I recently visited Big Bone Lick State Historic Site (Union, Kentucky) on the way back to Ohio from a weekend in Kentucky. I’ve been meaning to visit this place for years, so I’m glad I finally had a chance to do so! Big Bone Lick is an important site for paleontology, archaeology, and US history.
Big Bone Lick SP is the site of a salt lick, or area where animals come to obtain salt and other minerals by licking the soil for salt crystals. Natural salt and sulfur springs are the source of the minerals at Big Bone Lick, and they attracted animals from all over.
In historical times, white-tailed deer and North American bison visited the lick, but much larger mammals came during the Pleistocene epoch (2.5 million to 12,000 years ago), also called the “Ice Age.” The remains of extinct mastodons, mammoths, North American horses, ground sloths, and tapirs have been found here, as well as the still living bison, musk oxen, and peccaries. Some of them became stuck in mud and died, and their preserved skeletons became the source of the “big bones!”
Paleoindians hunted the megafauna at Big Bone Lick, and left behind their tools at the site. Native Americans continued to hunt here into colonial times, and told the Europeans about the big bones found in the soil. President Jefferson ordered Merriweather Lewis and William Clark to stop here on their expedition to investigate these reports. Specimens were excavated and eventually sent to France for analysis by Georges Cuvier, an anatomist credited with developing the concept of extinction. He compared the remains of Asian Elephants, African elephants, and the “elephants” found at Big Bone Lick and determined that these remains came a type of elephant that no longer lived. He named this animal Mastodon, but these fossils had already been described under the name Mammut. The study of these remains has given this site credit for the birth place of vertebrate paleontology in the United States.
Long after the bison were extirpated (no longer present in their native habitat, but not extinct) from Kentucky, Kentuckians mined salt and opened a health resort, at which people bathed in the mineral-rich water.
I have always loved the Pleistocene megafauna, and I make a point to see these fossils whenever I can. Mastodons are tied with Moropus(a distant relative of horses and rhinos, imagine a draft horse with claws!) as my favorite fossil animal, and get so excited seeing them!
The visitor’s center has nice displays about the megafauna found at Big Bone Lick, including fossil material and reconstructions of what they may have looked like. There is information about the Paleoindians that inhabited this region and their tools. Historical information about Lewis and Clark is also included in the displays.
Behind the visitor’s center are life-size statues that represent iconic Pleistocene megafauna. Many of them are“trapped” in the sediment, and are on their way to become fossils. This was the perfect opportunity for a selfie with a mastodon!
The site is actually quite large, and features a campground and several hiking trails. I took one of these trails to see the salt/sulfur springs. I could smell the sulfur as soon as I reached this point in the trail. It was pretty awful, and it amazes me that people came to bathe in these waters for the “medicinal properties” centuries ago.
I continued along a trail which follows Big Bone Creek. Fossils and artifacts are still exposed as the sediment washes away, and modern excavations occur when fossils are found on site.
Informational signs are included along the trails about the history of the site and about the animals that once lived in this region.
The park maintains a small herd of American bison (Bison bison) on its grounds. The animals are rotated around their paddock to allow the plants time to recover from grazing and trampling. Unfortunately for me, they were located too far away for me to see with them with my limited time. It is hoped that the ecosystem will be restored to its condition before the bison were extirpated from this area.
I had a great visit to Big Bone Lick State Historic Site! If you enjoy ice age megafauna, and are in or near Kentucky, consider stopping by! For more information, visit Big Bone Lick State Historical Site
Recently, I went to the Washington D.C. area to visit the Smithsonian Museum of Natural History (which you can read about here) and to attend a workshop on best practices for new faculty members. But while I was there, I spied some excellent geology right in the city! I already showed you some of those while I was in the museum itself, so I’ll show you some of the other amazing pieces of Earth history that I saw!
I want to remind you that looking at amazing geology doesn’t have to wait for you to be on vacation or in a faraway destination-you can see these sites anywhere, if you’re paying attention! If you want to read more of these types of posts, check out my post from last year on the geology of bathrooms.
