EES Seminar: Decoding the sedimentary record of early eukaryotes in Arctic Canada

John Wilder Greenman
Ph.D. Candidate
Department of Earth and Planetary Sciences
McGill University

Title: Decoding the Sedimentary Record of Early Eukaryotes in Arctic Canada

Abstract: The clearest tangible evidence for the diversification of complex life in the form of microscopic fossils (microfossils) of single-celled eukaryotes is captured in ca. 1 billion-year-old sedimentary rock successions scattered across the Arctic. Canada's impressive fossil endowment now includes the oldest occurrences of algae, fungi, and sponges (animals) as well as macroscopic green algae and evidence of eukaryovory (predation by eukaryotes). These fossils are found in sedimentary rock layers deposited ca. 1.0 billion years ago, an interval that was likely characterized by major changes in global biogeochemical cycles against a backdrop of low surface oxygen levels. These fossils show that ocean ecosystems were capable of supporting eukaryotes despite low oxygen and nutrient levels, and their diversification and expansion likely had an important impact on the evolution of Earth’s surface systems. Understanding the relationship between the emergence of complex eukaryotes in a low oxygen world and concomitant environmental changes requires more in-depth studies to determine the conditions of the niches suitable for habitation, and a more detailed view of how ecosystems changed through the Tonian period (1000-720 million years ago, the oldest period of the Neoproterozoic Era). This transitional interval—including eukaryotes' first appearance in the rock record and their subsequent ecological expansion—would have resulted in fundamental shifts to biogeochemical cycling in the Neoproterozoic. Here we explore the sedimentary record of northern Canada, particularly in the eastern Arctic where I have conducted my PhD studies. Next, we examine the critical fossil discoveries from northern Canada, including where they are found, and what clues they offer on how ecosystems were evolving ca. 1 billion-years-ago.

Academic history: I did my undergraduate at the University of Ottawa where I did double major in geology and biology. Near the end of my undergrad, I worked for the Geological Survey of Canada for two summers as a field assistant which is where I got my introduction to Proterozoic stratigraphy in northern Canada. This led to my MSc at Carleton University under the supervision of Rob Rainbird (from the GSC). This work was predominantly sedimentology and stratigraphy focused, but I also used carbon isotope chemostratigraphy to test and refine correlations between the Tonian-aged Amundsen and Mackenzie basins of the NWT and Yukon. I am currently a PhD candidate in the Department of Earth and Planetary Sciences at McGill University under the supervision of Galen Halverson. My current work is primarily focused on reconstructing the depositional history of the Bylot basins in northeastern Canada and northwestern Greenland. This fieldwork was done through the Fury and Hecla Geoscience Project in 2018 and 2019, led by the Canada-Nunavut Geoscience Office, and the Thule Basin Geoscience project, which I led in 2019. My goal is the reconstruct a robust depositional history of this region around 1 Ga so we can confidently conduct more focused studies relating to the emergence of complex life and the tectonic evolution of Arctic Laurentia through the amalgamation and breakup of the supercontinent Rodinia




Online via Zoom
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Owen Sherwood