Research

Environmental perturbations, Climate change, and mass extinctions: How can we relate forcing mechanisms to environmental response in ancient Earth systems?

Charles Lyell famously stated in his foundational book The Principles of Geology, “the present is key to the past.” In my research, I seek to utilize this same principle. Instead of relying on present day processes to inform past geological events, I aim to understand major events in Earth’s past and use them to inform our understanding of Earth’s future. In particular, I am interested in the processes behind major ecological crises in Earth’s history, working to understand how forcing mechanisms manifest themselves into environmental change and large-scale ecosystem collapse, as well as recovery. A key inhibitor to comprehending these major events in Earth history is poor chronology. An accurate timescale can inform us about rates of natural processes, can correlate rock sequences across distant localities and geological settings, and in turn can be used to help us understand the underlying mechanisms behind these major events. In my research, I seek to improve chronology for important periods of Earth history utilizing both ⁴⁰Ar/³⁹Ar geochronology and paleomagnetism. One period I’ve focused on is the Cretaceous-Paleogene (KPg) mass extinction.

The KPg mass extinction is one of the most important biotic turnover events in Earth history, yet, its cause is still highly debated and hypotheses center around two main triggers: the Chicxulub impact and Deccan volcanism. In my research, I seek to better assess the role of the Chicxulub impact and the Deccan Traps in the KPg crises by developing a high-precision chronologic framework that outlines the temporal sequence of biotic and climatic changes, and proposed perturbations, around the KPg using both ⁴⁰Ar/³⁹Ar geochronology and paleomagnetism. This work has been focused in three major areas: refining the timing of terrestrial faunal change, calibrating the age of circum-KPg polarity chrons, and refining the timing and tempo of Deccan Traps volcanism.

Circum-KPg environmental changes. Figure after Sprain et al.(2018).

Dinosaur tail from Grasslands National Park, Saskatchewan

Marine magnetic anomaly record, and plot of reversal frequency (black line) alongside average virtual (axial) dipole moment (VDM) measurements in 10 Ma bins (blue circles). Field values generally follow an inverse relationship with reversal rate, with lower VDMs when reversal frequency was high and high VDMs when reversal frequency was low. (From Sprain et al. 2016b)

Long-term trends in Earth’s magnetic field and links to deep interior processes

The current understanding of the Earth’s deep interior is limited to recent time where we have direct observations from geophysical data. Fortunately, one source exists that records ancient signals from the deep interior, and that is paleomagnetic data. Variations in the magnetic field occur on a broad range of timescales. While most variations are attributed to stochastic processes in the outer core, long-term variations (>10 Myr) have been suggested to be modulated by mantle convection. If observed variations in the long-term field can be tied to mechanisms predicted from numerical models, we can create a unique tool that would help to evaluate changes in the deep interior going back in time, adding a crucial dimension to our understanding of Earth’s planetary evolution.

In my research, it is my aim to develop this tool. Currently, there remain several challenges that impede its creation. I am working to overcome these challenges in following ways: improve the characterization of trends in the long-term magnetic field through paleomagnetic and geochronologic data collection and large scale data assessment, and develop new ‘Earth-like’ geodynamo simulations to test hypotheses related to the evolution of the deep interior.

Characterization of the Recent (0-10 Myr) Magnetic field

To provide testable hypotheses regarding long term field behavior, it is necessary to have a reliable characterization of recent magnetic data (past few Myr). A proper understanding of recent paleofield behavior requires measurements of the whole field vector, including direction and intensity. Unfortunately, paleomagnetic data for the last 10 Myr contain few estimates of magnetic intensity due to a lack of reliable recorders. A potential new candidate for obtaining reliable paleointensity data are clinker deposits, rocks baked and fused by in situ burning of coal deposits. Clinkers are ideal because they are found throughout the world, can be reliably dated ((U-Th)/He, possibly ⁴⁰Ar/³⁹Ar), and have the potential to be reliable paleointensity recorders.

In my research, rock magnetic, paleodirectional, paleointensity and geochemical studies on clinker deposits are currently being undertaken to test whether clinkers are viable paleomagnetic recorders. Preliminary results show that clinkers do contain magnetic materials amenable to recording direction and intensity, and preliminary paleointensity results yield quality, reproducible data with values expected for the time of clinker formation. This work will ultimately be accumulated to better assess the behavior of the recent magnetic field, and will help improve global magnetic field models for the Quaternary. This work additionally has the potential to expand to areas of paleoclimatology, with the possible development of a magnetic proxy for paleo-wildfires.

Clinker deposit exposed at the top of a butte in Teddy Roosevelt National Park.

Up close view of the remnants of a chimney within a clinker deposit along the coal vein trail in Teddy Roosevelt National Park.

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