This first image is of a beautiful stylolite in a marble countertop in the bathroom of a café in the center of Washington D.C. A stylolite is caused when rock, most commonly carbonate rocks like limestone (which we call marble when they are metamorphosed), are put under extreme pressure and the individual grains will compress and leak fluid, leaving behind a squiggly line, like what you see in image 1. Just beautiful!
Our next stop brings us to Union Station in Washington D.C., where I found this magnificent staircase completely by accident (image 2). I was visiting Gallaudet University and the first signing Starbucks, when I got turned around and ended up at a different Metro station than I had originally intended. Well, serendipitously, I found this absolute beauty, making the detour more than worth it. This rock, just like the image before, is a type of marble, though it has very different colors. The red color in this marble can be attributed to chemical impurities- red is typically what we’d see if iron and feldspar was present in the marble sample. You can also see veins filled with calcite and look like quartz all throughout the staircase! I was intrigued about where this marble came from, so I did a little research. There wasn’t a lot of information, but it seems that this marble likely came from Vermont (See this blog here: https://blogs.agu.org/magmacumlaude/2014/06/13/building-dc-union-station-just-the-floors/), which was created over 400 million years ago, when limestone produced from a shallow sea collided with a volcanic arc and metamorphosed in an orogeny, or a tectonic collision. This is a fairly common scenario with how we get a lot of our marble from the Paleozoic in North America.
Our tour continues to just outside of Washington D.C., to Arlington, VA, where I was visiting a friend in the area. As we were walking to breakfast, I was treated to a spectacular number of rocks featured in the buildings’ walls along the way. First, is a beautiful granite (image 3). The pink mineral is potassium feldspar (K-spar, for short), intermixed with the milky white mineral (quartz) and a lot of amphibole, the black colored mineral that’s heavily present on the left side of the block. Granite also usually contains biotite, a black mica. If you take a look at this granite, you’ll see that the individual crystals are quite large, which tells us a lot about its formation. It’s telling us that it was formed intrusively; meaning, it was formed in an area not exposed to Earth’s surface and it cooled slowly, giving the crystals time to grow. I stopped to take a photo of this because the amphibole (there are many varieties of amphibole-hornblende is the most common in granite) because the heavy presence of the swirling amphibole isn’t something I usually see in most granite samples. Second, I saw these gorgeous phyllite samples on the outer wall of a building (image 4). Phyllite is a low-grade metamorphic rock, which means it’s not exposed to extremely high amounts of heat and pressure, but it has undergone significant changes from its protolith (otherwise known as its parent rock). In the case of phyllite, its protolith was a shale (compacted mud). You can recognize phyllite by a few different characteristics. During the metamorphic process, muscovite (a soft mineral in the mica family) develops, giving phyllite a really lovely shiny appearance (you can think of mica as being like nature’s glitter; just like glitter, mica is nearly impossible to completely get rid of if you accidentally get it everywhere!). You can also recognize phyllite by the gentle bands that form. Many metamorphic rocks are foliated, which we can think of as banding across a rock. The more pronounced the banding usually indicates a higher amount of metamorphism applied to the rock. Phyllite has subtle banding, which indicates that lower amount of metamorphism.
So, this next image (image 5) isn’t in D.C., but it was found during this trip in College Park, Maryland on the University of Maryland’s campus. It’s another gorgeous example of granite, this time in a fountain. Sometimes it can be really hard to recognize rocks when you’re used to seeing them beautifully polished and sealed (like the granite in image 3, but you can definitely do it with practice!) Just like in image 3, if you look closely at this fountain, you’ll see large crystals, because it’s an intrusive rock, and the same types of minerals- our pink K-spar, milky quartz, and black amphiboles. An intrusive magmatic event from millions of years ago had to form and cool, and then that granite had to be exhumed (brought to the surface) for someone to make that fountain. So cool!
Last, but certainly not least, let’s look at the marble here in the Ronald Reagan airport (image 6). This gorgeous marble makes up part of a seafood restaurant right near the entrance to the airport, before you go through the security line. Sorry that the image is kind of far away, but this was the closest I was able to get before having to get through the security line! One of my favorite things about marble is how different it can look from sample to sample. This marble shows completely different features than the ones I showed in images 1 and 2-remember, the color of marble is driven by chemical impurities. You can see large scale veins of what is likely calcite all over the rock itself as well as some dissolution features on the left side.
