can really see textbook examples of geologic concepts displayed in a way that anyone can see. For example, the Great Unconformity is a famous example of an unconformity – a place where rocks were deposited or uplifted and then some time passed and/or erosion occurred before more rocks were deposited. The Great Unconformity is the place where the beautiful sedimentary rock layers that make up most of the Grand Canyon are deposited on top of older metamorphic and igneous rocks. The distinct sedimentary rocks layers we see exposed in the canyon help geologists understand what the environment was like at different times in the past. After all these rocks were deposited, the canyon itself was carved out by the Colorado River starting at least 6 million years ago (click here for more information), resulting in the Grand Canyon we see today.
A note from the editor (Jen): I wholeheartedly agree with this description, the view is beyond breathtaking. It takes a while to soak in the awe inspiring beauty. Time is so often taken for granted but when you can see so much time in the rocks, it gives you a new perspective.
This past June, I helped teach biology, with a focus on vertebrate evolution, with Tennessee’s Governor’s School, a program for high school students to come and experience college life for a month. Last year, Time Scavenger mastermind, Jen, wrote a post about what Governor’s School is, so I’m going to focus on the field trips that we went on!
Field trips are a really important part of learning about science, but can also be really valuable in showing young students what careers are available to scientists. Most students understand that scientists have all kinds of different research interests and biologists don’t spend their days rehashing high school biology curriculum, but it can be hard to imagine what else you would do with a degree in biology without seeing it in action. So, to show our students what all biology encompasses, we went on four field trips this year to the Gray Fossil Site, Oak Ridge National Lab, ProNova, and fossil collecting in east Tennessee!
Our first field trip was to the Gray Fossil Site, a Miocene (4.9-4.7 million years ago) fossil assemblage. This site is really cool because it is a lot younger than most fossil sites in east Tennessee and they have a plethora of vertebrate fossils preserved there. They have found everything from tapirs (similar in look to a pig) to alligators, mammoths, and even a new species of red panda! We unfortunately went on the paleontologist’s day off, so we didn’t see anyone actively working at the site, but we could see the pit that is being excavated this summer as well as peek into the preparation labs to see which fossils are currently being cleaned and put back together. After our tour we had some time to explore the museum that is a part of the Gray Fossil Site which does a good job of explaining what the preserved environment is like, how the site itself was discovered, and what the roles are of the scientists involved at this site.
The second field trip that we went on was to Oak Ridge National Lab. We are super lucky living in Knoxville that we have a national lab ~40 minutes away that is welcoming to visiting groups! Since we were talking about biology, our main tour was in the biofuels (fuel derived from living matter) lab. There we discussed the major setbacks to biofuels (large land areas needed to grow plant matter to turn into biofuels, making sure that the carbon footprint of the growing and production of biofuels was also lessened, etc.) and how scientists at Oak Ridge are trying to solve these problems to make biofuels more readily accessible for large-scale use. In addition to biofuels, we met with other scientists and talked about big data and the computing power of the supercomputers housed at Oak Ridge. There’s nothing like talking about supercomputers and all that they can to do to get a bunch of science nerds buzzing!
Our third field trip was to ProNova, a facility that is using proton therapy to fight cancer. This field trip was particularly exciting to our students because many of them want to go into the medical fields, but was also a great learning experience for me! Using protons to treat cancers is a relatively new treatment, so none of us had any idea of what to expect, or what we were going to learn. At ProNova, they use large electromagnets to generate a beam of protons that can be directed to target tumors and that beam has more control than radiation, so only the tumor is being “attacked” by the protons, not the tumor + healthy tissue. The coolest part of this field trip was being able to go behind the scenes and see the magnets and resulting beamline that then is directed into treatment rooms and eventually into patients!
Our final field trip was to go fossil collecting in east Tennessee. While we weren’t collecting vertebrate fossils (east Tennessee is chock full of lovely invertebrate fossils-I might be a little biased in calling them lovely!), many of our students grew to appreciate paleontology over the month-long course and were excited to be able to collect their own fossils to bring home. Most everyone found crinoid stems, receptaculitids (an algae that looks a lot like the center of a sunflower), and bryozoans (small colonial organisms). We also stopped to look at a wall that was made almost entirely of trace fossils!
