This analogy is fitting for my first two field seasons on Anticosti Island, a remote island in Québec (Canada). My first-ever field season was spent on the island over the summer of 2018. Trying to comprehend the rich fossil and geological records across the 200-kilometer-long island while camping in the wilderness for the first time ever left me in a bit of a daze. When I returned to Berkeley after two weeks, I was exhausted, but excited for the next opportunity to travel to the island. While I had not accomplished everything I had set out to do in my first field season, the experience was invaluable– I now knew what I had to do to prepare myself for my next trip to Anticosti. I spent countless weeks in preparation, pouring over monographs, travelling to visit collaborators in Canada to view their fossil collections, and working my way through the literature to understand the nuances of the geological record of Anticosti Island. By the end of the 2019 spring semester, I was itching to return to the field.
Thanks to support from the William B.N. Berry Memorial Research Fund, I was able to travel back to Anticosti Island during the summer of 2019 for a marathon month-long field season to study the Late Ordovician mass extinction. This event occurred at the Ordovician–Silurian boundary, roughly 443.8 million years ago, and eliminated almost 80% of global marine species diversity, the second largest mass extinction in the last 540 million years. While the extinction is intimately linked to climate change, it is unclear as to whether global cooling or warming drove the extinction. Because of the unique geological history of the Anticosti Island, we can investigate the relationship of the extinction to climate change at an unrivaled resolution, incorporating data from across the island into regional analyses of the extinction. To work towards this goal, my field assistant, Ryan Caspary (UCB, ’19), and I planned an ambitious field season on Anticosti, working at localities across the island. Each locality is its own adventure, requiring you to shimmy along coastal cliffs, hike along river canyons, and even go for a bit of spelunking! We began by working at localities along the west coast of the island, close to town. Here, we revisited the Ordovician–Silurian boundary at localities where we worked during our first field season in 2018. As we studied the fossil and rock records at these localities, we saw fossils we had never noticed before, and were able to document subtle (but important) changes in the rock record that fundamentally altered our understanding of geological record on Anticosti Island. We also decided to explore a new locality nearby, wading for kilometers across muddy tidal flats and bush-whacking through dense forests and unexpected bogs to reach an exquisitely preserved Ordovician–Silurian boundary interval (Figure 1). This new section was particularly valuable, exposing intervals of the rock record, several meters thick, that were absent from our first locality.
After exploring the western coast of the island, our next few weeks on Anticosti were spent on the far eastern coast of the island. The geological and fossil records on the eastern coast of Anticosti are strikingly different from the western coast of the island. While individual sections along the western coast of Anticosti are relatively similar, along the eastern coast of Anticosti the geological records among adjacent localities can be dramatically different from one another (Figure 2). A careful high-resolution analysis of the geological and fossil records on the eastern end of Anticosti is therefore crucial for properly correlating the stratigraphic record so we can better understand the fossil record of the Late Ordovician mass extinction. Revisiting the eastern coast of Anticosti Island after the 2018 field season, I became acutely aware of the complexity of the geological records at these localities (Figure 3)! Fortunately, we were visited by my advisor Seth Finnegan (UCMP) and collaborator André Desrochers (University of Ottawa) who aided us as we tried to puzzle together the rock record along the eastern coast of Anticosti Island.
While the changes in depositional environment across Anticosti make correlating among localities a challenge, these changes provide invaluable insight into the fossil record. By studying the fossil record in different depositional environments, we can begin to understand the environmental preference of ancient species. This is key for understanding whether the disappearance of a species from the fossil record is due to changes in the recorded environments or due to an extinction event! For example, if you were working at a locality that recorded an abrupt transition from a deep-water to a shallow-water environment, would you expect to see species that prefer deeper-water in the shallow-water environment, and would their disappearance signal an extinction? While this may seem intuitive and simple, studying environmental preference in the fossil record (the paleoecology of organisms) can be tricky, but very important for our understanding of mass extinctions in the fossil record.
With everything at a stand-still due to the developing pandemic situation, I am lucky to have had the opportunity to travel to Anticosti Island. Science, in its own way, provides some solace in these crazy times, and the data I collected from Anticosti continue to provide new and exciting insight into the fossil record. I am looking forwards to being able to return to Anticosti in the future, to continue to investigate this amazing fossil record and to begin the next installment in this series!