I recently went on a fossil collecting trip associated with a FOSSIL Project workshop on digitization and imaging of fossils. To preface this, whenever you are looking to go fossil collecting you should make sure to be aware of the laws and rules in place in your town. The spot we were heading to abuts private land so one of the coordinators made sure to reach out to them ahead of time to request permission and explain what we were doing. To give back to the community, we also cleaned up the creek while we were looking for fossils. There is always trash or debris and this is an easy way to give back to the community you are hunting in!
In Florida, you have to prepare to be out in the heat. Surprisingly the creek was pleasant and we were pretty shaded for most of the day. I wore a UV protectant shirt, shorts, sandals, and a hat. Insects can really get you, so it’s also best to know what to prepare for and use lotion or bug spray to prevent any spread of disease.
I was mostly observing and helping facilitate this trip but I was excited to see others getting really into the fossil collection. This location is in the Coosawhatchie Formation which is Miocene (~23-5.3 million years ago) in age. It overlies the Eocene (~56-33.9 million years old) Ocala Limestone. The Ocala Limestone fossils are very different from the Coosawhatchie so they are pretty easy to distinguish from one another. Most folks were finding shark teeth, ray plates, clams, snails from the Coosawhatchie Formation and things like small echinoids and large benthic foraminifera from the Ocala Limestone. Specimens from the Ocala Limestone were often a white-cream color whereas specimens from the Coosawhatchie were very dark.
We also spent some time observing the local insects and sharing education apps for identifying fossils and modern life! Workshop participants were from all over the country so there was some regular chit chat and getting to know one another. I had known several participants for some time from various online platforms so it was really great getting to meet them in person! If you want to check out what the group was up to here is the myFOSSIL group that everyone was posting in: Imaging and Digitization for Avocational Paleontologists Workshop
I was also helping my friend and collaborator, Rich, with a study. He was interested in thinking about participant dynamics at workshops and field trips. So we had a matrix and were recording interactions between participants at the workshop and facilitators (/people running the workshop). He then also gave everyone a survey to see how people’s perception of who they interacted with matched what we observed. They were pretty close but perceived interactions were higher, which could be due to a variety of things. It has been really fun getting into some of these observational studies!
The Ilulissat Art Museum is a charming red house with robin’s egg blue trim nestled up against a grassy hillside in the town of Ilulissat, Greenland. Almost 5,000 people live in this seaside town, including the art museum’s cheerful and friendly curator. His face lights up at the prospect of new visitors, and he enthusiastically greets us as we enter. This kindly curator shows us around the museum, offering us a wealth of knowledge about the paintings and the artists. He tells us that the lower level is primarily for paintings by Emanuel A. Petersen, a Danish painter who spent time in Greenland in the early 20th century. His paintings depict tranquil yet breathtaking scenes of the landscape surrounding Ilulissat and other Greenlandic villages. Many show icebergs stoically floating in the fjord, and tall, snowy mountains colored pink from the alpenglow. Some paintings have boats and kayaks out at sea, while others depict sleds led by teams of thick-coated dogs. While each scene may be different, each of Petersen’s paintings is so uniquely Greenland.
It’s no wonder Petersen produced enough paintings to fill an entire floor (not to mention the 150+ pieces of his artwork at the museum in Greenland’s capital, Nuuk). The landscape around Ilulissat is an alluring contrast of rounded green hills and blue-white icebergs. No more than 20 kilometers inland, the Greenland Ice Sheet spills out into channelized outlet glaciers like Jakobshavn Isbrae–the fast-flowing ice stream that produces the icebergs occupying Ilulissat’s fjord. Up and down the coast of Greenland, glaciers flow from the ice sheet and fill the valleys and fjords with ice.