While we spent a lot of time in the classroom discussing vertebrate evolution and all of the different aspects of science that play a role in understanding how life and humans evolved, our field trips provided our students with real world applications for the science that they were learning. And from my perspective, the field trips were a way to get ideas of how to present this kind of material in my classroom, as well as to collect current research examples to help answer questions of why biology and vertebrate evolution are important to our understanding of the world! Governor’s school is a really intense month for both the students and the teachers, but the field trips gave us all a chance to connect and have candid conversations about science. It also gave me a chance to reflect on the field trips I took as a young scientist, and how they shaped my desire to become a scientist–so remember, field trips may appear on the surface to be just fun and games, but are incredibly important to the learning process!
I couldn’t believe what I was seeing. I was on a tour of campus for my paleontology course, and Dr. Sandy took us to a low retaining wall in front of the Science Center. There it was: a large Pentamerus brachiopod (Fig 1). I’d walked by this wall for years and never noticed it before! During the rest of the tour, I saw fossils all over campus, and I had never even thought to look for them in the building materials.
Ever since then, I’ve taken closer looks at the stones used in buildings to see if there are fossils. You should, too! But ignore the igneous rocks and marble, just go for the limestone, dolostone, and sandstone pieces. The fossils I’ve seen include trace fossils and body fossils. Trace fossils are fossilized behavior of an organism, whereas body fossils are the actual skeletal or imprint of remains.
Primarily, I’ve encountered trace fossils. The Dayton Limestone, a formation found near Dayton, Ohio, is Silurian-aged (443.8-419.2 million years ago) limestone that was used for building foundations all over the state. It is full of burrows that are highlighted by a lining of hematite (Fig 2). The hematite likely came into the burrows after the organisms were done occupying them. This mineral helps the burrows stand out in the rock. The foundation on the left is a building on the campus of the University of Dayton. The founding on the right is a building in downtown Springfield.
Further exploration for urban fossils led me to find trails on the base of a lamppost outside of one of the courthouses in Springfield (Fig 3). I forgot a scale for this picture, but these trails were about 10 cm in length. I found this next burrow (Fig 4) in one of the retaining walls outside of the library at UD. See what I mean about fossils in places you wouldn’t expect them?
Marine animal body fossils are quite easy to find in building materials. I found these Silurian fossils in a retaining wall near some of the older buildings on UD’s campus. Large brachiopods and gastropods may be found in these stones (Fig 5), as well as colonial corals and horn corals (Fig 6). Sometimes it is difficult to recognize the fossils because the animal is within the rock and you are only getting a two-dimensional view of what it looks like.
Sometimes, the fossils can be very small and hard to pick out from the rock they are in. I walked by this wall for nearly 15 years and never noticed all of the gastropods, bryozoans, and crinoids until just a few weeks ago (Fig 7)! Another example of small fossils was found by Jen when she went to the Biltmore Estate in Asheville, North Carolina. She was chatting with her family when she looked down and recognized the rock, it was filled with small gastropods and bryozoans that she knew to be Mississippian (360-325 million years ago) in age (Fig 8).
Be sure to be on the lookout inside of buildings, too! Many building stones are made of fossiliferous rocks and they are quite visually appealing so they end up as table tops, counters, and even bathroom stalls! Jen saw this table, made of polished fossiliferous limestone, inside of the Biltmore house (Fig 9). I found these ammonites in the flooring at the Ohio Statehouse (Fig 10). Each side of the tile was about 2 ft in diameter.
Where Jen lived in Eastern Tennessee, the common limestone is called the Holston Limestone. This is the ‘marble’ that gave Knoxville the name of Marble City. Marble is a metamorphic rock whereas limestone is a sedimentary rock. Sometimes limestone can have really small grains that makes it look like marble. As a local rock it is used all over the city in a variety of places. It decorates the exterior of buildings downtown (Fig 11) and is even sculpted into monuments of past events (Fig 12).
