A change in geography to continue research into ancient paleogeographic change

Written by Nick Swanson-Hysell

Throughout July 2024 members of my research group were hard at work packing up our laboratory and sample collections for our move from UC Berkeley to the University of Minnesota. After 11 years on the faculty of Berkeley's Department of Earth and Planetary Science, I was returning to the University of Minnesota where I previously had been as an NSF Postdoctoral Fellow at the Institute for Rock Magnetism from December 2011 to June 2013. The opportunity to join the faculty of the Earth and Environmental Sciences Department, take on the role as Associate Director of the Institute for Rock Magnetism, and be back in my home state of Minnesota with its fascinating geology motivated the move.

On a hot and humid day in early August, Tate Hall's subbasement got heavier as we moved in our sample collections from places such as Ethiopia, Oman, Mongolia, the Grand Canyon as well as many rocks from the Lake Superior region that were returning closer to their place of origin. Research in our group seeks to place quantitative constraints on the long-term evolution of Earth through integrating geophysical and geochemical data sets that are developed within a rigorous geologic context. A major focus of our work is on paleomagnetic and rock magnetic data sets that we develop to test hypotheses about the migrating positions of continents (paleogeography), changes to the surface environment (particularly planetary climate change), and the evolution of Earth’s magnetic field. Rock samples from around the world that we have collected for these goals, and promised the National Science Foundation that we will continue to archive, are now organized in their new home. Myself, postdoctoral researcher Yiming Zhang, and PhD student Diego Osorio Afanador are in new homes too and have been settling into the department over the past 2.5 months. We have also been welcomed into the community of the Institute for Rock Magnetism which is now under the leadership of Prof. Josh Feinberg as its new director.

As many of you are well aware, Tate Hall is on top some fascinating geology. Right below the building are the Ordovician sedimentary rocks of the Decorah Shale, Platteville Formation and St Peter Sandstone that are exposed along the Mississippi River gorge. Continuing down through the rest of the Paleozoic sedimentary rocks there is then the "Great Unconformity" under which there are the sedimentary and volcanic rocks of the Midcontinent Rift. The Midcontinent Rift developed as a volcanic rift system 1.1 billion years ago leading to the thick accumulation of lava flows and associated intrusions that are beautifully exposed in the Lake Superior region. Eruptions over 25 million years led to an incredible archive of lavas. This archive is a central record to our understanding of the assembly of the supercontinent Rodinia.

The supercontinent Pangea that began to break up with the opening of the Atlantic Ocean 200 million years ago is both more widely known and better understood than Rodinia. Rich geologic, geochemical and geophysical data sets constrain that the supercontinent Rodinia assembled around 1050 million years ago with ancient North America at its core. Paleomagnetic data sets that we have developed and paired with high-precision radiometric dates from Midcontinent Rift lava flows reveal that there was an interval of extraordinarily rapid plate motion as ancient North America moved towards the equator. This rapid motion was associated with closure of the Unimos Ocean basin and resulted in the mountain-building of the Grenvillian orogeny on the present-day eastern margin of North America (which was the southern margin 1 billion years ago). It is this collisional mountain-building that formed the supercontinent Rodinia (see paleogeography figure).

The most recent paper from our research group, led by Yiming Zhang who is now a postdoctoral research in the Institute for Rock Magnetism, presented new data from contemporaneous Grand Canyon lava flows and intrusions. Paleomagnetic data paired with high-precision dates strengthen the record of North America's rapid plate motion at the time (with the associated oriented block samples being some of the heaviest now in the Tate subbasement). We are also using sedimentary rocks within the Midcontinent Rift to further our understanding both of paleoenvironmental conditions 1000 million years ago and of the assembly of the supercontinent. Recently developed data by Yiming and PhD student Anthony Fuentes show that the rapid plate motion of North America leading up to the assembly of Rodinia dramatically slowed following the initiation of the Grenville orogeny collision. Yiming is further delving into the paleomagnetic record of rocks within the Grenville orogen itself to improve our understanding of where the supercontinent went after it assembled. At the same time, PhD student Diego Osorio Afanador is advancing methods for synthesizing such data into paths of motion of North America's subsequent journey — including during the time of the supercontinent Pangea.

The changing position of continents and associated tectonic plates, known as paleogeography, plays a central role in global change on Earth's surface including long-term planetary climate change. Following Rodinia's formation, it rifted apart starting around 750 million years ago in what is known as the Neoproterozoic Era. Sedimentary basins that formed as the supercontinent rifted apart record the largest climate changes in Earth history with two Snowball Earth glaciations with the first occurring between 717 and 660 million years ago and the next between 640 and 635 million years ago. Snowball Earth is a climate state when there are Greenland-type ice sheets at all latitude — including in the tropics! We have developed the hypothesis that tropical mountains containing rocks with high carbon sequestration potential could have formed at this time and played a role in the onset of global glaciation. Evaluating this hypothesis requires that we develop new data from rocks such as those that we recently started studying in Oman on the Arabian Peninsula. We are actively developing data on Neoproterozoic rocks from Oman using instruments within the Institute for Rock Magnetism. And we just learned that this research will be supported over the next three years by a new grant from NASA's Exobiology program.

I am thrilled to have the opportunity to be moving forward our research program into ancient global change and paleogeography here in the School of Earth and Environmental Sciences. The fantastic faculty in the department combined with the resources and personnel of the Minnesota Geological Survey, the Continental Scientific Drilling Facility, and the Institute for Rock Magnetism make this a fantastic research environment. I look forward to teaching, learning, and researching with students and colleagues here at the University of Minnesota in the years to come.