Many local Greenlanders travel over this ice, including our friendly museum curator. He has a team of six sled dogs–which we’re told is a relatively small team–that pulls his sled across snow and ice. For years, he and his wife have been traveling with their sled dogs to a spot along the margin of the ice sheet. There, an outlet glacier flows into a water-filled valley with rocky hills forming the sides. Just a few years ago, the curator and his wife arrived at this spot and were met with a great surprise: a barren, rocky island protruded from the water in the middle of the channel. Had they never been there before, this would not have seemed odd. But this was a brand new island that was recently uncovered as the nearby glacier retreated up the fjord. Up until then, that spot had been covered with ice year-round, and no one had known that a small rocky protrusion lay beneath.
I was fascinated by his story and as I listened, I mentioned the words “ice retreat.” At that, the curator’s eyes lit up and with both passion and relief, he said, “Exactly.” It was clear that he needed us to understand his personal relationship with climate change. This was the first time I had met someone who has been so directly affected by warming temperatures and melting glaciers.
The island hasn’t made it on all the local maps yet, but it now has a name that means something like “the bald one” in English. In fact, this isn’t the only new island that has been uncovered by retreating ice. In the past twenty years, Steenstrup Glacier in northwest Greenland has also revealed a handful of new islands (2014 article, 2017 article). The effects of climate change in Greenland are complex–both for the ice sheet, the people, and the wildlife. In some cases, melting ice actually benefits certain Greenlandic industries like mining, fishing, or tourism. But shifts in these industries pose new problems and controversy. This guide to climate change in Greenland discusses what a warming climate means for people and for animals, and what new challenges may arise. Whether you’re a museum curator in Greenland or you’re somewhere else in the world, the effects of climate change will become more complex, more personal, and more prevalent. The burden of our future climate may seem daunting, but there are some small, every-day changes we can make to lessen our negative impacts. Check out this BBC article, Ten simple ways to act on climate change, to see how you can make a difference.
Please welcome Carmi, a new guest blogger here at Time Scavengers!
Carmi here –
In April, I was one of the trip coordinators for the spring meeting of the Florida Paleontological Society. The Florida Paleontological Society is a collection of professionals, amateurs, and every fossil enthusiast you could possibly imagine from all around Florida- and beyond! The society’s mission is to encourage and educate people on Florida’s rich paleontological history.
Usually, trips consist of field collecting (all over the state!), a series of talks given by paleontologists, and a silent auction, with many fossil goodies. In addition to being a member of the society, I also serve as the secretary, which means that I organize membership applications, coordinate trip logistics, and edit the newsletter… among other things.
The first evening of the trip is typically a dinner with all the members who have arrived early for the meeting. It is an optional event, but it acts as a time for folks to catch up and discuss topics of interest with each other. Following dinner, and a good night’s rest, we set off to the quarry to begin the day’s work.
The formation where we looked for fossils is the lower Miocene Torreya Formation (roughly 23 million years old), a limestone deposited when Florida’s sea levels were much higher. This unit is generally thought to be marine, though there is discussion as to the exact nature of the depositional environment – if you are curious to dive into the literature, GeoLex (one of my favorite ways to compile background literature on a geologic unit) has more publications on the Torreya Formation.
After we had our brief geologic and faunal overview, we set down the hill to begin the search. With the constant rain over the days leading up to the trip, the trip leaders were concerned that getting stuck in the clay rich sediments would be an issue – thankfully, the folks from the mine had smoothed out a portion of the road so that access to the collecting site was not too difficult. Small spoil piles were everywhere, full of all kinds of marine fossils, from shark teeth to impressions of different clams and snails.
One fun fact about the site: while many mines in Florida process material for road base (the material that makes up the highways that transport Floridians all over the state), this mine collected and refined clays used in the production of kitty litter!
The evening portion of the meeting took place at the Florida Geological Survey, who graciously accommodated dinner and our evening events. I gave a talk on my current research project – fossil cephalopods from the Cenozoic of Florida. Victor Perez, a graduate student at the Florida Museum of Natural History, was the other invited speaker and spoke on his dissertation research. Finally, the Assistant State Geologist, Harley Means, gave a talk on the history of the survey, and the services that the survey provides to the citizens of Florida!