Maggie and Jen went on a recent research trip to Oklahoma and noticed something interesting about their window sill in the kitchen (Fig 13). It was a nice pink color with lots of white specks. It happened to be the Holston Limestone from where they both were living in Eastern Tennessee! This rock has very specific features that allow you to identify it wherever you may be. Jen even discovered this rock in an old hotel (now a university) in St. Augustine, Florida.
These just a few examples of the fossils that we have seen used in construction and design. As you walk around city buildings, be on the lookout for limestone blocks, especially on older buildings. There may be a few fossils hiding in plain sight!
Do you ever see pictures of beautiful geology all over the world and think “WOW, I don’t think I’ll ever be able to see that in person”? Well, think again. This post is dedicated to helping you find amazing geological finds in a place I can guarantee you will visit just about every day: the bathroom (and no, I’m not just talking about coprolites)!
The goal of this post is to teach you a little about the types of rocks you might see the next time you’re in a restaurant bathroom, a bathroom at the beach, the library bathroom, or even the bathroom in your own house! You might be thinking “oh, but what can I learn from a bathroom?!” Well, you just might be surprised. So, let’s get to learning!
Our first stop is a small restaurant in Richmond, Virginia. The food was good, but the real treat was finding the granite countertops inside the bathroom (Figure 1)! Take a look! Granite is an intrusive igneous rock: meaning, the magma from which the rock was made cooled slowly underground. We know this because of the very large crystals that we can see! Crystals grow from the liquid magma; the longer they take to cool, the larger they grow. Now, let’s look more closely at these big crystals. If you look at the large, light pink colored crystals where my finger is pointing you might see that they are what we call “zoned”- meaning, there are alternating circles of slightly different colors inside the crystals- their rounded shape means we’d assign the term “concentric zoning” to them. This actually tells us something really cool about their cooling temperature!
Magma cools at different rates- depending on where it is on Earth or the types of materials from which the magma is made. This rate of cooling determines how and when certain minerals form, or crystallize. In other words, geologists know quite well at what temperature a mineral will form within a magma chamber as it cools down. This predictable pattern of mineral formation with cooling temperatures is called Bowen’s Reaction Series (Figure 2). When this happens, it means the chemistry of the still-liquid magma changes quite a bit!
To put this into a more delicious and more relatable example, think about a giant jar of Starburst-with red, pink, yellow, and orange evenly mixed in. Let’s say you give this jar to me (I really love Starburst). I will preferentially eat all of the orange ones out of it; then the pink; then the red; and finally, we’ll only be left with yellow (gross, who eats the yellow ones?!). We’ve changed the overall composition of the magma (i.e., the jar of Starburst) by preferentially pulling out one type of material in a specific pattern. Now, take a look at the giant crystal my finger is pointing to- the zoning is going back and forth between a sodium and a calcium rich solution in the feldspar (the name of the mineral)-this indicates that the temperature of the magma where this was cooling was changing slightly, alternating between a little hotter and a little cooler.
Now granite is really cool and it’s a very common bathroom countertop, so let’s look at another example (Figure 3)! This granite was part of a larger piece of rock that was installed in a private home bathroom in Fayetteville, North Carolina. This little piece was leftover, so the countertop store let me have it! This granite is similar to the granite from above, but it doesn’t have any zoning, meaning it all cooled without any weird changes in temperature. However, it does have one pretty cool feature-the garnets! These garnets (the little red crystals) are of the almandine variety. Almandine is a type of garnet that has a lot of iron and aluminum in it. Garnet forms in granite as an accessory mineral (meaning, not a major component) and different garnets can mean different things. In this particular sample, this almandine garnet means the magma was aluminous; meaning, there was a lot of aluminum in this magma!
