Large Igneous Provinces and Environmental Change
What role do large igneous provinces (LIPs) play in perturbing the Earth system?
Accurate and precise geochronology is required to assess the role of LIPs in environmental perturbations. We must assess the extent of correlation before ascribing causation!
Columbia River Basalt Group and Miocene Climate Optimum
The emplacement of the Columbia River Basalt Group (CRBG), Earth’s youngest, smallest, and best-preserved LIP, has been noted for its concurrence with the Miocene Climate Optimum (MCO), an interval of global warming and elevated atmospheric carbon dioxide from 17-15 Ma. However, legacy K-Ar and Ar/Ar ages were unable to resolve the timing and duration of CRBG emplacement. During my PhD, I produced the first high-precision timeline for CRBG eruptions using U-Pb zircon geochronology. I found that the basalts were emplaced in ~750 ka, twice as fast as previously thought, and have calculated volumetric eruption rates through the duration of the province (Kasbohm et al., 2023). As a postdoc I produced the first U-Pb ages across the MCO from ODP Site 1000 (Kasbohm et al., 2024). These ages calibrated a new high-resolution bulk carbon and oxygen isotope record, for a precise comparison between the timing of Miocene climatic fluctuations and known intervals of CRBG eruptions.
LIP Geochronology Review
As I pursued my work on the CRBG and MCO, I became interested in the temporal correlation of other LIPs and environmental change events. This correlation has led many workers to suggest that LIPs play a causal role in these global perturbations. However, I have encouraged the community of LIP researchers to be wary of the assumption of causation based on correlations made with ~1 Ma precision, when the environmental effects of LIP eruptions occur at 10-100 ka timescales. In an invited review paper (Kasbohm et al., 2021) I revisited 12 pairs of LIP and extinction or climate events and found that only 4 pairs (including my work on the CRBG/MCO) had been the subject of high-precision geochronology studies that investigated the timing of both the LIP and the corresponding perturbation. In 8 other pairs, either the LIP or the perturbation had been well-dated, which still leaves open the question of the extent to which these events are related.