After the talks, Harley led interested members throughout the survey, highlighting their museum of Florida fauna and amazing library. Inside the library, there were publications on geology of Florida as well as geology from all around the country. Not only does having these publications assist with understanding of similar earth systems elsewhere, but it acts as a way for state surveys to keep in touch and keep aware of developments in geologic mapping and other functions across the country.
Following the tour of the survey, the silent auction began. Items donated by club members were laid out on tables and folks would silently bid on what they found interesting or loudly dissuade others from bidding on these purchases. All the proceeds from the silent auction support student research in paleontology. My strategy is usually to team up with someone on a pile of publications – last year I won a vintage paleontology textbook, and this year I picked up a copy of my beloved Pliocene Mollusca, by Olsson and Harbison (which is another post entirely). After fierce competition, the auction items went home to various members – almost everyone left the auction with something exciting and new.
Of course, the activities were not over for the officers of the society – there was clean-up and then a board meeting the following day. However, trip participants agreed that it was a great experience.
When the students were on spring break a few weeks ago, I decided to take a few days off to go fossil collecting. The first site I went to was the spillway for the reservoir in Caesar Creek State Park. This is a special place for me: it’s the first site we went to collect fossils from during my paleontology course when I was a junior in college. I’ve been going back to this site for about 14 years, but I hadn’t been since 2013, when Jen, Adriane, our friend Wes, and I all went on a long weekend. During this time, Adriane and Jen were helping Alycia Stigall build the Ordovician Atlas. If you are interested in learning more about the organisms found, rock outcrops, and more head to that website!
This site is exposed Ordovician limestone and shales (click here to learn more about types of rocks), representing warm, shallow marine environments. Three rock formations are exposed: Waynesville, Liberty, and Whitewater. If you are interested in learning more about rock formations, click this link which will go into detail on formations! Because collecting is restricted to the base of the spillway, all of the rocks are mixed together and it is difficult to tell which formation the specimens come from. When collecting from Caesar Creek, one must obtain a pass from the Visitor’s Center—run by the Army Corps of Engineers—and agree to follow their rules. Probably the most frustrating rule is that one can’t use tools to extract specimens, not even another rock! But, regardless of these rules, this location is safe for individuals and families to come collect.
I was excited to see what would be exposed in the spillway. This was the first warm weekend of the year, and it had rained the day before. I figured fossils would have washed out from the wall and would not be picked over yet. Usually after a good rain you get lots of new fossils coming out of the rock due to the increased erosion of the outcrop. So it may be wet and gloomy but good for fossil collecting! It sure paid off because today was one of the best fossil collecting I’ve ever had at Caesar Creek!
This was the best haul I’ve had from Caesar Creek in a long time. I was not able to collect many of the really cool specimens I found. They were either way too big and/or stuck in a rock and I couldn’t use tools to remove them. I’m glad I got to see so many amazing specimens and take some home!
I recently took my geology students on a field trip to Blowing Rocks Nature Preserve on the eastern coast of Florida near Jupiter Island. This class is my upper level Sedimentary Petrology class made up of mostly geology majors (we mostly study the formation and identification of different types of sedimentary rocks, like sandstone and limestone). I wanted to show you all what we saw!
The rock that is shown here is the Anastasia Limestone, which was deposited in the late Pleistocene, which spanned about 2.5 million to 12,000 years ago. The ocean levels were much higher than they are currently, when this rock was made. We know this because the limestone that comprises the Anastasia was made underwater. Now, this limestone is exposed all along the eastern shore of Florida.
This limestone is really cool because once it was exposed, it began weathering in unique patterns. First, the energy of the waves is breaking the rocks down bit by bit. This is something we call mechanical or physical weathering. You can see evidence of this mechanical weathering by looking at how the rocks get narrower closer to the bottom-the waves usually only reach that point at high tide, so the rock above it isn’t nearly as affected (image 1). This mechanical weathering can make a few different types of features: sea arches (image 2) and sea stacks (image 2) are the kinds of things we can see here.