I found this gem at a women’s bathroom in the San Francisco airport (SFX) last year (Figure 4)! This rock is called a migmatite. A migmatite is unique in that it is a cross between an igneous (formed directly from cooled magma or lava) and a metamorphic rock (a rock that was exposed to heat and pressure after its original formation). The dark and the light material you see here are from two totally different processes. The light material here is mostly quartz (the same mineral that we call amethyst or rose quartz–quartz occurs in a variety of colors). The lighter material is much more viscous-meaning, it resists flowing (like honey or molasses), while the darker stuff (primarily from minerals called pyroxene or hornblende) has a lower viscosity and flows more easily. Now, do you see how the light colored material exhibits small and irregular folds? These folds are what geologists call “ptygmatic”. These ptygmatic folds generally occur at pretty high temperatures and pressure; these variables cause the layers to fold and buckle the way that they do because of the differences in viscosity. The high temperature and pressure, along with the high viscosity of the light material, will cause these types of folds to form (these are also known as “passive folds”).
I recently saw this one (Figure 5) at the St. Petersburg beach in Florida, pretty close to where I live. These blocks are part of the public bathroom walls and as you can see, these bathroom walls are chock full of fossils! Wow! These fossils are from Florida and they’re pretty recent–no more than 10-20 million years old. They’re also primarily mollusks, the large group that contains octopuses, clams, snails, and oysters. Imaged here are snail fossils-you can identify these snails by their long, delicate shells- and clam fossils-you can identify those by the much larger shells that have ridges along the edges. These types of fossils are called “molds”-this means that the shell itself has been worn away and all that’s left is the sediment that either filled in the shell or the sediment that formed around the shell. The internal molds are where you can see an actual 3D shape of the inside of the shell, whereas the external molds are where you only see an impression of the shell.
Last but not least, my mom snapped this picture of her bathroom just for this post (thanks, Mom!)! Labradorite is a beautiful mineral-it’s a type of feldspar, which is in the same group as the lovely pink minerals seen in the granite in Figure 1. What makes labradorite so different, though, is that this feldspar doesn’t form in granite-it forms in a very different type of rock, like basalt! Basalt is an extrusive igneous rocks, so it forms from lava that cools at the Earth’s surface. Basalt is found in places like Hawaii, where it comes out of volcanoes, or at mid-ocean ridges, where new seafloor is being made. Basalt is mafic, meaning that it is full of heavy minerals like iron and magnesium. Labradorite is famous for its iridescent sheen-you can see it here in Figure 6!
I hope that this post has shown you that you don’t need to travel to fancy and far away locations to see real and beautiful geology up close. Sometimes, interesting geology can be as close as the nearest bathroom! Next time you see one of these counters, stop and take a look! What do you see? Do you see fossils? Garnets? Zoning? Do you see something entirely different? Before I go, I’d like to thank geologists Cameron Hughes, Zachary Atlas, Elisabeth Gallant, and Jeffery Ryan for help with identifying some of the details in these rock samples!
If you haven’t read Part 1 of my Greenland field work experience, check it out here! If you have read it, you’re probably wondering what research we actually worked on for those three chilly weeks. What were our research goals? What type of data did we collect? And how did we collect that data? To answer those questions, I give you Part 2: An Attempt at Science.
The University of Wyoming and University of Montana’s glaciology group has become highly involved in Greenland Ice Sheet (GrIS) research over the past decade. Because the ice sheet has become of critical importance in our warming climate, many scientists are trying to better understand the dynamics of the GrIS. Our collaborative group asks questions such as, how does meltwater move through the ice sheet? What mechanisms are involved in ice sheet movement? Or, what conditions lay beneath the ice? Answers to these questions help us to better understand GrIS dynamics in a changing climate.
For this field season, we were mostly concerned with the first of those questions. More specifically, we ask: what is the fate of meltwater in the percolation zone? To better understand what the percolation zone is, let’s take a look at the different regions or zones of a glacier (Figure 1). Any glacier (or ice sheet) is divided into two main parts: the ablation zone and the accumulation zone. The ablation zone defines the lower elevations where there is net melting. In other words, over a year-long period this region has lost mass. The opposite is the accumulation zone. Here, there is net gain in mass due to snowfall. These two zones are divided by the equilibrium line altitude (ELA) where the amounts of accumulation and melting are equal. This may seem straightforward at first glance, but a rather unusual region exists within the accumulation zone. Just higher in elevation than the ELA, there is a section of the glacier where snow melts and percolates into the firn. Firn is just altered and compacted snow. We’re curious about the fate of meltwater in the percolation zone’s firn. When snow melts to water, does it flow into the firn and refreeze? Does it percolate all the way down to the glacial ice layers? Or does it runoff toward the terminus (“the snout”) of the glacier and reach the ocean?
