I recently returned from a five-week field camp in Scotland. Field camp is a course that most geologists participate in that is intended to teach students how to collect geologic measurements in the field, recognize geologic structures like folds and faults, understand age relationships of the rock, and ultimately make sense of all of this by making maps and cross sections (interpretations of what the surface geology looks like underground). Field camps are incredibly important as geology students because it reinforces the ideas that the best geologists are those that have seen the most rocks and that geology needs to be learned outside, not just in the classroom.
So, why Scotland for field camp? Scotland is an interesting location geologically, because for much of Earth’s history it was essentially a ping pong ball with sections of the country getting added on by collisions with other continents as it bounced around. If you look at a map of Scotland you can see two almost parallel lines dividing the country into three pieces (Figure 1). The top most fault is the Great Glen Fault which runs through the city of Inverness and Loch Ness (where the Loch Ness monster resides). The fault further to the south is the Highland Boundary Fault which does divide the country into the Highlands and Lowlands. Each of these pieces was accreted (added on) during a different collisional event. Surprisingly, the last, and youngest, collisional event that happened, when Baltica (Northwestern Europe) collided with Laurentia (North America, Greenland, Scotland), deposited the oldest rocks that you can see in Scotland. These rocks are ~3.2 billion years old and they lay on top of limestone that is ~540 million years old (Figure 2). Seeing this age relationship in the field tells us that something crazy was happening geologically!
Field camp is a lot like summer camp mixed with a typical college class-there is a lot of fun to be had with fellow rock nerds, but also a lot of learning and homework to be done. On a typical day we would leave our hostel or house by 8:30am, work in the field, mapping and collecting data, (either in small groups or individually), leave the field around 5pm, go home and cook dinner for your small group, then work on interpretations of our data and prettying up our maps. Usually at the end of the week we would have a larger project to hand in based on the maps that we had made that week and our interpretations of the area (Figure 3).
Going to field camp can seem daunting at first, especially if you are going on one outside of your home country, but truly is an important experience in learning to be a geologist. Like practicing a sport or instrument, you have to practice geology skills in order for them to become second nature and field camp is the best place for that practice. For a lot of people, this is where geologists have their first “I am a geologist” moment. So, for anyone who wants to be a geologist (or paleontologist or other earth scientist) get outside and look at some rocks and fossils and start observing, because the best geologist has seen the most rocks!
Every Spring, UMass takes its Historical Geology class on a weekend field trip to the Mohawk Valley in New York. The purpose of the trip is to show students the formation of an ancient ocean that once covered North America ~450 million years ago in the Ordovician and talk about the ancient environments that animals lived in. We also take the students to some locations on the second day of the trip to rocks that are a bit younger (~410 million years old) so they can collect fossils. In addition to talking about tectonics and fossils, we also show the students some really great sedimentary structures preserved in the rock record.
The first stop of the day involved looking at older limestones of early Middle Ordovician age in an abandoned rock quarry. At the second stop, we looked at finer-grained shales that were deposited in a deeper portion of the ancient basin. At the third stop of the day, we investigated the Utica Shale, one of the largest shale deposits on the east coast, and one that is commonly targeted by oil and gas companies because it produces these products at the right depths in the Earth. Here, we all found trilobite pieces (and a few whole specimens). The last stop of the day involved walking down to a waterfall on Plotter Kill Preserve (not really a welcoming name for a park) and investigate the shallowing or infilling of the ancient basin. In addition to beautiful scenery, there are also some really great sedimentary structures preserved at this location.
The second day of the trip is always the highlight of the weekend, at least for me! Our first stop was the Lower Devonian limestones of Schoharie, NY, which are highly fossiliferous. After we spent a few hours at this locality, we took the class to a locally famous locality called the Taconic Unconformity. Here, rocks of Middle Ordovician age (~460 million years old) are against Lower Devonian rocks (~410 million years old), meaning that a huge chunk of time (the entire Silurian Period) is totally missing. The unconformity is really apparent because the older Ordovician rocks are standing almost straight up, whereas the Devonian rocks are less tilted.
The last stop of the field trip was to another locally famous and well-loved locality called ‘Dinosaur Skin’. This name is wildly misleading, as the rocks here were formed about 250 million years before the first dinosaurs roamed the Earth, although the sedimentary features preserved in the rock do resemble dinosaur skin. Instead, the features preserved in the rocks at this location are called flute casts, which are a type of sole mark, a sedimentary feature that is formed and preserved on the bottom of sedimentary beds. In the Middle Ordovician, there were intense storms as well as earthquakes as other pieces of continents and island arcs collided with the east coast of ancestral North America. These caused sediment instability in the form of turbidites, which can be thought of as underwater landslides. So, the Dinosaur Skin is actually scoured sediment that was preserved in the rock record.
This past weekend several students, myself, and my lab mate Maggie went to a fossil locality near Hopkinsville, Kentucky. This rock is from the Mississippian and this locality is particularly interesting to me because of the amount of blastoids you can find in a single moment. They are falling right out of the rock! So we went with a specific question to answer. We are looking to better understand the gap in fossil preservation within some of the blastoids there. Let me explain some – there are specimens that range from 0.25 – 15 mm in height. But most scientists ignore everything below 5 mm because it falls apart more easily than the larger specimens.
Recently we have examined some of the very tiny (0.25 mm) specimens and we are interested to see how the growth of the organism may be affecting its ability to preserve in the rock record! So we did some surface collecting – looking around on the ground and picking up specimens that we can see with our eyes. We also did a lot of bulk collecting. By bulk collecting I mean we filled buckets of sediment with a shovel to take home with us. We will then sieve all the sediment to differentiate the different sizes of the specimens. We will have several different sieve sizes from 5 mm all the way to 64 microns (very tiny material). We will clean everything so that we can sort through the different sizes to find what we are looking for – pieces of small blastoids!
The fossils are found in limestone beds (see by Maggie’s leg – there is a bench like extension from the rock) and in the shale layers (drab gray colored rock that makes up most of the bottom) that occur between the limestone beds. The big rock on top of them is sandstone and is part of an ancient river system.
Every year in February, we (well, my advisor and his TA, which has been me the past two years) take our Historical Geology class to a fantastic barrier island system on Plum Island, MA. First of all, a barrier island is a type of landform that forms parallel to a shoreline, and is usually characterized by a beach, dunes, and a back dune area, which can be a marsh, lagoon, or other wetlands. We do this for several reasons, but mainly, so the students can see how different a beach looks during the winter, and to help them imagine how sea level will affect the main environments (beach, dune, marsh) at Plum Island.
As sea level changes, environments are pushed backward (during a sea level rise) or migrate out towards the ocean (sea level fall). Currently, as glaciers melt due to global climate change, sea level is rising at an alarming rate. This means that the environments at Plum Island will begin to be pushed backward. During times of sea level rise, we call this a transgression. This means that the beach will move to where the dunes currently are, and the dunes will migrate back to where the marsh is. The marsh will be pushed back more inland. But what will this look like in the rock record? Beach sand, when turned into rock, is called sandstone. Dunes will also turn into sandstone, but will exhibit angular bedding, called cross bedding. Marshes are characterized by very fine sediment, such as clay and silt, as well as lots of organic material (decaying grass, organisms, poop, etc.). Thus, marshes will be represented by siltstone, mudstone, and/or coal in the rock record. These environments are stacked on top of one another as they migrate landward. Thus, in the rock record, geologists would see sandstone, maybe with some shells (beach), topped with more sandstone that has abundant cross bedding (dunes), topped by siltstone/mudstone/coal (marsh).