The cool geology doesn’t stop here though! Chemical weathering (i.e., breaking down the rock using chemicals-the most common one is water) also affects the rocks strongly here. Limestone is easily eroded away in the presence of acid, so any acidity in the ocean water or from rain above can wear away the rock in interesting patterns. Water splashes up on top of these rocks from regular wave action-that water slowly erodes the rock away, leaving small pits in the rock (image 3). However, what makes this place famous are the large pipes that are created from a mix of the chemical and mechanical weathering processes here. These pipes are quite literally large cylindrical tubes that have been worn out of the rock through hundreds of thousands of years (image 4). Water, when it comes in from waves, rushes up through these tubes and explodes out of the top! Sometimes, these can spray as high as 50 feet-hence the name of the park, Blowing Rocks (video 1)! As we go forward into the future, these pipes will continue to grow larger because they are continuously being worn down by wave energy.
There were some cool fossils on this trip, too! If you look closely, you can see lots of trace fossils from creatures who made burrows into the rock (image 5) and you can also see a lot of clam and snail fossils (mollusks!) Many of these fossils are broken up and the edges have been rounded-this is because of the higher energy waves constantly breaking them down (image 6). My students and I also found a living Portuguese man o’ war (image 7)- this isn’t a jellyfish because it isn’t a single organism, but it’s a closely related colonial organism. The man o’ war has long tentacles that can give humans very painful (but rarely fatal) stings. If you see one on the beach, don’t touch it! They are fairly common on the eastern coasts of south Florida, so be warned! All in all, my students had a great time on this trip, and they learned a lot about how rocks can change due to weathering over time. I hope you enjoyed it, too!
A couple of years ago my mom and I took a road trip to eastern Washington state to visit Drumheller Channels in the Columbia National Wildlife Refuge. This is an area containing giant basalt columns, part of the Columbia River Basalt flows, as well as some of the landscape known as the Channeled Scablands, remnants of the catastrophic Ice Age floods (check out the Ice Age Floods Institute for more info).
The Columbia River Basalt Group (CRBG) is a large igneous province in eastern Washington. Large igneous provinces are usually made of very low viscosity (runny) lava which has erupted from fissures in the ground and spread out to cover a large area. The CRBG is a series of lava flows (more than 350!) that cover an area of about 163,700 km2 (63,200 mi2). These lava flows altogether are more than 1.8 km (5,900 ft) thick. These flood basalt eruptions occurred from about 17 million years to about 5 million years ago
As basalt cools, it forms a hexagonal pattern on the cooling surface exposed to the air, similar to the pattern you see in mud as it dries. From the side this pattern looks like rows of columns next to each other, and beautiful landscapes made up of several stacked flows of this “columnar basalt” are a common sight as you drive through eastern Washington. The other major component of the eastern Washington landscape, the Channeled Scablands, are the result of flooding that occurred toward the end of the last ice age. They are called Channeled Scablands because the landscape consists of many interconnected channels and coulees and appears very rugged. This landscape has turned out to be one of the most important pieces of evidence in shaping our current understanding of how geological processes have shaped the surface of the Earth.
Before J Harlen Bretz started studying this landscape in the 1920s, geologists thought all Earth processes were extremely slow and gradual in making any changes in the landscape. This was a reaction to the suggestion by young earth creationists that the earth was formed rapidly by catastrophic events. The response of geologists to this idea was to immediately dismiss any hypothesis that the landscape had formed rapidly and insist that everything had happened very slowly and gradually. J Harlen Bretz became interested in some interesting erosional features he saw in eastern Washington and began doing intensive fieldwork in the area in 1922. As he continued to map and record his observations of the features he saw there, he became more and more convinced that this landscape had not been formed gradually but had been shaped by giant floods from further east. There are giant ripples here, giant channels and coulees, and giant “potholes” where rock has been plucked up by water rushing past. These features could not be explained by very slow and gradual erosion. Today, geologists understand that while many features are formed slowly, the landscape has also been formed in places by catastrophic events, some of which we can see today in volcanic eruptions, earthquakes, and tsunamis.
If you want to know more, here are a couple of good books to start with. Check with your local public library!
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.