To answer these questions, we used a variety of research techniques that look at the structure and temperature of the firn throughout the full depth of the percolation zone, which is thought to be less than 100 meters thick in this area. The five principle tools we used were coring, hot water drilling, videography, temperature sensors, and radar. Coring involves extracting long cylinders of snow, firn, and ice from the ground below us, and then logging the densities and structures of the core. To reach greater depths than with coring, we used a hot water drill to inject hot water into the ground and create a borehole (Figure 2). Once we had a completed 100-meter borehole, we extended a video camera down the hole to visual identify interesting structures (e.g. ice layers) in the firn. In both the hot water-drilled boreholes and the boreholes remaining from coring, we installed long strings of temperature sensors that measure and record the firn temperatures at increasing depths. These temperature data will be recorded for the next year or two, so we will return next summer to collect the data. The final technique we use, ground-penetrating radar, provides insight into the firn layers below our feet. By transmitting radio waves into the ground and then receiving the waves, we can observe variations in firn density and estimate water content. Together, these five techniques provide a means to better understand the behavior of meltwater in the percolation zone.
Before arriving in Greenland, I was highly intimidated by all of the research techniques we had planned to use. I had never been involved in a full field season, never cored or drilled firn, and never even stepped on a glacier for that matter. However, I found that the best way to learn something is to actually just try doing it. With the guidance of a patient and knowledgeable advisor, I learned more than I thought was possible in three short weeks. Being in the field provides such an excellent opportunity to take an immersive approach to science: living, working, and learning in the presence of what you study.
This is the final post in the series of the geology of Maine and the Bay of Fundy. To recap for those of you who might not have read my first post, I documented all the geology I saw recently on a vacation my husband and I took to Maine and New Brunswick, Canada. This is the second post all about the geology of the Bay of Fundy! This one, though, will talk about the famous rocks of the bay and how they got the unusual shapes that made them famous. Remember, the Bay of Fundy is famous because it has the highest tides on Earth.
So what do these tides do to the rocks? To answer this, let’s first go to St. Martin, to the famous Sea Caves. You might be looking at this first image and think “what caves!”? Well, this first image is taken at high tide, so the caves are almost entirely underwater. High and low tide were separated by about six hours, so we saw high tide, admired the lovely scenery, and drove to see the Fundy Trail Parkway, a park that you can drive or hike the entire way through for some GORGEOUS scenery. There are spots to pull over and get out, hike short distances, or just look out from a cliff to see some beautiful sites. Here’s a picture overlooking the Bay of Fundy – remember, these lovely coastlines were largely created by the formation, movement, and melting of glaciers.
We returned to the Sea Caves to see it at low tide-take a look! This picture is from the SAME spot, give or take a few feet. This photo should show you the height and amount of water moved by tides every day in the Bay of Fundy. The presence of these caves is due to mechanical weathering-literally, the waves associated with the tides coming in and out are quite strong and they break down the rocks. Thousands of years of these waves have created immense caves and crevasses. Once you are able to walk across the seafloor at low tide, you can truly appreciate just how incredibly large these caves are and just how strong the tides are! Here’s an image of me inside one of the caves!
There’s one last thing I want to point out about these tides-the effect that they have on living creatures! Snails and barnacles live in high abundance all over the area affected by low tide and these creatures find incredible ways to survive when the low tide means that they aren’t covered by water! Snails will gather in small cracks in rocks where water will pool; barnacles will form more in shadier areas, so the rocks will remain more damp than those exposed to the sun. Sometimes, snails will hang on to a piece of algae just to survive until the water comes back! Check out this image of a snail holding on for dear life!
Now, let’s travel north to Hopewell Park, where the most famous rocks from the Bay of Fundy are. First, let’s look at the difference between low and high tide. These images are taken just about 4 hours apart. So the rock you see here was broken off from the cliffs due to chemical weathering-water percolating through cracks and breaking them apart. But, the odd shape that you see now, where the rock is much narrower on the bottom-that’s due to mechanical weathering. Wave action over thousands of years has caused these shapes to form. These rocks CAN fall without warning (and have, even recently), so park rangers are always making sure to look for signs of instability.
To really experience high tide, my husband and I signed up to kayak through these rocks. To say that the waves here were strong is an understatement! The waves were cresting at just under 4ft-so imagine sitting down on the beach front-you’d be completely covered (if you were curious, kayaking in 4ft waves and high winds was a blast, but also a little terrifying!)! Here’s an up close picture of that same rock you saw in the previous two pictures, from the kayak! Now you can really see where the rock is narrowed at the base-the line between the narrow and wider part of the rock marks the highest the tides can go.
I hope you’ve enjoyed this series! I think one of the most important things I can say here is that this trip made me rediscover my love of geology. Sometimes, when you work long hours every day as a geologist, it can become a little hard to remember just why you love it. If you’re feeling that way, I encourage you to get out and go explore for a little while- a few hours, or even a few months, if you can!
This post is a continuation of my first post, the geology of Acadia National Park. To recap for those of you who might not have read my first post, I documented all the geology I saw recently on a vacation my husband and I took to Maine and New Brunswick, Canada. This post will be all about the geology of the Bay of Fundy! Specifically, this will be about how glaciers have shaped the geology of the area.
The Bay of Fundy is an incredibly famous geologic area for a good reason-it has the highest tides on Earth, with the highest reaching nearly 56ft! The reason why the tides are so high here has to deal with the shape of the bay-the bay narrows quite a bit (as you can see from the map), so as all the water enters the bay, it’s forced to stack up on top of each other, making the tides reach these incredible heights.
Glaciers have shaped a lot of the geology along the Bay of Fundy; as glaciers advance and retreat, they leave telltale signs. One of the best signs are when you see rocks called tillites. These rocks are made of glacial sediment. They’re fairly easy to recognize-often, you’ll see rocks with very large, poorly sorted clasts (meaning, all kinds of different sizes of sediment). These are left behind by glaciers! Here is an example of tillite along the coast of the Bay of Fundy. Look at all of the different sizes of clasts in there! This rock was found at the Irving Nature Center, St. John, New Brunswick. The wave energy in this particular area is very high, which you can tell by the lack of small sand grains and the prevalence of much larger clasts (pebbles-boulders). Another sign of glacial activity is the presence of striations on rocks. Striations are scratches in rocks that are caused by glacial ice moving over them. These glaciers can have lots of rock and sand debris within it, so as they move over rocks, it can cause a lot of surface damage to the rock. Check out this picture of striations on volcanic rocks, also from the Irving Nature Park!
Arguably, the most famous area of the Bay of Fundy is the site called Hopewell Rocks. I’ll discuss a lot more about the Hopewell Rocks in my final post, but for now, let’s talk about how glaciers shaped these famous rocks. As glaciers last retreated from these areas (meaning, the Earth warmed and glacial ice melted), the water from the glaciers filled into the ground and caused cracks to form along the coast. This is called chemical weathering. Water is a chemical and it’s the most common chemical that rocks come into contact with when we’re talking about chemical weathering. These cracks eventually caused these large rocks to be separated from the cliff line. This phenomenon might be more familiar to you when you’re driving- when roads (in colder areas, especially) have small cracks in them and water gets into those small cracks, that water can freeze, causing the crack to expand. After multiple rounds of freezing and melting, these cracks become a real problem to drivers!
During our next (and final) piece about my trip through the Bay of Fundy, we’ll look at how these famous rocks are shaped by mechanical weathering, instead of chemical!